© 2025 Academia Brasileira de Ciencias. All rights reserved.The N5⁻ anion, known as pentazolate, represents a groundbreaking advancement in the field of energetic materials, offering promising applications in rocket propulsion, explosive devices, and pyrotechnics. Comprising five nitrogen atoms arranged in a cyclic structure with a negative charge, has captured significant interest due to its unique configuration and high energy potential. In this article, we provide a comprehensive overview of the N5⁻ anion’s potential as an energetic material, alongside the role of RMD simulations in elucidating its behavior. The ReaxFF forcefield was used to simulate the materials pyrolysis. The total energy behavior of different species containing pentazolate, across a range of temperatures (1500 K to 3000 K) revealed distinct trends and characteristics associated with the thermal dynamics and stability of the molecule under varying thermal conditions. Their mechanisms were elucidated, and the kinetic parameters were calculated, indicating that CNN5, with its low activation energy (39.14 kJ/mol), stands out as the most reactive, while PolyN5, with the highest activation energy (52.88 kJ/mol), is the most stable. Overall, the N5- anion represents a promising avenue for the development of high-energy materials.

© 2024, Academia Brasileira de Ciencias. All rights reserved.Currently, it is crucial for the lubricant formulation industry to explore cost-effective and environmentally friendly methodologies for analyzing the tribological properties of engine aviation lubricants under high-temperature and high-pressure operating conditions. This study demonstrates the feasibility of employing molecular dynamic simulations to gain essential insights into the evolution of the tribological properties of lubricants during operation. A three-layer molecular model was devised, comprising nickel aluminide molecules in the top and bottom layers, and polyol ester in the core. The impact of sliding velocities ranging from 20 km/h to 100 km/h was investigated under varying temperature and pressure conditions. Concentration, temperature and velocity profiles, radial distribution function, mean square displacement, and friction coefficient were calculated and analyzed in detail. Notably, the highest friction coefficients – ranging from 2.5 to 0.75-were observed at the lowest temperature and pressure conditions tested. Conversely, other sections of the gas turbine exhibited substantially lower friction coefficients – ranging from 0 to 0.01.Simulations demonstrate that increasing pressure and temperature reduce polymer chain mobility, leading to stronger internal interactions within the lubricant. Consequently, lubricant adsorption onto metal surfaces decreases. Furthermore, the lubricant performs exceptionally well when its molecules encounter higher velocities and temperatures. Based on the results obtained, the research demonstrates that the presented technique provides both quantitative and qualitative tribological information essential for understanding a system molecular behavior, serving as a guiding framework for researchers in the field.

Copyright © 2024 by the International Astronautical Federation (IAF). All rights reserved.Reactive molecular dynamics simulations were utilized to investigate the reaction between ammonium Perchlorate (AP) and aluminum (Al) particles. Two distinct sets of simulations were conducted, one involving a pure aluminum particle and the other featuring a passivated aluminum particle. The aim was to examine and compare the behavior of the reactive systems under different conditions. The simulations were performed using the ReaxFF force field, allowing for a detailed representation of chemical reactions at the atomic scale. Results revealed significant differences in the reaction dynamics between the two systems. The pure aluminum particle exhibited a more rapid and exothermic reaction with AP, leading to a higher release of energy and potentially enhanced propulsion performance. Conversely, the passivated aluminum particle displayed a slower and less exothermic reaction, attributed to the presence of an oxide layer inhibiting direct contact between aluminum and AP molecules. Additionally, kinetic parameters such as reaction rate constants were calculated for both sets of simulations, providing insights into the reaction kinetics of AP-A1 systems. Furthermore, the initial decomposition mechanism of AP was investigated, shedding light on the early stages of the reaction process. These findings provide valuable insights into the role of aluminum passivation in solid rocket propellant formulations and highlight the potential for optimizing energetic materials through molecular-level simulations. Overall, the comprehensive analysis presented in this study advances our understanding of AP-A1 interactions and offers a foundation for further research aimed at enhancing the performance and safety of energetic materials in propulsion applications.

Copyright ©2024 by the International Astronautical Federation (IAF). All rights reserved.Nitramines, like RDX and HMX, are also alternatives to AP as main components in smokeless propellants. They have high specific impulse but are moderately sensitive and have a slightly negative oxygen balance and are therefore unable to contribute positively to the oxygen balance of the propellant. Crystal defects are a constant in applied energetic materials (EMs) and play a crucial role in thermal degradation, combustion and ignition mechanisms, and subsequent aging. Defect engineering is the process of studying how defects affect an EM’s qualities and performances in order to design new EMs that meet the required specifications. An emerging field of study in energetic materials is crystal-defect engineering, which offers previously unheard-of opportunities for regulating physical, chemical, and electrical properties as well as propellants, explosives, and pyrotechnics compositions. There are numerous types of crystal defects, including line defects (dislocation), planar defects (twin, shear band, crack, and surface defect), and volume defects (void). Point defects also include orientational defects and element doping. In this study, ReaxFF molecular dynamics simulations were used to examine the effects of molecule vacancies on the reaction kinetics and thermal decomposition mechanisms of condensed-phase - HMX at different temperatures. The thermal decomposition of HMX is the primary event in the combustion process of solid rocket smokeless propellants, directly affecting the related performance of propellants and even rocket engines. Results showed that three primary initial decomposition mechanisms, namely, NNO2 bond dissociation, HONO elimination, and concerted ring fission, exist at both high and lower temperatures. Molecular vacancies affect how much each of the three pathways contributes to the initial breakdown of HMX, and these effects change with temperature. Molecular vacancies significantly enhance N-N bond cleavage and coordinated ring breaking at high temperatures (3200 K), while impeding the production of HONO bonds. The two main competing reaction pathways are N-N bond dissociation and HONO elimination, with the former being more prevalent during the first breakdown. Additionally, we calculated the first decomposition’s reaction rate constant and activation barriers for various vacancy concentrations. This RMD study showed that molecular vacancies accelerate the decomposition of condensed-phase HMX by increasing the reaction rate constant and reducing activation barriers.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Molecular dynamics simulations have emerged as a powerful tool for studying the passivation of metal surfaces by oxygen, providing insights into the mechanisms underlying this process at the atomic scale. In this study, we have used molecular dynamics simulations to investigate the passivation of an aluminium particle by oxygen, as aluminium is one of the most used metallic additives of solid rocket propellants. Specifically, the interaction between a single aluminium particle and oxygen molecules in a controlled environment. The simulations were performed using ReaxFF forcefield and involved the use of a variety of analytical techniques to analyse the results. The results of the simulations showed that the passivation of the aluminium particle by oxygen occurred through a sequence of reactions. Initially, the oxygen molecules adsorbed onto the surface of the particle, forming oxygen atoms that diffused into the bulk of the metal. This diffusion led to the formation of an oxide layer on the surface of the particle, which effectively passivated the underlying metal. Based on the behaviour observed, the passivation process was highly dependent on the temperature of the system. At low temperatures, the formation of the oxide layer was slower and incomplete, leading to the formation of a highly disordered oxide layer. At higher temperatures, the oxide layer formed much more quickly and was much more ordered, with a crystalline structure. Overall, the study provides valuable insights into the passivation of aluminium particles by oxygen, highlighting the importance of molecular dynamics simulations in the study of materials science. In particular, the results of the study shed light on the mechanisms underlying the passivation process and suggest that temperature plays a critical role in determining the structure and properties of the resulting oxide layer.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Molecular dynamics is a computational method used to study the behavior of molecules and atoms over time. By simulating the interactions between individual particles, researchers can improve insights into the physical and chemical properties of materials at the atomic scale. This approach has been applied to a wide range of fields, from drug design to materials science and even rocket propulsion. In this case, for ducted rocket. One area where molecular dynamics has been particularly useful is in the study of boron oxidation. Boron is a lightweight and high-strength material that has potential applications in the aerospace industry. However, boron is also highly reactive with oxygen, which can lead to oxidation and degradation of its mechanical properties. By using molecular dynamics simulations, researchers can study the process of boron oxidation in detail and identify ways to mitigate its negative effects. One potential application of boron in the aerospace industry is in ducted rocket motors. Ducted rockets are a type of propulsion system that use a duct to compress air before mixing it with fuel and igniting it to burn and then generate thrust. This approach has several advantages over traditional rocket motors, including higher efficiency and lower noise levels. However, ducted rockets also require materials that can withstand the high temperatures and pressures generated during operation. Boron-based materials are well-suited for use in ducted rocket motors because of their high strength and heat resistance. However, boron oxidation can also be a concern in this context, as the high temperatures and pressures can accelerate the oxidation process. By using molecular dynamics simulations, researchers can study the interactions between boron and oxygen at the atomic level and identify ways to protect the material from oxidation. In summary, molecular dynamics simulations have a wide range of applications in materials science and engineering. In the context of boron oxidation and ducted rocket motors, this approach can be used to study the behavior of molecules and atoms at the atomic scale and identify ways to protect boron-based materials from oxidation and degradation. With continued research and development, boron-based materials could play an important role in the development of next-generation propulsion systems for aerospace exploration and other applications. Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) was used in this study. LAMMPS is a classical molecular dynamics code with a focus on materials modelling.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Electrostatic discharge is recognized as a form of ignition of energetic materials and unanticipated events of this nature get attention due to the magnitude, delay in the development of projects and loss of life. Studies have established the correlation between metallic aluminum present in formulations and the sensitivity of solid propellants to electrostatic discharge (ignition and cracking). To evaluate the influence of the electric field on the formation of cracks in the composite, models were used in the software COMSOL Multiphysics relating the amount of aluminum and the sensitivity to ESD. An experimental design for simplex network mixtures with pseudocomponents was adopted and electrical permittivity was the property observed in hypothetical AP/HTPB/Al mixtures. A model built in the COMSOL simulated external and internal discharges in a rocket motor indicating sensitive points load accumulation - in its structure, represented by the superficial density of load. Furthermore, a model assigned by the Hong group of mechanics and structural materials from Iowa State University was used to evaluate crack formation and its relation to electrical permissiveness. The results associated to the equation obtained from the experimental planning show that the model presented for the study of rupture is in accordance with the literature. The studies carried out presented a new methodology for the study of the influence of electric fields on aluminized solid composites indicating the possibility of ignition via ESD.

© 2023 Sociedade Brasileira de Quimica. All rights reserved.DETERMINATION OF DEGRADATION KINETIC PARAMETERS AND FAILURE TIME ESTIMATION OF MAGNESIUM TEFLON® VITON® ELECTRONIC “FLARE” COUNTERMEASURES. Flare type countermeasures that use the composition designated as MTV (Magnesium, Teflon®, Viton®), are the most used by Air Forces around the world. In Brazil, these “flares” are used in several locations and are subjected to different handling, storage and operation conditions that can affect their performance and compromise their service life. In this work, the Monte Carlo method was applied to estimate an empirical model to predict the lifetime of these countermeasures, using as variables the temperature and the relative humidity of the place where the material is used. The results were analyzed using multiple linear regression and analysis of variance. The kinetic parameters of material thermal degradation, such as Activation Energy and Pre-exponential Factor, and the estimated failure times of these countermeasures were determined. The results pointed out to strong temperature influence on material degradation resulting in different lifetimes for each site studied.

© 2022 Elsevier B.V.This paper presents the results of the Density Functional Theory (DFT) calculations and reactive molecular dynamics (RMD) simulations of the furazanotetrazinedioxide (FTDO) explosive, a novel highly energetic material. The details of the mechanism of the FTDO decomposition have been elucidated for the first time. The calculated activation energy was found to be 30.96 ± 2.25 kJ/mol. The DFT calculation results suggested that FTDO is prone to the fragmentation and decomposition processes. The study results present original mechanisms for the FTDO detonation/decomposition along with the values for the activation energy and frequency factor with high linear determination coefficient.

© 2021 Elsevier LtdThe current work presents the simulation of the pyrolysis and combustion of alternative jet fuels by reactive force field molecular dynamics methods. A comparison has been done between saturated hydrocarbon farnesane and two unsaturated compounds, α-farnesene and β-farnesene, all of them obtained by the fermentation of sugars present in sugarcane juice. The pyrolysis and combustion mechanisms were elucidated for all the three species at a specified temperature. Significant differences have been observed among the compound reactions during the decompositions. Using a first-order approach, the Arrhenius parameters of the global process were obtained with three different temperatures, held constant over time. For the pyrolysis, the obtained activation energies for farnesane, α-farnesene, and β-farnesene were 132.55, 117.28, and 112.88 kJ mol−1, respectively, and for the combustion, the obtained activation energies were 71.63, 37.99, and 37.98 kJ mol−1, respectively. These data are compatible with the results found in the literature for hydrocarbon fuels. A detailed computational study of all three compounds was performed using the B3LYP/6–311 + G(d,p) approach in the gas phase. Analysis of structures, NBO charges, FMOs, MEP plots, and global reactivity parameters unequivocally supports the simulation results obtained using the ReaxFF code, proving noticeably higher potential reactivity of α- and β-farnesenes compared to farnesane, and furthermore higher reactivity of β-farnesene compared to α-farnesene.

© 2021 Wiley Periodicals LLC.The solid composite propellant is a viscoelastic material that retains the treatment received during its all-useful life. As a result, its manufacturing conditions induce differences in its final mechanical properties. The present study aims to evaluate the influence of the type and size of the reactor and the effects of the heating interruption during curing on the final mechanical properties of the propellant. Thus, four production processes with identical propellant formulations were performed in four different reactors. One of them was vertical, while the others were horizontal reactors. The heating interruption during curing was performed in 10 samples, at different moments of the curing process and with different duration. The study determines that vertical reactors tend to produce propellants less rigid than those produced in the horizontal type. In addition, the bigger the reactor size, the less rigid the propellant becomes. Finally, the heating interruptions at the beginning of the curing process tend to be insignificant. However, when they occur in an advanced stage of the curing process, they tend to hinder the curing progress, being more significant for interruptions of medium duration.

© 2021 Wiley-VCH GmbHThe present study evaluated the influence of the level of load in the mixer on the processability and mechanical properties of the solid composite propellant. The mixtures were processed with the same composition and process conditions but using different percentages of levels of the maximum mixing capacity of the mixer. Both vertical and horizontal types of mixers were used to verify the existence of an optimal level of operation and whether it would depend on the type of mixer adopted. Levels of 50 %, 60 %, 70 %, 80 %, and 90 % were adopted in each macerator. In terms of processability, the 70 % level for the horizontal macerator and the 60 % level for the vertical macerator was the most suitable ones. Regarding the mechanical properties, the optimal operating level to obtain propellants with better properties would be 60–70 % in the horizontal macerator and 70 % in the vertical macerator. The results were interesting as they demonstrated the influence of the level adopted on the final grain. In addition, it is necessary to avoid using the mixers close to their maximum capacity. Therefore, the mixer level should be considered in any rocket motor casting project, both in single-batch and multi-batch processes.

© 2021 Wiley-VCH GmbHIn the Brazilian Aerospace Program, even though all developed rocket motors are manufactured in the same plant of the Department of Aerospace Science and Technology, differences are observed in the magnitude of the masses applied in each motor. Thus, depending on the volume of the combustion chamber, it is common for the casting to carry out multi-batch processes when a required mass of solid propellant is greater than the maximum capacity of the reactor. In this context, the studies that systematically evaluate multi-batch processes on an industrial scale of composite propellants based on polyurethanes obtained from HTPB are incipient. Furthermore, each batch preparation of the casting process for large motors is carried out on different days, so that each of these has a different storage time until the day of the effective casting. As a result, this wait can generate changes in the properties of the propellant grain as a whole, which can modify the motor's performance. Thusly, through the analysis of data of multi-batch processes, the present study evaluated the influence of the storage time in the preparation of the propellant and on the final properties of the grain. It was concluded that the grain becomes softer with a reduction in its hardness, greater elongation at break, and less modulus for batches with longer storage times before casting.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.Energetic materials have been used over time in civil and military applications. Concomitantly, studies were conducted focusing on the combustion mechanisms of these materials, including their kinetic and thermodynamic behavior during firing. The objective of this work was to systematically study the mechanisms of thermal decomposition of ammonium dinitramide (ADN), and ADN formulated as a solid composite propellant with glycidyl azide polymer (GAP), through reactive molecular dynamics simulations. The main reactions of the mechanisms were elucidated and analyzed, and the Arrhenius parameters were determined for the global processes. Calculated activation energies for the systems were 127.84 and 354.72 kJ/mol for ADN and ADN/GAP, respectively. Comparison to literature data shows up to 14% of deviation, which proves the methodology useful for predictions and kinetic analyzes of combustion/pyrolysis reactions of energetic materials.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In propulsion systems, to ensure a suitable thrust, the selection of the pair fuel/oxidizer is of utmost importance. Combination of propellant influences the characteristics of the chemical reaction process, the fuel vaporization speed, the ignition temperature, the volatility of hot gases. After the propellant, a suitable injector design is important, which allows better use of the propellant mixture, and thus achieve better engine performance and less combustion instability. This study evaluated the radial injector data, compared with those for other types of injectors, orifice-plate and swirl. Combustion behaviour was analysed by reactive molecular dynamics simulations. It was analysed how each contributes to the engine’s performance, by using solid fuel-based paraffin and oxygen gas in the gas phase (GOx), constituting a hybrid propellant. For orifice plate and swirl injectors, the specific impulse values were higher at higher test pressures. However, for the radial injector, the Isp was increased to the test pressure up to 25 bar. All injectors yielded good operation and met the goal of injecting oxidizer flow efficiently. The RMD simulation was able to show the behaviour of paraffin during decomposition and combustion, as well as explain the pressure effects on the system by the gaseous molecules generation.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In this work are presented pyrolysis and combustion simulations of alternative jet fuels using reactive molecular dynamics methods. Three fuels obtained from renewable resources are compared: farnesane, α-farnesene and β-farnesene. The pyrolysis and combustion simulations were done in different temperatures. Significant differences have been observed among the compound reactions during the decompositions. The Arrhenius parameters of the global process were obtained for all species, considering a first-order approach. For the pyrolysis, the obtained activation energies for farnesane, α-farnesene and β-farnesene were 132.55, 117.28 and 112.88 kJ mol-1, respectively.

© 2021, Universidade Federal do Rio de Janeiro. All rights reserved.The present study evaluated different formulations of solid propellants based on HTPB / AP / Al modified by the short chain diols, 1,4-butanediol and 1,2-propanediol at different mass concentrations. In this context, this was done in order to obtain differentiated mechanical properties without neglecting the other imposed requirements, such as processability and ballistic properties. In this sense, a methodology for calculating the formulations was developed and their processing was carried out in a small reactor. Moreover, with a view to evaluating the influence of the mass content of plasticizer used, the formulation containing a higher content of 1,4-butanediol was also processed employing a greater amount of plasticizer. The post-processing dynamic viscosity profile and the evolution of the hardness during curing were evaluated, and a mechanical characterization was performed. In addition, a specific mass determination test, X-rays of samples and a calorimetric bomb test were carried out. Hence, it became evident that the formulations modified with 1,4-butanediol are promising. Nevertheless, it was not possible to achieve, in this study, all the requirements expected in a final product for immediate use.

© 2021, Academia Brasileira de Ciencias. All rights reserved.Hydroxyl-terminated polybutadiene (HTPB) is widely used in the formulations of solid propellants used in rocket motors. Furthermore, in general, chain extenders and short chain diols, such as 1,4-butanediol and 1,2-propanediol, can also be used in propellant formulations to improve mechanical properties, especially tensile strength. However, the incorporation of these diols can result in a considerable increase in the viscosity of the mixture during the processing of propellants. Thus, the present study evaluated the compatibility of these diols with the HTPB prepolymer, through a viscometric study, with the aim to determine the order of addition that results in greater homogeneity for the mixture. It was concluded that 1,4-butanediol, due to its larger chain size, has better compatibility with HTPB resin than 1,2-propanediol. On top of that, it was found that when the resin is added first, it results in mixtures with greater compatibility.

© 2021 Sociedade Brasileira de Quimica. All rights reserved.In recent years, research on the development of protective materials has expanded significantly in order to find efficient and economically viable solutions for application in various industrial segments. Among these materials, those aimed at protecting metallic substrates against high temperatures that end up causing corrosive processes, stand out due to the huge market demand. Advantages such as reproducibility in the process, cost reduction and reduction in environmental impact also directly contribute to the search for protective coatings as an efficient protective alternative. This article presents the characterization of a ceramic coating developed in a previous study that used silicon carbide as a filler, using potassium silicate (water glass) as a matrix (binder), and whose anti-corrosion and thermal protection properties stood out, mainly in applications in the aerospace industry. In this stage of the work, tests of thermal analysis (thermogravimetry) were carried out for the physical and chemical characterization of the material. The results corroborate those previously achieved when applying the coating on components of a hybrid rocket engine tested on a fixed-point bench.

© 2021, Academia Brasileira de Ciencias. All rights reserved.Dynamic loads continue to draw the interest of structural engineers. The sources of these loads can be earthquakes, blast effects or transportation loads from railroads or highways. Especially for blast loads, terrorist attacks or military actions have caused many loses of lives and damages in several buildings. The verification of structural behavior is necessary to help designers to plan structures that support these loads and reduce damages. Although computer simulation with, specific software, have helped these designers, full-scale tests can provide valuable information about the real response of the structure. This paper presents damage diagram from ten full-scale field tests using approximately 2.70 kg of non-confined plastic bonded explosive against reinforced concrete slabs with different scaled distance, reinforcement ratio and concrete strength. The damage diagram is expected to be a help tool for designers to understand the effects of blast loads on slabs.

© 2020 by the authors.The design and evaluation of structures subjected to blast loads has increased steadily since the 11 September 2001 terrorist attacks. While shock tube testing has filled some of the data gap by replicating blast waves in a controlled fashion, there is only scant field explosion data that is easily accessible for the structural engineering community for hypothesis testing or model validation. This paper summarizes experimental design, pre-test sensor verification, and data collection from 10 reinforced concrete slabs subjected to field explosions using a modest budget. The experimental record contains pressure, displacement, and acceleration measurements of each slab except in a few cases where the sensors have failed. The data is archived at George Mason Dataverse. Following detailed description of the experimental record for each slab, an example is provided in which the data can be utilized for finite element model verification.

© 2020 IOP Publishing Ltd. All rights reserved.Predicting explosion parameters is an important step when planning for blast tests or the design of blast resistant buildings and of explosive materials and formulations. This paper presents reactive molecular dynamics simulations of furazanotetrazinedioxide (FTDO) explosive, a new and highly energetic material, calculated with the software LAMMPS with ReaxFF force field. The decomposition steps and chemical mechanism of the material decomposition was elucidated and the Arrhenius parameters of the global decomposition reaction was calculated based on a first order approach with six different isothermal simulations sets. Results present an original mechanism for the detonation/decomposition and an activation energy and frequency factor with high linear determination coefficient. These results are the first ones published for this material and present a good comparison for future experiments.

© 2020 Sociedade Brasileira de Quimica. All rights reserved.The molecular dynamics simulations were used to study the epoxy ring-opening in the determination of kinetic parameters, with a temperature range from 1500 to 2500 K in a 20 x 20 x 20 Å unit cell containing 15 molecules of C2H4O (ethylene oxide) and 35 molecules of CH6N2 (methanediamine). The activation energy values for epoxy and diamine was 66 and 92 kJ mol-1, respectively. The simulation showed epoxy ring breakage in some of the molecules, but mainly the release of ammonia by diamine. It was observed that the activation energy involved in diamine consumption for ammonia formation is higher than for the epoxy ring opening. The results of the epoxy ring-opening study show that the polymerization occurs slowly, which leads to high computational simulation values.

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The design of solid rocket motors is considered relatively dominated technology in the various areas of knowledge. Even so, there are variables that still need to be better explored. Therefore, the topic presented in this work is related to problems found in designs of HTPB-AP-AL based solid rocket motors that are related to the formation of Plateau in the performance curves (pressure and thrust). This phenomenon has been studied by many researchers, in the way that studies mention different causes. Among the main causes studied, research reports that this phenomenon is related to Ammonium Perchlorate and its granulometric distribution and size, the thermal decomposition kinetics of Ammonium Perchlorate, the distribution and morphology of aluminum and also to the curing agents used in the propellant formulations. The main objective of this work is to present a model built with propellant formulations, considering these variables above mentioned in order to address a good practice to avoid this phenomenon. This work presents burning rates as a function of pressure of several propellant formulations based on ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene cured by isophorone diisocyanate (IPDI) and aluminum (Al), in order to evaluate values of the pressure exponent of the burning rate in distinct pressure ranges, termed as plateau burning rate trends.

© 2019, The Brazilian Society of Mechanical Sciences and Engineering.Propellants based on HTPB/AP (hydroxyl-terminated polybutadiene/ammonium perchlorate) are the most commonly used in most of the rocket engines used by the Brazilian Armed Forces. This work aimed at the possibility of extending its useful life (currently in 10 years) by performing chemical kinetic analysis of the energetic material via differential scanning calorimetry (DSC) and also performing computer simulation of aging process using the software Large-scale Atomic/Molecular Massively Parallel Simulator. The simulations presented the experimental behavior of the aging process, showing the bending and cross-link of the binder with the volume contraction and the energetic stabilization. Thermal analysis via DSC was performed in triplicate and in 3 heating ratios (5 °C, 10 °C and 15 °C) of rocket motor with 11-year shelf-life, using the Arrhenius equation to obtain its activation energy, using Ozawa and Kissinger kinetic methods, allowing comparison with manufacturing period data (standard motor). The obtained activation energies were 126.67 kJ/mol (Ozawa) and 122.85 kJ/mol (Kissinger), much higher than that of the aged propellants (~ 78 kJ/mol, based on literature data), showing that the propellant has not yet aged significantly. In addition, the kinetic parameters of internal pressure of the combustion chamber in 8 rocket engines with 11 years of shelf-life were also acquired, for comparison purposes with the engine start-up data.

© 2020, Eduem - Editora da Universidade Estadual de Maringa. All rights reserved.Predicting explosion parameters is an important step when planning for blast tests or the design of blast resistant buildings. This paper presents a comparison of recorded pressure that was reflected on the surface of reinforced concrete slabs with and without EPS (Expanded Polystyrene) foam retrofit measured from a detonation of 2.7 kg of non-confined plastic explosive. Two 50 MPa reinforced concrete slabs measuring 1.0×1.0×0.08 m, simply supported on two sides were tested. The explosive was suspended at a distance of 2.0 m from the upper surface of the slabs; one of the slabs had 5.0 cm thick foam on the top side. Eight piezoelectric pressure sensors were positioned at a distance of 2.0 m from the explosive. Results showed that the foam retrofit reduced the reflected pressure by approximately 57% when compared to the slab without EPS foam retrofit.

© 2019 Sociedade Brasileira de Quimica. All rights reserved.This work aims to determine the kinetic parameters of the thermal decomposition of a lubricating grease based on perfluoropolyether (PFPE) and the computational simulation of this decomposition. The determination of kinetic parameters of thermal decomposition was done by thermal analysis using thermogravimetry (TG) at different heating rates (β) of 10, 15 and 20 °C min-1. With the TG curves obtained, the kinetic parameters were determined by the kinetics methods of Goldfarb et al. and Duvvuri et al., Flynn-Wall-Ozawa and Kissinger. The activation energy of the thermal decomposition of the PFPE grease in the kinect models ranged from 63.54 to 112.3 kJ mol-1. The results of the thermogravimetry indicated that the PFPE grease is thermally stable up to 300 °C. A simulation of the thermal decomposition of the PFPE oil base was carried out by molecular dynamics simulation, using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) in a temperature range of 0 to 3500 K during 50 ps. The value of the activation energy in the simulation was 92 kJ mol-1. The results show that PFPE oil base and PFPE lubricant grease can be used in high-temperature applications.

© 2019 Sociedade Brasileira de Quimica. All Rights Reserved.Density, viscosity and calorific values are important physical properties to affect the utilization of biofuel. In this work, mixtures of farnesane and a “jet fuel”, QAv-1, were used to study the variation of density and kinematic viscosity as a function of the volumetric fraction of farnesane and temperature. Experimental measurements were carried out for nineteen farnesane blends and pure farnesane and QAv-1, at four temperatures in the range of 293 - 323 K. Variation of high heating (HHV) and low heating (LHV) values were also determined for different blends of farnesane/QAv-1. Several empirical correlations were used to predict the density, the kinematic viscosity, HHV and LHV values. By using some of these empirical correlations, the estimated values of those three properties studied are in excellent agreement with the experimental data, with low absolute average prediction error.

© 2019, The Brazilian Society of Mechanical Sciences and Engineering. This paper presents a study about injectors, where the radial injector was evaluated. This type of injector was chosen because only a small amount of information on it was found. Thus, the radial injector will be compared with other two types of injectors, the orifice plate and the swirl, in terms of parameters, such as discharge coefficient (C d ), regression rate r, and specific impulse (I sp ). In respect of the regression rate, the values appeared increasingly with the test pressure and, consequently, with the injection pressure. Thus, each injector model responded in the same way as for the regression rate behavior; however, the same behavior was not observed in relation to the specific impulse.

© 2018, Revista Ingenieria e Investigacion - Editorial Board. All rights reserved.This paper presents the results from blast tests conducted on four 50 MPa concrete slabs with reinforcement ratios of 0,175% and 0,37%. Two of the slabs were retrofitted with 50 mm thick foam in order to investigate the potential of using the foam as a strengthening option. The slabs were simply supported on two sides. Non-confined PBX (Plastic bonded explosive) was molded with the form of a cylinder measuring 20 cm in height and 10,5 cm in diameter. The explosive was detonated at 2 m stand-off distance. The equivalent TNT mass of the explosive ranges from 2,58 to 2,72 kg for the four tests. Accelerometers, displacement and pressure gages were used to measure blast wave parameters and global response of the slabs. A high-speed digital camera in conjunction with a rugged notebook recorded images. Qualitative and quantitative results are included. Slabs retrofitted with foam showed a different pressure pattern as recorded by the sensors and resulted in higher displacement, acceleration and linear momentum.

© 2018 Sociedade Brasileira de Quimica. All rights reserved.The combustion process of triethylaluminum is investigated by means of reactive molecular dynamics simulations using the ReaxFF force field. The behavior of the system in five different temperatures ranging from 2000-4000 K was evaluated. As a pyrophoric material, TEA reacts also with water, generating gaseous hydrogen, whose content increases with the system temperature. Rapid water formation and O2 depletion were observed and, using Arrhenius equation, the preexponential factor and activation energy were found to be 9.67E+09 s-1 and 1.242 kJ mol-1, respectively. The results obtained are in accordance to the expected for pyrophoric materials and the simulation in question can help elucidating and analyzing the complex reaction mechanism of TEA combustion.

© 2018 Sociedade Brasileira de Quimica. All rights reserved.Prediction of chemical explosions parameters is an important step for blast tests for civil and military applications. Applying computational chemistry and experimental results, this paper presents the decay rate of pressure in air from the epicenter of 2.70 kg of PBX-Plastic bonded explosive detonation to the distance of 2.0 meters. Pressure in the epicenter was calculated using reactive molecular dynamics simulations and the incident pressure at 1.3; 1.6 and 2.0 meters were measured with piezoelectric pressure sensors. The explosive for the full-scale test were non-confined in a cylindrical shape. Results of simulation and recorded values were consolidated and the rate of pressure decay was verified by statistic regression. Good agreement was verified between computational and experimental pressures data. This research can help designers to prepare protection devices in test areas, storages of explosives or important buildings for military proposes.

© 2018, DESIDOC.Explosions emanating from terrorist attacks or military weapons cause damage to civilian and military facilities. Understanding the mechanical behaviour of reinforced concrete structures subjected to blast is of paramount importance for minimizing the possible blast damage. A full-scale experimental program consisting of six reinforced concrete slabs with compressive strengths of 60 MPa, 50 MPa and 40 MPa, measuring 1.0 m × 1.0 m × 0.08 m, and subjected to 2.7 kg of non-confined plastic bonded explosive, was conducted in blast test area of Science and Technology Aerospace Department (Brazilian Air Force). This paper compares experimentally measured peak displacement values with theoretical values. Theoretical analysis was carried out using single degree of freedom (SDOF) models. The comparison showed that SDOF analysis worked very well in predicting the reinforced concrete slab peak displacement against blast effects. Qualitative analysis after the experiments showed that the blast wave shape generated by the cylindrical explosive was not uniformly distributed on the slabs for the standoff distance of 0.927 m/kg13.

© 2018, Journal of Aerospace Technology and Management. All rights reserved.The present study assesses the influence of non-metallic constituents and manufacturing parameters, such as compaction pressure and sintering temperature, to produce a metal matrix composite (MMC) of copper/iron, based on the brake disc of aircraft AT-29 SuperTucano. The samples were produced with six different compositions, by varying the amount of abrasive particles (quartz and zirconia silicate) and the solid lubricant (graphite), with one of the compositions manufactured without the addition of graphite. The compaction pressures were 210 and 420 MPa, with sintering temperatures of 950 °C and 1050 °C in a furnace with controlled atmosphere of argon + 10% H2. After sintering, the effectiveness of the sintering process was evaluated through the apparent density (Archimedes’s method), Brinell and Vickers hardness, and the microstructure by Scanning Electron Microscopy (SEM). The sintering process was severely affected by the solid lubricant (graphite): its reduction resulted in a density increase near 18%, and the hardness of the compound up to 62%. The hardness values demonstrated significant variation with compaction pressure, with a pronounced effect on compounds with less non-metallic elements. SEM analysis demonstrated that not only graphite, but also the ceramic particles affected the sintering process through the agglomeration of inclusions into the metal-metal interface. The samples without graphite exhibited almost the same value of pores after sintering, regardless of the compaction pressure, indicating that the graphite content affects directly the sintering process, regardless of the compaction pressure.

Magnesium/PTFE/FPM decoy flares, also named conventional flares, were designed in order to protect combat aircraft from the threat caused by infrared-guided missiles. Adverse storage or transport conditions may cause reactions that deteriorates chemical properties of the conventional flares, causing the aging and compromising its performance. The aim of this article was to characterize the influence of accelerated aging on conventional flares. The study was performed with the latest lot of conventional flares from Brazilian Air Force, subjected to 50 days exposure in a climatic chamber at 76 °C and 62% RH. Upon completion of the accelerated aging process, samples of aged conventional flares were compared with unaged material. Qualitative determination of chemical species present was carried out using the techniques FT-IR and SEM/EDS. Magnesium hydroxide, the main product of aging process and primary aging indicator on conventional flares performance, was determined using thermogravimetric analysis and the amount was correlated with results of the experimental techniques Density Determination, Calorimetry and Vacuum Stability Test. Formation of additional magnesium hydroxide mass, that increased 100% during the aging process, caused the passivation of magnesium, compromising the combustion process and making the composition less energy efficient, as verified in the results of the calorimetric tests.

Epoxy resins are an important class of thermostable polymers, widely used in structural applications or as adhesives. However, the low fracture resistance is their main weakness in many applications. Due to this fact, this study aims to modify a polymer matrix based on a novolac epoxy resin with an organo siloxane (AMS). The final properties of cured epoxys resins are affected by the curing process and the coatings modified in this study with AMS and cured with acid catalyst presented greater resistance to thermal decomposition compared to that cured with Aradur, demonstrating a higher content of crosslinking in the siloxane polyether and the novolak epoxy resin chains. This epoxy matrix modified was used to prepare coatings whose films applied to 1020 steel surfaces presented a resistance of 1010 Ohm-cm-2. This resistance value is one order of magnitude greater than that of epoxy resins films modified by siloxanes in published studies, which demonstrates a potential economy in terms of maintenance costs of metal structures and machines used in power plants (UTE). To obtain the developed inks in pilot plant scale, it was used an aromatic polyamine as curing agent, characterizing the product obtained as an epoxy bi-component paint for commercial use.

Solid rocket motors (SRM) are extensively employed in satellite launchers, missiles and gas generators. The design takes into account propulsive parameters with dimensional, manufacture, thermal and structural constraints. Gas generators and booster SRM frequently employ multiperforation in propellant grain geometries for rapid combustion. A computational tool for tracking the propagation of tridimensional interfaces and shapes is necessary for this task. In this sense, the objective of this paper is to present results using the developed computational tool (named RSIM) to simulate the burning surface regression during the combustion process of a solid propellant. This tool handles complex grain geometry for versatility, including multiple separate surfaces. The SRM internal ballistics simulation is based on 3D propagation, using the level set method approach. Geometrical and thermodynamic data are used as input for the computation, while simulation results of chamber pressure versus time are presented for multiperforated grains.

© 2017 by Begell House, Inc.Most of the coatings available on the market do not meet the protection requirements of high temperatures and oxidation of metallic surfaces exposed to chemically aggressive environments at high temperatures. Thus, the development of an inorganic base coating (potassium silicate) was proposed in the form of an aqueous solution for application in hybrid rocket motor metallic components. This coating distinguishes itself from others by supporting extreme operating conditions of operation without degrading or losing its original characteristics, thus forming a glassy film which anchors in/on the surface of the substrate in which it is applied, i.e., becoming a superficial layer. The investigation of the applicability of a high-temperature coating was studied in adverse conditions, as in the case of a hybrid rocket motor; different components of the engine have received the coating application. Once coated, the components were assembled as a hybrid engine and subjected to firing tests. The results were very promising, since the coating could reduce the erosion in the throat of the nozzle by 50%, improving the hybrid rocket motor operation time at temperatures around 2.000 Celsius.

In the solid propellant manufacturing process, one of the most important steps is the casting that consists in pouring the propellant in its more fluid state in a mold and then leaving it to cure or solidify. This step is very important because, if done wrong, could yield a propellant grain that contain lots of discontinuities such as voids and cracks and these could lead to a motor explosion. In a previous casting method, the propellant was subjected to stress of compression, but for candy propellants, that have a crystalline characteristics, this stress due to compression increase the chances of a crack in the grain. Thus, is necessary to change the casting process and the new process developed is described in this article.

© ASCE.Multiple blast tests were conducted on RC slabs at the Science and Technology Aerospace Department in Brazil. This paper presents the description of the experimental test set-up, instrumentation and results from a sub-set of the tests conducted on four 60 MPa concrete slabs with reinforcement ratios of 0.25% in two-way. In addition, one of the four slabs was retrofitted with 50 mm thick foam to determine if the foam has the capacity to reduce the blast response of the slab. The slabs were simply supported on two sides and the explosive was detonated at 2 m stand-off distance. The explosive charge was non-confined C4 plastic explosive cylinder. The equivalent TNT mass of the explosive ranges by 2.6-2.76 kg. Accelerometers, displacement and pressure gages were used to measure blast wave parameters and global response of the slabs. A high-speed digital camera in conjunction with a rugged notebook was used to capture images. Both qualitative and quantitative results are included. The foam on slab 3 varied the pattern of pressure recorded by the sensors and induced higher displacement, acceleration and linear momentum.

This article aims to estimate the shelf life of the PBX by thermal analysis estimated by the Arrhenius equation, equivalent to the time of storage at accelerated aging. The PBX was subjected to accelerated aging in an oven at controlled temperature 60 °C for periods of 5, 10, 15 and 25 weeks, which are equivalent to 5, 10, 15 and 25 of natural aging, respectively, at a temperature of 25 °C. The curves of thermal decomposition of the samples were obtained by the DSC (Differential Scanning Calorimetry) technique. The kinetic parameters, such as the activation energy and pre-exponential factor, were determined by the Ozawa method and the Kissinger method. Initial results of this study indicated that, for a period of 25 years of storage in the cargo hold, the material did not change this aging significantly. To study the life of PBX analyzes, vacuum chemical stability were also conducted to verify the safety of explosive handling.

© 2016, Springer-Verlag Berlin Heidelberg.This work presents a comprehensive DFT study on the interaction between hydrazine derivatives with a platinum catalyst surface, which is represented by a tetrahedral Pt4 cluster model. Three separate reaction pathways were investigated; two of which are related to possible pathways of NH3 formation. The first pathway describes the intramolecular transfer of one hydrogen atom in the hydrazine molecule forming the NHNH3 intermediate, then dissociating into NH and NH3. The second describes the addition of one external hydrogen atom to hydrazine forming N2H5, followed by its dissociation to NH2 and NH3. The third reaction pathway involves the formation of N2H3 by means of hydrogen abstraction by an external hydrogen. The reactions were studied in both the absence and the presence of a Pt4 cluster. We find that the assistance of the Pt4 cluster lacks a systematic effect on the reactions barrier heights. It is also shown that the ammonia formation can possibly proceed through the formation of the N2H5 intermediate, leading to more exothermic intermediate steps in the presence of the Pt4 cluster.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The ITA Candy Rocket Program is a student program of undergraduate students to develop and fly a sounding rocket motor and compete at the Intercollegiate Rocket Engineering Competition. The program was kicked off in August 2011 and every year the design is altered for improvements. This paper shows the solid propellant preparation from easily available raw ingredients. The propellants are potassium nitrate and sorbitol. The potassium nitrate was purified, sieved, and recrystallized. A ground test program with small and real scale tests was conducted to evaluate the motor design and development.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Solid rocket motors (SRM) are extensively employed in satellite launchers, missiles and gas generators. The design takes into account propulsive parameters with dimensional, manufacture, thermal and structural constraints. Experiments using real scale rocket models are expensive, therefore simulations are required to decrease the overall project time and cost. Solid propellant geometry and computation of its burning rate are essential for the calculation of pressure versus time and thrust versus time curves. The propellant grain geometry changes during SRM burning are also important for structural integrity and analysis. A computational tool for tracking the propagation of tridimensional interfaces and shapes is necessary for this task. In this sense, the objective of this paper is to present the developed computational tool (named RSIM) to simulate the burning surface regression during the combustion process of a solid propellant. This tool handles complex grain geometry for versatility, including multiple separate surfaces. The SRM internal ballistics simulation is based on 3D propagation, using the level set method approach. Geometrical and thermodynamic data are used as input for the computation, while simulation results of chamber pressure versus time are presented for NAWC SRM number 6.

© 2016. Journal of Aerospace Technology and Management. all right reserved.This paper describes the polycarbonate acrylic laminated development that can be applied in aeronautics and aerospace transparencies. The case studied is a laminated double-curved transparency (bubble form) used in an observation side window of a military aircraft. Side windows need strength and specific characteristics, similar to windshields, allowing the perfect visualization and image capture. Laminated transparencies composed by different materials have better qualities than the monolithic ones. This kind of transparency can offer high mechanical and chemical resistance, high transparency, no fragmentation and easy maintenance or recovery. A significant amount of information about materials and processes was jointed in order to build the reinforced transparency and validate this study. The final results were analyzed based on two points of view: mechanic resistance and, especially, optical quality.

© 2015, Journal of Aerospace Technology and Management, All rights reserved.In the last decades, hybrid rocket engines have been increasingly studied and used in space vehicles. However, the low regression rates and specific impulses still represent major drawbacks to this technology. The objective of this study was to quantify the relative improvement of regression rate values with the use of a swirling flow injector in comparison to an axial injector. Seven tests were conducted with axial injection and seven with swirl injection. Regression rate results were compared, and it was found that swirl injection improved regression rates in 50% for mass fluxes higher than 45 kg∙s–1∙m–2. It was possible to see radiation, kinetic and diffusion theory on the logarithmic plot of regression rate per oxidizer flux yielded by both injectors. A strong agreement with experimental findings of regression rates in the literature parameters is reported.

© 2014 American Chemical Society.Thermochemical and kinetics properties of the hydrogen abstraction from the hydrazine molecule (N2H4) by an oxygen atom were computed using high-level ab initio methods and the M06-2X DFT functional with aug-cc-pVXZ (X = T, Q) and maug-cc-pVTZ basis sets, respectively. The properties along the reaction path were obtained using the dual-level methodology to build the minimum energy path with the potential energy surface obtained with the M06-2X method and thermochemical properties corrected with the CCSD(T)/CBS//M06-2X/maug-cc-pVTZ results. The thermal rate constants were calculated in the framework of variational transition-state theory. Wells on both sides of the reaction (reactants and products) were found and considered in the chemical kinetics calculations. Additionally, the product yields were investigated by means of a study of the triplet and singlet surfaces of the N2H4+ O → N2H2+ H2O reaction.

Copyright © 2015 by the International Astronautical Federation. All rights reserved.Solid rocket motors (SRM) are extensively employed in satellite launchers, missiles and gas generators. The design takes into account propulsive parameters with dimensional, manufacture, thermal and structural constraints. Experiments using real scale rocket models are expensive, therefore simulations are required to decrease the overall project time and cost. Solid propellant geometry and computation of its burning rate are essential for the calculation of pressure vs time and thrust vs time curves. The propellant grain geometry changes during SRM burning are also important for structural integrity and analysis. A computational tool for tracking the propagation of tri-dimensional interfaces and shapes is necessary for this task. In this sense, the objective of this paper is to present the developed computational tool (named RSIM) to simulate the burning surface regression during the combustion process of a solid propellant. This tool handles complex grain geometry for versatility, including multiple separate surfaces. The SRM internal ballistics simulation is based on 3D propagation, using the level set method approach. Geometrical and thermodynamic data are used as input for the computation, while simulation results are presented in three test cases: simplified star, finocyl and multiperforated propellant grains.

© 2014, Springer-Verlag Berlin Heidelberg.Chalcones are an important class of medicinal compounds and are known for taking part in various biological activities as in anti-inflammatory, anti-leishmania, antimitotic, and antiviral. Chemically, chalcones consist of open-chain flavonoids in which the two aromatic rings are joined by a three-carbon α,β-unsaturated carbonyl system. The wide action spectrum has attracted our attention to synthesize, crystallize, and characterize the dimethoxy-chalcone C18H18O3. Aiming to understand the process of crystal lattice stabilization, a combination of technique has been used including X-ray diffraction, infrared spectroscopy and computational molecular modeling. The theoretical calculations were carried out by the density functional method (DFT) with the M06-2X functional, with the 6-311+G(d,p) basis set. The vibrational wavenumbers were calculated and the scaled values were compared with experimental FT-IR spectrum. The intermolecular interactions were quantified and intercontacts in the crystal structure were analyzed using Hirshfeld surfaces. Bond distances and angles described by the X-ray diffraction and theoretical calculation are very similar. The C-H….O contacts contributing to assemble the supramolecular architecture are also responsible for the molecular structure assembly.

Composite solid propellants prepared with HTPB prepolymer-Hydroxyl Terminated Polybutadiene, AP-Ammonium Perchlorate as oxidizer and aluminum particles as an additive metal, have characteristics of high electrical resistivity. The loading process of the polymer matrix did not obtain homogeneity, resulting in clusters, mainly of metal particles. The effect of clustering in the composite was studied and observed experimentally, and this effect was one of the factors explaining the phenomenon of electrical charging of the composite. This electrical potential, when discharged abruptly, can generate an electric spark with sufficient energy for sustained ignition of a solid rocket motor.

The aim of this work was to synthesize a polyurethane polymer matrix using polyols as a raw material to obtain a binder such as the hydroxyl terminated polybutadiene (HTPB) pre-polymer in energetic material formulation. The soybeanbased polyol was the best starting raw material for producing a binder for solid fuel formulation in rocket motor applications. Characterization of the obtained soybean-based polyurethane binder was carried out by employing FT-IR analysis and thermo analytical techniques that showed similar HTPB binder thermo decomposition behaviors, confirming their potential for use as polymer matrix composites.

The main objective of this research work was to obtain two formulations of ablative composites. These composites are also known as ablative structural composites, for applications in atmospherically severe conditions according to the hightemperature, hot gaseous products flow generated from the burning of solid propellants. The formulations were manufactured with phenolic resin reinforced with chopped carbon fiber. The composites were obtained by the hot compression molding technique. Another purpose of this work was to conduct the physical and chemical characterization of the matrix, the reinforcements and the composites. After the characterization, a nozzle divergent of each formulation was manufactured and its performance was evaluated through the rocket motor static firing test. According to the results found in this work, it was possible to observe through the characterization of the raw materials that phenolic resins showed peculiarities in their properties that differentiate one from the other, but did not exhibit significant differences in performance as a composite material for use in ablation conditions. Both composites showed good performance for use in thermal protection, confirmed by firing static tests (rocket motor). Composites made with phenolic resin and chopped carbon fiber showed that it is a material with excellent resistance to ablation process. This composite can be used to produce nozzle parts with complex geometry or shapes and low manufacturing cost. © The Author(s) 2014.

The aim of this work was to synthesize a polyurethane polymer matrix using castor oil as a polymer chain modifier, whose characteristics can be adjusted for use as a binder in the manufacture of energetic materials such as propellant and pyrotechnics for aerospace use. We attempted the partial substitution of hydroxyl-terminated polybutadiene (HTPB), a pre-polymer commonly used as a starting polyol in obtaining energetic matrix composites. Thermoanalytical techniques were employed to characterize the material based on castor oil and the unmodified HTPB. The results showed similar behaviors, confirming the possibility of their use as polymer matrix composites through the proposed adaptations.

Experimental investigation was conducted to determine the relative propulsive and combustion behavior of a polyurethane-based solid-fuel formulations containing 30% w/w of paraffin. In total, 4 solid fuel formulations were investigated. The thermal decomposition of the solid fuels was studied at different heating rates in dynamic nitrogen. Fuel containing paraffin was investigated with electron microscopy, paraffin spheres were visualized and measured. Firing tests with 4 configurations were performed. Thrust measurements indicated that the addition of paraffin increased thrust at about 57% and regression rates at about 83%. It was found that increase in regression rate is proportional to paraffin content.

© 2013, American Institute of Aeronautics and Astronautics Inc. All rights reserved.Experimental investigation was conducted to determine the relative propulsive and combustion behavior of a polyurethane-based solid-fuel formulations containing 30% w/w of paraffin. In total, 4 solid fuel formulations were investigated. The thermal decomposition of the solid fuels was studied at different heating rates in dynamic nitrogen. Fuel containing paraffin was investigated with electron microscopy, paraffin spheres were visualized and measured. Firing tests with 4 configurations were performed. Thrust measurements indicated that the addition of paraffin increased thrust at about 57% and regression rates at about 83%. It was found that increase in regression rate is proportional to paraffin content.

Experimental investigation was conducted to determine the relative propulsive and combustion behavior of several polyurethane-based solid-fuel formulations containing 30% w/w of paraffin or 10% of aluminum powder. In total, seven solid-fuel formulations were investigated, four containing 30% of paraffin and three with 10% of aluminum. The polyurethane was synthesized with pre-polymer technology. The oxidizer was gaseous oxygen, which was forced into the combustion chamber with axial and swirl methods. Firing tests with 7 configurations were performed. Thrust measurements indicated that the addition of paraffin increased thrust at about 57% and regression rates at about 70%. No relevant improvement in performance was obtained with aluminum addition. Specific impulse decreased when aluminum particles were added to the fuel. The mixture that produced the best ballistic parameters was polyurethane plasticized with castor oil and 30% w/w of paraffin with gaseous oxygen injected through a swirler.

Aluminum that is incorporated in an energetic material such as a propellant plays a significant role in the combustion process by means of stabilization with regard to the burning and generation of additional energy. The use of simulation softwares to model the combustion mechanism and kinetic parameters of the elementary reactions that compose the oxidation were used as the pressure variation of the combustion chamber of a rocket motor conditions. The behavior of the molar fraction of the chemical species during the combustion and its posterior stabilization were observed. The systems submitted to higher pressures tend to stabilize more rapidly, according to the greater chemical speed of the elementary reactions.

The burning simulation of hydrogen was carried on in the reactor model Aurora, present in the software Chemkin, with three different experimental data sets and one calculated set, by quantum chemistry methods (MP2). The analysis of the calculated parameters for each reaction was made and compared to the experimental ones through burning simulations. A detailed study of the mechanism was realized, while setting specific time inputs, showing the concentrations of chemical species and the rates of production/consumption of reactants, intermediates and products. The ignition step of the combustion was simulated, when varying the time from 0 to 3 nanoseconds. All the mechanisms showed different results in this step. More refinement is needed in the theoretical data in order to successfully simulate the ignition phase. This methodology allows the insertion of new reactions in several mechanisms and also the calculation of parameters for reactions which cannot be determined experimentally. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

The aim of this work is to develop a high regression rate fuel for hybrid rocket motors, this research encompasses binder synthesis and the addition of paraffin and aluminum metallic particles. The project started with the synthesis of polyurethane (binder) based on pre-polymer technology modified with castor oil. These binders were filled with granulated paraffin and micron-sized aluminum particles. Firing tests with 7 configurations were performed. Thrust measurements indicate that the addition of paraffin increased thrust at about 57% and regression rates at about 70%. No relevant improvement in performance was obtained with aluminum addition. Specific impulse decreased when aluminum particles were added to the fuel. The mixture that produced the best ballistic parameters was polyurethane plasticized with castor oil and 30% w/w of paraffin with gaseous oxygen injected with a swirler. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Dynamic mechanical properties of a polyurethane (PU) elastomer and a mortar processed with the same elastomer (modified polytetramethylene ether glycol (PTMEG)) were studied. The results obtained showed that the liquid aromatic amine ETHACURE® 300, used as cure agent, can be used to substitute the aromatic amine MOCA®, which is usually used as cure agent in high performance elastomers. The resulting mortar produced with ETHACURE® 300 presents similar dynamic-mechanical thermal properties when compared with MOCA ®. However, dynamic-mechanical thermal analysis studies showed that the mortar developed with ETHACURE® 300 presents some advantages such as the low values of tan δ, indicating a good capacity of recovery of the strain after retreating an applied force. © 2012 Wiley Periodicals, Inc.

The fuel was synthesized with polyurethane (binder) based on pre-polymer technology modified with castor oil with the addition of 30% of paraffin and 10% of aluminum powder. An axial and a swirl injector were used. The regression rates doubled with the addition of paraffin and the mechanical properties increased drastically. Thrust measurements indicate that the addition of paraffin increased thrust at about 57% and regression rates at about 70%. The mixture that produced the best ballistic parameters was polyurethane plasticized with castor oil and 30% w/w of paraffin with gaseous oxygen injected with a swirler. The swirl injector improved the efficiency and regression rate values. © 2012 by Flowtest Pesquisa Aeroespacial.

In recent years, Hybrid Propulsion is turning into a significant alternative to Liquid and Solid Propulsion Systems, it presents attractive features and good balance between performance and environmental impact. Thus, paraffin based propellant grains are indicated as a substitute for hydroxyl-terminated polybutadiene (HTPB), the actual solid propellant fuel grain. Despite being a wellknown material, scarce data on the relation of activation energy (Ea) and molecular weight (WC H ) of paraffin is available. In this work, the kinetic parameters (activation energy and pre-exponential factor) of microcrystalline 140/1450F paraffin have been raised through Thermo Gravimetric Analysis in conjunction with the Arrhenius kinetic mechanism, according to ASTM-E1461 and the dependence of molecular weight with melting point from Etessam and Sawyer approach. The 140/1450F paraffin activation energy calculated in this study was compared with different activation energy from alkanes and substances used as fuel in the propulsion systems field. The analysis indicated that the microcrystalline 140/1450F paraffin, manufactured by Petrobras, presents activation energy of 224 KJ.mol-1 and pre-exponential factor of 5.48x1022 min-1. Ignition was achieved with a 50 W pyrotechnic igniter. The firing test with 140/1450F paraffin fuel and gaseous oxygen (GOX) mass flux of 130 Kg.s- 1m-2 at pressure above 0.80 MPa, was easily sustained. Copyright © 2012 by ASME.

The combustion simulation of ammonium perchlorate was carried out with the software Chemkin, in two steps: the burning behavior of pure ammonium perchlorate and the one of formulated ammonium perchlorate with hydroxyl terminated polybutadiene binder. In both cases, the room pressure varied in order to verify its influence in the system. The burning environment conditions were diverse. During the combustion process, the data obtained from the kinetic chemistry simulation software were compiled. The flame structure can be described by the molar fraction of the burning products and the temperature evolution from the surface of the material.

Electro-explosive devices (an electric resistance encapsulated by a primary explosive) fundamentally convert electrical energy into thermal energy, to start off an explosive chemical reaction. Obviously, the activation of those devices shall not happen by accident or, even worse, by intentional exogenous influence. From an ordinary differential equation, which describes the electro-explosive thermal behavior, a remarkable, but certainly not intuitive, dependence of the temperature response on the time constant of the heat transfer process is verified: the temperature profile dramatically changes as the time constant spans a wide range of values, from much lesser than the pulse width to much greater than the pulse period. Based on this dependence, important recommendations, concerning the efficient and safety operation of electro-explosive devices, are proposed.

This research aims to provide a methodology for the project of labscale hybrid motors. This development begun with the thermal analysis of the fuel grain using the Flynn, Wall and Ozawa method; this provided the simulation entry data to maximize the motor performance. The computer simulation was performed with the Chemical Equilibrium Specific Impulse Code of the U.S. Air Force, also known as ISP Code. Based on the optimum oxidizer to fuel ratio, the literature was used to supply the mathematical background for the calculation of the motor geometrical parameters whose operating conditions were determined throughout the simulation. Finally, firing tests were conducted to verify the reliability of the project methodology. The firing tests were performed with three injectors: 2 swirling and one axial. The tests showed that the higher the operation pressure the more suitable is the project, meaning the methodology developed works best in hybrid rocket motors with high operating pressures. © 2011 by Aeronautics Institute of Technology and Flowtest Aeroespace Research. Published by the American Institute of Aeronautics and Astronautics, Inc.

The addition of nanosized metal particles in propulsion systems such as solid and liquid propellants, hybrid propellant and ramjet motors has recently became a major focus of research. Significant increases in the burning velocity and in the specific impulse are some of the advantages of using nano-scale energetic materials in many different types of propulsion systems. Aluminum has been largely employed as a metallic additive in energetic materials, also in a recently new propulsion system (aluminum/ice propulsion, "Alice"), and some studies show that the advantages of using nanosized aluminum instead of microsized aluminum are facilitating the ignition of the systems and allowing better incorporation of the components in the formulations and improving its homogeneity. Some of the combustion processes that require high pressures and even higher temperatures can occur in moderate conditions due to the increase of the surface area of the reactants, in this case, the metallic additive.

In missile propulsion technology it is conventional to employ solid rocket boosters. These boosters are loaded with solid propellants, which are energetic compositions where raw materials are comprised of solid particulates, such as fuel, and oxidizer particles, in which are dispersed and immobilized throughout a binder (polymeric) matrix. The processability of these compositions is not simple because it is difficult to incorporate a high percentage of solids in polymeric matrix. Its has been problematic to formulate a safe composition so as to prevent an accidental ignition of solid propellant or other device that uses energetic materials. Accidents and incidents with solid rocket motor, during production, handling and storage, without apparent causes, led to studies by independent groups [1,2,3,4]. These studies generated important conclusions on the realm of solid rocket motor safety; furthermore, subsequent investigations suggest that spontaneous motor ignition can be attributed to electrostatic discharge. The solid composite propellant grain can be considered in a microscale heterogeneous system in which conductive and nonconductive particles and different types of binders had direct influence in the grain electrical characteristics. Nonconductive particles have a geometrical effect to influence the spacing of the conductive particles [5]. The aim of this paper is to present the methodologies and the respective results of electrical and electrostatic discharge tests. These results allow us to choose a less ESD sensitive formulation of solid propellant increasing the reliability in manufacturing, handling and storage of solid rocket motor. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

This work describes the development of an acrylic laminated transparent compound that can be applied in aeronautics and astronautics transparencies. The case here studied, is a laminated double curved transparency (bubble form), used in an observation side window of a military aircraft. Side windows needs specific resistance and characteristics, like the windshields; it allows the perfect visualization and image capitation. Laminated transparencies composed by different materials, joint better qualities than monolithic, due this way achieves great mechanic and chemical resistance, high transparency, no spall and easy maintenance or recovering. Much information about materials and process was jointed, with the intention to build the reinforced transparence, and to make valid this information, by the analysis of the final results, in both of points of view: mechanic resistance and optical quality. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

The process of fuel injection in combustion chambers is of vital importance, under several aspects, for the ideal operation of each motor. The responsible element for the introduction of liquid and gaseous propellants in the combustion chamber of rockets and for the transformation of liquid masses in sprays is the injector, that converts the potential energy of the propelants in kinetic energy, for the pressure fall in its interior, forming a jet or liquid sheet that dissolves in drops. Swirl type pressurized injectors, mono or bipropelants, are object of constant studies to understand its operation in rocket-motor with liquid propelant, because they produce conical liquid sheets and present a serie of differences in relation to the axial type in terms of improvement of the combustion process as a whole. The fast formation of a high number of drops, of convenient diameters, distributed in an extensive area, favors the vaporization mechanisms due to the high surface of all, that quickly vaporize and enter in combustion. Its production is a challenge for the techniques of conventional fabrication, because of the complexity, dimensions, work conditions and its fixation in the injection head. Injectors production from preexistent designs and the assembly of a structure which allowed the tests of the same, was the object of this work, that generated pieces in brass which allowed cold tests with the fluids kerosene and cut oil to confirm the formation of the hollow conical spray and hot tests with melted paraffin to confirm the formation of spherical drops of several sizes, which were measured in a profile projector, and analyzed by the process of test sieving, revealing the existence of drops within the range of those already found in literature. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

During service, gas turbine blades and vanes are exposed to thermal stresses and to oxidation and hot corrosion from the hot combustion gas. Therefore, the coating process is a good alternative to protect the turbine. In the present work is studied the benefits of the application of two coating layers to enhance the corrosion and oxidation resistance of niquel base blades and vanes. The specimens were first cleaned and then the coatings were applied through a pre-programmed furnace. Photomicrographies of the specimens were taken, showing the steps of the coatings and the results of the oxidation tests. There was no evidence of damage and the oxidation characteristics of the two coatings were similar to one. The proposal to use multilayer VPA coatings increases the average of the coating deposited and as a result the life of the substrates. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

In this work, the combustion process of ammonium dinitramide, ADN, has been modeled in two different situations: decomposition in open environment, with abundant air and decomposition in a rocket motor internal, environmental conditions. The profiles of the two processes were achieved, based on molar fractions of the species that compose the products of ADN combustion. The velocity of formation, and quantity of species in the open environment was bigger than the ones in the rocket motor environment, showing the effect of the different atmosphere in the reactions kinetics.

The thermal decomposition of aged and non-aged samples of ammonium perchlorate(AP)/hydroxyl-terminated-polybutadiene(HTPB), the AP/HTPB solid propellant, were studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius parameters were estimated according to the Ozawa method. The calculated activation energies were 134.5 kJ/mol (non-aged) and 79.0 kJ mol-1 (aged), the pre-exponential factors, A, were 2.04 1010 min -1 for the non-aged samples and 1.29.106 min-1 for the aged samples and the reaction orders for the global composite decomposition were estimated in 0.7 and 0.6 (non-aged and aged samples decomposition, respectively) by the kinetic Shimadzu software based in the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for a comparison purpose. These results are here discussed. © 2008 by the American Institute of Aeronautics and Astronautics, Inc.

Carbon materials exhibit outstanding thermo-mechanical properties and low density (<2 g/cm3), which make them useful for structures submitted to high temperatures (T > 1000 °C). Solid rocket motor throats, thermal barrier protection systems, turbine rotors and high temperature process components are typical applications for these materials. The manufacture of carbon materials, such as carbon fibers and carbon reinforced fiber composites (CRFC), undergo a controlled pyrolysis process, where organic precursors such as resins, pitches, and polymeric fibres are converted over 800 °C into a solid carbon material. In the present work the activation energy from a carbon reinforced carbon composites were obtained by Thermogravimetry Analysis. The experiment involved heating samples of the mentioned materials at fixed constant heating rate schedule up to 1000 °C. The kinetic parameters were obtained by analyzing the weight loss curves. The non-linear fitting method based on Levenberg-Marquardt approach was used to fit the weights loss curves at five heating rates. © 2008 Elsevier B.V. All rights reserved.

The thermal decomposition of hydroxylterminated polybutadiene (HTPB)/ammonium nitrate (AN) based propellants, so called smokeless formulations, and raw materials were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). The thermoanalytical profile of different components and of propellant were evaluated and the Arrhenius parameters for the thermal decomposition of the propellant sample were determined by the Ozawa method. The kinetic parameters of the thermal decomposition of propellant samples were determined by DSC measurements. The values obtained for activation energy (Ea) and pre-exponential factor were 163 kJ mol-1 and 1.94×106 min-1.

The purpose of this work was to determine the safe shelf life of single-base propellants. The kinetic parameters relative to the consumption of the stabilizer diphenylamine (DPA) added to the propellant were determined as a function of the storage and ageing time. High Performance Liquid Chromatography (HPLC) with spectrophotometric detection was used to determine the DPA percentage before and after the artificial ageing at 60, 70 and 80°C. The experimental data were very well adjusted to a pseudo-first order kinetic model and the respective kinetic constants are 8.0·10-3 day -1 (60°C); 1.9·10-2 day-1 (70°C); 1.2·10-1 day-1 (80°C). The activation energy was calculated as 130_-kJ mol-1 and the half-time for depletion of the DPA at the hypothetical temperature of 40°C of storage was estimated as being 6 years.

The "Recoilless gun, analysis of internal and external ballistics" project consists in dimensioning, building and operating a prototype of a medium-caliber, smooth-barreled gun which has the least recoil possible upon firing. Such recoil reduction is made using a convergent-divergent nozzle (De Laval nozzle) in the rear end of the gun, through which part of the gases generated in the deflagration of the powder will flow and be accelerated, proving thrust to counteract the recoil effect. Hence, it could be applied in military aircrafts and as a man-portable land-based weapon. In this project many subjects were studied such as fluid dynamics, thermodynamics, chemical kinetics and structural analysis.

Inspired by the biological nerve system, artificial neural networks (ANN) have been tools of artificial intelligence for data classification and pattern recognition, and can be used to simulate a wide variety of non-linear complex scientific systems. Artificial neural networks are being used in medical applications; image recognition and control of dynamic systems, but only recently have been considered for the prediction of the mechanical behavior of materials and particularly composites. In this work, ANNs were considered specifically to predict the shear stress-strain behavior from carbon fiber/epoxy and glass fiber/epoxy composites. A multilayered neural network perceptron (MLP) architecture was used, and the results showed that the application of the Levenberg-Marquardt learning algorithm leads to a high predictive quality to epoxy composites, i.e. nearly 80% of standard error of prediction was found to be ≥0.9. The initial tests considered a simple architecture 3-[3-3]2-1 resulting in low predictive quality. However, increasing the number of neurons in the hidden layers and the number of training instances resulted in an enhancement of the neural network predictive quality. © 2007 Elsevier B.V. All rights reserved.

The purpose of this work was to study the kinetic depletion of stabilizers 2-NDPA in double-base propellants. Topics relatives at analytic method utilized and interferences in kinetic of depletion of stabilizers by presence of nitroglycerine and lead salicylate are presented. The kinetics parameters of depletion of stabilizers were determined by High Performance Liquid Chromatography (HPLC). The experimental data were adjusted to a pseudo-first kinetic model. The activation energy (Ea) and the pre-exponential factor (A) calculated were (1.22 ± 0.42) 102 kJ mol -1 and (1016 ± 106) day-1, respectively.

The purpose of this work was to determine the kinetics parameters of the thermal decomposition of a sample single-base (BS) and double-base (BD) propellants. The experimental data obtained by differential scanning calorimetry (DSC) were adjusted to the pseudo-first order kinetic model of Flynn, Wall and Ozawa. The respective parameters obtained are: BS REX 1200 (Ea) (2.3 ± 0.2) 102 kJ mol-1 and (A) 1.34 1025 min-1; BD-111 (Ea) (1.6 ± 0.1) 102 kJ mol-1 and (A) 3.31 1017 min-1. IR spectrum has confirmed the presence of salicilate in the double-base (BD) propellant and some correlations corroborate the conclusions about the decomposition mechanism.

This paper shows different aspects related to the application of different thermal analysis techniques in the study of energetic materials. The criteria used to choose the best technique and an exact approach to adjust the experimental data with a proper model are here discussed. The paper shows how to use the different thermal analysis results to help develop new compounds, to study the stability of some energetic materials and their compatibility, and the conditions necessary for a secure storing environment.

Thermal decomposition kinetics of solid rocket propellants based on hydroxyl-terminated poly-butadiene-HTPB binder was studied by applying the Arrhenius and Flynn-Wall-Ozawa's methods. The thermal decomposition data of the propellant samples were analyzed by thermogravimetric analysis (TG/DTG) at different heating rates in the temperature range of 300-1200 K. TG curves showed that the thermal degradation occurred in three main stages regardless of the plasticizer (DOA) raw material, the partial HTPB/IPDI binder and the total ammonium perchlorate decompositions. The kinetic parameters Ea (activation energy) and A (pre-exponential factor) and the compensation parameter (Sp) were determined. The apparent activation energies obtained from different methods showed a very good agreement.

The thermal decomposition of ammonium perchlorate (AP)/hydroxyl-terminated-polybutadiene (HTPB), the AP/HTPB solid propellant, was studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius parameters were estimated according to the Ozawa method. The calculated activation energy was 134.5 kJ mol-1, the pre-exponential factor, A, was 2.04·1010 min-1 and the reaction order for the global composite decomposition was estimated in 0.7 by the kinetic Shimadzu software based on the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for comparison. These results are discussed here.