© 2024 Elsevier B.V.The mechanical properties of parts built with material extrusion additive manufacturing are highly dependent on the material distribution within parts’ microstructure. This varies with the choice of process parameters. Therefore, when designing a functional printed part, one must tailor the printing parameters in order to obtain the desired properties, such as minimal voids. The present work proposes an optimisation method that designs printing parameters to minimise manufacturing time while keeping the void volume fraction at very low values (hence improving mechanical properties), keeping dimensions within tight tolerances and guaranteeing structural integrity. The new optimisation method utilises the authors’ previously developed software VOLCO-X, which is capable of efficiently predicting material distribution from filament extrusion within printed parts, including print track dimensions and microstructure geometry, without the need for any experimental calibration. In order to validate the proposed optimisation scheme, optimised printed parts using the scheme and parts using printing parameters determined by a commercial slicing software were manufactured and compared for different printing speeds and deposition strategies. At printing speed of 16 mm/s, it was possible to decrease the manufacturing time by more than 20% and structural mass by more than 5% in comparison to the commercial slicer printed part, whilst maintaining similar mechanical properties. At printing speed of 96 mm/s, due to the high printing speed, the commercial printed part presented gap faults between deposited strands, while the optimised part had structural integrity. At this printing speed, the optimised printed part presented significant improvements in terms of mechanical properties. The proposed optimisation methodology, in conjunction with VOLCO-X, is a powerful tool that can be used to improve manufacturing by filament extrusion. This innovative tool allows the identification of printing parameters without experiments and trial-and-error approaches, thus saving time and expense.

© The Author(s) 2021.This work presents the experimental determination of fracture mechanics parameters of composite specimens manufactured by fused filament fabrication (FFF) with continuous carbon fiber reinforced thermoplastic filaments, based on Linear Elastic Fracture Mechanics (LEFM). The critical mode I translaminar fracture toughness (KIc) and the critical energy release rate (GIc) are found for unidirectional and cross-ply laminates. The specimens were submitted to quasi-static tensile testing. Digital Image Correlation (DIC) is used to find the stress field. The stress fields around the crack tip are compared to linear elastic finite element simulations. The results demonstrate the magnitude of fracture toughness is in the same range as for polymers and some metals, depending on lay-up configuration. Besides, fractographic analyses show some typical features as river lines, fiber impression, fiber pulls-out and porosity aspects.

© 2021, The Author(s).In the last years, fiber-reinforced polymer composites have been under study for additive manufacturing. For this purpose, it is important to assess the behavior of these materials in terms of mechanical properties. The present experimental study evaluates the mechanical resistance of both PLA and carbon fiber reinforced PLA. The work used a full factorial Design of Experiments (108 tests) selecting as factors the infill density, infill pattern, material, number of perimeters and printing orientation. The main results highlight that the most influential factors on the tensile strength are both type of material and number of perimeters. In this study, the use of reinforcements did not improve the mechanical resistance attained by the corresponding virgin material. Particularly, for some selected specimens, the porosity measured in the fracture section is larger for the reinforced PLA specimens, so they showed a smaller cross-section.

© 2022 by the authors. Licensee MDPI, Basel, Switzerland.The present work describes a methodology to compute equivalent volumes representing the microstructure of 3D-printed continuous fiber-reinforced thermoplastics, based on a statistical characterization of the fiber distribution. In contrast to recent work, the methodology herein presented determines the statistically equivalent fiber distribution directly from cross-section micrographs, instead of generating random fiber arrangements. For this purpose, several regions, with different sizes and from different locations, are cropped from main cross-section micrographs and different spatial descriptor functions are adopted to characterize the microstructures in terms of agglomeration and periodicity of the fibers. Detailed information about the adopted spatial descriptors and the algorithm implemented to identify the fiber distribution, as well as to define the location of cropped regions, are given. From the obtained statistical characterization results, the minimum size of the equivalent volume required to be representative of the fiber distribution, which is found in the cross-section micrographs of 3D-printed composite materials, is presented. To support the findings, as well as to demonstrate the effectiveness of the proposed methodology, the homogenized properties are also computed using representative equivalent volumes obtained in the statistical characterization and the results are compared to those experimentally measured, which are available in the literature.

© 2021 The Author(s)The present work describes a computational mechanism based failure analysis conducted for 3D-printed continuous carbon fiber reinforced thermoplastic composites (CFRTPCs), which could not be seen in the available literature. The material failure is investigated based on intraply failure evaluation and adopts different failure criteria for the material constituents. The micromechanical modeling employs the Asymptotic Homogenization technique and comprises the selection of a representative volume element statistically equivalent to the microstructure of the material, which is identified from cross-section micrographs. In contrast to recent work, it is demonstrated that an additional relation is required for the macroscopic deviatoric stresses acting over the matrix. This avoids an overestimation of the matrix failure when the reinforced lamina is subjected to longitudinal and shear loads. The resulting failure envelopes are presented and compared to those provided by analytical failure theories available in the literature. The results obtained by the micromechanical approach showed its ability to predict failure of 3D-printed CFRTPCs, in addition to bring different elements for the discussion that could not be captured with analytical models. In this context, it is believed that the characteristics inherent to the microstructure reproduced in the RVE, particularly contributed to obtaining more realistic failure envelopes.

© 2021Parts produced by additive manufacturing have final characteristics (such as mechanical properties and dimensional accuracy) strongly dependent on how material is deposited during production. This study presents a modelling concept called VOLCO-X (VOLume COnserving model - eXtended version), which extends a recently developed simulation technique to be able to accurately simulate deposited structures that were not possible with the previous model. A major advantage of the proposed modelling approach is that it does not require any experimental calibration or fitting. The modelling approach is based on a principle of conservation of volume in a voxelized space, in conjunction with a new deposition modelling concept that re-distributes the deposited material when neighboring filaments are in contact. In addition, an acceleration-dependent extrusion rate correction was implemented in the software to predict changes in the material distribution as function of the printing speed, as well as a mechanism to effectively consider possible asymmetry of deposited filaments. The model is shown to accurately predict the geometry and porosity of specimens manufactured by Fused Filament Fabrication (FFF) with varied printing speeds, distance between filaments and extrusion widths. The numerical results correlated well with validation experiments, being able to capture the transition from triangle to diamond void shapes and to predict defects observed in printed parts. VOLCO-X could simulate printing conditions from fully dense structures to under-extruded structures with gaps. It has potential to aid in the design of functional printed parts by predicting the final dimensions, void shapes and void volume fraction of 3D printed parts, and represents an important step towards enabling the predictive simulation of full-sized parts.

© 2020 Society of Plastics EngineersAdditively manufactured composites have been demonstrating promising results with the development of new materials of high mechanical performance, which draws attention from several fields, for example, biomedical, electronics and aeronautics. However, as such materials are based on novel technologies, it is necessary to better understand their resulting characteristics and properties. For instance, evaluating the effect of environmental conditions on their mechanical performance is important, especially when moisture-sensitive polymers such as polyamide (PA) are employed as matrix. This work aims to understand and to characterize the moisture effect on the mechanical properties of additively manufactured Nylon and continuous carbon fiber (CF)-reinforced Nylon-based thermoplastic. Tensile and compressive tests were carried out in accordance with ASTM standards for the printed samples at their maximum moisture content and for samples submitted to drying after the saturated condition. Moreover, moisture absorption and swelling behaviors were assessed and discussed. The experimental results showed that moisture significantly affects the fiber/matrix interface, as well as the adhesion between printed filaments. These changes led to a decrease in the general mechanical properties in saturated state, including those in the fiber direction. Furthermore, a permanent degradation was observed in some properties after drying. Thus, the importance of considering water content and aging effect on the characterization and engineering application of 3D printed CF/PA composite was evidenced.

© 2020 Elsevier LtdHomogenization techniques are very important in describing the mechanical behavior of high performance composite materials. Among the different techniques applied to this modeling, the RVE (Representative Volume Element) and AH (Asymptotic Homogenization) play an important role. In this context, the present work aims to present a complete implementation methodology for Asymptotic Homogenization using ABAQUS® software. Although recent work have provided proper methodologies to describe the mechanical behavior of composite materials based on their constituents, the authors verified that gaps still exist. In contrast, this paper presents all the required steps in details. The application of periodic boundary conditions, which is not straightforward on ABAQUS® software, is described for all the load cases to be solved. The computation of required data from software output files as well as the calculation of the homogenized matrix are also described. The expanded equations to obtain the stresses at microscopic level using finite element commercial software, which could not be seen in recent literature, are detailed and the required emphasis is given. This paper also presents examples to validate and evaluate the obtained results.

© 2020, The Author(s).The Hashin’s strength criteria are usually employed in first ply failure and damage-onset analysis of fibre-reinforced composites. This work presents optimality conditions of local material orientations for these criteria, in terms of principal stresses and material strength parameters. Each criterion (matrix tensile/compressive, fibre tensile/compressive modes) has its conditions separately derived, analytically, based on a fixed stress field assumption. The conditions found show that orientations which coincide and do not coincide with principal stress directions may minimise local failure indices. These solutions are employed in a proposed algorithm, named HA-OCM (Hashin Optimality Criteria Method), which selectively satisfies the matrix failure modes (either tensile or compressive), iteratively and finite element-wise in composites. It is demonstrated that the HA-OCM is able to design single-layer plane structures with improved failure loads in comparison with designs following only maximum (in absolute) principal stress orientations. Results show that the material orientations have a trend to end up either aligned or at 90° with maximum in absolute principal stress directions. Global optima for compliance are, however, not guaranteed. To give an idea of gains in terms of failure loads, some HA-OCM designs show improvements of 71% and 140%, for example, in comparison with principal stress design.

© 2020 by the authors.The present work expands the application of Puck and Schurmann Inter-Fiber Fracture criterion to fiber reinforced thermoplastic 3D-printed composite materials. The effect of the ratio between the transverse compressive strength and the in-plane shear strength is discussed and a new transition point between the fracture conditions under compressive loading is proposed. The recommended values of the inclination parameters, as well as their effects on the proposed method, are also discussed. Failure envelopes are presented for different 3D-printed materials and also for traditional composite materials. The failure envelopes obtained here are compared to those provided by the original Puck and Schurmann criterion and to those provided by Gu and Chen. The differences between them are analyzed with the support of geometrical techniques and also statistical tools. It is demonstrated that the Expanded Puck and Schurmann is capable of providing more suitable failure envelopes for fiber reinforced thermoplastic 3D-printed composite materials in addition to traditional semi-brittle, brittle and intrinsically brittle composite materials.