Mechanical characterization of single- and multiple-batch solid propellants using digital image correlation method

Resumo

© 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.Solid propellants are usually characterized by their ballistic and mechanical properties. However, these properties are seldom homogeneous. Processing factors such as multi-batch, casting, curing and post-curing dynamics induce transfer of loads and defects along the propellant. This propellant heterogeneity is responsible for different ballistic and mechanical properties in the grain. This paper presents a novel experimental procedure to characterize the elastic properties of single- and multi-batch solid propellants based on the use of the two-dimensional digital image correlation (DIC) method. The proposed experimental procedure has been applied to two different specimen configurations namely SBIP (single-batch inert propellant) and MBIP (multi-batch inert propellant) propellants. The SBIP specimen was manufactured in a single shot aiming at a more homogeneous mechanical behavior and uniform degree of cure along the propellant length. On the other hand, the MBIP specimen was manufactured in three different stages where each stage has a different degree of cure. Both specimens have a diameter-to-length (L/D) ratio equals to 19, which is an aspect ratio representative of typical large-scale solid-fuel grain rocket configurations. Additionally, in order to validate the in-situ measured properties, tests at small coupon level were also carried out using small cylindrical coupons taken from the same regions of interest used to measure the mechanical properties of the SBIP and MBIP specimens. A very good agreement between the measured local and global (in-situ) strain fields and mechanical properties was found in both testing scales, thus validating the proposed testing procedure based on the DIC technique. Results showed an increase in the elasticity modulus in the specimen bottom due to gravity effects.

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