Micromechanical Investigation of Debonding Processes in Composite Solid Propellants

Abstract

The micromechanical damage of a composite solid propellant was observed by in situ scanning electron microscopy. Based on the damage characteristics, a cohesive interfacial element was adopted to model the debonding processes along the particles and the binder interface. The effects of interfacial strength and microcracks in the binder on the debonding process of propellant were also examined. The results show that interfacial debonding is the propellant's main failure mode under tension. Finite element method analyses with a cohesive interfacial element could predict the heterogeneous strain and stress fields as well as the processes of the particles separated from the binder. Interfacial strength plays a significant role in macroscopic behaviors of the propellant. Microcracks in the binder significantly influence the debonding process. The numerical simulation results reasonably reflect the corresponding experimental results. These results provide the basis for the prediction of mechanical properties and the optimal design of the composite solid propellant.

Relationship between local damage and macroscopic response of soft materials highly reinforced by monodispersed particles

“…Recent studies have explored the nonlinear response of hyperelastic rubberlike matrix filled with rigid inclusions using three-dimensional computational homogenization with perfect filler/matrix adhesion (Lopez-Pamies et al, 2013;Guo et al, 2014;Leonard et al, 2020). In propellants as in other elastomers filled with micron size particles, it is common to observe matrix debonding at the filler surface (Cornwell and Schapery, 1975;Oberth and Bruenner, 1965;Li et al, 2018), which demands to account for a damageable adhesion at the matrix/filler interface. For this purpose, cohesive-zone models (Tvergaard and Hutchinson, 1993;Park et al, 2009) have already been introduced in finite element simulations involving spherical particles dispersed in a matrix (Segurado and Llorca, 2005;Matouš and Geubelle, 2006;Spring and Paulino, 2015;Cho et al, 2017;Gilormini et al, 2017).…”

“…Early studies (Böhm et al, 2004;Llorca and Segurado, 2004;Segurado and Llorca, 2005, among others) were focusing on ductile matrices with infinitesimal strain formalism. More recently, account for composites with hyperelastic matrices, for which softening may result from the matrix/filler interface damage only, were considered in finite strain in two-dimensional (Moraleda et al, 2009;Toulemonde et al, 2016;Zhang et al, 2018;Li et al, 2018) and three-dimensional representations (Spring and Paulino, 2015;Gilormini et al, 2017). While some of these contributions have focused on the impact of the cohesive zone model parameters on the macroscopic behavior (Spring and Paulino, 2015;Toulemonde et al, 2016), others have looked at the distribution of stresses in the matrix (Moraleda et al, 2009;Li et al, 2018).…”

Comparison of the finite strain macroscopic behavior and local damage of a soft matrix highly reinforced by spherical or polyhedral particles

“…Previously three-dimensional numerical representations and mechanical simulations of such composites with interfacial damage dealt mostly with ductile matrices moderately filled with spherical fillers (see for instance Llorca and Segurado, 2004;Segurado and Llorca, 2005 among others), and fewer studies account for more realistic polyhedral fillers (Williams et al, 2012;Weng et al, 2019). Numerical studies considering composites with an hyperelastic matrix for which, unlike ductile matrix, the softening is due to the damage at the matrix/filler only and a very large stiffness contrast exists between the constitutive phases, are mostly two-dimensional (Moraleda et al, 2009;Toulemonde et al, 2016;Zhang et al, 2018;Li et al, 2018) with little three-dimensional contributions (Gilormini et al, 2017), all considering spherical particles. The most common generation process for obtaining microstructures filled with irregular polyhedra is based on random sequential additions (Widom, 1966) of identical (B€ ohm and Rasool, 2016;Drach et al, 2016) or different (Lavergne et al, 2015;Sheng et al, 2016) polyhedra.…”

Mechanical Properties of HTPE/Bu-NENA Binder and the Kinetics of Bu-NENA Evaporation

“…Any damage caused to a solid propellant under the aforementioned stresses can cause serious deterioration in the performance of the solid rocket motor [1]. As a consequence, the mechanical properties of a solid propellant are some of its most important physical properties [2][3][4]. Differing from other types of propellants, a composite solid propellant is a multiphase system composed of a polymer binder matrix and solid fillers.…”

“…At this point, the mechanical properties of an HTPE/Bu-NENA binder with a pl/po ratio of 1.2 can meet the requirements; the maximum tensile strength and the elongation at break of the binder were 2.39 MPa and 93.27%, respectively. The corresponding H-bonded proportion was 41.01% and the crosslinked density was 1.626•10 -4 mol/cm 3 .…”