Modelling the damage and deformation process in a plastic bonded explosive microstructure under tension using the finite element method

Abstract

Modelling the deformation and failure processes occurring in polymer bonded explosives (PBX) and other energetic materials is of great importance for processing methods and lifetime storage purposes. Crystal debonding is undesirable since this can lead to contamination and a reduction in mechanical properties. An insensitive high explosive (PBX-1) was the focus of the study. This binary particulate composite consists of (TATB) filler particles encapsulated in a polymeric binder (KELF800). The particle/matrix interface was characterised with a bi-linear cohesive law, the filler was treated as elastic and the matrix as visco-hyperelastic. Material parameters were determined experimentally for the binder and the cohesive parameters were obtained previously from Williamson et al. (2014) and Gee et al. (2007) for the interface. Once calibrated, the material laws were implemented in a finite element model to allow the macroscopic response of the composite to be simulated. A finite element mesh was generated using a SEM image to identify the filler particles which are represented as a set of 2D polygons. Simulated microstructures were also generated with the same size distribution and volume fraction only with the idealised assumption that the particles are a set of circles in 2D and spheres in 3D. The various model results were compared and a number of other variables were examined for their influence on the global deformation behaviour such as strain rate, cohesive parameters and contrast between filler and matrix modulus. The overwhelming outcome is that the geometry of the particles plays a crucial role in determining the onset of failure and the severity of fracture in relation to whether it is a purely local or global failure. The model was validated against a set of uniaxial tensile tests on PBX-1 and it was found that it predicted the initial modulus and failure stress and strain well.

Development of an image-based numerical model for predicting the microstructure–property relationship in alumina trihydrate (ATH) filled poly(methyl methacrylate) (PMMA)

“…The usage of the 2D geometries was also justified by its proven satisfactory accuracy (Arora et al 2015) and the low aspect ratio of the fillers (approximately 1.2, see Sect. 4.2).…”

“…The majority of the numerical modelling studies have used simulated microstructures or ideal, regular unit cell geometries. However, another implication of the advancement in finite element model simulations and computational power is that real microstructures as measured from microscopic studies may be used instead (Arora et al 2015;Dastgerdi et al 2016;Mcwilliams et al 2013). These lead to more accurate predictions of the mechanical properties (Tarleton et al 2013).…”

“…Numerical simulations from previous studies (e.g. Arora et al 2015;Basaran and Gunel 2013;Gunel and Basaran 2013a) only accounted for composite failure by interface debonding. In this work and for the first time, composite failure by both interface debonding and matrix cracking was incorporated.…”

Micromechanical model for isolated polymer-colloid clusters under tension

“…Several models have been developed to calculate the energy of the backbone chain [14,15] by representing the chain by a set of thin elastic rods [16] or using the concept of nodes-links-blobs chains [17,18]. Most recent works on the behavior of PC clusters under deformation are numerical studies based on finite-element analysis of accurate substructures [19][20][21][22][23]. Following the concept of the backbone chain, few physically motivated models have been developed to describe the behavior of clusters [6][7][8], but the underlying changes in the structure of clusters are rarely taken into account.…”

“…While the formation of the backbone chain and stress paths have been shown in several experimental studies [2,[36][37][38], few analytical and simulation studies have investigated the load transfer mechanisms in the aggregates with respect to the stress path formation [23,[39][40][41]. This study mainly focuses on polymer-colloid clusters in which the stress path formation occurs.…”