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Force-chain is the main load-bearing structure in the granular materials. The study of force chains and particle breakage is of great significance to understand the mechanical properties of the granular materials. At present, the internal relationship between the force chains and particle breakage is still unclear. It also has no idea about the crushing mode of the particle system with complex gradation and stress path. Therefore, in the present paper, the continuous-discontinuous numerical method (Numerical Manifold Method, NMM) is utilized to simulate the process of the force chains generation and particle breakage in granular material and to explore their internal connection mechanism. The simulation results show that the particle breakage is directly related to the force-chain network, and the particle breakage morphology is basically consistent with the direction of the force-chain network in the granular system. Small particles are broken firstly, producing large displacement to fill the voids in the system. Although the larger particles can also be broken, it is difficult to produce large displacement due to the influence of coordination number among particles. Furthermore, particle breakage can reduce the strength of the force-chain, resulting in that the larger particles in the force-chain will be broken slightly or not. [Display omitted] • A continuous-discontinuous coupling method is developed to simulate the fracture behavior of the granular material. • A topological fracture method is proposed to simulate the crack initiation and propagation. • The inner relationship between the particle breakage and force chains is revealed. [ABSTRACT FROM AUTHOR]

The polymer-bonded explosive (PBX) is a kind of multi-phase composite consisting of the polymeric binder and embedded energetic particles, in which the particle volume fraction (PVF) is often higher than 90%. In the present work, by using the Voronoi-polygon generation method along with the concept of gradation to generate Voronoi particles with given gradation, and with further operations including modification, shrinking, smoothing, etc. to the particles, a new meso-structure construction method for PBXs is proposed. The constructed meso-structures possess good gradation relationship and have high PVFs (94.99% in maximum) simultaneously. The strict periodicity on the boundaries of the meso-structure can also be achieved. To verify the constructed PBX meso-structures, the numerical manifold method (NMM) is used to simulate the effective modulus of the constructed meso-structures by considering different influencing factors such as the size of meso-structure, PVF, gradation, and initial defects, etc. The simulation results are analyzed qualitatively, and the causes of differences between the simulation results and available experimental results or other numerical results are discussed. The validity of the proposed method for the construction of PBX meso-structures is verified. This work also provides foundations for the further numerical studies of the mechanical and thermal behaviors of PBXs at the mesoscale. [ABSTRACT FROM AUTHOR]

The numerical manifold method (NMM) is developed to simulate the meso-scale failure behaviors of polymer bonded explosive (PBX). Representative volume element (RVE) with high particle volume fraction (higher than 90%) is constructed and meso-scale initial defects including interfacial debonding, voids, and micro-cracks, respectively, were considered. The deformation, failure, and the effective tension and compression strengths of PBX RVEs were investigated through NMM simulations. Polymer bonded explosive (PBX) is a composite consisting of the polymer binder and embedded explosive particles, along with a large number of the particle/binder interfaces as the third constituent. The particle volume fraction is often higher than 90%. In the present work, a visco-elastic constitutive model, an elastic visco-plastic constitutive model and a bilinear cohesive contact relationship model are implemented into the numerical manifold method (NMM) program, an open source code programmed with C language, to describe the deformations of the polymer binder, the explosive particles and the particle/binder interfaces, respectively. The fracturing of the polymer binder and explosive particles is described based on the maximum tensile stress and the Mohr-Coulomb criteria. Three categories of initial defects, including the initial interfacial debonding, initial voids in the polymer binder, and initial micro-cracks in the explosive particles, are considered in the PBX meso-structures under both uniaxial tensile and compressive conditions. The tension-compression asymmetry, the influence of the initial defects on the meso-structure failure modes/patterns and the macroscopic effective tensile/compressive strength of PBXs are investigated. The factors that cause the differences between the NMM results and other numerical or experimental results are analyzed and discussed. This work enables and proves the NMM to be an robust numerical tool for further simulation studies of the mechanical performances of PBXs, as well as other particle-filled composites, at the meso-scale. [ABSTRACT FROM AUTHOR]

• NMM is enhanced to simulate crack initiation, propagation and coalescence. • Four typical brittle cracking examples under dynamic loading are well simulated. • Mesh size, wave propagation, crack propagation velocity, etc. are analyzed. • Effects of pre-existing geometrical defects (hole and notch) are analyzed. Crack development in brittle materials under dynamic loading is widely involved in engineering, in which crack initiation, propagation and coalescence are typical phenomena. The numerical manifold method (NMM) is a unified continuous-discontinuous numerical method employing two cover systems, namely, mathematical covers and physical covers, which encounters no difficulty in the numerical representation of continua and complex discontinuities within one framework. In the present work, NMM is developed for the simulation of crack initiation, propagation and coalescence problems in brittle materials under dynamic loading based on the tensile strength criterion and the Mohr-Coulomb strength criterion for tensile and shear cracking, respectively. Four typical examples including the splitting of a rock bar, the Kalthoff-Winkler experiment, the cracking in tensile loaded pre-notched rectangular plates and the double-hole blasting of rectangular plates are simulated. The numerically derived crack development results are compared with corresponding theoretical or experimental results. The mesh size sensitivity is discussed for the first two examples; the dynamic cracking mechanism in the rock bar example is investigated along with the stress wave propagation analysis; the influence of the initial crack and hole locations on the crack path in the tensile loaded pre-notched example as well as the effect of the guiding notch in the double-hole blasting example are studied. Results indicate that the crack initiation, propagation and coalescence in brittle materials under dynamic loading are quite satisfactorily reproduced by NMM. [ABSTRACT FROM AUTHOR]