Materials Under Impact Loading, Micro-deformation Characteristics Of The Numerical Simulation Of A Preliminary Study

One of the important directions in solid mechanics and materials science is to study the mechanical and physical behaviors of materials at the meso- and micro- scales. In this work, by combining the finite element(FEM) and discrete element(DEM) methods, a numerical simulation has been done for the mesoscale responses of plastic bonded explosives(PBX) under shock loading. The FEM and DEM methods were used for explosive particles and binder, respectively. A combined FEM/DEM method was used for the interfaces between the particles and the binder. The mesoscale responses were simulated till the formation of hot spots without considering chemical reaction.The main points of this work are as follows.1) Firstly, by comparing the similarities and differences of the FEM and DEM methods, we evaluated the possibility of combining the two methods to simulate at the mesoscale the deformation of materials under shock loading.2) Then a combined FEM/DEM method was proposed, which is suitable for simulating mesoscale shock responses of homogeneous as well as heterogeneous materials. To evaluate the validity of this method, two test simulations were run with a 2D computer code. It was seen that shock waves not only got smoothly through the transition layer in homogeneous material, but also reflected and transmitted correctly at the transition layer in heterogeneous material. The simulation results were consistent with theoretical predictions, thus validating the feasibility of our method.3) A fracture criterion was implemented in the combined method and the 2D code, which allows for the separation between the elements in the transition layer once the deformation exceeds the fracture strain. Based on this, we have simulated the mesoscale phenomenon of shock wave induced fracture in binder and debonding of explosive particles from the binder.4) Lastly, according to the temperature calculation schemes in the FEM and DEM methods, a hot spot modeling program was developed, with which preliminary simulations were carried out for hot spots in PBX under shock loading.To conclude, an effort has been made in this work to numerically simulating the mesoscale deformation and especially the hot spot mechanisms in shock loaded explosives. The analyses here are mostly qualitative, and the simulated results can only preliminarily demonstrate some of the mesoscale deformation features of explosives under shock loading. Future work will aim at obtaining quantitative information of the mesoscale responses of explosives and establishing the relation between such information and the initiation.