Deformation Failure And Failure Of PBX Material Under Quasi-static Loading

Polymer bonded explosives(PBXs)are kinds of solid high explosives.PBXs are particulate composites consisting of explosives crystal,polymer binders and some other things.PBXs are widely used in weapon system and aerospace engineering.PBXs are quasi-brittle solids with initial damage,when it comes to loading flaws will generating.And flaws may lead to the material destroy or unexpected explode.So the deformation and failure behaviors of PBXS could affect both the safety and stability of weapon systems.Lubliner criterion is a strength criterion extend from Drucker-Prager criterion.It has revised the pressure independent characteristics of von-Mises criterion,and the singularity problems in numerical calculating of Mohr-Coulomb criterion has also been corrected by it.So,it is widely used in the numerical simulation of concrete material.The meridian line and yield surface of Lubliner criterion has been discussed in detail.And the constitutive relationship of the PBX is established,which is based on the extend Drucker-Prager model and the generalized plasticity theory,combining with the non-associated flow potential.Two parameters are proposed to respect the damage level of squash and stretch.A damage plasticity model,which can describe the deformation and failure of PBX in complex mechanical situation has been established by continuum mechanics theory.This model has been used to analyze the deformation and failure of PBX,containing a cavity and subject to compression.And the result is turned out to be close to the experiment.The quantity of practical damage is hard to get,but we can obtain an approximate parameter by phenomenological method.The squash and stretch damage parameters are combined by weighting method,so it's a way to solve the unsymmetrical materials' problem.Another way to simulate the crack behaviors is XFEM(extended finite element method).XFEM-based cohesive method,use maximum tensile stress crack initiation criterion and maximum circumference stress initiation expend criterion.In this study XFEM is applied to analyze the cracking failure mechanism,from local crack initiation to crack growth,in the PBX 9502 platelike specimen with cavity subjected to overall compression.Simulation shows that the local tensile stress arises around cavity in the specimen although loaded by overall compression,and this tension condition leads to local cracking initiation.The comparison between experimental data and simulation indicates they are in good agreement with each other on some aspects of crack behaviors,including overall trend of crack history,feature of crack-time curve,crack initiation moment,crack initial speed,etc.The numerical simulation results shows that the XFEM-based cohesive method is a suitable approach for modeling brittle cracking initiation and growth of PBX in mode I,and numerical simulation can obtain satisfactory prediction in behavior of crack initiation and growth.Polymer is not very much in PBX,but it can improve the PBX's mechanical property a lot.The mechanical property of polymer can also influence the PBX's mechanical property.The time-temperature equivalent theory,which is widely used in polymer,has been modified to rate-temperature equivalent theory to describe the relationship of failure stress and strain rate and temperature of PBX.We find that in the range of strain rate and temperature,the equivalent factor is constant.We acquire relationship data of failure stress vs.strain rate from the data of failure stress vs.strain rate by rate-temperature equivalent theory,this proved this theory is effective in PBX material.