Constitutive Models And Strength Criterions Of A TATB-based PBX Under Quasi-static Loading

Polymer bonded explosives(PBXs)have been widely used in the field of ammunition because of their superior detonation performance and safety properties.As the key part of weapons,the explosive components are required not only to provide energy but also to bear mechanical loads during storage,transport and application.Since the safety and battle performance of weapon systems are largely determined by the structural integrity of PBX components,it's important to study the deformation and failure regularity of PBXs.In consideration of the service conditions of explosive component,deformation and failure laws of a TATB-based PBX were investigated in this study within the framework of isotropous continuum mechanics.Constitutive model and strength criterion in quasi-static environment are the two problems studied in this paper.Both of them were divided into the real-time part that irrespective of the time effect and the long time part that depending on the time effect.The constitutive model was conducted with the part of nonlinear constitutive model and the part of creep constitutive model.According to the tension-compression stress-strain curves of the TATB-based PBX,a nonlinear constitutive model was established based on the Boltzmann function,which included a two-parameter model and a four-parameter model.Results show that the two-parameter model can satisfy the requirements of engineering well.Moreover,the four-parameter constitutive model could describe the constitutive behaviors of typical PBXs(PBX-9502,LX-17,PBX-9501,and EDC-37)as well as other materials with S-shaped stress-strain curves,such as polysulfone resin(PSU),carbon-fiber epoxy resin,cast iron,and copper based alloy.Based on the function of UPFs in ANSYS,the two-parameter model was verified through Brazilian disk and cutaway cylinder tests.Then,the limitations of the multi-element creep models were theoretically analyzed and the creep constitutive model of PBX was deduced based on the modified time hardening theory.With test data at different temperatures,initial stress levels,and creep time,the parameters and applicative limits of the tension and compression creep models were clarified.Quantitative analysis on the failure parameters after direct failure,creep failure,and failure after creep at various temperatures resulted in the conclusion that "failure occurs once the strain at one point reaches the critical value regardless of whether the strain is caused by load or time-temperature induced creep."This finding is of great importance in deducing the multi-parameter strength criterion model when the influence of viscoelasticity is considered.The stress multi-parameter strength criterion and the strain multi-parameter strength criterion are also studied in this work.According to the end-restraint collapse tests,the effect of intermediate principal stress and hydrostatic stress should be considered in strength analysis.Then the multi-parameter strength criterion mathematical models(including the mathematical model in which the influence of viscoelasticity is considered)were deduced by using 26-surface elements.Furthermore,an active confinement loading device was developed based on the characteristics of explosive materials,by which the confining failure data of the TATB-based PBX under different temperature and pressure were obtained.On the basis of theoretical analysis on adaptability,a five-parameter stress strength criterion for the TATB-based PBX and its stimulant were set up using piecewise function.According to the physical and the geometrical significance of the description accuracy in stress space,a method to characterize the precision of the strength criterion based on the ratio of the real polar axis to the theoretical polar axis was deduced.The description precision of this criterion was evaluated and its envelope line on the ? surface and envelope surface in the stress space was constructed at last.However,problems still exist in present study.The nonlinear constitutive model cannot describe the mechanical behaviors after the appearance of the maximum stress.In addition,the applicative limits of the parameters in the creep constitutive model needs to be broadened,and the description accuracy of the five-parameter stress strength criterion in the generalized tension stress state cannot be evaluated.