Evolution Law And Numerical Simulation Of Shear Band In PBX Substitute Materials Under Compressive Loading

The polymer bonded explosive(PBX)is an explosive mainly composed of energetic particles and high polymer binders.Various damages will be induced in PBX during production,processing,transportation and storage.These damages would not only deteriorate the mechanical properties of PBX,but also bring safety problems to users.Therefore,it is significant to study the mechanical properties and failure mechanism of PBX.In this paper,for the safety consideration,sugar was selected as the substitute material for energetic particles in PBX.Binder was dominantly composed by epoxy resin E-51 and oxalic acid.At first,we studied the effect of dwell time on the strength of PBX substitute materials during pressing,found that the dwell time will increase the strength of the specimen.Subsequently,we established a new constitutive model considering the influence of dwell time.In the experiment,we found that the initial modulus of the material changes with the dwell time,which can be roughly divided into three stages.These stages are similar to stages of material density change during pressing.Next,we carried out the speckle experiment of PBX substitute material under quasi-static compressive loading,found that the material shear band always started in a certain direction.Shear bands appear in alternating order.Under quasi-static compressive loading,the effects of tensile failure are not negligible.Because the tensile failure of the specimen is closely related to the damage inside the material,So the shear failure of the specimen usually occurs in the dense zone of the material.While in the sparse zone,there is a greater possibility of tensile failure.The stress distribution of materials which include an ellipsoid was calculated by finite element software ANSYS.In order to further explore the effect of voids on the form of material failure,the voids were simplified into spherical pores.The macroscopic finite element model of PBX substitute materials with randomly distributed pores was successfully established by Monte Carlo method.After the calculation by using ANSYS/LS-DYNA.It is found that the tensile stress concentration of the upper and lower poles of the sphere is the key cause of the tensile failure in the material.So the effect of the void on the tensile failure in the material is verified.Subsequently,a mesoscopic model of PBX substitute materials was established.Related calculations shown that the existence of voids was closely related to theoccurrence of tensile failure on the one hand,and also reduced the strength of the material on the other hand.Finally,we briefly explored the effect of particle size dispersion on particle reinforced composites.Only the debonding of the particles was considered,the particles were taken in a small range,and the influence of the dispersion was negligible;while the particle size range was large,the increase in dispersion would reduce the mechanical properties of the material.The finite element calculation considered the influence of the matrix's fracture,the results also shown that the dispersion had an effect on the mechanical properties of the material at this time.Destructive cracks of particle reinforced composite could be roughly divided into three categories: debonding cracks between particles,debonding cracks of individual particles,and cracks in matrix.The crack is initiated in the vulnerable area between the particles,extending along the particle boundary to the matrix,and finally through the entire model.Debonding of the particles occurs first when the material is destroyed.