Research On The Damage And Fracture Behavior Of PBX Under Impact Load

Polymer Bonded Explosives(PBX),consisting of energetic particles and binders,have the properties of high energy and low sensitivity and are often used in solid propellants and large destructive weapons.In the process of transportation,storage and use,PBXS are prone to impact loads,resulting in microvoids,interface debonding,matrix cracking,crystal breakage and other mesoscopic damages.Further stimulated by external loads,these mesoscopic damages may cause large deformation of PBXS with low particle content and low strength,seriously affecting their mechanical properties.Or continue to evolve to fracture PBX with strong brittleness and high particle content.Therefore,it is of great significance to study the deformation,damage and fracture behavior of PBX under impact load to improve its storage security and service reliability.In this paper,the Hopkinson bar(SHPB)test was carried out for PBX-1 with high binder content,and the notch half disc bending(NSCB)test was carried out for PBX-2 with low binder content.Based on the macro and micro multi-scale finite element model,the dynamic mechanical properties and damage evolution behavior of PBX-1 and the crack growth behavior of PBX-2 are studied respectively,mainly including the following aspects:1.Based on Voronoi diagram,the micro-geometric models of PBX-1 and PBX-2were constructed respectively,and a python program was written to modify the INP file of the micro-geometric model,which realized the batch insertion of cohesive force units.A hybrid KF/Hook-Jeeves inversion strategy is employed to optimize the cohesive parameters.The boundary condition is analysed and the convergence of the macro and micro model is verified.The results indicate that the model can predict the macroscopic mechanical behavior of PBX well.2.Based on the improved Hopkinson pressure bar device,the stress-strain curves of PBX-I under different strain rates are obtained.The results show that PBX-1 has an obvious strain rate effect.Both the modulus and the strength increase with the increase of strain rate,and the large deformation characteristics are distinct.3.The dynamic uniaxial compression of PBX-1 was numerically simulated using the macro and mesoscopic model,and the damage distribution and crack length in the mesoscopic components were quantified.The influence mechanism of the mesoscopic damage evolution and the mechanical behavior of the mesoscopic components on the macroscopic nonlinear deformation,damage mode transformation and crack growth mode transformation was revealed.4.The NSCB test was designed based on the improved Hopkinson bar device.The Crack propagation gauge(GPG)and the Strain gauge(SG)pasted on the surface of the sample were used to obtain the type I fracture characteristics and crack growth behavior of PBX-2 at different loading rates,and the crack propagation process was captured by a high-speed camera.The behavior of PBX-2 cracking,instability expansion and collaborative toughening under pure tensile load was studied.5.The macro and mesoscopic model is used to simulate the type I crack propagation of PBX-2 numerically.The synergistic toughening mechanism in cracking initiation and instability fracture of PBX-2 is elucidated with respect to rate effect of binder and particle deviation toughening.The results show that the synergistic toughening behavior of PBX-2 at high strain rates is due to the intrinsic and extrinsic toughening mechanisms.The synergistic effect of the two mechanisms leads to the simultaneous increase of initiation toughness and crack propagation toughness.