Research On The Impact-induced Initiation Threshold Of PTFE/Al Composite By Gas Gun Experiments

PTFE/Al composite is a type of impact-initiated composite material,characterized by chemical energy release under impact loading and improved damage level of the targets.Therefore,researches on impact-induced initiation thresholds of PTFE/Al composites will play an important role in material design and the application security.Fabrication,quasi-static compression experiments,gas gun loading impact,mesoscale dynamic compression simulation were studied to investigate the impact-induced initiation threshold of PTFE/Al composite.The pressed and sintered PTFE/Al samples were prepared under 290?and 300?while that the former showed better quasi-static compression properties.Furthermore,a finite element method was proposed to study the quasi-static mechanical properties.According to the statistics on Al particles and microvoids from the scanning electron microscope?SEM?images,three types of representative volume element?RVE?models considering particles and microvoids distribution as well as geometries were reproduced:2D real microstructure-based models?R?,simulated microstructure modes?S?and simulated3D models.By using ABAQUS,uniaxial compression of both 2D and 3D models were simulated.Results indicate that all the models are effective methods to predict the quasi-static mechanical properties of PTFE/Al.The stress distribution indicated that the stress on particles was larger than that within the PTFE matrix,and the maximum stress occurred near the particles.45°shear bands occurred on PTFE.With the growth of Al fraction,elastic modulus,yield stress and hardening modulus of PTFE/Al composite increased.Split Hopkinson Pressure Bar?SHPB?tests under various strain rates(1?10²¹?10⁴s^-1)were performed and stress-strain curves were obtained,the results implicated that the properties of PTFE/Al composite varied at different strain rates stage.Tests in high strain rate stage were conducted,and Johnson-Cook elasto-plastic model was chosen to describe the constitutive relationship of the material and was verified.An investigation on impact-induced initiation threshold through SHPB was proposed.Steel and Aluminum SHPB with different striker length were applied to various sizes of PTFE/Al samples to study the impact-induced initiation threshold.Under the same impact velocity with Aluminum bars,fire was caught when steel bars collided with each other.Impact stress and loading strain rate were studied as two main factors on the impact-induced initiation threshold.Based on all the experimental results,an analytical model including stress and strain rate was established,and the theoretical curves were proposed to predict the impact-induced initiation threshold of PTFE/Al composite under SHPB tests,furthermore the stress and strain rate criteria for initiation were obtained.