Spallation Mechanism And Damage Evolution Of Conical Target

The damage and fracture process of materials under high-strength loads has always been a basic research topic in the field of weaponry and civil equipment.The essence of material damage is that the non-uniform part of the material is activated to form micro-damages under the action of high load,and these micro-damages form a macro-fracture with the evolution of space and time.Since the research mechanism of dynamic tensile fracture of materials has been based on the onedimensional strain plate impact test,in real life,materials are often damaged and fractured under complex stress conditions.Therefore,based on the flat plate impact test,a new method of coneshaped target spallation test is proposed in this paper.The experimental research and numerical calculation of the initial spallation and complete spallation behavior of high-purity copper under non-one-dimensional strain impact conditions are carried out.The damage distribution characteristics and microscopic fracture mechanism inside the cone-shaped target are discussed.The intrinsic relationship between the typical characteristics of the cone-shaped free surface velocity and the damage evolution is analyzed.The results show that:(1)In the cone target with initial spallation,a continuous damaged area appears along the direction parallel to the cone surface from the bottom to the top of the cone,showing the different damage states of the micro-hole growing independently,the micro-hole local gathering and the micro-hole gathering forming the macro crack damaged area,which is attributed to the spatial evolution of tensile stress amplitude and duration in the cone target.(2)Quantitative statistical analysis of the damage degree of the cross-sectional damaged area of the cone-shaped target reveals that the process of micropore nucleation and early growth in the early stage of damage evolution is random,while the micropore assembly process in the late stage of damage evolution has significant localization characteristics.(3)The measured free-surface normal particle velocity profiles at different positions on the cone generatrix show a typical spalling pullback signal.The comparative analysis with the internal damage distribution characteristics reveals that the high-purity copper spalling strength obtained based on the pullback speed reflects the micropores The critical stress of the nucleation of the hole,the spallation strength has nothing to do with the degree of internal damage,and the pullback rebound slope and rebound amplitude depend on the damage evolution process,reflecting the change of damage evolution rate and the stress relaxation caused by the damage degree,respectively.(4)The CDE damage and fracture model was added to the finite element commercial software ABAQUS,and the numerical calculation and experimental results of the outer surface free surface velocity curve during the internal damage of the cone were compared.Numerical calculations show that as the tensile stress amplitude increases,the nonlinear hydrostatic pressure decreases more rapidly,indicating that the material damage evolution rate is positively related to the stress amplitude.(5)The finite element calculation model of flat plate impact was constructed on the microscopic scale,and the continuous process of nucleation,growth,and aggregation of highpurity copper tensile fracture holes was analyzed.The effects of different nucleation stress,different loading stress amplitude,and different tensile stress time on the macro free surface velocity are discussed.