Research On The Failure Mechanism Of The Mechanical-thermal Coupling In Adiabatic Shearing Of Metal Materials

Adiabatic Shear Failure(ASF)is a typical dynamic mechanical and thermal coupling failure behavior,which plays a crucial role in the dynamic strength design of materials and structures of high-end national defense equipment such as aerospace.Since this concept was proposed in 1928,it has always been a difficult problem in the field of impact dynamics.However,due to the lack of experimental methods,the early experimental studies were mainly based on a single dynamic deformation/temperature field.The adiabatic shear dynamic force-thermal coupling mechanism could not be fully revealed.Based on the foundation of the research group’s previous high-spatial-resolution infrared thermal imaging technology and instruments.In this paper,the dynamic synchronous experimental characterization method,the mechanical-thermal coupling experiment of different metal materials,the dynamic mechanical-thermal coupling simulation and failure mechanism research have been systematically carried out.The main work is as follows:(1)Aiming at the problem of experimental characterization of adiabatic shear forcethermal coupling failure,a high temporal and spatial resolution simultaneous loading/deformation/temperature testing technology is developed.A micro-scale(20μm diameter,50μm etching depth)micro-loss subtractive speckle preparation method based on laser etching is proposed.The traditional speckle shedding problem of dynamic loading is solved,and the in-situ measurement of the Adiabatic Shear Band(ASB)with high spatial and temporal resolution(time resolution 1 μs;spatial resolution 5 μm)is realized.In addition,the experimental technology of laser focusing and blackbody calibration has been overcome,and the problems of optical focusing and temperature calibration in the ultra-high-speed64×64 area array infrared temperature measurement system have been solved.Subsequently,the physical occlusion experiment technology was developed to solve key technical problems such as the light interference of the high-energy flash of the ultra-high-speed camera system on the ultra-high-speed area array infrared detector.The same strain gage trigger signal generator is used to simultaneously trigger the ultra-high-speed camera and ultra-high-speed area array infrared detector to solve the problem of microsecond-level time synchronization.(2)Based on the self-built experimental platform with high spatial and temporal resolution,two materials,TC4 and YT01 Fe,were selected to carry out the experimental study of dynamic mechanical-thermal coupling failure.The time series of the ASB evolution process of two types of metallic materials were quantitatively characterized,and the experimental phenomenon characteristics of the non-uniform deformation field and temperature field during the ASB evolution process were reported,and the evolution characteristics of the ASB deformation field and temperature field in different stages were obtained.Among them,TC4 generated a temperature of about 200 °C in the ASB initiation stage.The adiabatic shear band evolutes from both edges to the middle,and the greater the strain in the band,the more concentrated,and the narrower the ASB width.And the diffusion width of temperature is slightly larger than the deformation field width.Correspondingly,YT01 Fe generated a temperature of 130 °C at the initiation of ASB,and multiple locations in the band simultaneously initiated and developed to form ASB.The larger and more concentrated the strain,the narrower the ASB width.The temperature diffusion width is smaller than the deformation field width.The distribution of temperature diffusion at different locations within the band is relatively uniform.(3)Aiming at the problem that the failure mechanism of dynamic-mechanical-thermal coupling in adiabatic shear zone is not clear in the previous chapter,two kinds of materials are studied for mechanical-thermal coupling simulation and failure mechanism.A threedimensional numerical model was established,and two factors,temperature softening and damage softening,were considered.The simulation results of the temperature/deformation field of the adiabatic shear process of the two materials are in good agreement with the experimental results.Further analysis shows that the obvious temperature rise time of TC4 material lags behind the initiation time of ASB,and the temperature rise time of YT01 Fe material is basically the same as the initiation time of ASB,but the overall temperature of ASB is not high.It is preliminarily determined that the adiabatic shear failure mechanism of TC4 material is dominated by damage softening,while YT01 Fe material tends to be dominated by temperature softening and damage softening,of which temperature softening is the main factor.