Effect Of Machining Hardening Layer On Shear Band Behavior Of Titanium Alloy Cylindrical Shell

Axisymmetric cylindrical shell structure is a typical representative of combat components,and its deformation and failure under explosive load has always been a hot topic.In the process of explosive loading,the maximum shear stress is located on the inner surface of the cylindrical shell.The formation of shear band and self-organization behavior are more sensitive to the case hardened layer.In this paper,the effects of different inner surface hardening layers on the shear band behavior of two kinds of titanium alloy cylindrical shells were studied by means of external explosion loading experimental technology and finite element simulation,combined with surface treatment technology,microstructure characterization and shear band theoretical model.The main conclusions are as follows:(1)The number and length of shear bands in TC4 samples increase with the increase of the thickness of the case hardened layer in the cylindrical shell.The greater the thickness of the inner surface hardening layer,the easier it is to make the shear band form a single rotation structure.The increase of inner surface hardening layer will increase the refined grains,increase the length and homogeneous nucleation rate of shear band in TC4 cylindrical shell,and reduce the spacing of shear band.The simulation results are basically consistent with the experimental results.The thicker the hardening layer,the greater the maximum shear stress on the inner surface of TC4 cylindrical shell,the faster the development of shear bands,and enhance the shielding effect between shear bands.(2)With the increase of the thickness of the hardened layer,the number and rate of shear band nucleation of TA7 titanium alloy cylindrical shell increase at the initial stage;With the increase of strain,the length and propagation rate of shear band in cylindrical shell increase,the thickness of hardened layer increases,the length difference of shear band increases,and the shielding effect between shear bands increases.The plastic flow of grains in the hardened layer often follows the tensile deformation direction of grains,which makes the grains show a streamlined arrangement,resulting in the same fragmentation direction of deformed grains,so as to promote the development of nucleation shear band in the same direction.TA7 titanium alloy presents a completely single rotation shear band due to the deflection of grains in the hardened layer.(3)The work hardening layer has an effect on the adiabatic shear sensitivity of different titanium alloys.Under the same explosion load and hardening layer thickness,the number,length,nucleation rate and propagation rate of shear bands in TC4 cylindrical shell in the same period are higher than those in TA7;The length difference of shear band in TC4 cylindrical shell is more obvious,and the shielding effect is enhanced.It is easier for TC4 alloy to form fine detonation band under shear;TA7 titanium alloy has less slip system than TC4.Under the action of shear stress,plastic deformation requires more energy,and it is more difficult to form and expand shear band than TC4.