EFFECT OF SURFACE PROCESSING PLASTIC LAYER ON SELF-ORGANIZED SINGLE ROTATION INITIATION OF SHEAR BANDS IN METAL CYLINDRICAL SHELL

In the process of high-speed collapse of metal cylindrical shell loaded by external explosion, the shear band formed by plastic shear instability has high self-organization characteristics, and even forms a single direction spiral pattern - shear bands are dominant in clockwise or counterclockwise direction. When the cylindrical shell collapses, the maximum shear stress is located on the inner surface of the cylindrical shell. The nucleation and propagation behaviors of the shear band are significantly affected by the mesoscopic state of the material on the inner surface. In this paper, AISI 1020 steel cylindrical shells with plastic layers of different thickness on the inner surface are obtained by selecting materials and controlling the cylindrical shell processing technology. The effect of surface processing plastic layer on the initiation of self-organized single rotation phenomenon of adiabatic shear band of metal cylindrical shell and its physical mechanism are studied by using thick-walled cylinder experiment. The experimental results show that the processed plastic layer on the inner surface of the metal cylindrical shell significantly changes the initial conditions of the shear band. Shear bands are nucleated and distributed in the clockwise and counterclockwise direction. The proportion of clockwise or counterclockwise shear bands in the total shear bands is dependent on the thickness and grain stretching direction of the plastic layer in samples. The results indicate that the thicker plastic layer with a single grain stretching direction is easier to form a single direction spiral structure of shear bands, either clockwise or counterclockwise. In addition, samples with a thick layer have a higher nucleation rate, a smaller spacing and a higher propagation velocity of shear bands, in comparison with those of a thin layer at the same effective strain. The results can provide a valuable reference for understanding the dominant orientation of adiabatic shear bands in the process of high-speed collapse of metal cylindrical shell.