Effect of Shear Strain Rate on the Susceptibility of Selected Engineering Alloys to Plastic Instability in Torsion

Abstract

The effect of shear strain ratp ill torsion on the sllscejJtibility to plastic imtability in Imre shear was studied in A / Sf 43-10 steel at tensile strength levels of /80 alld 220 ksi, unalloyed titanium, Ti-6A I-4V, Ti-13\!-I I Cr-3 AI, and 7075 aluminum alloy, using (l range of shear slrain rates of 0.007 10 2.81 lIlin-J. The steel showed ilil/lOrtallt delJendellCY on strain rate, whereas the nonferrolls ailo)'s were relativel) insensitive. A critical strain rate was observed for the steel at 180 k,i. below which 110 illstabilil)' balld forms bifore filial .Factllre. The nonferrOIiS alloys cOllsiJtently formed a single strollg instability band illllllediate(y IJrior to Factllre, and showed straill hardening res/Jonse II/J to the final strong instability. The high strength steel showed more tolerance to instability bands prior to filial {ractll/'e, as com/Jared to the nonferrolls alloys. The shearing instability bands are demonstrated to IJenetrate 10 Ihe center q/ Ihe >/JeCilllell, and are IIOt merely swface /Jhenolllena .