Tensile fracture characteristics of heavily drawn chromium

Abstract

Heavily drawn chromium wires (80–99·7 % R.A.) were fractured at a variety of temperatures and strain rates. The condition for fracture was that the yield or flow stress exceeded some critical value which depended on the reduction and the test conditions. The increase in the critical value with decreasing temperature or increasing strain rate was consistent with the behaviour of a friction stress, leading to the conclusion that crack-initiation was the critical stage of fracture. Transmission micrographs showed elongated, ′clean′ cells. Both yield and fracture stresses varied approximately linearly with (cell diameter)^−½. The variation of effective shear stress at fracture with cell diameter was consistent with both the Stroh (1957) and Cottrell (1959) theories of fracture.

The observations raise the possibility of reducing (or even eliminating) the embrittling effects of notches by producing extremely fine sub-grain structures.