Determination of the multi-axial stress creep fracture criterion using a modified tensile creep unit

Abstract

Identification of the complex-stress criterion governing creep fracture in metals has been shown to be of fundamental significance in the assessment of component life. In the present paper the authors consider the problems encountered when deriving the criterion without access to sophisticated complex-stress testing equipment. These have been solved by comparing the results of direct double-shear creep fracture tests with predictions of those results, made on the basis of tensile creep rupture data in association with either an octahedral shear stress criterion or a maximum principal tensile stress criterion. An Al alloy, Cu, a Ni alloy, a Ti alloy, cast iron, and two steels have been investigated at temperatures where creep conditions are operative,. the results have shown that the method may be used to predict, with sufficient accuracy, the complex-stress creep fracture criterion for the metals studied.