Bauschinger and yield effects during cyclic loading of high temperature alloys at 550°C

Abstract

High strain fatigue experiments were carried out on thirteen different high temperature alloys at 550°C. By means of multiple step tests and interrupted tests in the steady state, the asymmetrical nature of the Bauschinger effect was examined, i.e. having regard to the magnitude and direction of the stress reversal point during the course of the hysteresis loop. The cyclic stress–strain curve was characterised using the well known Ramberg—Osgood deformation relationship, and distinction was made between actual curve shape and the locus approximation. The yield stress during the course of a cycle could be made to vary according to the reversal point in the interrupted tests, but even in steady state cycling, the cyclic yield point was found to decrease as the total strain range was increased. Limited investigations were also performed during evolutionary (hardening or softening) cycling and all results were interpreted in terms of the prevailing back stress and friction stress. A formula to predict yield was hence derived for engineering use.

MST/1907