Some considerations on low cycle fatigue under axial and diametral strain controlled conditions.

Abstract

The low cycle fatigue tests were performed under axial and diametral strain controlled conditions. Then, the test results obtained under the two strain controlled conditions were compared. The Poisson's ratio in the plastic strain range, νp was determined so that the axial strain transformed from the diametral strain coincides with the measured axial strain. The value of Poisson's ratio was approximately 0.45 in JIS SNCM 439 alloy steels, instead of 0.50 which has been commonly approved. The cyclic stress-strain curve obtained under the diametral strain controlled condition overlies the one under the axial strain controlled condition even if the axial strain is estimated from the diametral using νp=045. The specimens tested under the diametral strain controlled condition have a longer life than those tested under the axial strain controlled condition for a given axial strain range. The life estimated through the analysis of the small crack growth rate explains well the difference in the fatigue life between the two tests.