Comparison of local strain at the notch root between FEM analysis and experimental strain measurement under creep-fatigue conditions.

Abstract

This paper describes the accuracy of FEM analysis for the estimation of local strain at the notch root under creep-fatigue conditions, comparing the local strain calculated by FEM with the measured strain using high temperature strain gages. The specimens used are commercial pure aluminum notched plates with both sides grooved, whose elastic stress concentration factors are 1.5 and 2.0. The tests were made at 473 K in air. In no hold-time fatigue test, FEM analysis accurately estimates the local strain at the notch root. In the hold-time test, on the other hand, FEM analysis estimates a smaller strain range in comparison with the actual strain range occurring at the notch root. The reason for the disagreement between FEM analysis and the actual strain results from the change in material response die to creep loading. Under creep fatigue conditions, the so-called plastic creep interaction which FEM analysis does not take account of, occurs. The local strain calculated from conventional methods, Neuber's rule, Stowell-Hardrath-Ohman and Koe's methods are also compared with the strain measurement in no-hold-time tests. All the methods overestimate the strain concentration at the notch root.