Prediction of Residual Stress Relaxation During Fatigue

Abstract

This paper presents a model for the prediction of the residual stress distribution during and after fatigue. Finite element software is used for incorporating cyclic plasticity into the calculations. A simplified inelastic analysis was applied. Its essential feature consists of the introduction of a group of internal parameters that characterize local inelastic mechanisms and a group of transformed internal parameters that are linearly linked to the previous ones through a symmetrical non-negative matrix. With this approach, the treatment of the local plastic yield conditions can be made easily from simple elastic analysis. This method was applied on two quenched and tempered alloy steels: shot-peened 35NCD16 (nominal 0.32 to 0.39 C, 0.30 to 0.6 Mn, 0.1 to 0.4 Si, 1.0 to 2 Cr, 3.6 to 4.1 Ni, 0.25 to 0.45 Mo) grade steel and ground 42CD4 grade steel (UNS G41420). The influence of different parameters of fatigue testing are studied, including the number of cycles and applied stress. The computed values of relaxed residual stress distributions were compared with experimental results obtained by X-ray diffraction measurements.

The Effect of Shot Peening Coverage on Residual Stress, Cold Work and Fatigue in a Ni‐Cr‐Mo Low Alloy Steel

“…It is well known that fully reversed bending of the highly compressive shot peened surface can drive the surface beyond yield in compression, causing rapid loss of compression in the initial cycles of the test. (19) The compressive overload relaxation process has been accurately modeled (22) and verified experimentally. (7,22) The benefits of shot peening are then reduced or lost entirely early in the test, depending upon the stress amplitude.…”

“…(19) The compressive overload relaxation process has been accurately modeled (22) and verified experimentally. (7,22) The benefits of shot peening are then reduced or lost entirely early in the test, depending upon the stress amplitude. The observed fatigue improvement with increased coverage may be due to increasing yield strength with work hardening of the surface with higher coverage.…”

A literature survey on the stability and significance of residual stresses during fatigue

“…Flavenot and Skalli 225 performed experimental measurements of the initial and cyclically relaxed residual stress profiles in 42CD4 grade steel due to different grinding conditions. Lu, Flavenot and Turbat 128 used their finite element model (cited earlier in the treatment of peening residual stresses) to predict this relaxation behaviour.…”

Integrated Design for Fatigue Life Estimation of Structures

“…Using the 2D finite element method, we have modelled residual stress relaxation and the influence of the various factors involved. A criterion for determining the stability of the residual stress as a function of the cyclic characteristics of the materials [3] and [4] has been proposed. For a material with cyclic softening, there is gradual relaxation of residual stress whereas, for a material with cyclic hardening, the residual stress is stabilised after several fatigue cycles ( Fig.…”