The effects of long-range residual stress, elastic follow-up and applied load on creep crack incubation and material toughness

Abstract

Creep crack incubation of Type 316H stainless steel at 550°C is explored in this article. Fracture mechanics specimens, subjected to combinations of residual and applied loads and in the presence of elastic follow-up, are tested. The design of two new test rigs is described. The rigs introduce planned levels of elastic follow-up together with combined residual and applied loading conditions to the specimens. A series of high-temperature elastic-plastic and elastic-plastic-creep experiments are undertaken to compare the experimentally determined values of elastic follow-up with the theoretical values. A further series of fracture mechanics tests are performed to measure creep crack incubation and material toughness for samples subjected to constant load and for tests under combined loading with elastic follow-up. It is demonstrated that for tests subjected to the same initial reference stresses, longer incubation times are attained for elastic follow-up tests compared to constant load tests. Also, combined loading tests exhibit longer creep crack incubation times based on the same measured material toughness obtained from constant load tests. This suggests that not all the available strain energy provided by combined loading to a specimen at high temperature contributes to creep crack incubation.

Multi-axial creep-fatigue life prediction considering history-dependent damage evolution: A new numerical procedure and experimental validation

“…In detail, node 3 in the interior region appears to be more of a stress controlled mode (Fig. 5) than node 1 does at the notch root, tending to produce less stress relaxation rate as well as more obvious inelastic strain accumulation (Smith and Shirahatti, 2015;Wang et al, 2018b). From the viewpoint of a discontinuous geometric structure, it can also be characterized by elastic follow-up factor, Z , as shown in Fig.…”

Draft Rules for Alloy 617 Creep-Fatigue Design Using an EPP+SMT Approach

“…Elastic follow up can significantly influence the creep-fatigue life of structural components in elevated temperature service. When a structure consisting of components with differing elastic stiffnesses is subjected to a deformation-controlled load, large elastic follow-up can occur, especially in the case that the stiffer region occupies a great portion of structural elements [35][36][37][38]. For high temperature structural components the effect of elastic follow up is a reduction in stress relaxation at a material point when compared to stress relaxation under a displacement controlled load.…”