Application of linear matching method to creep–fatigue failure analysis of cruciform weldment manufactured of austenitic steel AISI type 316N(L)

Abstract

IntroductionThis paper demonstrates the recent extension of the Linear Matching Method (LMM) to include cyclic creep assessment [1] in application to a creep-fatigue analysis of a cruciform weldment made of the stainless steel AISI type 316N(L). The obtained results are compared with the results of experimental studies implemented by Bretherton et al. [2] with the overall objective to identify fatigue strength reduction factors (FSRF) of austenitic weldments for further design application. These studies included a series of strain-controlled tests at 550°C with different combinations of reversed bending moment and dwell time t. Five levels of reversed bending moment histories corresponding to defined values of total strain range tot in remote parent material (1%, 0.6%, 0.4%, 0.3%, 0.25%) were used in combination with three variants of creep-fatigue conditions: pure fatigue, 1 hour and 5 hours of dwell period t of hold in tension. An overview of previous works devoted to analysis and simulation of these experiments [2] and highlight of the LMM development progress could be found in [3].Recently [1] the LMM has been much improved both theoretically and numerically including more accurate predictions of the stabilised cyclic response of a structure under creep conditions, and more accurate assessments of the resulting cyclic and residual stresses, creep strain, plastic strain range, ratchet strain and the elastic follow-up factor. Previously, Ponter and Chen In fact, the analyses presented in this paper revisit previous LMM assessments [4] of the same experimental studies [2] using the improved method [1], more accurate modelling of the weld structure and the material behaviour of its regions including LCF endurance, creep and long-term strength properties. In contrast to [4], creep damage is assessed using time fraction rule instead of ductility exhaustion recommended in R5 Procedure [5], which provides over-conservatism in combination with time-hardening creep law. The non-linear creep-fatigue interaction diagram instead of linear is also found to be more suitable for the assessment of critical creep-fatigue damage.