Creep-fatigue life assessment of cruciform weldments using the linear matching method

This paper presents a creep-fatigue life assessment of a cruciform weldment made of the steel AISI type 316N(L) and subjected to reversed bending and cyclic dwells at 550 degrees C using the Linear Matching Method (LMM) and considering different weld zones. The design limits are estimated by the shakedown analysis using the LMM and elastic-perfectly-plastic material model. The creep-fatigue analysis is implemented using the following material models: 1) Ramberg-Osgood model for plastic strains under saturated cyclic conditions; 2) power-law model in "time hardening" form for creep strains during primary creep stage. The number of cycles to failure N-star under creep-fatigue interaction is defined by: a) relation for cycles to fatigue failure N* dependent on numerical total strain range Delta epsilon(tot) for the fatigue damage omega(f); b) long-term strength relation for the time to creep rupture t* dependent on numerical average stress (sigma) over bar during dwell Delta t for the creep damage omega(cr); c) non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N-star for different Delta t and Delta epsilon(tot) shows good quantitative agreement with experiments. A parametric study of different dwell times Delta t is used to formulate the functions for N-star and residual life L-star dependent on Delta t and normalised bending moment (M) over tilde, and the corresponding contour plot intended for design applications is created. (c) 2013 Elsevier Ltd. All rights reserved.