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 550C 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? under creep-fatigue interaction is defined by: a) relation for cycles to fatigue failure N dependent on numerical total strain range "tot for the fatigue damage !f ; b) long-term strength relation for the time to creep rupture t dependent on numerical average stress ¯ during dwell t for the creep damage !cr; c) non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N? for different t and "tot shows good quantitative agreement with experiments. A parametric study of different dwell times t is used to formulate the functions for N? and residual life L? dependent on t and normalised bending moment ˜M , and the corresponding contour plot intended for design applications is created.