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

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 material models: Ramberg-Osgood model for plastic strains under saturated cyclic conditions and 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 relation for cycles to fatigue failure N* dependent on total strain range Delta epsilon(tot) for the fatigue damage omega(f), long term strength relation for the time to creep rupture t* dependent on average stress (sigma) over bar during dwell Delta t for the creep damage omega cr and non-linear creep-fatigue interaction diagram for the total damage. Numerically estimated N* for different Delta t and Delta epsilon(tot) shows good quantitative agreement with experiments. A parametric study of different dwell times Dt is used to formulate the functions for N* and residual life L* dependent on Dt and normalised bending moment (M) over tilde.