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

Abstract

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°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 Δϵtot for the fatigue damage ωf, long term strength relation for the time to creep rupture t* dependent on average stress during dwell Δt for the creep damage ωcr and non-linear creep–fatigue interaction diagram for the total damage. Numerically estimated N* for different Δt and Δϵtot shows good quantitative agreement with experiments. A parametric study of different dwell times Δt is used to formulate the functions for N* and residual life L* dependent on Δt and normalised bending moment .