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

• Published in: The International journal of pressure vessels and piping Vol. 104; pp. 1 - 13
• Main Authors: Gorash, Yevgen, Chen, Haofeng
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2013
• Subjects: Austenitic stainless steels; Creep; Creep (materials); Damage; Dwell; Fatigue failure; Finite element analysis; FSRF; Low-cycle fatigue; Matching; Mathematical models; Strain; Type 316 steel; Weldment; Weldments; FSRF; Creep; Low-cycle fatigue; Type 316 steel; Finite element analysis; Damage; Weldment
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/j.ijpvp.2012.12.003

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 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 Δεtot for the fatigue damage ωf; b) long-term strength relation for the time to creep rupture t∗ dependent on numerical average stress σ¯ during dwell Δt for the creep damage ωcr; c) 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 M˜, and the corresponding contour plot intended for design applications is created. ► Ramberg–Osgood model is used for plastic strains under saturated cyclic conditions. ► Power-law model in time-hardening form is used for creep strains during dwells. ► Life assessment procedure is based on time fraction rule to evaluate creep damage. ► Function for cycles to failure is dependent on dwell period and normalised moment. ► Function for FSRF dependent on dwell period takes into account the effect of creep.