溶接残留応力を考慮した疲労き裂伝播寿命の推定に関する研究

抄録

It is well known that fatigue crack propagation (FCP) rate of welded joints is different from that of the base metal because of the existence of welding residual stress. However, the quantitative analysis for the effects of the residual stresses on FCP has not been made sufficiently.
In this paper, the predicting method of the FCP lives of welded joints, regarding the effect of the residual stress as that of the stress ratio, R (=K_min/K_max), on base metal, is proposed as follows.
(1) Stress ratio considering the residual stress of the welded joint, Rres, is obtained from the equation R_res= (K_min+K_res) / (K_max+K_res), where K_res is stress intensity factor caused by the release of the initial residual stress as the crack propagates.
(2) The FCP rate of the welded joint, (da/dN) res, is obtained by substituting R_res into U-R and da/dN-ΔK_eff relationships on base metal, where U is crack opening load ratio and ΔK_eff is U·ΔK.
(3) The FCP life of the welded joint, (N_p) _res, is obtained through integrating (da/dN) _res.
In order to examine the validity of the method, the FCP tests are carried out on welded joint and base metal of high tensile strength steel, using center cracked specimen.
As the result, the FCP behaviors of the welded joint is greatly different from that of the base metal, particularly under zero-compression loading. Even in that case, the predicted FCP behavior of the welded joint is in good agreement with the FCP test result. Thus, it is shown that the proposed method is valid enough to predict the FCP life of welded joint.