An equivalent crack method based on a set of high load level fatigue test results as reference points was pro-posed to study the fatigue life of welded structures in view of the diversity,complexity and random dispersion of welding defects.Using the fatigue test results as a reference,the initial crack in an intact plate was assumed to equate the defects and stress concentration effects in the welded structure,and the equivalent crack growth life was calculated as the fatigue failure life of the welded structure based on the linear elastic fracture mechanics and Paris formula.First,a structural fa-tigue life calculation process was proposed based on the equivalent cracking method.Secondly,fatigue tests on aluminum alloy T-shaped welded joints were carried out to fit P-S-N curves.Subsequently,based on the weld root failure mode of T-welded joints,the calculated P-S-N curves of T-joints were predicted based on the equivalent cracking method,with a relative error within 10％when compared with the experimental fitted curves,which verified the feasibility and effective-ness of the method.Finally,the relative errors of a set of fatigue tests with variable amplitude load spectra compared with the predicted P-S-N curves were less than 15％,and the applicability of the method for variable amplitude loads was also verified.The evaluation of predicting the fatigue life of a full range of T-welded joints based on a set of fatigue test results was achieved.With simplified process of evaluating probabilistic fatigue life by achieving a definite fatigue life with less testing and cost,the method can be extended to other welded joint life assessments.
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