An Experimental Study of Effect of Welding Residual Stress upon Fatigue Crack Propagation Based on Observation of Crack Opening and Closure(Welding Mechanics, Strength & Design)

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The effect of welding residual stress on fatigue crack propagation was studied experimentally with chief attention paid to the crack opening-closure phenomenon. Two series of tests were carried out ; one being made on longitudinally SAW-butt-welded specimens and the other on base metal specimens. Both series of tests used the same 80kg/mm^2 high tensile strength steel center-notched specimens with the identical geometry and size. The observation of crack opening and closure was made by attaching extremely small wire strain gages at the points quite close to the crack line. It was found that the data of welded and base metal specimens with different stress ratios which scatter extensively on a da/dN-ΔK plot fall within a narrow band if they are replotted using ΔK_<eff> This indicates that the effect of stress ratio and that of welding residual stress may be evaluated quantitatively on a systematic basis, if attention be paid to the crack opening and closing behavior and the crack tip stress intensity be evaluated by ΔK_<eff>.
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