Experimental Determination of Fatigue Crack Closure in 316 (N) Weld Using a Global CMOD Method

摘要

The crack closure phenomenon is important in order to assess the fatigue crack growth. Hence, the accurate measurement of the opening load of the crack is essential for the determination of the effective stress intensity factor range (DELTA K_(eff)). The crack opening or closing point is commonly measured from load-displacement or load-differential displacement records. In spite of much effort devoted to the measurement and interpretation of closure, there seems to be no accurate method for evaluating the crack closure loads. This paper describes a "global crack mouth opening displacement" (GCMOD) method for the measurement of crack opening load on CT specimens. The crack opening load was determined from the change in the slope of the load versus displacement curve and is used to characterize closure loads in 316 (N) austenitic stainless steel weld at different a/W ratios during fatigue testing. A good correlation was obtained for DELTA K_(eff)/DELTA K = -0.265(a/w) + 0.590(for R = 0.1) in the range 0.35<=a/W<=0.55. The loading-unloading hysteresis is clearly observed. Experimental results indicate that the closure load is almost independent of the crack lengths.