Electrical Potential Drop Observations of Fatigue Crack Closure

Fatigue crack closure is widely recognized to promote fatigue crack growth retardation behavior through contacting of fracture surfaces in the crack wake and the resulting reduction in the effective stress intensity factor range (∆K) that promotes crack advance. Experimental measurements of crack closure are typically made using conventional compliance methods, but electrical potential drop has also been used to characterize crack closure behavior. Electrical potential drop measurements have detected electrical shorting across fracture surfaces of stainless steel, nickel base weld, and A508 steel tested in high temperature water environments under cyclic loads. These observations have consistently occurred under loading conditions (low R, following overloads) where closure effects are expected to be prominent and have been shown to correlate with reductions in fatigue crack growth rate. These findings suggest that electrical potential drop measurements may serve as a useful tool in assessing the influence of crack closure on corrosion fatigueCorrosion fatigue retardation behavior.