Effect of overload on fatigue crack growth behavior of thin copper foil

Abstract

Smart stress-memory patch (SSMP) which consists of electrodeposited copper foil has been proposed as a sensor to measure fatigue loading for structural health monitoring in previous researches. In this study, the fatigue crack growth behavior of the copper foil was examined under constant amplitude loading with single overload and variable amplitude loading in order to evaluate the applicability of SSMP to the actual loading conditions. Under the overload condition, the fatigue crack growth rate gradually decreased after the overload and reached a minimum value, and then recovered to the baseline. Since the retardation behavior was different from one of thick specimen, a new model to quantify the crack growth in the thin specimen was proposed based on a modified Wheeler model. The proposed model successfully reproduced the fatigue crack growth curve under the single overload condition. Additionally, the proposed model was extended to the variable amplitude loading conditions by including cycle-by-cycle calculation procedure. The results showed that the fatigue crack growth behavior can be represented by the proposed model under the variable amplitude loading condition. Therefore, the feasibility of applying SSMP to actual loading conditions was demonstrated.