Development of fatigue testing system for in-situ observation by an atomic force microscope and small fatigue crack growth behavior in α-brass

Abstract

A small in-plane bending fatigue testing machine for in-situ observation of small fatigue crack growth behavior by means of an atomic force microscope (AFM) was successfully developed. The multiple layer piezoelectric ceramics were adopted as an actuator in order to miniaturize the fatigue loading facility operating on the stage of an AFM. Small fatigue crack growth test under constant amplitude loading was then carried out on α-brass and successive observation of small fatigue crack growth behavior was performed by the AFM. The fatigue crack tended to grow along one slip direction with the highest Schmid factor, as the crack driving force of a small crack was not large enough to operate other slip directions with lower Schmid factors simultaneously. Frequent crack branching and deflection behavior were also observed during crack growth. It was considered that the constraint of slip deformation due to the cyclic strain hardening was mainly responsible for crack branching and deflection behavior. The intervals of branching or deflection were affected by the difference of mobility among slip planes.