Measurement of the Elastic-Plastic Boundary Around Coldworked Fastener Holes

Abstract

Coldworking the material near the edge of a fastener hole is one important means of increasing fatigue life. The stresses, strains, and location of the boundary between elastic and plastic regions have been analyzed by various theoretical studies. The purpose of this research is to experimentally evaluate the theories’ capabilities of predicting the boundary location. Specimens of 7075-T6 aluminum 6.35 mm and 3.18 mm thick with a 6.60 mm hole were coldworked various amounts by an industrial process. The elastic-plastic boundary was located by foil gage and thickness change measurements; both techniques gave similar results. Theories based on plane stress agreed well for the thinner specimens.