Finite element analysis of the stress intensity factor and the residual stress by cold expansion method in CT specimen

Cold expansion method retards the crack initiation due to the compressive residual stress developed on a hole surface. Most previous researches have shown only the beneficial distribution of residual stresses in the retardation of the crack initiation at the stress concentration area. Also, there have been only few studies on the relation between crack growth and residual stress around other adjacent holes. A few fastener holes of aircraft structures is a shot distance which is less than 20mm between holes. The purpose of this study is to provide better understanding of the residual stress effect around a hole in a structure as crack growth starts from another hole. By finite element method, this study showed that residual stress in a CT specimen is redistributed by cold expansion process and that tensile stress increases in proportion to the cold expansion ratio in the vicinity of the crack. Stress intensity factor increases as the cold expansion ratio increases.