Fatigue crack growth under compressive loading

S/C magnets have many components which were designed to be compressively stressed. This paper describes a possible fatigue crack growth even under fully compressive stresses. In general crack is thought to close under compressive stress condition. But, if there is a tensile residual stress field in the specimen, the crack can open and grow to a considerable length. Compressive cyclic loading tests were made on the compact tension specimen with a hole at the center of ligament region where a tensile residual stress field was introduced by an excessive compressive pre-stress. Elastoplastic Finite Element Method (FEM) analysis indicated that the crack growth relaxed and re-distributed the residual tensile stress to some extent. In consequence it is experimentally verified that the crack grew to the length nearly to the fracture.