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. (C) 1998 Elsevier Science B.V. All rights reserved.