Standing contact fatigue

A novel experimental method for testing the resistance of a material to contact fatigue, called standing contact fatigue (SCF), is presented. It comprises a spherical indenter, repeatedly pressed onto a plane specimen in pure normal contact without lubrication, friction or wear. The SCF method is here applied to three case-hardened steels, and results in ring/cone cracks initiated at the surface. The connection between SCF and spalling is discussed. The experimental results are presented in the form of P-N curves, where P is the normal contact load and N the number of cycles required for fatigue crack initiation. The experimental results are supported by numerical simulations of the tests. The elasto-plastic properties of case-hardened materials are graded, i.e. functions of the depth from the carburized surface. The gradation is estimated from independent experiments and is included in the analysis.