Analytical and Experimental Investigation on Crack Generated in Diameter - Enlargement Section

Abstract

This paper clarifies analytically and experimentally reasons why an original cold plastic working causes a crack to generate in the root of a stepped section. The new cold working method has been proposed for enlarging the diameter of a short section of a metal shaft using a combination of a cyclic bending load and an axial compressive load that is almost the same as the yield stress of the sample material. The method features large plastic deformation easily progresses in the processed section under a low axial compressive load at room temperature. However, we face a big problem that a crack sometimes generates in the stepped section during the processing. In this study, first, processing experiments were carried out to investigate that where and when the crack started and progressed and uncover influence of processing conditions on the crack. Next, simulation analyses were conducted by finite element method to calculate behaviors of stress and strain during processing. Finally, it was identified based on experiments and analyses that fatigue damage caused a fatigue crack to start and progress depended on processing conditions, and the fatigue strength was predicted successfully by the Coffin-Manson' law.