Analysis of Crack Generative Region in Crater Machined by Impulsive Electrical Discharge.

In Electrical Discharge Machining(EDM), the residual stress generates on the surface of the workpiece because of repetitive heating and cooling process. The stress causes decrease of fatigue strength, delayed fracture and stress corrosion which affect quality of the workpiece. In the previous papers, the distributions of temperature and thermal stress in impulsive EDM has been analyzed by means of Finite Element Method taking into consideration the temperature dependency of mechanical properties and thermal physical properties of workpiece material. In this paper, the procedure for analysis of the region in which the crack must be generated is developed and time variation of the region is investigated under various machining conditions. The result shows that, on the machined surface, it is possible to generate cracks along radial and circumferential directions, because the residual stress exceeds the tensile strength.