FATIGUE FRACTURE FOR BEAD-FORMED SHEET OF AUSTENITIC STAINLESS-STEEL

A metallic gasket for the cylinder head of the automobile engine is ma de of an austenitic stainless steel sheet. It commonly has a press-for med bead which seals the high pressure gas in the combustion chamber. Because the fatigue characteristics of the sheet with the bead do not correspond to those of the plain sheet without bead, it is not easy to judge the suitability of the materials for the metallic gasket. We in vestigated the fatigue behavior for the sheet with the bead, especiall y the number of crack origins and the fatigue crack propagation rate. As a result, the fatigue strength at the number of 10(6) cycles was no t dependent on the mean stress but the stress amplitude. In addition, the discrepancy between the fatigue characteristics of the sheets with and without the bead resulted from fine wrinkle-like bands of plastic deformation which occurred at a part of bead profile foot during the bead-forming.