Fatigue Crack Propagation and Final Fracture of High Speed Rotating Disk under Cyclic Start and Stop

Abstract

Cyclic start-stop test of notched disk and fatigue test of compact specimen were made for an Al-alloy (JIS 6061-T6). Effects of the symmetricity of notch and the thickness of disk on the crack growth and the fatigue life were investigated. These effects were found pretty small. Relations between the crack growth rate and the cyclic range of stress intensity factors for both disk- and compact specimen-tests were found to be nearly coincident with each other. Criteria on the final fracture of disk were discussed based on the critical crack length. K_Ic criterion predicted a too small life (of a too small critical crack length), while mean stress criterion gave a little longer life (or a little larger critical crack length). Authors' formulae derived from rigid plastic analysis showed a fairly good agreement between the calculations and the experiments.