EXPERIMENTAL-DETERMINATION OF STRESS INTENSITY FACTORS FOR CRACKS IN TURBINE DISKS

Stage-II fatigue crack growth paths in firtree fixtures have been pred icted using a photoelastic technique. Initiation was assumed to occur at the edge of contact on the load-bearing flanks and, subsequently, t he cracks were extended in the direction of the maximum circumferentia l stress. After a short initial length, in which propagation was perpe ndicular to the contact surface, the direction of crack growth was, in a broad sense, equivalent to the hoop direction in the disc. Stress i ntensity factors were found for the majority of the crack path using d ata taken from the isochromatic fringe patterns. It was concluded that the most catastrophic failure was likely to occur from the innermost land of the firtree and that the width of the firtree had little influ ence on the stress intensity factors.