Issue 24

A. A. Shanyavskiy, Frattura ed Integrità Strutturale, 24 (2013) 13-25 ; DOI: 10.3221/IGF-ESIS.24.03 18 Stage II of crack growth occurs as soon as the fatigue-striation mechanism is suppressed while transgranular slip and grain-boundary sliding become dominating. This is evidence that the fast transgranular slip does not bring about dominating grain-boundary damage of the material. Figure 4 : Fracture (general view) in one of the Stage-III turbine discs (NK8-2u engine) has broken in service; (1) and (2) the sequence (schematic) of the crack propagation in a disk. (a) (b) (c) (d) Figure 5 : Fracture morphologies of a in-service fatigued turbine disk (a–c) at the stages of (a) early steady and (b, c) accelerated growth of a fatigue crack and (d) by slow in-flight cracking under repeated static loading (see also Fig. 3).