FATIGUE-CRACK GROWTH-BEHAVIOR OF 2 CONTRASTING TITANIUM-ALLOYS

Fatigue crack propagation rates have been measured for Ti-6A1-4V and T i-5331S aeroengine disc materials using compact tension and corner-not ched tensile testpieces. The loadings used simulate both the start-sto p operations of aeroengines that lead to low-cycle fatigue and the in- flight vibrations that may cause high-cycle fatigue. It is suggested t hat the different fatigue crack growth behaviour of Ti-5331S, relative to that of Ti-6A1-4V, arises largely from the greater proportion of c rack closure and short crack growth occurring in this alloy. Ti-5331S also exhibits a crack retardation effect due to the interaction betwee n the processes of cyclic cleavage and striated crack growth which are associated with the high- and low-cycle fatigue components of the loa ding, whilst Ti-6A1-4V does not.