Significance of dwell cracking for IN718 turbine discs

High temperature ‘dwell cracking’ of the nickel-base superalloy IN718 was investigated as part of a European project on military aircraft turbine discs. Dwell and fatigue crack growths tests under simple loading conditions indicated that dwell cracking would be unlikely to occur under actual flight loadings and that standard fracture mechanics specimens may be inappropriate for predicting crack growth in discs. Flight-by-flight loading tests showed that dwell cracking was either absent or limited.