S. K. Jha, Universal Technology Corporation, Dayton, OH; M. J. Caton, J. M. Larsen, Air Force Research Laboratory, Wright-Patterson AFB, OH
Physics-based probabilistic methods are essential in appreciably reducing the uncertainty in fatigue life prediction. Towards this objective, the role of competing mechanisms in producing dual-fatigue variability behavior in turbine engine materials is discussed. The competing modes could be related to randomly occurring microstructural configurations, differing in the degree of heterogeneous deformation accumulation in fatigue. The fatigue variability is described as a sequence of mechanisms, probabilistically originating from these configurations, in the order of decreasing heterogeneity level. These mechanisms separated into two primary contributions to the lifetime probability density: (i) the mean-lifetime response and (ii) the crack-growth-controlled, life-limiting behavior. A model incorporating this dual behavior was developed and provided reasonable predictions of the influence of material and extrinsic variables on the lifetime density and the probabilistic lifetime-limit.
Summary: A physics-based probabilistic life prediction methodology is discussed with respect to turbine engine materials including alpha + beta titanium alloys, Ni-base superalloys, and gamma-TiAl based alloys.
