Physics-Based Prognostics for LCF Crack Nucleation Life of IMI 685 Aero-engine Compressor Disc

A life cycle management-expert system (LCM-ES) framework is employed in this work for physics-based prognostics of a compressor disc. The modeling approach involves the integration of both global behavior and localized response of component at the microstructural level. This paper presents the results of a low cycle fatigue (LCF) case study for a near alpha titanium alloy (IMI 685) high pressure compressor disc using a microstructure based damage model and finite element analysis results. Both deterministic and probabilistic crack nucleation lives are determined at the two critical locations. The lognormal distributions of α-grain structure of IMI685 and hard alpha (HA) inclusions is considered in the probabilistic analysis, while the deterministic life is predicted based on their extreme values that would represent the worst life. In the LCF modeling, the plastic strain estimation assumes an empirical coefficient that has a strong dependence on the alpha grains and defect size. The proposed life prediction model is capable of capturing the effect of the grain size and hard alpha particle density variation on the LCF crack nucleation life. The worst case deterministic life corresponds well with 0.1% probability of failure and lie around 3542 and 4710 cycles respectively for the primary fracture critical location in the disc.