Structural Life Prediction and Analysis Technology.

Abstract
An improved low cycle fatigue (LCF) life exhaustion method has been developed for gas turbine engine disks subjected to complex mission history loading. The method has been incorporated into a computer program for LCF life exhaustion prediction as a function of component, material, mission history, and mission ordering. Principal advances in LCF life modeling include a simple strain range-mean stress correlation model, a predictive model for the effects of strain hardened surface layers due to machining and the effects of dwell (creep) due to elevated temperature exposure time, a fracture mechanics-based nonlinear, cumulative damage model, a statistical basis for minimum part life prediction, and full-scale component verification. Simplified procedures for nonlinear stress (strain) analysis of notches were developed and calibrated with finite element results. Recommendations for further research emphasize the need for improved constitutive models of cyclic creep/plasticity, a better definition of the effects of various machining operations on material work hardening, as well as residual stresses. Calibrated models for small flaw fracture mechanics would benefit the definition of the cumulative damage algorithm. Finally, the need to control process variability in order to improve part life is emphasized. (Author)

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