Understanding Materials Uncertainty for Prognosis of Advanced Turbine Engine Materials

Abstract : Materials damage prognosis offers the opportunity to revolutionize life management of advanced materials and structures through a combination of improved state awareness, physically based predictive models of damage and failure, and autonomic reasoning. Historically, lifetime and reliability limits for advanced fracture-critical turbine engine materials have been based on expected worst-case total life under fatigue. Recent findings in a variety of advanced propulsion alloys indicate that the life-limiting mechanisms are typically dominated by the growth of damage that begins at the scale of key microstructural features. Such behavior provides new avenues for management and reduction of uncertainty in prognosis capability under conditions that depend on damage tolerance. To examine a range of sources of uncertainty in behavior and models of such behavior, this paper explores the following topics: (1) Duality in Fatigue, (2) Relaxation of Surface Residual Stresses in Laboratory Specimens, (3) Relaxation of Bulk Residual Stresses in Components, (4) Nonlinear Acoustic Parameter for the Detection of Precursor Fatigue Damage, (5) Elevated Temperature Fretting Fatigue, (6) Crack Growth under Spin Pit Environments, and (7) Crack Growth Under Variable Amplitude High Cycle Fatigue (HCF) Loading. Based on the findings, we outline avenues for further technology development, maturation, validation, and transition of mechanistically based models that have the potential to reduce predictive uncertainty for current and future materials.