The Effects of LCF Loadings on HCF Crack Growth
Final rept. Aug 1999-Aug 2000, Phase 3
PORTSMOUTH UNIV (UNITED KINGDOM) DEPT OF MECHANICAL AND MANUFACTURING ENGINEERING
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Continuing service failures in aero-engines and the increased use of aging aircraft have highlighted the limitations in the current technical and fundamental understanding of the fatigue integrity of engineering components. There is at present insufficient guidance to enable an engineer to account for the reduced high cycle fatigue HCF life consequent upon various forms and amounts of damage, such as low cycle fatigue LCF, foreign object damage FOD, corrosion, fretting etc., each of which promotes crack initiation, thereby compromising the MCF life. Thus it is that the US Secretary for Defence has declared that HCF is the number one readiness issue in the USAF. It is known for example that galling and fretting can reduce the HCF strength of titanium alloys by 80 and 60 respectively. The two major concerns however are FOD and the complexity of the interactions between LCF and HCF. The second technical challenge is to incorporate non-destructive evaluation as an element of fatigue management. The concern here will always be to characterize the largest defect that is not detected in large structures and complex systems where inspectability may be difficult.