Strain distribution of a fir-tree tenon/mortise structure under combined high and low cycle fatigue loads

The fir-tree tenon/mortise structure in areo-engine suffers from the combined high and low cycle fatigue (CCF) loads during service. The structural integrity of the tenon/mortise structure is significantly affected by the local strain distribution, while the strain value under the CCF loads is difficult to acquire. In this study, a simulated specimen of tenon/mortise structure is designed, and the CCF test is carried out using a divided-path loading fixture to avoid interference between the high cycle fatigue (HCF) loads and the low cycle fatigue (LCF) loads. The high speed digital image correlation (DIC) method is adopted to acquire the real-time strain distribution during CCF test. According to the strain results, the critical position of the mortise and its strain variation are determined. The high cycle strain of the mortise is proportional to the vibration amplitude of the tenon. The experimental results can provide basis for strength and life assessment. A combined high and low fatigue test system is designed to study the strain variation. The real-time strain distribution is obtained by high speed digital image correlation (DIC) method. The strain exhibits sinusoidal variations when applied to the combined high and low cycle fatigue (CCF) loads.