Fatigue assessment of directionally solidified superalloy thin plates under bimodal random processes

During actual service, aviation aircraft often experience multiple complex alternating loads coupled with each other. If the frequency range of the excitation load spectrum covers the first two resonance frequencies of the structure, it can significantly impact the vibration fatigue life of the structure. In this study, bimodal random vibration fatigue tests were conducted on thin plates composed of DZ125L directionally solidified superalloy. The impact of low-frequency and high-frequency vibration signal intensities on the vibration fatigue behavior of DZ125L alloy thin plates was investigated separately during bimodal random processes. The crack propagation mechanism of bimodal random vibration fatigue was proposed based on the fracture morphology observed in DZ125L alloy thin plates that failed due to vibration fatigue. The study findings indicate that the number and location of crack initiation zones can influence the mechanism of fatigue crack propagation. Additionally, a new model was developed in this study to enhance the sensitivity of the frequency domain method to the intensity of low-frequency and high-frequency vibration signals in bimodal random processes. Compared to traditional frequency domain methods used for broadband and bimodal processes, the new model can effectively describe the variation characteristics of bimodal fatigue life with different component process intensities. Furthermore, it has broader applicability for predicting the vibration fatigue life of bimodal random processes with varying vibration signal intensities.