Abstract
In this article, a new method for fatigue reliability analysis of crack growth life based on the maximum entropy theory and a long crack propagation model is proposed. A modified generalized passivation-lancet model for long fatigue crack propagation rate is presented with explicit physical meaning. Experimental results for turbine disk alloy ZSGH4169 under different strain ratios and temperatures (at 650°C and room temperature) are used to verify the applicability of the new model. Results show that predictions by the proposed model are almost identical to the experimental data. The presented model is better than the other three models to reflect the rapid propagation characteristics of the crack. In order to perform fatigue reliability estimation, the probabilities of failure are calculated using the maximum entropy theory based on the fatigue crack growth life that derived from the proposed modified crack propagation model and the above existing three models. Results have shown that maximum entropy theory is very apt for fatigue reliability analysis of turbine disk under different loading conditions with a limited number of samples because it does not need any distribution assumptions for random variables. The effectiveness and accuracy of the combination of fatigue crack propagation models and maximum entropy method for fatigue reliability analysis are demonstrated with examples.
Highlights
By considering the effects of relative ratio, crack propagation threshold is approached at different rate, respectively, near DKth and (1 À R)KIC, which overcomes the disadvantage of slowly linear approximation from YX Zhao model near crack fracturing point, and by considering the cyclic characteristic of superalloy, the presented model is verified by experimental data
By considering the effects of relative ratio, crack propagation threshold is approached at different rates near the threshold and critical crack point, respectively, at 650°C and room temperature
The maximum entropy method is employed for fatigue reliability analysis for turbine disk ZSGH4169 superalloy
Summary
Fatigue fracture failure is one of the main failure modes for aero engine components under cyclic loadings.[1,2,3,4,5,6] Fatigue life usually consists of crack initiation life and crack growth life, and as an important performance index, fatigue crack growth life must be taken into account in damage tolerance design for aero engine components.[7,8] As the key parts of the aero engine, damage tolerance design for turbine disk plays an important role on improving the structural fatigue reliability and ensuring the safety during the service life.[9]Fatigue crack growth theory has become a considerable research subject for ensuring the aero engine integrity. Keywords Crack propagation model, life prediction, maximum entropy theory, fatigue reliability, failure probability
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