Abstract
Failure analysis and fatigue life prediction are necessary and critical for engineering structural materials. In this paper, a general methodology is proposed to predict fatigue life of smooth and circular-hole specimens, in which the crack closure model and equivalent initial flaw size (EIFS) concept are employed. Different effects of crack closure on small crack growth region and long crack growth region are considered in the proposed method. The EIFS is determined by the fatigue limit and fatigue threshold stress intensity factor △Kth. Fatigue limit is directly obtained from experimental data, and △Kth is calculated by using a back-extrapolation method. Experimental data for smooth and circular-hole specimens in three different alloys (Al2024-T3, Al7075-T6 and Ti-6Al-4V) under multiple stress ratios are used to validate the method. In the validation section, Semi-circular surface crack and quarter-circular corner crack are assumed to be the initial crack shapes for the smooth and circular-hole specimens, respectively. A good agreement is observed between model predictions and experimental data. The detailed analysis and discussion are performed on the proposed model. Some conclusions and future work are given.
Highlights
Life prediction and failure analysis are indispensable and critical for engineering structural materials, but continue to be challenging issues
The fatigue crack growth method based on linear elastic fracture mechanics (LEFM) is becoming a more important and promising alternative for total fatigue life analysis
Liu and Mahadevan [5] recently proposed a method to predict the fatigue life of smooth specimens based on the equivalent initial flaw size (EIFS)
Summary
Life prediction and failure analysis are indispensable and critical for engineering structural materials, but continue to be challenging issues. The value of EIFS is determined by fatigue limit σ f and threshold stress intensity factor Kth. the difference of growth behavior between small crack and long crack is not considered in this method. A general method is proposed to predict fatigue life based on the crack closure model and the EIFS, in which the small crack effect is considered. A total fatigue life prediction model considering the crack closure, is established; a large number of experimental data, for smooth and circular-hole specimens on three different alloys (Al2024-T3, Al7075-T6 and Ti-6Al-4V), under multiple stress ratios collected from the open literature, are employed to validate the proposed model. Estimation of the actual IFS is another challenge These issues make fatigue life prediction based on crack growth analysis difficult. Fatigue Life Prediction Based on Crack Closure and Equivalent Initial Flaw Size
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