Fatigue evaluation method based on fracture fatigue entropy and its application on spot welded joints

The present paper is devoted to the fatigue evaluation of material or structure based on thermodynamic entropy approach. The fracture occures once the cumulative entropy reaches a critical value, the fracture fatigue entropy(FFE). Therefore, in this paper, the relationship between entropy and F-N curves is studied, and an entropy-load-number of cycles(E-F-N) surface is developed. Meanwhile, the FFE-based F-N curve can be obtained at the critical entropy value. To verify the utility of proposed method, the E-F-N surface and FFE-based F-N curve are applied to the fatigue evaluation of spot welded joints during high-cycle fatigue. It is shown that the E-F-N surface can effectively represent the fatigue performance. And the accuracy of the FFE-based F-N curve is confirmed by comparing with the traditional traditional three-parameter power function F-N curve. The maximum relative error of the fatigue limits obtained by two different methods is 10.9 %.