Issue 40

L. Zou et alii, Frattura ed Integrità Strutturale, 40 (2017) 137-148; DOI: 10.3221/IGF-ESIS.40.12 147 Experiment Results and Analysis As could be seen from Tab. 3 and Tab. 6, the values of SSE from Mean 1 to Mean 6 based on the fatigue characteristics domain are all smaller than that of the Mean in the whole domain. Except Mean 3 , the value of R-square of Mean 1 to Mean 6 is closer to 1 than Mean in the whole domain. Each value of Adjusted R-square of Mean 1 to Mean 6 is closer to 1 than Mean in the whole domain. Except Mean 4 , the value of RMSE of Mean 1 to Mean 6 is closer to 0 than Mean in the whole domain, which indicates that the scatter degree of the fatigue data is further reduced when fatigue characteristics domain is divided and S-N curves are fitted in each independent domain. Thus fatigue life prediction by using S-N curve modeling method based on the fatigue characteristic domains would be more accurate than that by traditional master S-N curve. C ONCLUSION n this work, on one hand, nodal force based structural stress is used in the S-N curve modeling method based on the fatigue characteristics domain, thus such problems as how to accurately select the S-N curve and to calculate the stress that existed in the traditional nominal stress method have been overcome in the proposed method. The fatigue characteristics domain is determined by using rough set granularity theory, which can achieve knowledge acquisition relying only on the data itself without depending on the prior knowledge or experience knowledge. On the other hand, the entire fatigue test samples of aluminum alloy welded joints are divided into 6 characteristics domains according to the attributes reduction result of the rough set theory, and the Mean S-N curves form Mean 1 to Mean 6 are fitted respectively. As could be seen from Tab. 6, the value of SSE which indicates the dispersion in each fatigue characteristics domain is significantly lower than that of the single master S-N curve obtained in the nodal force based structural stress method. Statistical analysis results show that dispersion of the fatigue data is reduced while the proposed S- N curve modeling method based on fatigue characteristics domain is used. Therefore, compare with the single master S-N curve in the nodal force based structural stress method, to determine the design S-N curve according to the fatigue characteristics domain is more targeted with a lower dispersion degree. Thus the fatigue calculation results will be more accurate if the proposed S-N curve modeling method based on the fatigue characteristics domain is used. Future work will be concentrated on the aspects of the application of the proposed S-N curve modeling method based on fatigue characteristics domain in the practical engineering practice. A CKNOWLEDGMENTS he authors would like to thank all the reviewers for their constructive comments. This research was supported by the National Natural Science Foundation of China (51175054), Natural Science Foundation of Liaoning Province (2015020169), Dalian High Level Talent Innovation Support Plan (2016RQ053). R EFERENCES [1] Dong, P., A structural stress definition and numerical implementation for fatigue analysis of welded joints, International Journal of Fatigue, 23 (2001) 865-876. DOI: 10.1016/S0142-1123(01)00055-X. [2] Dong, P., Hong, J. K., Osage, D. A., et al., Master S-N curve method for fatigue evaluation of welded components, Welding Research Council Bulletin, (2002) 1-44. [3] Dong, P., Prager, M., Osage, D., The Design Master S-N Curve in ASME Div 2 Rewrite and its Validations, Welding in the World Le Soudage Dans Le Monde, 51 (2007) 53-63. DOI:10.1007/BF03266573. [4] Bandara, C. S., Siriwardane, S. C., Dissanayake, U. I., et al., Developing a full range S–N curve and estimating cumulative fatigue damage of steel elements, Computational Materials Science, 96 (2015) 96-101. DOI: 10.1016/j.commatsci.2014.09.009 [5] Benachour, M., Benguediab, M., Hadjoui, A., et al., Fatigue crack growth of a double fillet weld, Computational Materials Science, 44 (2008) 489-495. DOI: 10.1016/j.commatsci.2008.04.015. [6] Fouchereau, R., Celeux, G., Pamphile, P., Probabilistic modeling of S – N curves, International Journal of Fatigue, 68 (2014) 217-223. DOI: 10.1016/j.ijfatigue.2014.04.015. [7] Zhou, Y., Tang, X., S-N Curve Modeling for Finite Life Range under the Assumption of Linearly Changing Scatter, Sae International Journal of Materials & Manufacturing, 7 (2014) 454-464. DOI: 10.4271/2014-01-0970. I T