Research On Estimation Method Of Fatigue Life Scatter Of Stractural Details

Because of the limits in experimental time and expense, it is difficult to get enough test data for the conventional statistical requirements. As a contrast to the small sample size of structural fatigue test, there have already been a lot of fatigue test data of materials in engineering practice. Thus the studies on the processing method of fatigue test data and fatigue properties scatter have not only the important theoretic significance, but also a practical value. Referring to the test data and study achievement of fatigue properties published in the literature, how to process the fatigue data scatter and estimate fatigue life scatter of structural details is discussed in this thesis.An S-N curve fitting approach, which fused both fatigue data from group test and staircase test, was proposed based on the double weighted least square method, in which the effects of fatigue test method, fatigue data scatter and test sample size on S-N curve were included. Nineteen sets of experimental data of metals and PMMA are employed to verify the ability and rationality of the presented method. It is shown that the fitted S-N curves have higher accuracy and credibility.The field of application of the double weighted least square method has been extended to fitting of any reliability stress-life curve. Seventeen sets of experimental data of metals and PMMA are employed to verify the ability, rationality and accuracy of the presented method. It is shown that the established P-S-N curves have higher accuracy and credibility.A method for estimating the fatigue strength scatter of notched specimen is proposed in this thesis, only based on P-S-N curves of smooth specimen and geometries of notched specimen. Respectively, fatigue strength distribution of smooth specimen is solved by amended equivalent failure probability method and fatigue notch factor distribution is obtained by stress field intensity approach and historical information. Thus fatigue strength distribution of notched specimen is calculated. The estimated fatigue strength agrees well with the experimental ones. Finaly, the fatigue life of aeronautical engineering structural details is calculated by nominal stress approach.