In the small sample fatigue test space, in order to obtain the master S-N curves of each reliability of the titanium alloy welded structures. Firstly, the Bootstrap method is combined with the equivalent structural stress to determine the minimum number of samples under each level of equivalent structural stress, and the appropriate resampling times are obtained through residual analysis. Secondly, based on the fatigue test data of titanium alloy welded joints with different plate thicknesses, materials, types and stress ratios, the linear regression model of master S-N curves are determined by using the traditional group method and Bootstrap method, and its reliability is 99%, 95%, 84%, and 50% respectively. Finally, the comparative analysis shows that the titanium alloy fatigue test samples obtained by Bootstrap method tends to be more stable, which improves the fitting degree of the titanium alloy fatigue life test data and the accuracy of the fatigue life prediction when the sample is small. A more accurate regression model of the master S-N curves of titanium alloy welded structures was obtained and verified.
PurposeThis paper aims to study and modify the notch equivalent stress method, as well as to establish the notch equivalent stress range S–N curve and apply it to the fatigue assessment of engineering examples.Design/methodology/approachThis paper studies the notch equivalent stress method and puts forward the concept of “singular equivalent crack”. Combined with the fatigue test results, by proposing to consider the singular coefficient of the transition angle of the welded structure and the introduction of material correction factors, this paper derives the notch equivalent stress equation for commonly used welded joints applicable to steel, and finally establishes the notch equivalent stress range of the S–N curve.FindingsThe obtained results show that the dispersion of fatigue data is 65.6 and 75.4% for T-joints and transverse cross-joints, respectively, under S–N curves using notched equivalent stress compared to the nominal stress range. The fatigue evaluation error of the modified notch equivalent stress equation for transverse cross welded joints improved by 50.65%, 53.1 and 39.6% on average, respectively, compared to the original other methods. The fatigue evaluation error for T-joints improved by 13.4 and 13.9%, respectively, compared to the original other methods.Originality/valueThere are relatively few studies on the fatigue assessment of notch equivalent stress method. In this paper, the notch equivalent stress method is studied and modified to improve the accuracy of fatigue assessment of welded structures with singular stresses.
In order to reduce the potential safety hazards in the operation of rail vehicles, a new parameter table optimization algorithm based on the particle swarm optimization algorithm is proposed to carry on the failure assessment and fatigue life calculation of welded joints. This algorithm reduces the number of iterations by adding connection pools to connect the parameter selection database. In addition, based on this algorithm, combined with Python language and BS7910 standard, a calculation program for failure assessment and fatigue crack growth life is written. The algorithm program is validated by taking the commonly used T-type, butt, and lap joints as examples. In terms of failure assessment, the calculation results of the algorithm program are securer and more conservative, and the safety accuracy of the algorithm program is improved by 8%–12%. In terms of fatigue crack growth life, the error between the calculated value of the algorithm program and the test data is within the engineering allowable range. At the same time, the algorithm program can give the evaluation calculation results more intuitively and quickly, which provides a reference for the failure assessment and life calculation of the welded structure.
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