Fracture resistance analysis of pressure vessel equipment:

Fractal crack stress intensity factor When the length effect and bending effect of fractal crack are considered, in the conventional evaluation of plane defect fracture, the fractal effective stress intensity factor is: In the fatigue evaluation, the fractal effective stress intensity factor is not considering the fractal effect. The I-type stress intensity factor at the time, the fuzzy reliability calculation of the pressure vessel fracture is carried out by the literature, the conventional assessment of the plane defect is carried out by the method of the general failure assessment diagram, that is, in the safe area, due to the influence of various objective factors, it is random. Variables and fuzzy variables, the principle of fuzzy probability must be used to discuss the fracture of the pressure vessel with the probability distribution of fracture ratio, and the fuzzy reliability combines the probability distribution with the membership function.

In the anti-fracture analysis of pressure vessels, the calculation and assessment are carried out with the safety assessment 6 of pressure vessels with defects. The criteria are based on the straight forward propagation of the crack. The research so far shows that the actual crack is not straight, but expands forward with irregular bending. It is considered that the crack has fractal characteristics and is a fractal curve. The use of crack fractal can quantitatively describe the fluctuation range of stress intensity factor and fatigue. The change of crack growth rate In engineering practice, the size of the pressure vessel, the size of the defect and the material performance parameters are not definite values, but fuzzy values, which are distributed according to a certain distribution law. In addition, there are still many deviations in the pressure vessel fracture criterion, which limits the reliability of the literature application to a certain extent.

 It should be pointed out that among the steels commonly used in pressure vessels, only a few steels have fractal dimension data, and it is necessary to accumulate steel data in fractal dimension experiments in the future.