Research on safety margin of fatigue crack of pressure vessel based on time variation of attenuation path

Abstract:

The traditional pressure vessel safety margin characterization model does not consider the time-varying nature of the crack propagation process, which makes it impossible to accurately reflect the residual safety margin. This paper establishes a large pressure vessel residual safety margin model based on the velocity product concept. The form of crack growth directly affects the determination of safety margin, so the Paris formula is used to obtain the crack growth law formula with the closure effect, and the theory of Newman and Raju numerical calculation of the stress intensity factor is used to obtain the correlation function of the changes in the depth and length of different cracks. Taking surface cracks as an example, the safety attenuation path is obtained based on the correlation function model, then the characterization change of the path velocity product safety margin model is calculated, and the path velocity product safety margin model is evaluated from the perspective of life safety margin. It is shown that as the crack propagation changes at different speeds, the safety evaluation results are more consistent with the actual safety margin changes, and provides new ideas for engineering applications.