Research On Dynamic Fatigue Life Of Pressure Vessels Containing Defects

In the field of engineering applications,the working environment of pressure vessels is complex;in order to ensure the safe and reliable operation of equipment,it is very necessary to evaluate the safety and reliability of pressure vessels with defects.This research was supported by the National Natural Science Foundation of China "Research on Probabilistic Fracture Analysis and Safety Assessment of Defective Structures under Multi-factor Coupling";the research on the fatigue life of pressure vessels with defects under the action of alternating loads was carried out to provide a basis for more accurate safety assessment of pressure vessels.First,different forms of non-penetrating semi-elliptical cracks are set on the inner wall of the tank,and a three-dimensional finite element analysis model of the cracked pressure vessel is established;by setting different constraint forms,the defect-free pressure vessel and the non-perforated pressure vessel are calculated.The natural frequency and vibration mode of a semi-elliptical cracked tank.The rationality of the constraint setting is analyzed,and the first-order natural frequency and mode shape of the tank vibration are obtained,which provides control parameters for the subsequent calculation of the fatigue life of the tank.Secondly,using ANSYS software,an analysis model for obtaining the stress intensity factor is established for the dynamic load of the plate with a central penetrating crack,with the finite element calculation carried out.In this way,the value of the dynamic stress intensity factor at the crack tip is accurately obtained and compared with the theoretical solution.The command stream for obtaining the dynamic stress intensity factor of the crack during the whole process of the structure from forced vibration to free vibration is compiled;the method for combining the interaction integration and the additional external excitation is used to extract the stress intensity factor of the crack tip under vibration conditions when the three-dimensional crack is contained,obtaining the change amplitude of the stress intensity factor of the crack tip when the tank body vibrates(?KI).The results show that when the peak dynamic load is the same as the quasi-static load,the peak stress intensity factor under dynamic load is greater than the stress intensity factor under static load,and the failure modes of the two are also completely different.At the same time,the dynamic stress intensity factor enters a stable fluctuation stage as the loading continues,providing an accurate stress intensity factor amplitude for the fatigue life calculation of the structure.Finally,the dynamic stress intensity factors under the influence of different crack parameters during free vibration of the tank are calculated,and on this basis the life of the tank is predicted.The results show that the change of crack depth has the greatest impact on the dynamic fatigue life of the pressure vessel;the change of crack direction,the difference in the amplitude level of the initial excitation and the position of the crack also have a non-negligible effect on the dynamic fatigue life of the structure.This paper explores the method for extracting the stress intensity factor of the three-dimensional crack problem during vibration,and gives the prediction of the fatigue life of the cracked pressure vessel.The research method can be used for the analysis of dynamic fatigue problems,and can further provide a reference basis for the dynamic reliability assessment and safety assessment of pressure vessels.