Structural Strength Analysis And Residual Life Evaluation Of Cracked Cylindrical Shell

The cylindrical shell structure is widely used in various fields of civil and military because of its excellent structural form and mechanical properties.However,small defects will inevitably occur due to external factors during the manufacturing,transportation,and service of cylindrical shells.Under the action of fatigue load,the small defects will continue to develop with the load cycle.When the crack reaches a certain size,the structure will completely fail or even break.In this paper,with the aid of the British BS7910 failure evaluation standard and the crack propagation force evaluation technology,the safety analysis of the cracked cylindrical shell under tension and compression conditions,and the fatigue remaining life of the cylindrical shell are evaluated respectively.The main contents of the paper are as follows:(1)The basic mechanical performance parameters of the cylindrical shell material ZQ390 steel under quasi-static tension have been measured by the test;the fracture toughness of the material ZQ390 steel has been obtained through the quasi-static fracture toughness test of the CT standard specimen;For the a-N curve of the material under three stress ratio,the a-N curve is processed by a seven-point incremental polynomial method,and the fatigue crack growth parameters of the material are obtained by fitting in the double logarithmic coordinate system.(2)The ABAQUS software was used to build a model of a cylindrical shell with circumferential through cracks.Based on the British defect-containing structure acceptance standard BS7910 failure evaluation chart,a 3C level evaluation curve was constructed.The effect of the crack length on the failure evaluation curve was discussed.The failure evaluation curve was compared with the loading path of the load acting on the cylindrical shell analyzes the critical load change trend of the cracked cylindrical shell under different crack lengths.Secondly,considering the eccentricity of the load acting on the cylindrical shell in actual engineering,the influence of the crack length on the critical load of the cylindrical shell under the eccentric load is discussed.(3)Based on the method of Crack Driving Force,the failure form of a cracked cylindrical shell under eccentric compression load is analyzed.The results show that when the load eccentricity is small,the failure of the cylindrical shell is dominated by the buckling failure mode,and the equilibrium path of the cylindrical shell is not affected by the crack length;when the load eccentricity is large,the cylindrical shell changes from buckling failure to Damage caused by cracks.(4)The finite element model of the standard CT specimen was established.According to the fatigue crack growth rate parameters measured by the test,the accuracy and reliability of the sub-model method and the mesh reconstruction method in calculating the crack growth life were verified.Based on the crack propagation theory of fracture mechanics,the fatigue life of a cracked cylindrical shell under a given fatigue load spectrum is calculated,and the residual fatigue life of the cylindrical shell structure under different initial cracks and different stress amplitudes is calculated by linear cumulative damage theory.In addition,the influence of eccentric load on the remaining fatigue life of cracked cylindrical shells is analyzed.The study on the fatigue life of cylindrical shells in this article provides valuable references for the design of cylindrical shell structures and reasonable maintenance cycles.