Studies Of Safety Assessment Methods For Aluminum Alloy Thin-Walled Pressure Vessels With Surface Cracks

Aluminum alloy thin-walled pressure vessels are widely used in aerospace vehicles,which demand the structural safety extremely.In engineering,current researches of safety assessment concentrate mostly on higher-toughness steel vessels in nuclear and chemical industry,lacking systematic studies on aluminum alloy thin-walled pressure vessels.Aimed at the toughness fracture of aluminum alloy thin-walled structures,this paper focuses on the safety assessment method research of aluminum alloy thin-walled pressure vessels with surface cracks.This paper includes the aspects following:1.Based on Kirchhoff plate theory,the solutions for thin plate with a through crack are modified to suit elastic-plastic problems.And based on fully-plastic solutions of single-edge cracked panel(SECP)under pure tension and pure bending,this paper introduces a modified elastic-plastic constitutive relations for SECP.Combining the two aspects above,we obtain an improved nonlinear line-spring model.Numerical results show that the agreement between finite-element method and line-spring model is remarkable,thus proving the rationality and accuracy of the model.2.By the nonlinear line-spring model modified,researched are the influences of the external loads,crack sizes and plastic work hardening exponents on the J values of crack tips.The material hardening parameter has a significant influence on the J integral curves,but the crack length has little effect on the J integral.3.Based on the R6 J-integral analysis curve,the nonlinear line-spring model modified is combined with failure assessment diagram to obtain a quick safety assessment method for surface cracked structures,and then an example is studied to prove its feasibility.Practice suggests that the safety assessment method obtained has the advantages of engineering applications.4.The accurate elastic and elastic-plastic J values of surface crack tips are computed to draw the Failure Assessment Curves(FACs)by the line-spring model modified.Then the influences of crack sizes and plastic work hardening exponents on the FACs are studied.Compared to the R6 general curve,FACs in this paper tend to be conservative,which can comprehensively reflect the difference in crack sizes and hardening exponents,thus the safety assessment based on them is more reliable.5.For engineering structures,based on the improved constitutive relations for line-spring,the nonlinear line-spring model for surface cracked cylindrical shell is modified;based on the principle of plastic superposition,a new nonlinear line-spring model is established for surface cracked plates with modified R-O relation material.