| In recent years,aluminum alloys have been widely used in bridge engineering and space structure because of their strong corrosion resistance,light weight,high strength,and environmental protection.Aluminum alloys have a low elastic modulus,only 31 of that of steel,and its structural stability is more prominent.The stress-strain curve of aluminum alloys is nonlinear.It has no yield plateau,and shows significant strain hardening after the yield point.Therefore,the constitutive relationship of aluminum alloys cannot be simplified to an elastic perfectly-plastic model like steel.The strong nonlinearity of the constitutive relation of aluminum alloys makes it difficult to solve the stability problem of aluminum alloy members analytically.On the other hand,with the development of high-rise buildings and long-span structure,normal aluminum alloys can no longer meet the strength requirements,and high-strength aluminum alloys are increasingly used,so the applicability of design code for aluminum alloy structure needs to be further discussed.The strengthening effect of aluminum alloys is ignored in the design code of aluminum alloy structure.However,reasonable use of the strengthening characteristics of aluminum alloys can significantly reduce the material consumption and engineering cost.Therefore,intensive research on the stability of aluminum alloy structure is of great significance for theoretical improvement and engineering applications.In view of the above problems,an analytical approximation method was proposed in this dissertation to analyze the elastic global stability of axial compressed aluminum alloy members,which revealed the influence of material nonlinearity on the post-buckling equilibrium path from the theoretical level;the global stability ultimate bearing capacity of high-strength aluminum alloy members was studied by experiment and finite element numerical simulation;the possible exploitation of strain strengthening in design was explored.The main works are as follows:(1)The elastic global stability of aluminum alloy members under axial compression was studied by analytical approximation method.Based on the Euler-Bernoulli beam theory,the equilibrium differential equation of aluminum alloy members considering the nonlinear constitutive relation was established.The concise and high-precision analytical approximation solutions for post-buckling deformation of aluminum alloy members with different boundaries were constructed,and the accuracy of the analytical approximation solutions were verified by comparing with the finite element results.The effects of main factors such as length,hardening index and boundary conditions on the post-buckling equilibrium path of aluminum alloy members were revealed.In addition,an initial rotation angle was introduced into the equilibrium equation to construct an analytical approximation solution of post-buckling deformation of aluminum alloy members with initial geometrical imperfections,and the influence of initial geometrical imperfections on the post-buckling equilibrium path was analyzed.(2)The global stability of high-strength aluminum alloy members was studied by experiment and finite element numerical simulation.The tension coupon tests and global stability tests on 7A04-T6 aluminum alloy members were carried out,the essential material mechanical property parameters of 7A04-T6 aluminum alloys as well as the global stability ultimate bearing capacity and the mid-span equivalent initial eccentricity of the members were obtained.Numerical analysis of the global stability of aluminum alloy circular hollow section members under axial compression was carried out by employing finite element software,and the reliability of the finite element numerical simulation was verified by comparing with the experimental results.The influence of material properties and global initial geometrical imperfections on the global stability of the members was analyzed parametrically.According to the existing global stability experimental and finite element numerical results of axial compressed 6061-T6,6082-T6 and 7A04-T6 aluminum alloy circular hollow section members,the correlation coefficient in Perry's formula of global stability bearing capacity was modified.Compared with the code and the existing formula for calculating the global stability bearing capacity,the modified formula proposed in this dissertation has higher precision.(3)The possible exploitation of material strain strengthening in design was explored.The ultimate bearing capacity and axial deformation of aluminum alloy stub columns with circular hollow section were obtained by axial compression experiment.Numerical analysis for local buckling of the stub column was carried out by using finite element software,the reliability of finite element numerical simulation was verified by comparing with experimental results.The influence of the main factors such as material properties and local initial geometrical imperfections on the local buckling bearing capacity of the stub columns was analyzed parametrically.According to the existing experimental and finite element numerical results of the aluminum alloy stub column with circular hollow section,the recommended regularized cross-section diameter-thickness ratio limit was given;a formula of the cross-section resistance for the stocky circular hollow section stub column with local buckling after the yield point was proposed based on the continuous strength method,this formula takes into account the strain hardening effect of aluminum alloys and improves the utilization efficiency of cross-section strength,and compared with the code and the existing formulas for calculating cross-section resistance,the modified formula proposed in this dissertation has higher accuracy.The research results in this dissertation revealed the post-buckling behavior of axial compressed aluminum alloy members from the theoretical level,and obtained concise and high-precision analytical approximation solutions for predicting post-buckling deformation of aluminum alloy members;modified the calculation formula of global stability coefficient of axial compressed aluminum alloy members and its application range was extended to high-strength aluminum alloy members;proposed a calculation formula of the crosssection resistance for aluminum alloy stocky circular hollow section considering the strain hardening effect,which significantly improves the economy of the design of aluminum alloy members. |
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