| High-strength 7075 aluminum alloy exhibits high strength and low plasticity at room temperature,and the self-piercing riveting connection cannot be directly performed in the body assembly at room temperature.In addition,the unstable mechanical properties of the aluminum alloy resistance spot welded joint and the low heat resistance of the adhesive process make it impossible to use a large amount of the aluminum alloy into the mass production of the automobile body structure.In response to the above problems,a new type of Thermal Self-Pierce Riveting?T-SPR?process has been proposed.Due to the strength of the7075 aluminum alloy can be effectively reduced in the elevated temperature environment,the plasticity can be improved.At the same time,the corresponding hot plate-cold mold self-piercing riveting can ensure the riveting quality and joint performance of the aluminum alloy.Based on the above-mentioned new self-piercing riveting joint process,this paper focuses on the simulation of the T-SPR self-piercing riveting joint process,analyzes the actual riveting effect by evaluating the joint profile parameters,and uses the finite element software to evaluate the joint quality under different process factors.The specific research content is as follows:1.Based on the thermal tensile test,the high temperature mechanical behavior of high strength 7075 aluminum alloy at 300oC,350oC,400oC and strain rates of 0.001s-1,0.01s-1and 0.1s-1 was measured.The experimental results show that the high temperature can significantly reduce the yield strength of 7075 aluminum alloy,inhibit the hardening properties of the material,and greatly improve the plasticity of the material.Among them,the tensile strength of the material at 400oC is 5%at room temperature,and the yield strength and fracture strain of the material at higher strain rate are relatively increased.The fracture strain of the material under 0.1s-1 condition can be increased by about 16%with respect to 0.001s-1.2.Based on the Johnson-Cook constitutive relationship and the numerical inverse calculation process,the characteristic parameters of the high temperature thermal-mecha nical behavior of 7075 aluminum alloy are obtained.The hardening and fracture para meters of the original J-C model and a modified J-C model were compared,and the stress-strain curves under different high temperature conditions and strain rates were fit ted.Using the correlation coefficient and relative error to further evaluate the accuracy of the two types of J-C models in data fit.The results show that the modified J-C model can better characterize the high temperature thermal-mechanical behavior of 7075 aluminum alloy because it considers the co-coupling effect of temperature softening and strain rate strengthening,which is helpful to establish an accurate finite element s imulation model.3.The thermal self-piercing riveting experiment under three conditions?300oC,350oC,400oC?was carried out,and an accurate T-SPR finite element simulation model was established.The numerical simulation of the 7075 aluminum alloy thermal self-piercing riveting process was carried out by introducing the fitted J-C parameters.The experimental and simulation results were compared to analyze the relevant parameters of the T-SPR half-section joint?interlocking value,residual thickness,tail tensor?,the optimal riveting temperature range?350-400oC?of the T-SPR process was obtained.Furthermore,numerical simulation was carried out to evaluate the influence of other process factors?rivet size,pad height,thickness matching and number of sheets?on the riveting effect of T-SPR joints.The results show that the riveting temperature and rivet size are the main factors affecting the self-piercing riveting effect of T-SPR. |
PDF Full Text Request