Lightweight Design And Deformation Behavior Of Aluminum Thin-walled Structure

Thin walled structure with light weight, high strength and good deformationstability are widely used in modern automotive body structure. Typical deformation ofthin-walled structure are bending and axial compression. In this paper, deformationbehaviors and design methods of aluminum thin walled structures were studied. Theresults could be used for the design and optimization of automotive aluminiumstructures.The finite element analysis software based on explicit dynamic method wasapplied to the topology optimization of aluminum bumper using hybrid cellularautomata (HCA) as an optimizing model. The results of topology optimization showthat the simulated annealing method can be used for the optimization design of thebumper thickness. The simulation and experiment of bending, charpy impact andcrash were performed. The results indicate that comparing with steel bumper, themass of aluminum bumper was25%lighter, the flexural strength was52%higher andthe crash energy absorption was45.6%higher. The aluminum bumper designed withHCA topology optimization could meet regulatory requirements with goodcrashworthiness and improve the safety performance of vehicles.The deformation mode and energy absorption of6063aluminum beam wereinvestigated by quasi-static axial compressions. The aluminum samples were aged attemperature of180℃from30min to540min, respectively. The axially compressedexperiments of aluminum thin-walled beam were studied by using WAW-E600universal testing machine. The load was recorded by computer automatically. Theaxial compression performance of aluminum beam with different heat treatment wereevaluated. The results indicate that the deformation mode of the6063beam graduallychanges from Euler mode to Concertina mode, the mean load and energy absorptionincreases with the increasing of aging time. The sample aged for540min deforme s inconcertina mode, the energy absorption increased about99%as compared with theNo-HT sample. The elastic modulus and tangent modulus of thin-walled structure hassignificant impact on the deformation mode during compression. The referencecoefficient of deformation modes φ was proposed to evaluate the deformationbehavior of thin-walled structure. With the reducing of φ, deformation mode of thespecimen changes from Euler mode to Concertina mode. The deformation of aluminum thin-walled structure gradually changes to Concertina mode with thereducing of strain harden rate.By reasonably inducing a single row of holes at the end of aluminum beam, thefirst peak load could be reduced about7%-12%, and the deformation mode is alsochanged. The deformation behaviors change from Euler mode to Mixed mode, or fromDiamond mode to Concertina mode with inducing holes. Comparing with the originalsample in the same aging state, the deformation process of thin-walled beams withinducing hole is more regularity and stability. A series of axial compression tests withmulti-rows of induced holes were studied for30min aged aluminum beams at180℃.The results showed that the position and diameter of induced holes ha s greater impacton the deformation behavior of specimens. Especially, when induced holes diameterare too large, the position at45°diagonal of holes occurred bucking distortion. Thethin-walled beams deforms in a new mode, the Lantern mode. In this deformationmode, the fluctuation of deformation load is low. Because of the less compressiondistance, the total energy absorption of aluminum beams reduced in Lantern mode.Tensile tests with traditional samples and S-shaped samples were carried out. Theaxially compressed experiments of aluminum beam were studied by WAW-E600tester.In the compression process,6061aluminum beams fracture along the specimens, and6063samples deforms without failure. However, the tensile test results show that thetwo materials have the same elongation. Tension specimens was observed by opticalmicroscope, the results showed that the surface morphology of6061alloy was orangepeel, and the surface of6063alloy was smooth. The microstructural of deformedspecimens were observed on MM-6metallographic microscope, it was found that6063was typical equiaxed recrystallized microstructure, while6061was coarse grain.The Cockcroft-Latham ductile fracture criterion was used to predict the deformationcracking. According to uniaxial tensile test results and numerical simulations, thecritical strain energy of aluminum fracture was obtained. Comparison between thepredition and experiment results indicates that Cockcroft-Latham criterion is verysuitable for predicting vehicle structures failure during collision with high accuracy.