Study On Energy Absorption Capability Of Aluminum Foam-filled Tubes And Its Application In Automotive Front Rails

Lightweight and safety are the pursuing goals in the design of modern cars. So, how tomeet the requirements of lightweight design, but also to ensure the collision safety is achallenging task before the automotive design engineers. As a sort of lightweight and energyabsorbing metallic material, the closed-cell aluminum foam has some advantage features ofstrong specific stiffness and specific strength with a low density, good impact resistance andenergy absorbability. With this motivation, the energy absorption capability of aluminumfoam and foam-filled structures is carried out in the present work. Then the aluminum foam isapplied to automotive front rails, which aims at the requirements of both safety performanceand lightweight design. The detailed research contents and results include the followingaspects.(1) The uniaxial compression tests are conducted to investigate the deformation behaviorof closed-cell aluminum foam materials under quasi-static conditions. Four stages are evidentin the stress-strain curves and deformation maps, namely the linear elastic deformation stage,initial yield stage, yield plateau stage and the densification stage. The closed-cell aluminumfoam material is found to be isotropic, and the pore size has little influence on its mechanicalproperty. The mechanical property of aluminum foam is strongly affected by relative foamdensity, when the relative density increased, also the compressive strength and plateau stressraised, while the densification strain decreased. Based upon a multitude of experiment data,the fitting functions of young’s modulus, plateau stress and densification strain of closed-cellaluminum foam are obtained, respectively.(2) The dynamic impact tests are conducted with a large-diameter (74mm) SplitHopkinson Pressure Bar (SHPB) device. It is found that the analyzed aluminum foam doesnot present any significant sensitivity to the strain-rate (at about10-3~102s-1), which meansthat the strain rate effect don’t have to be taken into account during the numerical simulationof vehicle crash safety.(3) The assessment criteria of energy absorption ability are put forward, and interactioneffect between the aluminum foams and thin-walled tubes is verified. The plastic deformationof thin-walled tubes are increased because of intercoupling effect between aluminum foam and tube wall. The experimental results show that the foam-filled structures can improvebearing capacity and energy absorption capacity by33%and72%, respectively.(4) It is concluded that the energy absorption of foam-filled structures basically varies inlinear mode with crushing distance under axial impact. Assume the diameter of tube isconstant, when the diameter-thickness ratio increased, the energy absorption capacitydecreased. The function relations between energy absorption and diameter-thickness ratiowith different aluminum foam porosities are obtained in this paper. The diameter-thicknessratio is found has significant influence on energy absorption capacity and specific energyabsorption, while the effect of aluminum foam density is insignificant. However, the influenceof diameter-thickness ratio will be more prominent when the foam density decreases.(5) The multi-objective optimization that the maximum energy absorption, maximumcrushing force efficiency and minimum weight are chosen as optimization objective isproposed, where response surface models are established, and the Pareto optimal solution setis obtained through Non-dominated Sorting Genetic Algorithm (NSGA-II). The results yieldfrom the optimizations indicate that when energy absorption and weight of foam-filledstructures are comprehensively considered, the optimal diameter-thickness ratio varies from36.7to37.3, and the porosity of aluminum foam should be76%.(6) When aluminum foam materials are filled into automotive front rails, the energyabsorption and specific energy absorption can be promoted by15.3%and25.4%, respectively.Meanwhile, the weight of front rails can be lighten by8.4%. At last, draw a conclusion that ifaluminum foam materials are applied to automotive energy absorption structures, the crashsafety can be significantly improved and lightweight performance is also considered. Thealuminum foam materials have a good application prospect.