Deformation Behavior and Crashworthiness of Functionally Graded Metallic Foam-Filled Tubes Under Drop-Weight Impact Test
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STRUCTURAL crashworthiness is the ability to prevent detrimental acceleration forces from being transmitted to the occupants and minimize the severity of injuries under impact conditions.[1] New cost-effective energy absorbing structures, also called crash absorbers, have been developed to simultaneously reduce the weight of automotive bodies and enhance the crashworthiness.[2] Metallic foams are lightweight materials with high strength-to-weight ratio and excellent impact energy absorbing features, and their use in automobile components is expected to improve fuel consumption and safety.[3–5] In fact, the most prominent characteristic of metallic foams is an extensive stress plateau in the compressive response, during which a further increase in strain induces cell walls buckling, stretching, and cracking inside the localization bands.[6,7] The nearly stable and long plateau region allows for the large energy absorption at constant or slightly increasing stress. So, metallic foams can dissipate the impact
M. SALEHI, S.M.H. MIRBAGHERI, and A. JAFARI RAMIANI are with the Department of Materials and Metallurgical Engineering, Amirkabir University of Technology, Tehran, 158754413, Iran. Contact e-mail: [email protected] Manuscript submitted January 29, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
energy by the orderly collapse of pores and concurrently limit the deceleration under dynamic conditions.[8–10] In comparison with bulk metals, cellular metals exhibit complex response when dynamically loaded. The impact behavior of metallic foams not only depends on the base material, density, and cell morphology, but also on the impact parameters such as impactor velocity, size, and shape. The dynamic response of metallic foams at intermediate strain rates (transitional dynamic regime) can be studied using various test methods such as drop-weight. The drop-weight impact test is the best-suited method to predict the minimum energy absorption capacity with low mass and high velocity. A free fall drop hammer is used for this low-velocity impact evaluation technique. It has been suggested that the main factors determining the strain rate effect of metallic foams are the strain localization, cell walls buckling, micro-inertia effect, shock wave propagation, characteristics of cell wall material, and collision among the contacted cell walls. The strain rate hardening of collapse stress in transitional dynamic conditions mainly arises from the microscopic strain rate sensitivity of base material and micro-inertia effect. In other words, at intermediate strain rates, the cell walls or struts tend to deform in a way to minimize the internal energy of the whole structure under force balance, and the micro-inertia may restrain the lateral motion of material. So, the buckling mode is retarded, while the uniaxial compression is promoted.[8,11,12]
Islam et al.[5] investigated the drop-weight impact response of closed cell Al foams at loading velocities ranging from 2 to 8 m/s. The results indicated significant dependence of
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