Deformation Behavior and Crashworthiness of Functionally Graded Metallic Foam-Filled Tubes Under Drop-Weight Impact Testing

This article investigates the low-velocity impact behavior and crashworthiness of metallic foams and functionally graded foam-filled tubes (FGFTs). Closed cell Zn, Al, and A356 alloy foams fabricated by the direct foaming method are used as axial grading fillers for the manufacture of single-, double-, triple-, and quad-layer structures. The microstructural examinations are implemented by an optical microscope and a field emission scanning electron microscope. The drop-weight impact testing is performed on the metallic foams and FGFTs with a free fall velocity of 5.42 m/s and energy of 294.3 J. The influence of material, density, number, and arrangement of foam layers on the deformation behavior and specific energy absorption (SEA) is studied. The results indicate the multiple crushing response and stepwise increment of stress through distinct plateau regions in the FGFTs. The A356 foam with low density and great inherent strength provides the highest SEA, whereas high density and brittle matrix of the Zn foam deteriorate the SEA of FGFTs. The maximum SEA of 261 J/(g cm−3) is achieved in the double-layer A356-Al foam-filled tube. The best crashworthiness is fulfilled in multilayer A356-Al structures owing to a combination of high SEA and low peak crushing strength (σpeak).