Abstract：Metal foams are widely used as advanced lightweight construction or kinetic energy absorbers in many industrial fields. Graded metal foam is becoming a research hotspot due to its outstanding designability. The dynamic compressive mechanical behavior of closed-cell aluminum foam with continuous negative density gradient under different impact velocities was investigated using the finite element software ABAQUS. First, the random 3-D Voronoi technique was employed to construct graded closed-cell foam models. Then different impact velocities were applied at the impact end of foam along the negative density gradient direction. Like the uniform foam, three deformation modes, i.e. quasi-static mode, transitional mode and shock mode were observed with the increase of impact velocity. The densification factor was introduced to define the critical velocities of mode transition. A new method was proposed to define the local densification strain by contrasting the nominal stress-strain curves with deformation modes. This method took the effects of relative density and density gradient into account. Deformation maps of impact velocity versus relative density and density gradient were respectively presented for the graded foam. Finally, the effect of density gradient on energy absorption ability was discussed. The finite element simulation results indicated that the first critical velocity was insensitive to the relative density, while the second critical velocity increased with the increase of relative density. The critical velocity decreased with the increase of density gradient. It was found that the smaller the absolute value of density gradient was, the more energy the foam would absorb at the initial stage of deformation under low impact velocity; and the larger the absolute value of density gradient was, the stronger energy absorption ability of the foam material at the initial stage of deformation under high impact velocity would be. These research results could be applied to the design of optimal energy adsorption structure with graded metal foam.
2017, Vol. 38 
