Mechanism of the Strain Rate Effect of Metal Foams with Numerical Simulations of 3D Voronoi Foams during the Split Hopkinson Pressure Bar Tests

With the demand of lightweight structure, more and more metal foams were employed as impact protection and efficient energy absorption materials in engineering fields. But, results from different impact experiments showed that the strain rate sensitivity of metal foams were different or even controversial. In order to explore the true hiding behind the controversial experimental data about the strain rate sensitivity of metal foams, numerical simulations of split Hopkinson pressure bar (SHPB) tests of the metal foams were carried out by finite element methods. In the analysis, cell structures of metal foams were constructed by means of 3D Voronoi, and the matrix metal was assumed to be no strain rate sensitivity, which helps to learn the strain rate effects quantitatively by the foam structures. Numerical simulations showed that the deformation of the metal foam specimen is not uniform during the SHPB tests along the specimen, and the strain-stress relations of the metal foams at two ends of the specimen are different; there exists strain rate sensitivity of the metal foams even the matrix metal has no strain rate sensitivity, when the strain of the metal foams is defined by the displacement difference between the ends of the specimen; localized deformation of the metal foams and the inertia effect of matrix metal are the two main contributions to the strain rate sensitivity of the metal foams.