Study On The Failure Behaviors Of Gradient Metalic Foam Under Biaxial Loading

Metallic foams,as a new type of multifunctional material,offer significant performance gains in light,stiff structures,for efficient absorption of energy,for acoustic control and other more specialized applications.In practical applications,metallic foams are usually subjected to multiaxial loading and occurs fracture behavior.The heterogeneous meso structure significantly affects metallic foam's mechanical properties.However,the study of the meso-structure parameters of metallic foam on its failure surface and mechanism under multiaxial conditions is controversial.In this paper,we explored a numerical method to study the failure behaviors of gradient metallic foam under biaxial loading based on three-dimensional(3D)Voronoi mesostructures.Effects of both anisotropy and gradient parameter on failure surface were discussed in detail.The main studying contents of this paper are as followings:(1)The finite-element model of gradient metallic foams based on 3D Voronoi mesostructure was established and verified.The 3D Voronoi mesostructure with a continued gradient change of size irregularity was constructed employing modified voro++.The statistic feature as well as the spatial distribution of both shape irregularity and size irregularity were analyzed.Uniaxial compressive and tensile tests of closed-cell aluminum foams were conducted to verify the finite element model.(2)Effects of gradient parameter of metallic foam on uniaxial compressive and tensile properties were explored.The uniaxial compressive properties are dependent on the statistic of shape irregularity and the spatial distribution of size irregularity,but independent on the statistic of size irregularity.While,the uniaxial tensile properties are affected obviously by the statistic of shape irregularity and size irregularity,the spatial distribution of size irregularity because of the significant local deformation of mesostructure.The parabolic function was proposed to describe the effects of the gradient parameter on peak stress and plateau stress.(3)The failure criterion for anisotropic metallic foam under biaxial loading is recommended: the earliest peak characteristic of the axial stress of each direction,von Mises equivalent stress and hydrostatic stress.This criterion is also reasonable for anisotropic foam under triaxial loading.(4)The failure surface of gradient metallic foam was analyzed based on numerical simulation experimental data under biaxial proportional loading.In stress plane,the failure surface including gradient direction is smaller than the failure surface including non-gradient directions,which means it is easier to failure in gradient direction.Owing to the anisotropy of metallic foam and the asymmetry of failure suface in tensile and compressive state,failures surface of gradient metallic foam should be normalized by uniaxial compressive failure stress and uniaxial tensile failure stress of each axial respectively,which leads to the conclusion that normalized failure surfaces of gradient metallic foams are almost independent on both the anisotropy and gradient parameter.The normalized failure surface is nearly an ellipse.Properties of failure surface of gradient metallic foam in strain plane were discussed in detail.These studies contribute to the optimization design and simulations based on macroscopic model of metallic foams.