Elastoplastic properties of transversely isotropic sintered metal fiber sheets

Sintering of layered metal fiber sheets produces a structured, tunable, paper-like material that holds promise for thermal and biomaterial applications. Particularly promising for these areas is a material system synthesized by the sequential-overlap method, which produces a networked, transversely isotropic open cell porous material. Engineering application of these materials has been limited due in part to uncertainty about their mechanical responses. Here, we present a comprehensive structural and mechanical characterization of these materials, and define a modeling framework suitable for engineering design. X-ray tomography revealed a layered structure with an isotropic fiber distribution within each layer. In-plane uniaxial compression and tension tests revealed a linear dependence of Young's modulus and yield strength upon relative fiber density. Out-of-plane tests, however, revealed much lower Young's modulus and strength, with quartic and cubic dependence upon relative density, respectively. Fiber fracture was the dominant mode of failure for tension within the "in-plane" directions of the fiber layers, and fiber decohesion was the dominant mode of failure for tension applied in the "out-of-plane" direction, normal to the layers. Models based upon dispersions of beams predicted both in-plane and out-of-plane elastoplastic properties as a function of the relative density of fibers. These models provide a foundation for mechanical design with and optimization of these materials for a broad range of potential applications.