Plastic dissipation mechanisms in periodic microframe-structured polymers

Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations.Here, the plastic dissipation andmechanical response of polymeric microframe structures is investigated using micromechanicalmodelingof large deformations.Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensileloadingaswellasnegativenormal stressduringsimplesheardeformation. The effects of structural geometry on mechanical response are also studied to tailorandoptimizemechanicalperformanceatagivendensity.Thesequantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy.