| Materials with significant porosity, generally termed cellular materials, have considerably lower bulk density than their solid counterparts. However, at the cost of reducing the mass of a material by introducing porosity, mechanical properties such as the strength and elastic modulus are significantly diminished. Ordered cellular structures generally exhibit an increase in modulus and peak strength relative to random cellular configurations by changing the mode of deformation from bending-dominated to stretch/compression-dominated within the microstructure during elastic loading. Nevertheless, techniques to fabricate three-dimensional ordered open-cellular materials, particularly with feature sizes ranging from tens to hundred of microns, are limited. Presented in this dissertation, is a new technique to create cellular materials with a truss architecture from a three-dimensional interconnected pattern of self-propagating polymer waveguides. The self-propagating effect enables the rapid formation ( 5 mm) three-dimensional open-cellular micro-truss structures from a single two-dimensional exposure surface. The process also affords significant flexibility and control of the resulting truss microstructure.;The structure-property relationships in these new polymer micro-trusses have been investigated, correlating compressive and shear behavior with structural features, such as density, cell size, truss angle, and unit cell architecture. The compression and shear modulus compare well with analytical predictions; however the measured peak strength was significantly lower than predicted. The deviation of the measured peak strength from the idealized predictions was attributed to imperfections in the structure and the nonlinear behavior of the solid polymer. The affect of imperfections can be reduced by developing unit cell architectures with increased waveguide connectivity that ultimately increase nodal stability and decrease the waveguide truss member slenderness ratio. |
