Shear behavior of polymer micro-scale truss structures formed from self-propagating polymer waveguides

The shear behavior of micro-scale truss structures formed from a three-dimensional interconnected pattern of self-propagating polymer waveguides was investigated. These structures had sub-millimeter size features and comprised a repeating octahedral-type unit cell designed to suppress bending in the truss members prior to initial failure. For a typical shear loading method, the experimentally measured shear moduli deviated from predicted values as the relative density decreased. However, the mechanical behavior changed when the shear loading condition was altered to distribute the load more uniformly between all truss members and the measured shear modulus was aligned with predicted values. The shear strength and total plateau strain of these structures were strongly dependent on the mode of failure and the uniformity with which the truss member failure was distributed through the thickness of the structure. Furthermore, plateau strains of up to 60% were achieved when all truss members in compression buckled uniformly. Thermo-oxidation reaction of the polymer micro-truss structures caused an increase in the shear modulus and maximum shear strength (up to 2.9 MPa), although oxidized structures fractured at the maximum shear strain.