Assessing the role of loading direction on the uniaxial compressive response of multilayered ice-templated alumina-epoxy composites

This work is motivated by the structural gradient observed in natural materials to investigate the influence of the loading direction on the compressive response of ice-templated alumina-epoxy composites. Although this investigation is not on the development of multilayered composites with a structural gradient, the current results can help understand the mechanical behavior and design of such materials. Ice-templated alumina materials were developed from 20 vol% suspensions at high freezing-front velocity (FFV) and from 30 vol% suspensions at high and low FFVs. From porous ceramics, specimens were extracted at different orientations relative to the growth direction of ice crystals and infiltrated with epoxy. The resultant composites varied in ceramic fraction and morphology. For compression along the growth direction of ice crystals, specimens exhibited either high strength with brittle-like (catastrophic) failure or low strength with ductile-like (progressive) failure. Away from growth direction, strength decreased significantly, and failure was ductile-type. The strength exhibited a strong dependence on ceramic fraction and morphology. At each orientation, strength data of both porous ceramics and composites showed significant variability, and Weibull analysis suggested a connection between their strength. Direct visualization revealed the influence of loading orientation and morphology on deformation and failure in composites. Using the Tsai-Hill failure criterion, the role of competitive failure mechanisms on the compressive response of composites was evaluated. From the knowledge of composition, compressive and bend strength of ceramic phase, and yield strength of polymer phase, upper bound and lower bound of strength were predicted, which encompassed the strength of composites.