Mechanics of composite sandwich structures with bioinspired core

Abstract Synthetic sandwich composite materials have been fabricated using carbon fiber–epoxy face sheet and polymeric foam core by mimicking the structure of a natural composite material, Palmetto wood. The foam core of the sandwich composites has been reinforced by pultruded carbon rods to replicate macrofiber reinforcement of Palmetto wood within the porous microstructure for enhanced flexural behavior and energy absorbance. Sandwich structures have been characterized to elucidate the multiscale deformation behavior under quasi-static three point bend test using multiscale Digital Image Correlation (DIC). The damage evolution in the sandwich materials has been evaluated using a model developed to decouple the effect of pore collapse and plastic strain. It has been observed that the longitudinal reinforcement of pultruded carbon rod in foam core by the bioinspiration from the hierarchical structure of Palmetto wood increases the flexural strength, elastic energy absorbance of the sandwich with bioinspired core compared to that with the conventional un-reinforced core, however, at the cost of damage initiation strain. The sandwich composites with bioinspired core exhibits an increase of approximately 100% in flexural stiffness compared to that of sandwich with conventional foam core. The strength and volumetric energy absorbed are found to increase by approximately 10× and 14× from the sandwich with conventional core. These results validated using Palmetto wood as a source of bioinspiration for increasing the energy absorbing capability of sandwich composites. The analysis of the experimental results also indicated that the macroscopic flexural response of the sandwich composites is similar to that of the Palmetto wood. This similarity is attributed to the evolution of damage mechanisms associated with pore collapse and plastic strain being nearly identical between the bioinspired core and Palmetto wood. Furthermore, it is found that the reinforcement does not significantly affect the damage evolution characteristics in the bioinspired core, only the damage initiation is affected similar to what was observed in Palmetto wood.