Bioinspired microstructure design simultaneously enhances strain-rate stiffening and toughening of composites

Keratinous biological materials, such as baleen, pangolin scales, and human hair, have similar constituent materials. However, their strain-rate dependent mechanical properties vary due to differences in their microstructures. Inspired by the microstructures observed in baleen, here we present novel microstructural designs of three types of lamellar-tubular fibers, namely the lamellar-tubular fiber (LTF), mineralized lamellar-tubular fiber (MLTF) and hollow mineralized-lamellar-tubular fiber (HMLTF). We systematically investigated their strain-rate dependent mechanical behaviors with comparison to the conventional cylinder-fiber (CF) reinforced composites. Through the finite element analysis (FEA), we found that the baleen-inspired composites have superior strain-rate stiffening and toughening effects than the conventional fiber reinforced composite. Rate-dependent constitutive models decoupling elastic and inelastic regimes were constructed for these bioinspired composites. Based on the FEA results, three constitutive parameters were obtained to quantitatively characterize the rate-dependent mechanical behaviors of these composites, especially the microstructure-induced difference. Furthermore, our study found that the baleen-inspired tubular microstructure improves stiffness and strain-rate stiffening through raising the stress levels of all phases and improves toughness and strain-rate toughening through enlarging the deformation in the inelastic region. This novel bioinspired design is hopeful to pave ways for the development of advanced composites with simultaneously enhanced strain-rate stiffening and toughening.