The mystery of coconut overturns the crashworthiness design of composite materials

Abstract The natural structures inspires human beings to find new composite material design for the crashwothiness. The mystery of outstanding crashworthiness of a coconut is revealed in multilayered and multiscale structures, including its macroscopically organized pericarp and microscopic disordered mesocarp. The pericarp consists of parallel fibers well-aligned in the tangential direction. The fibers of coconut pericarp is macro ordered. The mesocarp is the thickest layer among three layers of the pericarp. The coconut mesocarp is micro disorderly. In this paper, the coconut fruit free drop experiments and quasi-static experiments were carried out, and the theoretical analysis was carried out to explain the rule of the coconut fiber arrangement, and finally the numerical computational models were built to verify the theoretical analysis. This work shows that the bottom part of the coconut fruit is always the contact part during the free drop experiments without initial angel, and the fiber orientation of the bottom of the coconut fruit can increase the energy absorption ability, and the fiber arrangement of the coconut fruit can influence the propagation of the stress wave to protect the coconut endocarp. A bio-inspired template has been provided for the functional composite material design.