An ingenious composite microstructure of mantis shrimp appendage for improving impact resistance

Mantis shrimp appendage, as an important weapon for hunting, have remarkable impact resistance due to their unique microstructure. In this study, the appendages were subjected to falling ball impact tests and their fracture surfaces were observed by scanning electron microscopy. It was observed that the outer layer was prone to brittle fracture, while the inner layer was more flexible and turned the brittle fracture into a ductile fracture. Our study supported the idea that the unique microstructures in the appendages act as barriers against crack growth and therefore play a leading role in the toughening of the entire appendage structure. Based on the bionic inspiration of the appendage microstructure, a bionic composite structure was designed, which consists of a rigid outer layer and a flexible inner layer. The fibers in the flexible layer show a longitudinal and sinusoidal arrangement to provide shielding to the crack tip when the fracture occurs. The toughening mechanism of the microstructure was further corroborated through finite element simulations, which demonstrated that the longitudinal arrangement of fibers played a pivotal role in spreading stress concentration and thereby delaying the fracture process. The sinusoidal arrangement of fibers was also found to be instrumental in not only bridging the rigid and flexible layers, but also in directing the deviation of the crack path. This work was enlightening for the structural design of impact-resistant composites.