Mechanical implications of the arthropod exoskeleton microstructures and the mechanical behavior of the bioinspired composites

Many biological materials possess complicated hierarchical and multiscale structures, after millions of years of evolution. Most of them also demonstrate outstanding mechanical properties, along with multi-functionality. Arthropod is the most widely distributed and the largest phylum of animals in the planet. Their exoskeletons are well-known for excellent mechanical performance and versatility, and consequently emerge among the best sources to study and uncover the mystery of nature in devising its own material systems.;This work first investigated the microstructures of the exoskeletons from selected arthropods, including Homarus Americanus, Callinectes sapidus and Popillia japonica, which exhibit highly complex but interesting hierarchical structures. Exoskeletons are chitin-protein based material systems organized into horizontally well-defined multi-region and multi-layer patterns, with elaborate structures interweaving in the vertical direction. Using SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscope), the characteristic and distinctive structural features of the exoskeletons were revealed for all the species investigated. In particular, distinct patterns (e.g., stacking sequence of multiple layers) were identified in each region of exoskeletons studied. For example, the “helicoidal structure” is characterized by a stacking sequence in which layers are continuously and unidirectionally rotating a small angle with respect to their adjacent layers. Important mechanical implications of those unique structural features were subsequently evaluated and compared using mechanics-based modeling and analysis, as well as numerical simulation.;After the structure-property-function relationship of the investigated biomaterial systems was established, attempts were made to reveal and extract the design strategies employed by nature in designing its own materials and structures. One of the most predominant structural patterns observed in the investigated exoskeletons, the helicoidal structure, was incorporated in the design and manufacture of the subsequent bio-inspired laminated composites. The mechanical performance of the resulted composites was evaluated and significant improvement over the traditional man-made structures was observed.;This original research work encompassed a full cycle for a particular bioinspired material development, starting from the bio-material structure observation, the corresponding mechanical modeling and analysis, and the final bio-inspired composite design, manufacture and evaluation. Important knowledge on the microstructures of the investigated exoskeletons was established or clarified, and their mechanical implications were revealed for the first time based on appropriate modeling and simulation. The resulted bio-inspired composites demonstrate superior mechanical performance over the traditional composite structure widely used in industry, thus possess the potential for future practical application.