Influence of bone teeth on strength and toughness of sutured bone plate of turtle shell

The bone plate of turtle shell carapace is formed by several individual ribs through the suture structure of bone teeth. Based on the tensile and bending experiments as well as finite element analysis, the influence of bone teeth at the suture on the strength and toughness of the bone plate of turtle shell carapace is studied in this paper. Precisely morphological characterization shows that the bone teeth at the suture of bone plate are mainly formed by triangle and quadrilateral grooved cones instead of the perfect cone that is often assumed. Similar to the bone plate, 3D printed samples with suture structures formed by triangle or quadrilateral grooved conical teeth are then prepared. Based on the natural and printed samples, the tensile tests combined with the finite element calculations find that the peak-to-valley ratio of bone teeth is a key factor that can explain the strength and toughness of the sutured bone plate varying with the shape of bone teeth, instead of the supposedly lateral surface area or the project area of bone teeth. For bone teeth with a given shape, the larger the peak-to-valley ratio, the larger the strength and toughness of the bone plate are. Comparison of the bending experimental result of 3D printed suture structures with grooved conical bone teeth and that of the natural sutured bone plate of turtle shell carapace further verifies the finding that the peak-to-valley ratio is a decisive parameter on the strength and toughness of suture structure of bone teeth. The results of this paper should be of significance to the biomimetic design of suture structures with high strength and toughness.