Abstract: Although the fracture behavior of sea urchin spines has been extensively investigated, there is as yet a lack of quantitative estimation on the effect of growth rings on the fracture properties of sea urchin spines. In sea urchin spines, much denser pores present in growth rings rather than porous layers. The tensile strength and fracture toughness of sea urchin spine samples with different numbers of growth rings are measured by the Boundary Effect Model (BEM). The experimental results of single-edge notched three-point bending tests indicate that the BEM is an appropriate method to estimate the fracture toughness of the present porous sea urchin spines, and the number of growth rings plays an important role in the fracture properties of spines. Specifically, the tensile strength and fracture toughness of sea urchin spines can be significantly improved with the increase in the number of growth rings, and their fracture toughness can even reach a relatively high value compared with some other porous materials with an identical porosity. The present research findings are expected to provide a fundamental insight into the design of high-performance bionic materials with a highly porous structure.

Key words: Sea urchin spine , · Growth ring , · Boundary Effect Model , · Porous structure , · Tensile strength , · Fracture toughness