title: Bending mechanics of the red-eared slider turtle carapace.
abstract: The turtle shell is a natural shield that possesses complex hierarchical structure, giving rise to superior mechanical properties. The keratin-covered boney top (dorsal) part of the shell, termed carapace, is composed of rigid sandwich-like ribs made of a central foam-like interior flanked by two external cortices. The ribs are attached to one another in a 3-D interdigitated manner at soft unmineralized collagenous sutures. This unique structural combination promotes sophisticated mechanical response upon predator attacks. In the present study mechanical bending tests were performed to examine the static behavior of the red-eared slider turtle carapace, in different orientations and from various locations, as well as from whole-rib and sub-layer regions. In addition, the suture properties were evaluated as well and compared with those of the rib. A simplified classical analysis was used here to rationalize the experimental results of the whole rib viewed as a laminated composite. The measured strength (~300MPa) and bending modulus (~7-8.5GPa) of the rib were found to be of the same order of magnitude as the strength and modulus of the cortices. The theoretical prediction of the ribs' moduli, predicted in terms of the individual sub-layers moduli, agreed well with the experimental results. The suture regions were found to be more compliant and weaker than the ribs, but comparatively tough, likely due to the interlocking design of the boney zigzag elements.
authors: Department of Materials & Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel. Electronic address: Ben.Achrai@weizmann.ac.il.
authors: Ben
authors: B
authors: Achrai
authors: Department of Biomaterials, Max-Planck Institute of Colloids and Interfaces, Research Campus, Golm 14424, Germany. Electronic address: Benny.Bar-On@mpikg.mpg.de.
authors: Benny
authors: B
authors: Bar-On
authors: Department of Materials & Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel. Electronic address: Daniel.Wagner@weizmann.ac.il.
authors: H Daniel
authors: HD
authors: Wagner
mesh_terms: D060105:Animal Shells; D000818:Animals; D001696:Biomechanical Phenomena; D008422:Materials Testing; D055595:Mechanical Phenomena; D014426:Turtles / Q000033:anatomy & histology*
keywords: Biological composites; Flexural rigidity; Laminated structure; Three-point bending; Turtle carapace