Department of Materials & Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
Department of Biomaterials, Max-Planck Institute of Colloids and Interfaces, Research Campus, Golm 14424, Germany.
J Mech Behav Biomed Mater. 2014 Feb;30:223-33. doi: 10.1016/j.jmbbm.2013.09.009. Epub 2013 Sep 19.
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.
龟壳是一种天然的护盾，具有复杂的层次结构，赋予其卓越的机械性能。贝壳的角质覆盖骨顶（背部）部分，称为背甲，由刚性的类似三明治的肋骨组成，中间是泡沫状的内部，两侧是两个外部皮质。肋骨以三维交错的方式附着在柔软的未矿化胶原缝合线上。这种独特的结构组合促进了在受到捕食者攻击时的复杂机械响应。在本研究中，进行了机械弯曲测试，以检查红耳滑龟背甲在不同方向和位置、以及整个肋骨和子层区域的静态行为。此外，还评估了缝合线的特性，并将其与肋骨的特性进行了比较。这里使用了简化的经典分析，将整个肋骨视为层合复合材料，对实验结果进行了合理化。测量的肋骨强度（约 300MPa）和弯曲模量（~7-8.5GPa）与皮质的强度和模量处于同一数量级。根据各个子层的模量预测肋骨的模量的理论预测与实验结果吻合良好。缝合线区域比肋骨更柔软和脆弱，但相对坚韧，可能是由于骨头的锯齿状元素的互锁设计。
