海胆牙齿ST区变形行为和失效机制的原位研究

The stone, the main working part of sea urchin tooth, is undergoing abrasion in scraping process. The deformation and fracture of the structural elements by this process is the main factor to decrease its wear property. Currently, the hierarchical architectures and mechanical properties of the stone has been studied. While its deformation and failre mechanisms have not been comprehensively recognized, which may influence the reliability realization of the relationship of microstructure and wearable property. In this work, the stone will be selected as a research object and its in-situ test method will be established. By using in-situ TEM technology, we investigate deformation behaviours, twinning and cracks in the stone in real time. Combinng with simulation results and quantitative experiments, the deformation mechanism and mechanical design strategies of wearable properties of the stone will be further expored. Therefore, this project exhibits important scientific valur for which can not only reveal the deformation mechanisms of the stone, but also provide significant research methods for studing the sources of excellently mechanical properties. Unraveling its design strategies could provide inspiration for the pursuit of high-performance artificial composites.

ST区是海胆牙齿的主要工作区域，在刮取食物的过程中会不断磨损，这一过程中内部结构单元在应力作用下的变形乃至失效是导致ST区耐磨性下降的重要因素之一。目前，对ST区的多级结构和宏观力学性能虽已有了初步的认识，但由于尚未认识其形变和失效机制，而在一定程度上影响了微观结构和耐磨性能关系的揭示。本项目拟以海胆牙齿ST区为研究对象，在建立生物复合材料原位实验方法的基础上，借助原位力学加载及观测技术，捕捉载荷作用下ST区的变形、孪晶的形成以及裂纹萌生和损伤演化过程，从而揭示ST区的形变机制。结合数值模拟结果和定量检测，从微观结构的应力响应行为入手揭示影响ST区耐磨性能的本质。所以，本项目的研究对揭示生物复合材料优异力学性能根源的研究具有借鉴意义，可以为设计与合成具有特殊功能的人造材料提供新的思路。

牙齿是海胆从岩石表面刮食海藻并在岩石上钻孔筑穴的重要工具，虽然海胆牙齿主要由含镁方解石构成，作为磨削工具，其展现出了优异的力学性能。揭示海胆牙齿复杂的变形机理可以为仿生材料的设计提供理论基础。本项目通过设计过渡支撑夹具，制备出了海胆牙齿原位拉伸试验用的样品。通过原位拉伸实验，揭示了海胆牙齿ST区在受力变形时，基体自我牺牲，将有机物孔洞成为裂纹萌生和扩展的位点，以此增加裂纹扩展路径，从而起到耗散形变能量的目的。不仅如此，晶间有机物在变形过程中被拉长，有机物的大变形进一步耗散了形变能量。在纳米压痕的损伤局域化定量试验中，本项目计算了海胆牙齿的能量耗散密度，观察到海胆牙齿具有损伤局域化的特点，并在变形的纤维中观察到了e型和r型形变孪晶。形变孪晶的发现，进一步丰富了海胆牙齿ST区的变形机理，充实了生物矿物形变局域化理论。在此基础上，本项目开展了基于ABAQUS有限元软件建立的压痕三维实体有限元模型模拟。结果显示，基体较纤维更易变形，且纤维变形并产生e型和r型孪晶时，r型孪晶所需应力载荷更大，r型孪晶的界面滑移量也更大，说明r型孪晶界更易裂纹萌生和扩展。本项目通过观察载荷作用下矿物相、界面、有机物和缺陷对裂纹萌生和损伤演化的影响，阐明ST区的形变和失效机制，进一步揭示微观结构与力学性能的联系。