珍珠母多级微结构协同增强增韧机制的跨尺度计算研究

Simultaneously high strength and toughness are always being highly desired in advanced synthetic materials, driven by a mount of need from both civil and military industries such as mobile vehicles, warships, aircrafts, and etc. Nacre is mainly composed of brittle mineral (aragonite, occupy more than 95% in volume), but through an elegant hierarchical architecture and a low fraction of biopolymer it achieves 1 and 3 orders of magnitude higher strength and toughness than that of aragonite, respectively, sets an excellent example for the strengthening and toughening design of synthetic materials. In the past half century, many possible strengthening and toughening mechanisms have been proposed, based on the mesoscale, microscale, or nanoscale structure features observed in nacre. However, which mechanism is mainly responsible of the high strength and toughness of nacre is still unknown, because the existing experimental data and phenomenological models don’t or can’t provide sufficient information on 1) the physical mechanisms originated from group behaviors of atoms and molecules, 2) the synergies among different microstructures or mechanisms, 3) the quantitative evaluation of the contribution of every individual mechanism. To fill these gaps, the project aims to develop a multiscale and cross-scale computational method, bottom up from atomic and molecular level to investigate the strengthening and toughening behaviors of each individual structure feature, and to probe the synergistic effect in strengthening and toughening among different structure features. With the strength and toughness data from the multiscale and cross-scale simulations, an evaluation system with synergistic factor, dovetail interlocking factor and extrinsic toughening factor will be built up to quantitatively characterize the role and contribution of every individual mechanism in the overall strengthening and toughening of nacre. The evaluation system will help recognize what structural features are more critical for the strengthening and toughening in nacre, and further provide useful guidelines for developing nacre-inspired synthetic materials with simultaneously high strength and toughness.

高强度和高韧性是高性能材料领域永恒的研究主题，在汽车、战舰、航天器等民用和军用领域都有着巨大的需求驱动。珍珠母通过多级微结构和少量的有机聚合物（体积分数<5%）实现了对普通矿物质（文石）1-3个量级的增强增韧效果，为人工材料的增强增韧设计提供了参考范本。半个世纪以来，基于对珍珠母微结构的观察，人们在介、微、纳观尺度上提出了多种可能的增强增韧机制。然而，哪种机制在起主导作用仍不得而知，这主要由于当前的研究存在以下不足：1）对原子或分子层次上物理机理的揭示不足2）对不同微结构间的协同效应研究不足3）对每种机制的贡献缺乏量化评价等。针对这些不足，本项目拟发展一套多尺度耦合、跨尺度的计算模型，从原子和分子层次出发系统研究各微结构独自的增强增韧机理，以及不同微结构间、不同机理间的统合综效。在此基础上，建立一套量化评价体系，评定各微结构在增强增韧中的角色和贡献，为人工仿生材料的设计提供清晰系统的指导。

高强度和高韧性是高性能材料领域永恒的研究主题，在汽车、战舰、航天器等民用和军用领域都有着巨大的需求驱动。珍珠母通过多级微结构和少量的有机聚合物（体积分数<5%）实现了对普通矿物质（文石）1-3个量级的增强增韧效果，为人工材料的增强增韧设计提供了参考范本。本项目采用理论建模和分子动力学—有限单元法多尺度计算，系统研究了“雉尾卯榫结构”、“矿物桥”、“包状矿物凸起”、生物聚合物粘弹性等多级微结构特征对珍珠母类承力生物材料刚度、强度、韧性和冲击防护性能等的影响。主要结果和发现包括：1）雉尾卯榫结构相较于规则矩形结构和反雉尾卯榫结构具有更高的刚度、强度和断裂韧性，并且具有奇特的负泊松比性质；2）矿物桥式强连接可以有效地调控和改善增强相之间的界面性能，一方面可以保障增强相之间载荷的有效传递，一方面可以调控破坏模式改善断裂韧性；3）包状矿物凸起可以大幅地提高矿物质增强相界面间的等效摩擦系数和摩擦能量耗散，从而起到增强增韧的作用；4）贝壳类承力生物材料优异的冲击防护性能是微结构、生物聚合物体积比和粘性综合优化作用的结果。这些结果和发现对于加深人们对珍珠母类承力生物材料“结构—功能”关系的认识，对于指导仿生高性能材料的设计和制备，都有重要的理论价值和实际意义。