矿物凸起在贝壳珍珠母界面中摩擦耗能机理的研究

论文建立了珍珠母矿物质板相对滑移时表面矿物凸起相互攀爬摩擦的理论模型，得到了界面等效摩擦性能可以表示为两个无量纲参数的函数：凸起高宽比α=A/l、凸起高度与板厚度比β=A/D。理论预测与有限元模拟结果对比，两者符合良好，验证了理论模型的有效性。通过理论和计算分析，得到以下结论：（1）矿物质表面凸起的存在对板间界面摩擦起到了显著的增强作用；（2）等效界面摩擦系数随α增大而增大，但与β无关；（3）α和β的提高均能提高界面等效剪切强度和摩擦耗能。该研究揭示了矿物质板表面凸起的微结构特征对界面摩擦耗能机制的影响规律，对于理解珍珠母贝壳等承力生物材料的界面增强增韧机理和指导相关仿生复合材料的设计有重要意义。

Study on Friction and Energy Dissipation Mechanism of Mineral Asperities in the Interface of Nacre

Although composed of relatively weak constituent materials (stiff but brittle minerals and tough but soft biopolymers), nacre can achieve excellent mechanical properties through fabulous designs of multiple structural hierarchies. At microscale, nacre exhibits the well-known “brick-and-mortar” structure, which has attracted considerable research attention. At nanoscale, the mineral platelet (i.e., “brick”) surfaces are featured with distributed nanoscale asperities, which is believed to play an important role in the interface strengthening and toughening. Based on the kinetic and contact analysis, a theoretical model was established herein to characterize the friction and energy dissipation behaviors between the neighboring mineral platelet surfaces in nacre. In the model, the equivalent interface friction coefficient, shear strength, and energy dissipation can be expressed as functions of two dimensionless geometrical parameters: the asperity aspect ratio α=A/l, and the ratio of asperity height to platelet thickness β=A/D. The theoretical predictions were compared with the finite element simulation results, and the good agreement validated the theoretical model. Further studies via the theoretical model led to the following three major findings: (1) the presence of asperities on the mineral platelet surfaces significantly enhances the interface friction, strength and energy dissipation during their relative sliding; (2) the equivalent interface friction coefficient increases with α, but is independent of β; (3) the increases of α and β can both improve the equivalent shear strength and frictional energy dissipation. These results and conclusions are of great significance not only for understanding the interface strengthening and toughening mechanism in nacre but also for guiding the design of related biomimetic composite materials. It is worth noting that the current work mainly focused on the role of mineral asperity, and did not take into consideration the influence of mineral platelet deformation along the interface, biopolymer matrix, mineral bridge, etc. To better understand the interface strengthening and toughening mechanism of nacre, the individual and synergistic roles of these possible factors should be further clarified, which correspondingly asks for more complicated theoretical and numerical models.