纳米结构材料由于具有较大的比表面积，其力学性能显现出明显的尺寸相关性，即纳米结构材料的表/界面效应。已有表/界面效应的理论模型几乎都引入表/界面弹性常数，该参量的确定给理论应用带来一定的困难。本项目主旨是发展一种有效的理论模型，避免表/界面弹性模量的引入。首先，考虑表面原子与体原子晶格失配、外载荷作用以及表面原子不饱和配位对表/界面能密度的影响，建立表/界面效应引起的额外面力与表/界面能密度的关系。结合体平衡方程，形成一种刻画表/界面效应的新理论模型。其次，应用新理论模型分析不同种类纳米结构材料，包括纳米线、纳米膜、纳米颗粒、纳米复合材料等，系统研究表/界面效应对纳米结构材料力学行为影响。最后，系统开展同种材料制备纳米悬臂梁及固支梁微弯曲实验，测量并分析纳米梁等效弹性模量，揭示表/界面效应引起纳米结构材料软、硬化现象的物理本质。新的模型可为纳米结构材料设计和应用提供更方便可行的理论指导。

Due to the relatively large ratio of surface area to volume, nano-materials exhibit obviously size-related mechanical characteristics, i.e., the surface/interface effects of nano-materials. A surface/interface elastic constant was introduced in the existing theoretical models considering the surface/interface effects, which is very difficult to be determined and results in difficulty for the applications of the theories. The main motivation of the present project is to develop a valid theoretical model without introducing the surface/interface elastic modulus. First, considering the influences of the mismatch between the surface atomics and volume ones, the external loading and the unsaturated coordination of surface atoms on the surface/interface energy density, we will establish the relation between the extra tractions induced by the surface/interface effects and the surface/interface energy density. Combining the equilibrium equations of the body, a new theoretical model considering the surface/interface effects is then developed. Secondly, we will analyze several different nano-structured materials using the new theoretical model, such as nanowires, nano-films, nano-particles, nano-composites, and so on, in order to systematically investigate the influence of the surface/interface effects on mechanical behaviors of nano-materials. Finally, micro-bending experiments on cantilevered nano-beams and two-end fixed ones, which are made from the same material, will be carried out. The effective elastic modulus of nano-beams will be measured and analyzed. The physical essences of softening and stiffening of nano-materials induced by surface/interface effects will be studied. The new theoretical model should be helpful for the design and application of nano-materials.