薄膜压痕的三维效应研究

项目名称： 薄膜压痕的三维效应研究

项目编号： No.50805079

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 生物科学

项目作者： 佘崇民

作者单位： 南京航空航天大学

项目金额： 20万元

中文摘要： 压痕实验在分析评价薄膜的力学特性以及界面结合特性方面起着非常重要的作用，然而压痕实验强烈的三维尺寸效应使得从载荷-位移曲线到材料参数的反问题求解变得异常复杂和困难。本项目针对压痕及界面裂纹的"尺寸效应"问题，采用内聚力模型、三维断裂力学和有限元法相结合的方法，在实验的基础上研究了压痕和界面裂纹扩展以及薄膜断裂的三维尺寸效应，揭示压痕三维应力应变场和各材料属性"尺寸效应"之间的关系，建立相应的数学力学模型，取得了一下主要成果：1） 发展了裂纹的等效厚度理论，基于离面约束因子Tz，从理论上发展了裂纹在三维结构中的等效厚度概念，为三维断裂理论在界面结构以及复杂结构中的应用奠定了理论基础；2） 研究发现界面强度对界面裂纹萌生起着决定性作用，界面裂纹的扩展主要受界面能的影响，研究了压痕尺寸和薄膜厚度对界面分层裂纹的影响；3）针对 BD/Si薄膜系统进行了压痕实验研究，并获得了分层裂纹的形成和形状演化过程，并采用采用内聚力模型、三维断裂力学方法成功模拟了界面裂纹的扩展和形状演化过程,提出一个简单的分辨二维和三维应力状态的方法；4）研究了应力集中的三维效应和三维 I-II复合型裂纹的弹塑性应力特性。

中文关键词： 薄膜；压痕；内聚力模型；裂纹；三维断裂力学

英文摘要： The interface delamination in a ductile film/hard substrate system induced by wedge indentation is studied in this project. The three-dimensional (3D) effect of the indentation and interface delamination are studied by use of traction-separation law, 3D fracture mechanics and finite element method based on the indentation test. Some meaningful results are obtained: 1) The equivalent thickness theory for a crack is proposed in this research. The equivalent thickness conception is developed based on the out-of-plane stress constraint factor Tz, which can help the application of 3D fracture mechanics in interface structures and complex structures. 2) It is found that the interfacial strength has more significant effects on the critical indentation load and depth for the initiation of interfacial delamination than the interfacial energy, while the interfacial energy plays a more important role in the crack propagation. The effects of the wedge indenter length and the film thickness on the interface delamination cracks are also analyzed. 3) The shapes of the interfacial delamination crack and stress states during wedge indentation in a soft-film-on-hard-substrate system were investigated systematically using the 3D finite element simulation and wedge indentation experiment. A straightforward criterion based on the curvature of the delamination crack front was proposed to indicate the transition of stress states during the interfacial delamination. A guideline was therefore proposed to classify the 2D and 3D stress states for extracting the interface adhesion properties. 4) Based on the 3D I/II mixed-mode fracture experiments, the coupled effects of mixed loading and thickness on the elastic-plastic field near the crack front and initial angle of crack are analyzed. The 3D effect of stress concentration are also studied systematically.

英文关键词： Film; Indentation; Traction-separation law; Crack; 3D fracture mechanics