压痕法测定热压MoSi2基复合材料K1C值的研究

用不同的压痕方程计算了纳米ＺｒＯ２粒子韧化ＭｏＳｉ２基复合材料的室温断裂韧性Ｋ１ｃ值，同时研究了压痕载荷对Ｋ１ｃ值的影响。结果表明，试验材料在试验条件下的断裂韧性不遵从半月状裂纹系统方程，而遵从巴氏裂纹系统方程，其室温压痕断裂韧性保持与压痕载荷的独立性。     

周期阵列压痕奇异应力场与开裂（PartⅡ：压痕开裂临界载荷）

周期阵列压痕方法是研究微观摩擦学的工具之一。由于周期阵列刚性压头压在半平面弹性体的表面时,会产生周期的Ⅰ型奇异压应力场,该奇异应力场的应力集中达到一定程度时,即达到临界条件时,该奇异应力场所在的边界将开裂。压痕边界的开裂问题是一个新型的断裂力学问题,通过边界移动的能量释放率的分析给出了压痕边界开裂能量释放率数学表征,并给出边界开裂的临界载荷和临界开裂角。     

基于图像处理的自动聚焦技术及应用

自动聚焦技术是提高压痕直径测量系统测量精度、智能化和自动化的重要手段.介绍了采用图像处理法实现压痕直径测量系统的自动聚焦技术,核心就是选择一个合适的图像清晰度评价函数.在研究了众多图像清晰度评价函数的基础上,提出了基于向量模型和改进DCT变换的图像清晰度评价函数,实验表明,提出的算法具有良好的单峰性、准确性、稳定性、可靠性和快速性.最后通过基于COM组件技术的Matlab与VB混合编程来保证算法实现和软件设计.     

J-积分在镀层基体平面压痕边界开裂中的应用

当二维平端刚性压头作用在镀层基体的表面时,在镀层材料的表面形成一个平面压痕,同时在压痕的边界处将诱生奇异应力场和K-控制区。与裂纹问题类似,该应力场的平面压痕应力强度因子是描述奇异应力场应力集中程度的唯一参量。本文将利用守恒积分,讨论镀层基体平面压痕守恒积分的主要特征,同时给出镀层基体平面压痕应力强度因子的远场积分计算方法。     

Mechanical properties determined by nanoindentation tests of [Pb(Zr,Ti)O3] and [Pb(Mg1/3Nb2/3)1−xTixO3] sputtered thin films

As the introduction of piezoelectric materials into micro electromechanical systems increases, there is a correlating requirement for understanding the mechanical properties of these films. We have investigated the mechanical properties of unpoled PZT [Pb(Zr,Ti)O₃] and PMNT [Pb(Mg_1/3Nb_2/3)_1−xTi_xO₃] thin films deposited by sputtering. In this study, nano-indentation, a technique which allows determination of the transverse mechanical properties, is used. It is the easiest method for assessing the biaxial elastic modulus and the hardness of thin films. It was confirmed that neither cracks, nor pile-ups, were observed for indentation depths below 20% of the film's thickness.The continuous stiffness method was used and allowed us to demonstrate that the indentation modulus decreases continuously with increasing grain diameter. This can be explained by the orientation changes of the crystallites with increasing grain diameter. The indentation modulus measured under load, or at almost null load (that is when the ferroelectric domains are or are not oriented by the stress) are coherent with those determined by the same method with a hard bulk ceramic. These results tend to show that the compliance C_ij of the hard bulk ceramic can possibly be used with sputtered thin films. The hardness is almost independent of the grain diameter (H_b ≅ 7.5 ± 0.9 GPa) and higher than that for the bulk PZT ceramics considered in this study. PMNT and PZT films have appreciably the same mechanical characteristics. No influence of the film thickness was found on the values of both of these parameters.     

The kinking behaviour of a bimaterial interface crack under indentation loading

The aims of this paper are twofold. The first is to evaluate the applicability of the formula for the crack kink angle—based on the maximum principle stress criterion—for predicting the interface kink angle in a bimaterial sample undergoing indentation loading. This formula was developed for cracks in homogenous materials but in this paper, it is used to predict the kink angle using the mode mixity at the tip of a crack lying on a bimaterial interface. The second aim is to examine the behaviour of the system, in terms of the crack kink angle and contact radius, for various coating thickness', crack lengths and combinations of properties of the coating and substrate. The system that is analysed consists of a planar bimaterial sample undergoing indentation with a tungsten-carbide spherical indenter. Two-dimensional, axisymmetric models are created to represent the system, with subdomains used for modelling the cracks. In order to determine the applicability of the kink angle formula, the angle predicted is compared to the angle that is directly calculated using boundary element method models that establish the angle of the kink which yields the maximum mechanical energy release rate. The second aim of the paper is achieved by varying the material property combinations and coating thickness of the bimaterial sample and observing the effect on the kink angle of the interface crack and the contact radius. The methodologies employed are initially verified on homogenous samples with known solutions.     

Advanced methods for mechanical and structural characterization of nanoscale materials for 3D IC integration

Managing the emerging internal mechanical stress in chips, particularly if they are 3D stacked, is a key task to maintain performance and reliability of microelectronic products. Hence, a strong need of a physics-based simulation methodology emerges. This physics-based simulation, however, requires material parameters with high accuracy. A full-chip analysis can then be performed, balancing the need for local resolution and computing time. The key for an efficient simulation of a 3D stacked IC is a comprehensive database with material properties for multiple scales of the affected materials. Therefore, effective “composite-type” material data for several regions of interest are needed. Advanced techniques to measure FEA- and design-relevant properties such as adhesion properties and effective CTE values are presented.     

A reinvestigation of the validity of the indentation fracture (IF) method as applied to ceramics

Poor correlation between indentation fracture resistance, K_IFR, and fracture toughness, K_IC, has long been considered a weak point of the indentation fracture (IF) method of materials analysis. The present work therefore assessed the reliability of the experimental data that has historically been used for comparisons of K_IFR and K_IC. A painstaking survey of primary literature reports concerning the IF method revealed that the comparisons of K_IC with K_IFR in most studies were imperfect because both K_IC and K_IFR were measured using unreliable techniques and because improper test materials such as silicate glass were employed. These findings indicate that the standard objections against the use of the IF model are not well supported, and also that the majority of the empirically-derived calibration constants used in various IF equations are suspect. Accordingly, it is evident that new experimental measurements using the latest and most reliable techniques will be required to allow well-informed discussions of the validity of this test method in future.     

Indentation fatigue of WC grains in WC–Co composite

Indentation fatigue of WC grains on basal and prismatic planes in WC–Co cemented carbide has been investigated using instrumented indentation at nano level and applied loads from 5 mN to 50 mN. The influence of indentation load and crystallographic orientation of WC grains has been studied. Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and atomic force microscopy (AFM) have been used for the characterization of microstructure, orientation of WC grains, topography of indents and slip lines in WC grains. Significant influence of the crystallographic orientation of WC grains on the indentation fatigue has been found. The indentation depth increased with the increasing load more intensively during the fatigue test of the prismatic planes than the basal planes. This behavior is probably connected with the different slip and dislocation mechanisms during the indentation of basal and prismatic planes.