数字梯度敏感法测量PMMA板裂纹尖端的应力强度因子

用数字梯度敏感法(DGS)测量了聚甲基丙烯酸甲酯(PMMA)板的张开型应力强度因子(SIF)。用DGS方法测量了PMMA板裂纹附近应力集中区的应力梯度(或偏转角)。此方法先用数字图像相关法(DIC)测量了透明试件裂纹尖端附近的全场位移,再根据光弹效应获得光线在透明固体应力集中区的全场偏转角,在平面应力条件下,偏转角可以与应力梯度建立联系从而获得应力集中区的应力梯度。由应力梯度场测量了裂纹尖端的应力强度因子。在应力强度因子的求解过程中提出了一种迭代最小二乘拟合应力梯度场的方法,此方法可同时得出应力强度因子与裂纹尖端位置。将实验结果与理论值进行了比较,结果显示数字梯度敏感方法准确地测量了复合型应力强度因子。     

数字散斑相关技术及其应用

在一些特殊的全场变形测量场合中引入了数字散斑测量技术,即利用材料表面散斑点的随机分布模式来测量变形。本文利用数字散斑相关技术研究了固体炸药的破坏模式,测量了预制裂纹尖端附近的变形分布,表明裂纹对尖端位移分布有显著影响。在电子封装结构的热变形分析中也引入了数字散斑相关技术,测量了封装结构中焊点附近区域的变形分布,显示出在焊点位置产生了由热变形不协调引起的变形梯度的高度集中。结果表明数字散斑相关技术在材料和结构的全场变形测量方面具有良好的应用前景。     

垂直于双压电材料界面裂纹的反平面问题研究

研究了双压电材料中垂直于界面裂纹的反平面问题。在裂纹面为可通导的边界条件下,通过对控制方程进行傅里叶(Fourier)变换,并利用边界条件将问题转化为奇异积分方程进行求解,得到了裂纹面的位移函数、裂纹尖端的应力强度因子、电位移强度因子和裂纹尖端能量释放率的表达式。数值分析了双压电材料的材料属性对裂纹尖端能量释放率的影响。     

密质骨双裂纹反平面模型问题复变方法研究

文章构建密质骨双裂纹反平面模型,通过复变方法求解了该模型问题,并给出了裂纹尖端处应力及应力强度因子的解析表达式。数值算例分析了骨单元与基质的剪切模量比、裂纹尖端处与骨单元中心的距离和裂纹长度对裂纹尖端应力强度因子的影响。     

全息干涉法研究裂纹尖端应力状态分布

本文以弹性理论为基础,通过全息干涉实验,确定θ=0°时各点的r值和n值以及无限远处的n值,从而可以确定应力强度因子,同时可以显示裂纹尖端的应力状态分布。     

不同WC含量下WC/Cu复合材料弹性模量实验研究

为了研究数字图像相关方法运用于小试样下WC/Cu复合材料弹性模量测定的准确性,采用粉末冶金法制备出了WC含量不同的WC/Cu复合材料,对试件表面用白漆配合碳粉方法进行制斑,并在万能材料试验机上进行拉伸实验,用CCD相机记录其散斑图。对记录的散斑图进行相关运算,并通过畸变校正理论校正位移计算结果,计算出小应变范围内WC/Cu复合材料的应力应变曲线,得到弹性模量;与传统电测方法结果进行对比,数据吻合较好。结果表明,采用数字图像相关方法和小试件制斑方法运用于WC/Cu复合材料弹性模量的测定是较为精确可靠的。     

散斑照相法与测量力学常数E、μ值

本文介绍了散斑照相法的一般原理、力学量记录及测量方法,导出了离焦散斑技术在转角测量中的近似关系式,最后提出了用散斑照相法测量材料的杨氏模量E和泊松比μ的特实,并给出了试验结果,它与以往其它方法相比,显得简单、准确、有效。目前,在实验应力分析中,散斑照相法已从最初作为全息法的补充(测量面内位移)发展到测量转角、振动,并推广到三维透明物体的内部位移场的测量。在工程中已用于测量平板弯曲、振动、裂缝尖端的张开位移等。     

基于梯度法的数字散斑图像相关亚像素搜索算法

数字散斑图像相关法是对全场位移和应变进行测量的十分有用的无损检测技术.设计精确的亚像素搜索算法是提高测量精度的关键问题.研究了数字散斑图像相关技术的基本原理,在梯度法的基础上,提出了一种基于梯度法的变步长的亚像素搜索算法并应用到相关搜索中,通过对模拟散斑图的位移分析证明了该算法的可靠性和稳定性,并对刚体平移实验进行了测...     

数字散斑相关技术最优光照条件研究

研究了光照条件对数字散斑相关技术(DSCM)测量精度的影响,获得了数字散斑相关计算最优的取值参数及光照条件。通过分析DSCM测量理论模型,获得误差与空间频率和平均灰度梯度的关系式,通过计算机模拟数字散斑图像,确定了最优散斑尺寸、最佳拟合窗口和计算窗口。实物实验中引入GSI编码技术,精确地标定了刚体位移,并对不同光照条件下的DSCM测量结果进行了误差分析,结果表明散斑图像的空间频率和平均灰度梯度与光照条件成规律性变化,并与理论分析结果一致。研究结果表明,DSCM测量的最优光照强度为8000 lx,此时图像平均灰度梯度高,DSCM测量精度高。     

基于任意偏振态的数字全息散斑去噪

数字离轴全息图重建的物体图像会有明显的散斑噪声,本文利用降低相干度的方法来实现散斑去噪。具体方法是通过任意偏振态的物光和线偏振态参考光实现干涉记录,通过这些光场进行平均处理可以有效减少数字全息中产生的散斑噪声。通过控制三个波片的旋转实现任意偏振态,得到多种偏振态下的全息图,多偏振态下重建物体图像的散斑对比度各有不同,对各个重建图像进行对比分析得到最优结果。之后再将各偏振态下的全息图叠加进行重建,重建图像中的散斑噪声得到很好的抑制且比单偏振态下效果更好。从实验结果的分析中能看到这种方法对抑制散斑噪声的有效性。     

Solder joint crack propagation analysis of wafer-level chip scalepackage on printed circuit board assemblies

The solder-joint reliability of a low-cost wafer-level chip scale package (WLCSP) on printed circuit board (PCB) under thermal fatigue is studied. The solder joints are subjected to thermal cycling and their crack lengths at different thermal cycles are measured. Also, the stress intensity factors at the crack tip of different crack lengths in the corner solder joint are determined by fracture mechanics with finite element method. Furthermore, an empirical equation for predicting the thermal-fatigue life of flip chip solder joints is proposed     

Finite element analysis of interface cracking in semiconductorpackages

The application of enriched crack tip finite elements for the prediction of interface fracture parameters, e.g., strain energy release rate and mixed mode stress intensity factors, is presented. Of particular interest, is the comparison between fracture results obtained from two-dimensional (2-D) models and related three-dimensional (3-D) (generalized plane strain) calculations. These results show that for thermal cycling problems, one cannot anticipate 3-D fracture results based on 2-D calculations alone, i.e., plane stress, plane strain, and axisymmetric models. On the other hand, it is shown that the 2-D models are quite adequate for modeling interface fracture in the case of pressure loading on the interface, e.g., pressure due to water vapor expansion during solder reflow. The fracture results presented in this paper were obtained using special enriched crack tip elements that contain the analytic asymptotic displacement and stress field. Enriched crack tip elements for 2-D and 3-D elements are shown to provide highly accurate results for simulating debonding in semiconductor packages subjected to thermal cycling and/or moisture absorption     

关于PBGA中“爆玉米花”现象的分析

本文运用断裂力学法分析塑料焊球阵列封装(PBCA)的爆玉米花现象,专门对封装粘片中发生的裂纹,粘片中的裂纹增大以及焊料掩模和铜之间界面处裂纹增大进行研讨,通过两种方法(裂纹尖端开度位移法和有效裂纹闭合技术)确定裂纹尖端参数,诸如应变能释放率,应力强度系数及不同裂纹长度的相角。     

硅基玻璃光纤断裂的化学动力学模型

通过化学动力学模型描述了硅基玻璃光纤中裂纹扩张速率与外部应力和光纤表面反应物种的函数关系，并用传统的光纤断裂模型把裂纹顶端原子键断裂过程看作应力水化反应。对应变二氧化硅环状结构的水化速率测定可导出硅氧烷水化与应力的依赖关系。由硅氧烷水化引起的应力产生了２．０ｃｍ ３／ｍｏｌ的活化体积，这与硅基玻璃光纤断裂产生的应力一致。此结果支持了基于绝对反应速率理论的光纤断裂模型并预测了裂纹扩张速率与外部应力强度的关系     

Influence of temperature, humidity, and defect location ondelamination in plastic IC packages

The modified J-integral and the stress intensity factor based on linear elastic fracture mechanics can be applied to predict the growth of interfacial delamination in integrated circuit (IC) packages. One of the key parameters required is the interfacial fracture toughness. This paper describes the measurement of the interfacial fracture toughness as a function of temperature and relative humidity using a three-point bending test. The interfacial fracture toughness was found to decrease with temperature and relative humidity. It is proposed that delaminations propagate from very small voids or defects present at the interface. The effect of the location of these interfacial defects or cracks on delamination was studied. The IC package evaluated in this paper was an 80-pin quad flat package with a 0.2 mm defect or crack at the edge or at the center of the interface. It was found that as the temperature of the package was increased, the stress intensity factor of the edge crack was higher than that of the center crack. However, whether the edge crack will propagate first as temperature is increased depends on the ratio of mode II interface toughness to that of the mode I interface toughness. For the package under investigation, it was established that when this ratio is less than 2.69 the edge crack would propagate first, otherwise the center crack would. For small defects, it was found that the water vapor pressure developed at the interface did not have a significant effect on the value of the crack-tip stress intensity factor     

HVEM study of crack-tip dislocations in Si crystals prepared by FIB and twin-blade cutting method

Crack-tip dislocations in silicon crystals have been examined by using high-voltage electron microscopy. Cracks were introduced by the Vickers indentation method at room temperature and the indented specimens were annealed at high temperatures to induce dislocations around crack tips under the presence of residual stress due to the indentation. A selected area around a crack tip was thinned by a focused ion beam (FIB) technique. Specimens were thinned in advance by a twin-blade cutting (TBC) method, which is a simple cutting process for saving FIB machine time. A combination of FIB and TBC can be a useful thinning procedure for the efficient preparation of transmission electron microscopy specimens. Characteristic dislocation structures were observed around the tip of a crack, aiding the elucidation of dislocation processes, which is essential to increase the fracture toughness of materials.     

激光合金化对疲劳裂纹扩展速率的影响

在45#钢基体上以TH-2激光合金化专用粉进行激光合金化处理，通过扫描电镜动态原位观察裂纹从基体向激光合金化区(LAZ)扩展的过程，研究了疲劳裂纹扩展速率与应力强度因子幅(SIFR)的关系，分析了疲劳断口形貌和表面裂纹扩展路径的组织形态。经历一定循环次数之后，激光合金化区内部也出现裂纹，但是合金化区的边界能强烈阻滞裂纹的扩展，一旦基体中的裂纹与合金化区中的裂纹汇合，裂纹失稳扩展。裂纹扩展速率与应力强度因子幅之间的关系不满足传统的Paris公式，裂纹在基体中扩展的断口形貌有典型的疲劳辉纹，而合金化区的断口呈脆性断裂的形貌。从抗疲劳裂纹扩展的要求来看，有必要针对不同的基体材料，设计不同的合金化粉末，通过适当增加合金化区的韧性相，进一步提高激光合金化区抗疲劳裂纹扩展的能力。     

改善数字全息再现像质量的背景强度补偿法

为了完全消除CCD背景噪声和杂散背景光对数字全息再现像质量的影响,在全息图强度分别减去参考光波和物光波强度相减法和全息图强度分别减去参考光波和物光波强度及CCD背景噪声相减法的基础上,提出了改善数字全息再现像质量的背景强度补偿法。介绍了背景强度补偿法的原理,并实验对比了全息图的直接再现像及应用背景强度补偿法对不同背景强度下获得的全息图处理后的再现像。结果表明,背景强度补偿法显著地改善了再现像质量,降低了对数字全息图记录环境的要求。     

A study of the mixed-mode interfacial fracture toughness ofadhesive joints using a multiaxial fatigue tester

In this paper, a new technique is introduced for the control of the far field and mixed-mode crack tip of a single lap shear specimen with a crack along the interface. An investigation has been conducted to use one single lap shear specimen to obtain a series of values of interfacial fracture toughness as a function of the mixed-mode phase angle. The interfacial fracture behavior of the single lap shear specimen subjected to multiaxial concentrated line loads was investigated using a unique six-axis submicron tester coupled with a high density laser moire interferometer. The six-axis submicron tester was used to provide the displacement-controlled multiaxial concentrated line loads, whereas the moire interferometry technique was used to monitor the crack length during the test. In addition, a finite element technique was simultaneously used to determine the near crack tip displacement fields of the single lap shear specimen. The interfacial fracture toughness and phase angle were computed by using these near tip displacement variables through the analytical energy release rate and phase angle expressions derived by the authors. The results show that the facilities and methodology used in the current study can indeed be proved to possess the ability to control the far field and the mixed-mode conditions at crack tip, and to efficiently perform the mixed-mode fracture test