微电子元件制造过程中的应力分析

本文分析了一个典型的微电子元件在制造过程中残余应力的分布和演化。与以往大多数类似的分析工作的不同之处在于，我们并不是对一个已成型的结构再回过头去仅仅分析其温度历史下相应的应力状态，而是追踪了该结构成型过程的各个方面，尤其是由于工艺过程中结构几何形状的变化而引起的应力重分布。采用的方法则是控制某些材料所对应的单元在某一特写的时刻以后才起作用，这种方法对于各种制造过程的分析非常有效。     

Z-pin复合材料细观模型固化残余应力研究

针对植入Z-pin后碳纤维增强复合材料的微观结构，通过施加Z-pin周期性边界约束条件，建立了Z-pin复合材料单层板单胞细观模型．考虑固化过程中树脂体积收缩、弹性模量随固化度变化和纤维因Z-pin进入偏转因素，运用有限单元法计算了单胞结构在固化成型工艺过程中树脂和纤维应力发展和分布，并研究了Z-pin直径和分布密度对单层板面内残余应力的影响．结果表明：凝胶点之前，树脂模量和残余应力很小，凝胶点之后，树脂模量和残余应力增加较快；残余应力分布与纤维偏转有关；Z-pin直径和分布密度增加会使固化残余应力增大．     

高分子材料注塑固化阶段的残余应力分析

在结晶性高分子材料注塑过程的固化阶段，温度分布、材料细观结构和应力应变之间相互耦合，因而其变化规律非常复杂．本文在井上等人考虑材料细观结构变化的金属热加工工艺应力分析［３～６］的基础上，发展了一套用于高分子注塑固化阶段残余应力分析的本构描述和有限元分析方法．在本构模型中，同时考虑了温度变化、结晶和“冻结取向”对变形的贡献．     

旋转壳及附属结构应力分析软件系统

本文概述了近年来旋转壳应力分析软件系统的一些最新发展。它主要是结合电力建设中超大、超高冷却塔设计和施工中提出的壳筒、离散支柱的整体静力分析及抗震研究，不均匀地基及其沉陷，大塔稳定性，离散支柱局部缺断后的壳体应力分布等力学问题，通过新单元的开发和新算法的数值实现两个方面的工作，在文［１］的基础上，开发了一个旋转壳及附属结构应力分析软件系统．近年来这个系统对一些工程的实际应用表明，它是有效可靠的．     

随机振动载荷作用下结构Von Mises应力过程的研究

随机振动载荷作用下结构的多轴疲劳分析非常复杂，利用Von Mises应力准则将多轴应力响应转换为单轴应力是一条简单而有效的途径，其关键问题是Von Mises应力概率密度函数的确定。本文提出了Von Mises应力过程近似服从Weibull分布的假设，同时给出了确定Weibull参数的方法，为进一步直接利用Von Mises应力进行结构多轴疲劳分析创造了条件。     

复杂三维结构物的光弹性实验研究

应用光弹性原理和方法，根据有关相似原理，对研究对象的几何尺寸进行缩比、模型设计及加工成型．然后将模型在危险载荷作用下，进行应力冻结、切片及应力分析．确定了模型不同截面上的应力及其变化规律，为优化设计和调整数值计算方法提供了有价值的依据．     

金属成型过程接触分析的有限元法

以往通常将加工好的成型构件实物进行疲劳试验，以检验构件设计的合理性。这种实物试验方法在构件设计阶段，显得费时费力，成本很高，并且带有一定的盲目性。本文用大变形条件下的弹塑性有限元接触法模拟了某钢管构件的挤压成型过程，在算得残余应力的基础上，进一步分析了构件服役时在交变载荷作用下的应力，研究构件的最危险点及其应力谱。在算得危险点残余应力以及应力谱的基础上，再结合材料Goodman疲劳极限线图，对成型加工构件服役后的疲劳强度进行校核，有效提高产品的安全可靠度。该方法为成型加工构件的抗疲劳断裂设计提供了方便快捷的手段，降低了成型加工构件设计阶段及产品研发阶段的成本。     

脆性岩石破裂过程损伤与渗流耦合数值模型研究

大量的实验结果表明，脆性岩石的渗透性不是一个常量，而是应力和应力诱发损伤破裂的函数．建立了一个描述非均匀岩石渗流-应力-损伤耦合数学模型(FSD Model)，开发出岩石破裂过程渗流-应力-损伤耦合分析计算系统(F-RFPA^2D)．在该系统中，单元的力学、水力学性质根据统计分布而变化，以体现材料的随机不均质性，材料在开裂破坏过程中流体压力传递通过单元渗流-损伤耦合迭代来实现．该系统能够对岩石试件在孔隙水压力和双轴荷载作用下裂纹的萌生、扩展过程中渗透率演化规律及其渗流-应力耦合机制进行模拟分析．最后，给出两个算例：算例1模拟载荷作用下岩石应力应变-渗透率全过程．模拟结果表明，非均匀性对岩石的应力峰值强度、峰值前后其渗透性演化规律及其破裂机制影响十分明显，模拟结果和实验结果较为一致；算例2模拟孔隙水压力作用下岩石拉伸断裂过程，通过和物理实验对比验证，验证了模型计算结果的可靠性。     

结构动态应力计算方法研究

复杂结构动态应力的准确计算是一个没有圆满解决的问题。本文以最小余能原理为基础，提出了计算结构动态应力的最小伤痛有法。该方法采用二次分析思想，首先采用常规有限元对结构进行适当离散，计算输出结构所需应力区域的有限元结点位移和加速度动力时程反应，再应用最小余能法计算所求部位的动态应力值。这种方法的优点是它可以与现有的有限元程序有机结合，方便使用；动应力在区域内的分布规律可以由计算者根据具体情况而确定，一般情况下，可以选用二次曲线来逼近动应力在区域内的实际分布，避免了常规有限元法计算结构动应力时必须对单元形函数求导的做法，从而提高了动应力计算精度。计算结果表明：本文方法计算结构动态应力结果较常规有限元法的计算结果有明显改进，特别是当结构变化剧烈时，改进效果更为明显。     

塑性成型弹塑性有限元模拟的静水压力间接计算法

在单元内偏应力导数精度分析的基础上，了偏应力导数佳点逐层积分建立了修正的静水压力间接算法，将该方法应用于金属成型过程的弹塑性有限元模拟中，较好了解决了大步长时应力计算精度低的问题，提高了计算效率，算例表明，在变形总量和应变步长都较大的情况下。用庐方法计算得到的应力和变形载荷仍具有较好的精度。     

金属增材制造过程中材料微观组织演化的模拟研究

金属增材制造是集设计、制造一体化的一种新型金属构件制造技术, 在航天航空、交通运输、生物医疗等领域具有广阔的应用前景. 金属增材制造材料的力学性能与其材料微观组织密切相关. 因此, 发展金属增材制造过程中材料微观组织的模拟方法, 有助于指导和优化金属增材制造的工艺参数和流程, 从而制备出性能优异的金属材料. 本文发展了基于连续体假设的热传导模型与元胞自动机相结合的模拟方法, 并利用生死单元方法, 考虑晶粒的重熔和再生长过程, 解决了金属增材制造中多层粉末制造的数值模拟问题. 本文采用该方法模拟了镍基合金IN718、不锈钢316L和高熵合金FeCoCrNiMn的增材制造过程, 并获得了这些增材制造合金的典型材料微观组织, 其模拟结果与实验结果相吻合. 同时, 将该方法拓展到三维尺度的模拟, 研究了镍基合金IN718增材制造过程中三维晶粒的形核和生长. 最后, 对金属增材制造过程中材料微观组织演化的模拟研究中的主要问题进行了总结和展望.      

A modified Drucker-Prager Cap model for die compaction simulation of pharmaceutical powders

In this paper, we present a modified density-dependent Drucker-Prager Cap (DPC) model to simulate the compaction behaviour of pharmaceutical powders. In particular, a nonlinear elasticity law is proposed to describe the observed nonlinear unloading behaviour following compaction. To extract the material parameters for the modified DPC model, a novel experimental calibration procedure is used, based on uniaxial single-ended compaction tests using an instrumented cylindrical die. The model is implemented in ABAQUS by writing a user subroutine, and a calibration process on microcrystalline cellulose (MCC) Avicel PH101 powders is detailed. The calibrated parameters are used for the manufacturing process simulation of two kinds of typical pharmaceutical tablets: the flat-face tablet and the concave tablet with single or double radius curvatures. The model developed can describe not only the compression and decompression phases, but also the ejection phase. The model is validated by comparing finite element simulations with experimental loading–unloading curves during the manufacture of 8 and 11 mm round tablets with flat-face (FF), single radius concave (SRC) and double radius concave (DRC) profiles. Moreover, the density and stress distributions during tabletting are used to analyse and explain the failure mechanism of tablets. The results show that the proposed model can quantitatively reproduce the compaction behaviour of pharmaceutical powders and can be used to obtain the stress and density distributions during compression, decompression and ejection.     

金属基复合材料中的热残余应变场及其对材料细观行为的影响

基于SiC／Al基复合材料中的SiC颗粒周期性排布的假设,采用轴对称体胞方法研究了金属基复合材料中的热残余应变场与粒子形状、体积分数等参数间的内在联系;在此基础上,探讨了热残余应变对夹杂内部和基体—夹杂界面的应力集中因子的影响．所得结果对于理解热残余应变对空洞形核的影响有参考价值。     

Numerical and Experimental Evaluation of Dispersion Coefficient for Resin Transfer Modeling

Resin transfer molding (RTM) is a composite manufacturing process. A preformed fiber is placed in a closed mold and a viscous resin is injected into the mold. In this article, a model is developed to predict the flow pattern, extent of reaction, and temperature change during the filling and curing in a thin rectangular mold. A numerical simulation is presented to predict the free surface and its interactions with heat transfer and cure for flow of a shear-thinning resin through the preformed fiber.To simulate this process, using local thermal equilibrium assumption, it is essential to include the thermal dispersion term in energy equation. The best method to achieve this result is experimental simulation and preparing proportionate system at simple conditions without curing. By comparison of recorded temperature values (using installed instruments at various locations), and the corresponding results from numerical solution for different estimated values of dispersion coefficient, this coefficient has been evaluated based on the best matching estimate. The results show that, to simulate composite manufacturing process by RTM method, the effect of dispersion term in energy equation shall not be neglected.     

Application of X-ray diffraction, micromagnetic and hole drilling methods for residual stress determination in a ball bearing steel ring

A basic understanding of distortion problems requires the analysis of a complete manufacturing process including an almost complete overview of residual stress states in the component during each production step. To reduce the measurement time in the future, three measurements methods (X-ray diffraction, micromagnetic and blind hole drilling methods) have been used to analyze residual stress states in machined AISI 52100 ball bearing rings. X-ray diffraction was used as a state-of-the-art method for machining induced residual stresses with pronounced gradients. The ring exhibited a complex residual stress state with high tensile residual stresses at the surface, a strong gradient in depth, and also showed some variation along the outer circumference due to a superimposition of machining induced residual stresses and effects from the clamping device process. Due to this surface state, micromagnetic signals depend on the analyzing frequency. A calibration of the signals was only possible with the X-ray diffraction data. The results of the three different measurement methods correlate reasonably well.     

Residual stress measurement for injection molded components

Residual stress induced during manufacturing of injection molded components such as polymethyl methacrylate(PMMA) affects the mechanical and optical properties of these components. These residual stresses can be visualized and quantified by measuring their birefringence. In this paper, a low birefringence polariscope(LBP) is used to measure the whole-field residual stress distribution of these injection molded specimens. Detailed analytical and experimental study is conducted to quantify the residual stress measurement in these materials. A commercial birefringence measurement system was used to validate the results obtained to our measurement system. This study can help in material diagnosis for quality and manufacturing purpose and be useful for understanding of residual stress in imaging or other applications.     

Yielding characterization of waxy gels by energy dissipation

The rheological behaviors of yield stress fluids are commonly interpreted from the energy perspective, yet this perspective has rarely been applied for waxy gel. In this study, we calculated the energy dissipated into the waxy gel caused by viscous strain during the deformation process with the aid of a well-tested elasto-viscoplastic thixotropic model. The energy dissipation shows a power-law dependence on the strain regardless of the stress ramping rate. The energy dissipation has been shown to be useful to characterize the ductility of waxy gel, that is, the larger the energy is dissipated during fracture, the more ductile the waxy gel is. When the waxy gel is induced to the same strain by different stress ramping rate, the energy dissipation during the deformation process shows little dependence on the stress ramping rate. However, if during the loading process the stress is increased to the same value by different ramping rate, a higher stress ramping rate causes lower energy dissipation. These findings are helpful to elucidate the widely observed experimental observation for waxy gels that the measured yield stress depends on the stress ramping rate whereas the measured yield strain shows little dependence.     

改进SPH方法在陶瓷材料层裂数值模拟中的应用

为了探讨铝飞片撞击陶瓷材料时的层裂现象,采用改进SPH方法模拟应力波在陶瓷材料中的传播。结果表明,当离散粒子分布不均匀时,数值模拟计算的自由面速度时程曲线与实测曲线吻合良好。对比CSPM方法,改进SPH方法的精度更高。提出适用于数值模拟的陶瓷材料损伤演化方程,对脉冲载荷下陶瓷/钢层合板层裂的破坏过程进行数值模拟,结果表明,由于陶瓷的波阻抗高于钢的,且抗压强度远高于抗拉强度,因此拉应力引起的层裂破坏是主要的。即使在材料内部传播的只是弹性压缩波,当弹性波到达材料界面时,由界面反射引起的卸载波也能导致陶瓷发生层裂破坏。     

马氏体相变微结构演化过程的模拟与分析

实验中观察到形状记忆合金在应力诱发马氏体相变过程中,出现多界面的微结构,马氏体相会逐渐长大变粗,同时会出现由马氏体形核造成的应力突然降低.用多阱的弹性能函数来刻画此相变与微结构演化过程,发现相变时会出现多界面的微结构且伴随着马氏体相的形核至奥氏体相的消失过程,出现了界面数先增后减的变化,同时应力会出现跳跃而不连续.相对应的动力学模型的有限差分的计算结果同样显示形核时出现了多界面的微结构并伴随着应力的大幅振荡,随着载荷的增加界面位置随之移动,使得马氏体相区域逐渐长大.理论分析与数值模拟的结果较好地刻画了实验中观察到的马氏体相变过程中的形核,产生多界面,再到马氏体逐渐长大这一微结构的演化过程.     

Analysis on high-temperature oxidation and growth stress of iron-based alloy using phase field method

High-temperature oxidation is an important property to evaluate thermal protection materials. However, since oxidation is a complex process involving microstructure evolution, its quantitative analysis has always been a challenge. In this work, a phase field method (PFM) based on the thermodynamics theory is developed to simulate the oxidation behavior and oxidation induced growth stress. It involves microstructure evolution and solves the problem of quantitatively computational analysis for the oxidation behavior and growth stress. Employing this method, the diffusion process, oxidation performance, and stress evolution are predicted for Fe-Cr-Al-Y alloys. The numerical results agree well with the experimental data. The linear relationship between the maximum growth stress and the environment oxygen concentration is found. PFM provides a powerful tool to investigate high-temperature oxidation in complex environments.