三维编织复合材料渐进损伤的非线性模型及强度分析

建立了考虑周期性位移边界条件的细观体胞模型，对三维编织复合材料的渐进损伤过程进行数值模拟。采用Eshelby-Mori—Tanaka方法计算含损伤裂纹的材料的剐度矩阵，并将有限元网格尺寸和单元裂纹尺寸引入损伤演化方程，有效地降低了模拟结果对有限元网格的依赖程度。通过计算得到了材料应力应变的非线性关系和失效时的极限强度，并分析了材料的破坏机理。结果表明，大编织角材料的破坏模式主要是基体失效与纤维横向拉剪破坏，模拟计算结果与文献中的实验值吻合较好。     

单元类型和尺寸对裂尖疲劳塑性数值模拟的影响研究

本文采用Jiang-Sehitoglu循环塑性模型和多轴疲劳准则对紧凑拉伸式样裂尖的循环塑性变形、裂纹扩展速率和残余应力进行了有限元数值模拟,着重考察了单元的类型和最小单元尺寸对裂尖循环塑性和裂纹扩展速率的影响.紧凑拉伸试样的材料为1070钢,数值模拟采用了线性单元(四节点)和二次单元(八节点)两种单元,裂尖附近有限元单元的最小尺寸从0.007mm到0.24mm不等.文中将裂纹扩展速率的预测值与实验值进行了比较,通过对裂纹扩展速率的比较,确定在疲劳塑性分析时对单元类型和尺寸进行合理选取.     

基于夏比冲击试验的材料失效模型参数

结合夏比冲击试验和ABAQUS显式动力数值模拟，对Q370d钢进行了Johnson-Cook失效模型参数研究。首先，在不考虑材料失效的情况下，通过3种不同厚度的无缺口试件冲击实验对有限元模型参数设置和材料本构模型的准确性进行了验证，同时还讨论了试件断裂区网格的合适尺寸；在此基础上，基于正交设计，通过大量的有限元数值模拟得到失效模型参数样本，利用回归分析求得冲击功与失效模型参数的回归方程组；最后结合夏比V型缺口冲击试验，求解Q370d钢的失效模型参数，并对断裂截面的力学特性进行了分析，可为工程应用提供参考。     

低周疲劳随机损伤过程的有限元模拟

讨论了一种低周疲劳下随机损伤演变过程 数值模拟方法，借助于Ｌｅｍａｉｔｒｅ＆Ｄｕｆａｉｌｌｙ给出的代表性体元的微观力学模型，建立了损伤与微裂纹尺寸的关系，采用随机初始损伤反映材料中固的的微缺陷，将所得模型与有限元结合对低周疲劳损伤过程进行了数值模拟。     

黄土中爆炸挤密实验与数值模拟

为研究爆炸挤密加固技术在黄土中的应用，规避在既有公路上进行大规模爆炸挤密现场实验的风险，验证借助计算机软件进行数值模拟的可行性和可靠性，先设计实施了小型爆炸挤密室外实验，再利用室外实验的材料参数和几何尺寸建立与各实验工况相对应的有限元模型，利用ANSYS/LS-DYNA进行数值模拟，通过将爆腔体积、爆后土壤密度和作用于土壤的峰值压应力3个方面对数值模拟结果和实测结果进行对比，验证了将ANSYS/LS-DYNA用于数值模拟爆炸挤密技术加固黄土的可行性和可靠性，并得出上述三个方面的变化规律，可为根据现场路基状况和几何尺寸进行数值模拟提供借鉴和参考。     

应变控制的热机械疲劳行为的数值模拟

根据高温合金材料的力学性能，以弹粘塑性本构模型为基础，用数值模拟方法研究材料的热机械疲劳循环特性，模型将应变分为弹性应变、温度应变和粘塑性应变三部分，认为材料在高温循环载荷下呈现明显的弹粘塑性特征，根据虚位移原理建立轴对称体的弹粘塑性计算有限元格式，对于循环机械载荷和循环温度载荷，程序中采用了增量法迭代求解，在非线性项中不仅考虑了机械载荷增量的影响，同时也考虑了温度增量的影响，根据应变控制热机械疲劳的特点，发展了应变增量法的有限元计算方法、通过数值模拟，得到材料在各种循环载荷下的应力—应变响应，数值模拟较好地反映了粘塑性变形过程以及温度变化的效应，所描述的不可逆系统在某一时刻的状态完全由当时的状态参数、内变量、承载时间及塑性应变累积量决定，对带缺口试件的模拟结果显示了程序对复杂轴对称结构进行热机械疲劳计算的有效性。     

电子封装技术中金属基板结构的热失效行为研究

本文将电子散斑干涉与有限元数值计算相结合，对金属基板结构的热失效行为进行了研究。获得了低维氧化物绝缘薄膜的热失效温度，以及失效过程中基板表面的变形分布；测定了25μm厚度绝缘氧化薄膜的热膨胀系数，室温下弹性模量和失效应力等三个重要的材料常数；结合实验所测定的材料常数和研究的基板结构及性能，用有限元数值方法，模拟计算了绝缘氧化薄膜在不同缺陷形状时的失效过程。并给出了不同温度下绝缘氧化薄膜的最大应力集中值。     

非均质材料弹塑性破裂过程的数值模拟研究

阐述了岩土类材料的非均质特性，根据这种特性提出了对材料参数进行随机赋值的方法。为了对非匀质类材料的弹塑性破裂过程进行数值模拟研究，必须在有限元计算中实现材料的参数随机赋值。还给出了实例－－平面应力状态下试样的弹塑性破裂过程的数值模拟分析。     

点焊瞬态热过程的有限元分析

基于ANSYS有限元分析系统，建立了用于点焊瞬态热过程分析的电热耦合有限元模型．分析中考虑了随温度变化的材料特性参数、相变问题以及对流边界条件等，对点焊过程中的接触问题进行了适当简化，以避免耗时的迭代算法．通过对低碳钢薄板的分析，得到了整个焊接过程的热历程以及焊件各部位的温度分布，并且可以求得焊核及热影响区的形状和尺寸，同时本模型也可用于其它材料的点焊过程分析．     

混凝土损伤与试件尺寸效应

本文在运用概率方法确定了混凝土材料的初始损伤门槛值εＤ的前提下采用已有内时损伤本构模型，利用有限元方法对单边切口混凝土梁在三点弯曲荷载和四点剪切荷载作用下的力学行为进行了分析，计算了所有试件 的极限荷载Ｐｍａｘ，运用计算结果对混凝土断裂力学参数的尺寸效应规律进行了分析，并与已有试验结果进行了比较，其结果表明本文的数值分析怀华权及其它方法的分析结果吻合较好。     

A finite element model for numerical simulation of thermo-mechanical frictional contact problems

Two kinds of variational principles for numerical simulation of heat transfer and contact analysis are respectively presented. A finite element model for numerical simulation of the thermal contact problems is developed with a pressure dependent heat transfer constitutive model across the contact surface. The numerical algorithm for the finite element analysis of the thermomechanical contact problems is thus developed. Numerical examples are computed and the results demonstrate the validity of the model and algorithm developed. The project supported by the National Key Basic Research Special Foundation (G1999032805), the National Natural Science Foundation of China (50178016, 10225212) and the Foundation for University Key Teacher by the Ministry of Education of China     

非均质材料热传导问题的扩展有限元法

针对非均质材料,提出了以导热系数为基本参数的热传导扩展有限元法。划分网格时不需要考虑材料界面的存在,因此网格的形成可以大大地简化,且可以获得高质量的网格。不含材料界面的单元,其温度场函数将退化为常规有限元的函数。含材料界面的单元,采用基于水平集的加强函数加强常规温度的近似,加强函数用于模拟界面。数值算例结果体现了该方法...     

相变传热问题的灵敏度分析与优化设计方法

研究了相变传热问题的优化设计及其灵敏度分析方法. 在有限元-时间差分和等效热容 法求解相变温度场的基础上，提出了相变温度场对设计变量一阶灵敏度的计算方法，给出直 接法和伴随法两种计算格式并分析了它们的特点，建立了相变温度场优化的模型和算法，在有限元分析与优化设计软件JIFEX中实现了该方法. 数值算例表明了灵敏度计算的精度和优 化方法的有效性.     

A numerical approach to model non-isothermal viscous flow through fibrous media with free surfaces

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 fibre preform the flow part of the simulation is based on the finite element/control volume method. Since the traditional control volume approach produces an error associated with a mass balance inconsistency, a new method which overcomes this issue is proposed, the element control volume method. The heat transfer and cure analysis in the simulation are based on the finite difference/control volume method. Since heat conduction is dominant in the through-thickness direction and most of the heat convection is in-plane, heat transfer and cure are solved in fully three-dimensional form. A simple concept of the boundary condition constant is introduced which models a realistic mould configuration with a heating element located at a distance behind the mould wall. The varying viscosity throughout the mould associated with the strain rate, temperature and degree of cure distribution may be accounted for in calculating the mould-filling pattern. This introduces a two-way coupling between momentum and energy transport in fibrous media during mould filling.     

基于特征分裂有限元准隐格式的共轭传热整体耦合数值模拟方法

共轭传热现象在科学和工程领域中大量存在. 随着计算能力的发展, 对共轭传热现象进行准确有效的数值模拟, 成为科学研究和工程设计上的重要挑战.共轭传热数值模拟的方法可以分为两大类: 分区耦合和整体耦合.本文采用有限元法对共轭传热问题进行整体耦合模拟. 固体传热求解采用标准的伽辽金有限元方法.流动求解采用基于特征分裂的有限元方法. 该方法是一种重要的求解流动问题的有限元方法, 可以使用等阶有限元. 该方法的准隐格式与其他格式相比, 具有时间步长大的特点. 将稳定项中的时间步长与全局时间步长分开, 改进了准隐格式的稳定性. 基于改进的特征分裂有限元方法的准隐格式, 发展了一种层流共轭传热数值模拟的整体耦合方法. 采用这种方法可以将流体计算域和固体计算域作为一个整体划分有限元网格, 并且所有变量都可以采用相同的插值函数, 从而有利于程序的实现. 通过对典型问题的模拟, 验证了这种方法的准确性. 本工作还研究了固体区域时间步长对定常共轭传热问题数值模拟收敛性的影响.      

具有非线性表面换热系数半圆柱薄壳在快速冷却过程中的热分析

用实验和数值计算相结合的方法，得到半圆柱壳体快速冷却过程中内外表面的非线性表面换热系数。在此基础上，用有限单元法对半圆柱壳体的热应力和变形进行了分析。在数值计算中，模拟钢的CCT图，计算了奥氏体、珠光体、贝氏体和马氏体的体积百分比，并将热物理性质和力学性能处理为相变体积百分比和温度的函数。所得结果表明，在半圆柱壳体快速冷却过程中的热应力和变形计算中，有必要考虑非线性表面换热系数、相变等非线性效应。     

Direct numerical simulation of turbulent heat transfer in a square duct with transverse ribs mounted on one wall

Turbulent heat transfer in a ribbed square duct of three different blockage ratios are investigated using direct numerical simulation (DNS). The results of ribbed duct cases are compared with those of a heated smooth duct flow. It is observed that owing to the existence of the ribs and confinement of the duct, organized secondary flows appear as large streamwise-elongated vortices, which intensely interact with the rib elements and four sidewalls and have profound influences on the transport of momentum and thermal energy. This study also shows that the drag and heat transfer coefficients are highly sensitive to the rib height. It is observed that as the rib height increases, the impinging effect of the flow on the windward face of the rib strengthens, leading to enhanced rates of turbulent mixing and heat transfer. The influence of sidewalls and rib height on the turbulence structures associated with temperature fluctuations are analyzed based on multiple tools such as vortex swirling strengths, temporal auto-correlations, spatial two-point cross-correlations, joint probability density functions (JPDF) between the temperature and velocity fluctuations, statistical moments of different orders, and temperature spectra.     

Computer diagnosis system for thermal analysis of engine piston

This study presents a finite element heat-transfer model for the prediction of piston temperature distributions in a real time operation engine. The thermal boundary conditions are specified adequately in the model for various operations. The time-mean, area-averaged gas temperature and heat transfer coefficient could be obtained from the engine simulation. The ambient tremperatures along piston ring belt and skirt were estimated with a formula and the corresponding heat transfer coefficients were evaluated through equivalent thermal circuit analysis. The model is also calibrated and the predicted and measured temperatures compared for the operating engine. The predictions are reasonable, providing confidence in the use of the simulation model.     

Thermo-mechanically coupled investigation of steady state rolling tires by numerical simulation and experiment

In this contribution, a numerical framework for the efficient thermo-mechanical analysis of fully 3D tire structures (axisymmetric geometry) in steady state motion is presented. The modular simulation approach consists of a sequentially coupled mechanical and thermal simulation module. In the mechanical module, the Arbitrary Lagrangian Eulerian (ALE) framework is used together with a 3D finite element model of the tire structure to represent its temperature-dependent viscoelastic behavior at steady state rolling and finite deformations. Physically computed heat source terms (energy dissipation from the material and friction in the tire–road contact zone) are used as input quantities for the thermal module. In the thermal module, a representative cross-sectional part of the tire is employed to evaluate the temperature evolution due to internal and external heat sources in a transient thermal simulation. Special emphasis is given to an adequate material test program to identify the model parameters. The parameter identification is discussed in detail. Numerical results for three different types of special performance tires at free rolling conditions are compared to experimental measurements from the test rig, focusing especially on rolling resistance and surface temperature distribution.