Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites(3D C/SiC).Represent volume element(RVE)models of microscale,void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites.An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture.The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions.Three RVE models of cuboid,hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale.Besides,the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models.The prediction results at the mesoscale correspond closely to the experimental values.The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration.The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

Ultrasonic Welding of Magnesium–Titanium Dissimilar Metals:A Study on Thermo-mechanical Analyses of Welding Process by Experimentation and Finite Element Method

Ultrasonic welding is an effective ways to achieve a non-reactive/immiscible heterogeneous metal connection, such as the connection of magnesium alloy and titanium alloy. But the thermal mechanism of magnesium alloy/titanium alloy ultrasonic welding has not been defined clearly. In this paper, the experimental and the finite element analysis were adopted to study the thermal mechanism during welding. Through the test, the temperature variation law during the welding process is obtained, and the accuracy of the finite element model is verified. The microscopic analysis indicates that at the welding time of 0.5 s, the magnesium alloy in the center of the solder joint is partially melted and generates the liquid phase. Through the finite element analysis, the friction coefficient of the magnesium–titanium ultrasonic welding interface can be considered as an average constant value of 0.28. The maximum temperature at the interface can exceed 600 ℃ to reach the melting point temperature of the magnesium alloy. The plastic deformation begins after 0.35 s and occurs at the magnesium side at the center of the interface.

Finite Element Analyses and Instrumentation Layout for Single Coil Testing of TF Coils in HT-7U

The HT-7U tokamak is a magnetically-confined full superconducting fusion device, consisting of superconducting toroidal field (TF) coils and superconducting poloidal field (PF) coils. These coils are wound with cable-in-conductor (CICC) which is based on UNK NbTi wires made in Russian '. A single D-shaped toroidal field magnet coil will be tested for large and expensive magnets systems before assembling them in the toroidal configuration. This paper describes the layout of the instrumentation for a superconducting test facility based on the results of a finite element modeling of the single coil of toroidal magnetic field (TF) coils in HT-7U tokamak device. At the same time, the design of coil support structure in the test facility is particularly discussed in some detail.

A MULTI-COUPLED FINITE ELEMENT ANALYSIS OF RESISTANCE SPOT WELDING PROCESS

A two-dimensional axisymmetric finite element model is developed to analyze the transient thermal and mechanical behaviors of the Resistance Spot Welding （RSW） process using commercial software ANSYS. Firstly a direct-coupled electrical-thermal Finite Element Analysis （FEA） is performed to analyze the transient thermal characteristics of the RSW process. Then based on the thermal results a sequential coupled thermo-elastic-plastic analysis is conducted to determine the mechanical features of the RSW process. The thermal history of the whole process and the temperature distribution of the weldment are obtained through the analysis. The mechanical features, including the distributions of the contact pressure at both the faying surface and the electrode-workpiece interface, the stress and strain distributions in the weldment and their changes during the RSW process, the deformation of the weldment and the electrode displacement are also calculated.

Finite element analysis of dynamic response and structure borne noise of gearbox

A dynamic finite element method combined with finite element mixed formula for contact problem is used to analyze the dynamic characteristics of gear system. Considering the stiffness excitation, error excitation and meshing shock excitation, the dynamic finite element model is established for the entire gear system which includes gears, shafts, bearings and gearbox housing. By the software of I-DEAS, the natural frequency, normal mode, dynamic time-domain response, frequency-domain response and one-third octave velocity grade structure borne noise of gear system are studied by the method of theoretical modal analysis and dynamic response analysis. The maximum values of vibration and structure borne noise are occurred at the mesh frequency of output grade gearing.

Design and Structural Analysis of Flexible Wearable Chair Using Finite Element Method

The flexible wearable chair is like a light weight mobile exoskeleton that allows people to sit any-where in any working position. The traditional chair is difficult to move to different working locations due to its large size, heavy weight (~5 - 7 kg) and rigid structure and thus, they are inappropriate for workplaces where enough space is not available. Flexible wearable chair has a gross weight of 3 kg as it utilizes light-weight aluminium alloy members. Unlike the traditional chair, it consists of kinematic pairs which enable taking halts between continuous movements at any working position and thus, it is capable of reducing the risk of the physical musculoskeletal disorder substantially among workers. The objective of this paper is to focus on the mechanical design and finite element analysis (FEA) of the mechanism using ANSYS® software. In the present work, all the parts of the mechanism are designed under static load condition. The results of the analysis indicate that flexible wearable chair satisfies equilibrium and stability criterion and is capable of reducing fatigue during working in an assembly line/factory.

FINITE ELEMENT ANALYS IS AND OPTIMUM DESIGN FOR THE FRONT－FUSELAGE WITH SANDWICH CONSTRUCTIONS

AbstractFinite element analysis and optimization subject to stress, displacement and side con-straints for composite sandwich structures are mainly treated. The square isoparametricsandwich plate / shell elements are used to perform structural analysis. The thickness ofthe faceplates and the depth of the core are taken as design variables in optimization pro-cess. The number of layers for each laminate is also taken as design variables if the compo-site faceplates are used. A few widely applied approximation concepts, such as design vari-able linking, regionalization method and temporary deletion technique of passive con-straints are employed to reduce the number of both design variables and constraints. Theadvanced hybrid approximation techniques combining with dual solutions are cmployed inoptimization. The corresponding software is applied to the analysis of experimental modeland to the optimum design for the composite sandwich front-fuselage, and satisfactory re-sults are obtained.

Finite Element Structural Analysis UsingObject-Oriented Techniques

This paper describes the object-oriented implementational method of finite element structural analysis, gives the basic concepts of the object-oriented method and objectoriented programming, develops a complete class hierarchy structure of object-oriented finite element structural analysis, and gives a part C+ + code description.

Finite Element Analysis of Dynamic Damper for CV Joint

Constant Velocity [CV] Joints are one of the most important components of front wheel drive axles. It is subjected to various stresses such as bending stress, shear stress and bearing stress. Apart from these stresses, it is also subjected to vibrations, due to out of balance tire or wheel and an out of round tire or wheel, or a bent rim. The main objective of this work is to reduce the stiffness of the damper, so that the damper can withstand within the required constraints [i.e. the forced frequency range of 80 Hz to 150 Hz]. The free vibrational and forced vibrational effects are investigated to predict the resonance phenomenon of the damper. Finite Element Analysis in ANSYS-11 software was performed to predict the dynamic behavior of the system under the required vibrational frequencies ranging from 80 Hz to 150 Hz at given loading conditions.

Stress Analysis of Buried Pipeline Installed by Horizontal Directional Drilling Using ANSYS Finite Element Software

In designing a horizontal directional drilling (HDD) pipeline project, designers face the challenge of determining the regions of maximum and minimum stresses on pipelines, ensuring the stability of the bore-hole from collapse and minimizing the stresses induced on the pipeline due to the bore-profile. This study analyses the stress induced on an HDD pipeline system using the ANSYS Version 18, mechanical APDL finite element (FE) software. The pipeline used as the case study was a gas transmission pipeline installed in south-west Nigeria. A macro-file for ANSYS Version 18, mechanical APDL used to model the pipeline was developed. The results showed that the maximum and minimum stresses induced on the HDD pipeline were at the top and bottom of the pipe, respectively;while the stresses on the sides were uniform (≈888 kg/cm2) all through the pipeline, irrespective of element number. The maximum stress occurred at the curvature point with the highest entry angle (10°), resulting in a maximum deflection at this point. The model stress validation performed by comparing results with theoretical solutions, both with respect to radius of curvature and internal pressure, showed percentage difference (errors) less than 10%. The cross sectional area validation showed a percentage difference of 0.059%.

Conventional versus minimally-invasive cervical discectomy for treatment of severe degenerative disease at C5-C6: a biomechanical comparison using a model of the full cervical spine and finite element analysis

The purpose of this study was to determine the dif-ferences in biomechanical responses of tissues in the cervical spine when pain and other problems secon-dary to severe disc degeneration disease are surgi-cally treated by conventional discectomy (CONDIS) compared to minimally-invasive discectomy (MIVDIS). A validated three-dimensional model of an intact, healthy, adult full cervical spine (C1-C7) (INT) was constructed. This model was then modified to create two models, one simulating each of the above-men-tioned two techniques for discectomy of the severely degenerated C5-C6 disc. For each of these three models, we used the finite element analysis method to obtain three biomechanical parameters at various tissues in the model, under seven different physio-logically relevant loadings. For each of the biome-chanical parameters, the results were expressed as relative change in its value when a specified combi-nation of simulated discectomy model and applied loading was used, with respect to the corresponding value in the intact model. We then computed the value of a composite biomechanical performance in-dex (CBPI) for CONDIS and MIVDIS models, with this value incorporating all of the aforementioned relative changes. We found that CBPI was marginally lower for MIVDIS model. This trend is the same as that reported for the relative complications rate and outcome measures following conventional and mini-mally-invasive discectomies in the lumbar spine. From a healthcare perspective, one implication of our finding is that minimally-invasive cervical discectomy should be considered an attractive option provided that detailed patient selection criteria are clearly de-fined and strictly followed.

Relationships between femoral strength evaluated by nonlinear finite element analysis and BMD,material distribution and geometric morphology

Precisely quantifying the strength of the proximal femur and accurately assessing hip fracture risk would enable those at high risk to be identified so that preventive interventions could be taken.Development of better measures of femoral strength using the clinically

Design of Industrial Floors TR34 and Finite Element Analysis (Part 2)

The design of industrial floors will be presented in this paper. In the first part of this article the calculation methods of the TR34 British guideline will be discussed. In the second part the state of the art design methods using advanced finite element methods will be presented. The design itself may seem as slow considering the actual computer efficiency, however comparing the results to theoretical analysis and to designing methods, precision and economical nature of the method can be justified. A large number of foreign industrial floor designs were made by this method;some of them will be shown as reference at the end of the article.

Finite Element Simulation on the Spin-forming of the 3D Non-axisymmetric Thin-Walled Tubes

The roller movement trace for the 3D non-axisymmetric thin-walled tubes is a complex space curve. Besides the roller rotation caused by contact with the blank, the roller rotates around the workpiece together with the main spindle, and also moves simultaneously along the direction of the revolution radius. The method to correctly establish the finite element （FE） models of the metal spinning is based on the MSC. MARC software was introduced. The calculation formulas considering both the revolution and rotation of the roller were obtained by the mathematical deduction. The saving calculation points m should be a multiple of 4 for one revolution of the roller around the workpiece to obtain the maximum forming force for the spinning of the 3D non-axisymmetric thin-walled tubes. The simulation results conform well to the experimental ones for several spinning methods; the maximum error is less than ±15%.

Virtual ballistic impact testing of Kevlar soft armor:Predictive and validated finite element modeling of the V0-V100 probabilistic penetration response

This works presents the first fully validated and predictive capability to model the V_0-V_(100) probabilistic penetration response of a woven fabric using a yarn-level fabric finite element model. The V_0-V_(100) curve describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this paper comprises of a single-layer, fully-clamped, plain-weave Kevlar fabric impacted at the center by a 17-gr, 0.22 cal FSP or fragment-simulating projectile. Each warp and fill yarn in the fabric is individually modeled using 3 D finite elements and the virtual fabric microstructure is validated in detail against the experimental fabric microstructure. Material and testing sources of statistical variability including yarn strength and modulus, inter-yarn friction, precise projectile impact location, and projectile rotation are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, with each model comprising unique mappings. The impact velocities together with the outcomes(penetration, nonpenetration) are used to generate the numerical V_0-V_(100) curve which is then validated against the experimental V_0-V_(100) curve. The numerical Vi-Vrdata(impact, residual velocities) is also validated against the experimental Vi-Vrdata. For completeness, this paper also reports the experimental characterization data and its statistical analysis used for model input, viz. the Kevlar yarn tensile strengths, moduli, and inter-yarn friction, and the experimental ballistic test data used for model validation.

基于FEA与应力在线监测的RTG钢结构疲劳寿命预测

疲劳是轮胎式集装箱门式起重机(RTG)钢结构发生破坏的主要因素之一。针对RTG的工作特点和动力学特性,提出一种适用于RTG钢结构的疲劳寿命预测方法。采用有限元分析(FEA)获取其自重应力,与应力在线监测获取的外载荷应力进行线性叠加,获得其工作过程中的完整的应力谱样本;采用雨流计数法获取S-N特征曲线,基于Miner法则进行时域疲劳寿命预测;采用Welch函数进行快速傅里叶变换,将应力谱样本转换为频域信号,基于Dirlik、ZB模型进行频域疲劳寿命预测。分析结果表明,3种模型的相对误差非常小,时域方法需要大量的应力谱样本,频域方法计算效率更高,3种模型均可应用于工程实际。

基于Midas FEA的箱涵套管加固效果分析

以湖北省某农村公路提档升级项目中箱涵套管加固为工程背景,考虑混凝土的材料非线性,简化填土与箱涵之间的接触非线性,利用Midas FEA建立箱涵套管加固的精细化有限元模型,对比分析了箱涵套管加固前后的受力性能。计算分析表明:箱涵加固后其水平变形、竖向变形分别下降98.21%、96.53%,混凝土的第一主拉应力、第一主压应力最大值分别下降82.09%、94.95%,钢筋的拉应力、压应力最大值分别下降93.26%、85.00%,裂缝宽度最大值一定程度降低,箱涵采用套管加固效果明显;套管加固后,套管内钢筋以及填充区混凝土应力较小,考虑工程经济性,可在规范允许范围内适当降低套管配筋率、选取低强度钢筋、降低填充区混凝土标号,建议在石料充裕时采用片石混凝土代替混凝土。

弹上电子产品加固防护可靠性分析研究

提出一种弹上电子产品球栅阵列封装元器件的新型加固防护工艺方法,对使用不同加固防护方法的电子产品进行了随机振动试验与有限元仿真分析,研究对球栅阵列封装(BGA)元器件焊点可靠性的影响;采用Steinberg疲劳寿命模型分析焊点的疲劳寿命。研究表明,纳米疏水剂、四角点胶配合3D打印壳体封装的组合新型弹上电子产品加固防护方法能有效提升产品可靠性。

装配式混凝土墙板新型键槽接缝受剪性能研究

为研究适用于低多层装配式混凝土(PC)墙板的新型键槽接缝界面的受剪性能,设计并制作2组共8个键槽式接缝连接的PC墙板试件,开展单向推剪加载试验和扩展参数数值分析,分别探讨轴压比、结合面砂浆强度及键槽构造形式等因素对键槽界面受剪性能的影响;提出新型键槽接缝界面的受剪承载力计算公式,并构建键槽接缝界面的剪力-滑移模型。研究结果表明:轴压比对接缝破坏形态和受剪承载力均具有显著影响,增大轴压比后,裂缝发展更为充分,局部混凝土出现剥落甚至压溃,接缝的受剪承载力与轴压比近似呈线性关系。提高结合面砂浆强度可较大幅度地提升接缝的受剪承载力,对比普通填充砂浆,采用高强砂浆连接试件的受剪承载力提高了57.2%。合理的键槽界面构造可有效提高接缝的受剪承载力,相较于传统的平直缝界面,深度为50 mm、倾斜倒角为11.3°的键槽界面的受剪承载力提升了16.5%。本文所提公式受剪承载力计算结果与试验结果吻合较好,所提模型能准确预测键槽界面的受剪行为。

PET材料改性及加工应用

为了提高聚对苯二甲酸乙二醇酯(polyethylene glycol terephthalate,PET)材料的性能,课题组采用熔融共混法向PET中添加接枝弹性体POE-g-GMA,通过考察测试了不同添加量的接枝弹性体对PET材料结构与性能的影响。研究结果表明:随着接枝弹性体POE-g-GMA体积分数的增大使材料的冲击强度先增大后降低、拉伸性能略有下降。有限元分析验证了改性后PET材料的承压性能没有表现出明显的下降。