柴油机活塞热冲击问题有限元分析

利用Galerkin法原理,建立了轴对称热冲击问题的有限元方程,以PA6-280柴油机活塞为例,进行了数值分析,对其热冲击期间应力变化规律做了分析和讨论,其结果表明,本文理论为研究活塞的热冲击及热损伤机理提供了数值分析方面的基础。     

Fatigue Analysis on Thermal Characteristics for PBGA by Using Finite Element Method

The stress and strain of Plastic Ball Grid Array (PBGA) is investigated for reliability evaluation, failure analysis, or manufacturing. A one-eighth model is built to estimate the thermal stress and strain of PBGA under thermal cycling temperature (0°C–100°C). The different 3D elements such as Visco107 and Solid45 were selected for modeling of material 37Sn63Pb and Print Circuit Board (PCB), silicon die, substrate, and Epoxy Molding Compound (EMC), respectively. The results show that the maximum equivalent stress and equivalent plastic strain occur in the second outer solder joint and close to the position of chip. The key solder joint can be obtained and the key node of solder joint is 41402. The results indicate that the integrating 3D model can provide a more comprehensive profile for the thermal investigation of the PBGA package than from using any 2D model. The investigation provides a basis for improving reliability of PBGA product in engineering design.     

Thermal Buckling Analysis of Functionally Graded Thin Circular Plate Made of Saturated Porous Materials

This study presents the buckling analysis of thermal loaded solid circular plate made of porous material. It is assumed that the material properties of the porous plate vary across the thickness. The edge of the plate is clamped and the plate is assumed to be geometrically perfect. The geometrical nonlinearities are considered in the Love–Kirchhoff hypothesis sense. Equilibrium and stability equations, derived through the variational formulation, are used to determine the prebuckling temperatures and critical buckling temperatures. The equations are based on the Sanders non-linear strain-displacement relation.The porous plate is assumed of the form where pores are saturated with fluid. Also, the effect of pores distribution and thermal distribution on the critical buckling temperature is investigated.     

Two-Variable Refined Plate Theory for Thermoelastic Bending Analysis of Functionally Graded Sandwich Plates

The thermoelastic bending analysis of functionally graded sandwich plates using the two-variable refined plate theory is presented in this paper. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory presented is variationally consistent, has strong similarity with classical plate theory in many aspects, does not require shear correction factor, and gives rise to transverse shear stress variation such that the transverse shear stresses vary parabolically across the thickness satisfying shear stress free surface conditions. The sandwich plate faces are assumed to have isotropic, two-constituent material distribution through the thickness, and the modulus of elasticity, Poisson's ratio of the faces, and thermal expansion coefficients are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic ceramic material. Several kinds of sandwich plates are used taking into account the symmetry of the plate and the thickness of each layer. The influences played by the transverse shear deformation, thermal load, plate aspect ratio, and volume fraction distribution are studied. Numerical results for deflections and stresses of functionally graded metal–ceramic plates are investigated. It can be concluded that the proposed theory is accurate and simple in solving the thermoelastic bending behavior of functionally graded plates.     

Thermal Post-Buckling Analysis of Nanoscale Films Based on a Non-Classical Finite Element Approach

A size-dependent finite element (FE) formulation including surface free energy effect is developed in this article to study the post-buckling behavior of nanofilms under the action of thermal loads. The Gurtin-Murdoch surface elasticity theory is utilized to consider the surface effects. Moreover, the principle of virtual work is used so as to derive the equilibrium equations. The proposed FE formulation is based on the first-order shear deformation theory (FSDT). The von Kármán nonlinear relations are also employed to take the geometric nonlinearity into account. After deriving the FE equations, the resulting set of parameterized non-linear equations is solved using the pseudo arc-length continuation algorithm, and bifurcation diagrams of nanofilms are obtained. Selected numerical results are presented for the influences of surface stress on the thermal post-buckling characteristics of nanofilms subject to different types of boundary conditions.     

活塞热冲击有限元分析

在热冲击试验的基础上,采用ANSYS软件对活塞在高、低周波矩形热冲击模式下的温度响应、热应力进行了计算和分析。计算结果表明:在高、低周波热冲击下,活塞的温度响应有着不同的特性。计算结果对活塞热疲劳分析有着重要的参考价值。     

基于有限元的增压器背盘变形分析

背盘是影响增压器质量的重要因素.利用有限元方法分析某型增压器背盘产生较大变形的原因及其背盘结构改进的方向.首先分析了背盘在正常条件下的变形,然后分析了在不正常手持时的背盘变形,最后分析了不正常装配是否会产生较大变形.通过上述几种分析结果获得了该背盘大变形的原因及解决办法.     

工业锅炉平管板和凸形管板结构的有限元分析比较

通过利用有限元方法对工业锅炉管板进行定性的分析,得出工业锅炉常用两种类型的三种管板在同样尺寸规格和受力条件下的变形和应力分布,以及最大应力数值和位置.并对三种管板的应力分布情况进行了比较,为工业锅炉管板的设计计算提供了一定的参考依据.     

Coupled Efficient Zigzag Finite Element Analysis of Piezoelectric Hybrid Beams under Thermal Loads

A new one-dimensional beam finite element is developed for hybrid piezoelectric beams under thermal load, using a coupled efficient layerwise (zigzag) theory developed recently by the authors. The theory accounts for the layerwise variations of the axial and the transverse displacements while keeping the number of displacement variables independent of the number layers. The beam element has two nodes with four mechanical and a variable number of electric potential degrees of freedom at each node. In the thickness direction, the thermal and the electric fields are approximated as piecewise linear across an arbitrary number of sublayers in a layer. Cubic Hermite interpolation is used for the deflection and electric potentials at the sublayers and linear interpolation is used for the axial displacement and the shear rotation. The thermal field is computed using a consistent six-noded thermal finite element with a quadratic interpolation along longitudinal direction and a linear interpolation along thickness direction. The formulation is validated by comparing the results with the Navier-type solution of the zigzag theory for simply-supported hybrid beams. The element is free from shear locking. The accuracy of the zigzag theory is established by comparing the results of hybrid composite and sandwich beams with the two-dimensional finite element results using ABAQUS for cantilever and clamped-clamped end conditions under different thermal loads. The control of thermal deflection by the application of actuation potential is illustrated. The effects of electric boundary conditions and the pyroelectric effect on the response are discussed.     

锅壳式锅炉管板应力有限元分析及优化设计

针对某锅壳式锅炉管板的结构仿真分析和强度计算问题,根据相关的理论和方法建立了有限元仿真模型,并采用通用有限元软件ANSYS Workbench的结构静力分析模块进行应力计算,得到了管板的变形云图和应力云图。在结构分析的基础上,根据相关强度理论和材料标准对模型进行应力结果的评定和分析,结果显示,所有部件满足强度要求并且留有较大的设计余量。在保证强度要求的前提下,对锅炉的锅壳和管板进行结构优化,减少了锅炉的整体重量并降低了材料成本。     

Thermal Response of Symmetric Cross-Ply Laminated Plates Subjected to Linear and Non-Linear Thermo-Mechanical Loads

The flexural response of symmetric cross-ply laminated plates subjected to uniformly distributed linear and non-linear thermo-mechanical loads is presented using trigonometric shear deformation theory. The in-plane displacement field uses sinusoidal function in terms of thickness coordinate to include the shear deformation effect. The theory satisfies the shear stress-free boundary conditions on the top and bottom surfaces of the plate. The present theory obviates the need of shear correction factor. Governing equations and boundary conditions of the theory are obtained using the principle of virtual work. Thermal stresses and displacements for three-layer symmetric square cross-ply laminated plates subjected to uniform linear and nonlinear and thermo-mechanical loads are obtained. The results of present theory are compared with those of classical plate theory, first-order shear deformation theory and higher-order shear deformation theory.     

在温度和机械载荷作用下活塞应力与变形的三维有限元分析

根据有限元法解得的温度场，。利用微机对ω型燃烧室的柴油机活塞进行温度载荷和机械和作用下应力和变形的三维有限元分析。单元网格划分中采用了３１８６个节点、２２１０个８节点六面体等参元，将计算输出的各单元形心的六个应力分量换算为三个主应力分量，再选择合适的插值求得各节点的主应力分布。     

Thermal Buckling of Functionally Graded Plates According to a Four-Variable Refined Plate Theory

In this article, a four-variable refined plate theory is presented for buckling analysis of functionally graded plates. The theory, which has strong similarity with classical plate theory in many aspects, accounts for a quadratic variation of the transverse shear strains across the thickness and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using shear correction factors. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present theory. The non-linear governing equations are solved for plates subjected to simply supported boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The influences of many plate parameters on buckling temperature difference will be investigated. It is noticed that the present refined plate theory can predict accurately the critical temperatures of simply supported functionally graded plates.     

Thermal Bending Analysis of Doubly Curved Composite Laminated Shell Panels with General Boundary Conditions and Laminations

Thermal bending analysis of doubly curved laminated shell panels with general boundary conditions and laminations is presented. The equations of equilibrium are derived in the form of two coupled sets of ordinary differential equations based on a general shell theory and solved through the state-space approach in a repeated manner. It is depicted that the results of the present method are in great agreement with analytical solutions. Cylindrical shell panels with general boundary conditions and laminations, where no analytical solution is available, are solved. It is found that the present method exhibits a high convergence rate as well as presenting accurate results in all cases.     

柴油机活塞热应力轴对称边界元数值分析

本在推出轴对称热应力问题的边界积分方程的基础上采用２次等参插值函数将边界积分方程离散为边界元方程，进一步运用开发的程序分析了某１３５柴油机活塞的热应力场，分析结果表明边界元法在动力机械零部件热应力问题的分析中，与其它数值方法相比，具有计算精度高，数据准备简单和计算时间少等独特的优点。     

钢板横向感应加热磁-热耦合的有限元数值模拟

采用电磁-热耦合二维有限元法模拟钢板感应加热,得到了加热频率和电流密度对加热时间、加热速度和温度均匀性的影响。结果表明,采用U型线圈加热钢板,可以形成一个完整的磁回路,符合感应加热钢板的要求;频率增加能够缩短加热时间和扩大钢板温度的温差;而电流密度增加,加热时间缩短,其对温度均匀性的影响则随电流增加温差增大。     

30/38柴油机活塞热力耦合有限元分析研究

采用有限元软件ANSYS,分析了30/38柴油机活塞的温度场、热应力及热变形;并通过热-机耦合的方法,分析了该机活塞的耦合应力场。研究结果表明:活塞顶部应力以热应力为主,温度对活塞的应力和变形起主导作用。在此基础上提出了有关活塞的研制建议。     

Stress Evolution and Thermal Shock Computation Using the Finite Volume Method

This work presents a novel numerical approach to thermal shock and transient thermal stress distribution based on the Finite Volume method. A unified approach was developed based upon the coupling between a three-dimension thermal solution and a linear thermo-elastic, multi-layered plane stress approximation. Temperature distributions were compared to analytical solutions for a flat plate and to experimental results using a temperature-dependent heat transfer coefficient. The numerical results were assessed against three analytical methods: Timoshenko and Goodier, Lu and Fleck, and Collin and Rowcliffe. This work demonstrates that the FVM provides also accurate results for thermal stress distributions in solids.     

基于有限元的柴油机油底壳加强板的振动分析与结构控制

本文采用有限元分析和实验模态分析方法对带有加强板的油底壳的振动进行分析。在该模型基础上，通过改变该模型的加强板结构来进行改进。结果表明，改变加强板结构可以减小油底壳的振动，进而降低了发动机的噪声。