Finite element scheme for transient 3D eddy currents

A transient 3-D finite-element model is presented. The method is based on the solution of the magnetic scalar potential in nonconducting regions and the magnetic vector potential and an electric scalar potential in eddy-current regions. Multiply connected regions of magnetic scalar can be avoided by extending the region modeled by the magnetic vector potential to fill any holes in the conducting regions. The model was used to simulate the FELIX brick experiment     

Finite element modelling of tow geometry in 3D woven fabrics

A finite element model of a 3D woven angle interlock fabric undergoing compaction based on the multi-element digital chain technique has been developed. The aim was to create a kinematic model to predict the internal architectural features in a commercial off-the-shelf code. A statistical analysis of yarn crimp and resin channel size was carried out on sections from the model at increasing levels of compaction and compared to laboratory-manufactured samples with the same weave style. Results show a good correlation between overall mean crimp values in the warp, weft and weaver yarns as well as reasonable accuracy in the frequency distribution of local crimp angles. The trend in resin channel size with respect to increasing levels of compaction was also good but significant discrepancies in the absolute dimensions of a resin channel were present due to limitations in controlling the yarn bundle internal interactions in the model.     

3D机织复合材料多向接头有限元分析

为了探究3D机织复合材料桁架接头的机械性能,采用有限元软件ANSYS对3D机织复合材料多向接头所在桁架总体进行有限元模拟,模拟中根据纤维走向对多向接头不同轴向圆管建立相应坐标系,并赋予材料属性,使用MPC多点约束法施加载荷.求解分析后结果表明:模拟结果与实测结果中最大应变的位置与数值基本吻合,确定了模拟的有效性;将最大应力与破坏应力对比发现接头在当前载荷下可能发生轻微破坏,破坏位置应位于副管顶部;通过模拟判断了实测中发生轻微响声的原因;将4种角联锁结构的多向接头模拟结果对比发现,带有衬经结构的复合材料为多向接头最佳材料.此次模拟补充了实测中无法得到的数据,为接头的优化设计和实际使用提供一定的帮助.     

朗之万换能器振动模式的有限元三维分析

本文主要运用3D有限元分析方法来分析应用于水下声纳的朗之万换能器的振动模式,频率从40KHz-160KHz.限于篇幅,本文只从理论计算上分析了以下三种情况即换能器总长度大于其直径;换能器总长度与其直径相当;换能器的总长度小于其直径.计算结果显示出换能器纵向振动与径向振动两种模式的情况以及其耦合情况,并且表明在实际应用中可以采用激励压电片的直径大于或等于换能器的纵向长度的这种情况.     

三维整体中空复合材料压缩性能的有限元分析

利用有限元软件ANSYS, 建立了三维整体中空复合材料结构模型, 进行压缩力学性能分析。利用该模型, 以芯材高度、 芯材密度和材料特性(弹性模量)为参数, 详细研究了其对材料压缩性能的影响, 并对其影响特征进行了分析和讨论。结果表明: 三维整体中空复合材料在受压状态下, 芯材与上下面板相接处应力最大, 最容易发生压缩破坏; 材料的压缩性能随着芯材密度、 材料弹性模量的增加而提高, 随着芯材高度的增加而下降。该研究结果可为整体中空复合材料的结构优化提供参考。      

Finite element evaluation of residual stresses in thick plates

This paper makes use of the Finite Elements Method (FEM) to study and analyze residual stresses in the cold bending and welding of thick plates. The welding model consists of two steps: first, performing of the thermal transient analysis model; and second, the carrying out of the mechanical transient analysis based on the temperature pattern at each node on each particular time. Used in these models is the inelastic temperature-dependent material. The output of the model includes residual stresses and permanent distortion; these were then compared with verified experimental results. The validated model and the results exhibit satisfactory agreement up to a 15-percent difference. As for the cold bending of thick plates, it is modeled using another finite element model and the residual stresses and permanent curvature of the thick plates are computed numerically. Again, the FEM model was validated against some official experimental results and satisfactory agreement between them was observed. Finally, the effects of these two different sources of residual stresses were combined, the combined effects established, and the results then discussed.     

Finite element modeling concepts and linear analyses of 3D regular open cell structures

Various Finite Element modeling concepts and linear analyses of 3D regular cellular solids (lattice structures) with relative densities ranging from 10% to 20% are presented. Continuum element based models and beam element based models are employed, the latter with and without an adaptation of stiffness in the vicinity of the vertices. Space filling unit cell models are used for a constitutive characterization of four different structures in terms of density and directional dependence of their Young's moduli. Finite structure models of different size are simulated for investigating the influence of free surfaces and being compared to results of uniaxial compression tests of samples fabricated by two different Rapid Prototyping techniques.     

Finite element operators: Inexpensive evaluation of upwind schemes

This paper introduces the notion of the finite element operator, and shows its application to the evaluation of several upwind finite element schemes. It is demonstrated that these operators supply good qualitative information on the performance of these schemes in an inexpensive as well as visual manner. In addition, this method gives insight into grid dependent effects which often characterize finite element solutions.     

三维正交机织复合材料低周弯曲疲劳力学性能有限元模拟

为了深入理解三维正交机织复合材料（3DOWC）疲劳性能,改进材料抗疲劳设计,结合三维正交机织复合材料试样经纱方向准静态三点弯曲及60%应力水平下的三点弯曲疲劳实验与ABAQUS有限元软件,构建了全尺寸三维实体模型,研究了三维正交机织复合材料在低周循环载荷下的弯曲疲劳性能,经分析得到循环加载下模型应力分布情况和疲劳损伤形态。结果表明：经纱为材料最重要的承载部件,中间加载区域为材料应力集中区,损伤主要位于应力集中区的Z纱通道处的经纱上,随着循环增加,逐渐在中心加载区域的上部和下部形成三角形损伤区域,该研究在复合材料设计与优化中具有指导意义。     

Finite element evaluation of free-edge singular stress fields in anisotropic materials

A finite element formulation based on the work of Yamada and Okumura¹⁴ is presented to determine the order of singularity and angular variation of the stress and displacement fields surrounding a singular point on a free edge of anisotropic materials. Emphasis is placed on the computational aspects of this method when applied to configurations including fully bonded multi-material junctions intersecting a free edge as well as materials containing cracks intersecting a free edge. The study shows that the singularity of the three-dimensional stress field may be accurately determined with a relatively small number of elements only when a proper level of numerical integration is used. The method is applied to isotropic and orthotropic materials with a crack intersecting a free edge and an anisotropic three-material junction intersecting a free edge. The efficiency and accuracy of the method indicates it could be used to develop a numerical solution for the singular field that could in turn be used to create free-edge enriched finite elements.     

Finite element analysis of 3-D eddy currents

The authors review formulations of three-dimensional (3-D) eddy current problems in terms of various magnetic and electric potentials. The differential equations and boundary conditions are formulated to include the necessary gauging conditions and thus to ensure the uniqueness of the potentials. Different sets of potentials can be used in distinct subregions, thus facilitating an economic treatment of various types of problems. A novel technique for interfacing conducting regions with an electric vector and a magnetic scalar potential to eddy-current-free regions with a magnetic vector potential is described. Finite-element solutions to several large eddy-current problems are presented     

Finite element analysis and experimental evaluation of ductile-brittle transition in compact tension specimen

Using finite element analysis, metallographic observations and statistical analysis, the stress field ahead of stationary and growing cracks and the ductile-brittle transition mechanism in compact tension (CT) specimens have been evaluated. Compared to a stationary crack, a growing crack elevates the opening stress on the remaining ligament and this may be partially attributed to the re-sharpening of the crack tip after ductile growth. The area of material covered by the high opening stress of the same magnitude also increases with ductile crack growth. In this study, no significant difference for measured cleavage stress can be found for the specimens fractured with and without ductile crack growth. There is a large scatter for the distance between the cleavage initiation site and the stationary or growing crack tip. Cleavage fracture after some amount of ductile crack growth is attributed to the increase of both the opening stress and the area of material under high opening stresses. Finally, the lower bound toughness is predicted using a small data set statistical model in connection with constraint correction. The predicted values give the same trend as the lower bound of the experimental measurements from the lower-shelf to the temperature at which ductile crack growth occurs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Finite element evaluation of mixed mode stress intensity factors in functionally graded materials

This paper is directed towards finite element computation of fracture parameters in functionally graded material (FGM) assemblages of arbitrary geometry with stationary cracks. Graded finite elements are developed where the elastic moduli are smooth functions of spatial co‐ordinates which are integrated into the element stiffness matrix. In particular, stress intensity factors for mode I and mixed‐mode two‐dimensional problems are evaluated and compared through three different approaches tailored for FGMs: path‐independent J^*_k‐integral, modified crack‐closure integral method, and displacement correlation technique. The accuracy of these methods is discussed based on comparison with available theoretical, experimental or numerical solutions. Copyright © 2001 John Wiley & Sons, Ltd.     

三维有限元网格节点编号优化

在有限元分析中,节点编号对整体刚度矩阵的带宽起着决定性的作用。优化网格节点编号的目的是为了减小同一单元中的相关节点编号之间的差值,从而减小整体刚度矩阵的带宽。基于有限元网格的拓扑分析,提出通过有限元网格的整体拓扑阵和单元—节点拓扑阵,对AKHRAS和DHATT方法进行改进,开发了一种有限元网格的节点编号优化的新方法。实例应用表明该方法执行效率高,计算速度快。     

Finite element simulation and experimental study on mechanical behavior of 3D woven glass fiber composite sandwich panels

The results of finite element simulation followed by an experimental study are presented in order to investigate the mechanical behavior of three-dimensional woven glass-fiber sandwich composites using FE method. Experimental load–displacement curves were obtained for flatwise compressive, edgewise compressive, shear, three-point bending and four-point bending loads on the specimens with three different core thicknesses in two principal directions of the sandwich panels, called warp and weft. A 3D finite element model is employed consisting of glass fabric and surrounding epoxy resin matrix in order to predict the mechanical behavior of such complex structures. Comparison between the finite element predictions and experimental data showed good agreement which implies that the FE simulation can be used instead of time-consuming experimental procedures to study the effect of different parameters on mechanical properties of the 3D woven sandwich composites.     

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

Finite element in adhesion analyses

Finite element computer programs have been used successfully for stress analysis of bodies with complex geometries and loads, and the use of these programs in cohesive fracture mechanics analysis is now widely accepted. Similar numerical procedures have been developed for use in adhesive fracture mechanics, but rather strong stress oscillations near the point of debonding have been shown to occur both analytically and numerically. This paper discusses the effect of these oscillations upon the calculation of the stress and strain energy, and demonstrates that in this potentially difficult problem, finite element codes can be used with sufficient precision for fracture analysis.

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Zusammenfassung Finite Komputerverfahren wurden erfolgreich angewandt zur Untersuchung der Spannungen in Körpern mit komplizierter Geometrie und Belastung, und der Gebrauch dieser Verfahren ist jetzt weitgehend angenommen im Gebiet der kohesiven Bruchmechanik.Ähnliche numerische Verfahren wurden für die adhesive Bruchmechanik ausgearbeitet, aber ziemlich starke Spannungsschwankungen nahe am Trennungspunkt wurden sowohl analytisch wie numerisch gefunden. Dieser Bericht befaßt sich mit dem Einfluß dieser Schwankungen auf die Berechnung der Spannungen und der Verformungsenergie, und beweist daß in diesem sehr schwierigen Gebiet die finite Verfahren mit genügend Genauigkeit zur Untersuchung des Bruches angewandt werden können.

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Résumé Les programmes de calcul par éléments finis ont été utilisés avec succès pour l'analyse des contraintes dans les pièces dont la géométrie ou la mise en charge est complexe, et l'emploi de ces programmes est à présent largement introduit dans l'analyse de la mécanique de la rupture par décohésion.Des procédures similaires ont été développées pour traiter de la mécanique de la rupture par décollement, mais on a constaté, tant sur le plan théorique que sur le plan expérimental, des oscillations prononcées de la contrainte au voisinage du point de décollement.Ce mémoire discute les effets que peuvent avoir ces variations sur le calcul de la contrainte et de l'énergie de déformation, et démontre que, dans ce problème difficile, les méthodes de calcul aux éléments finis peuvent néanmoins être utilisées avec une précision suffisante pour analyser les ruptures.

     

Finite element analyses for design evaluation of biodegradable magnesium alloy stents in arterial vessels

Biodegradable magnesium alloy stents (MAS) can provide a great benefit for diseased vessels and avoid the long-term incompatible interactions between vessels and permanent stent platforms. However, the existing MAS showed insufficient scaffolding to the target vessels due to short degradation time. In this study, a three dimensional finite element model combined with a degradable material model of AZ31 (Al 0.03, Zn 0.01, Mn 0.002 and Mg balance, mass percentage) was applied to three different MAS designs including an already implanted stent (Stent A), an optimized design (Stent B) and a patented stent design (Stent C). One ring of each design was implanted through a simulation in a vessel model then degraded with the changing interaction between outer stent surface and the vessel. Results showed that a proper stent design (Stent B) can lead to an increase of nearly 120% in half normalized recoil time of the vessel compared to the Stent A; moreover, the expectation that the MAS design, with more mass and optimized mechanical properties, can increase scaffolding time was verified numerically. The Stent C has more materials than Stent B; however, it only increased the half normalized recoil time of the vessel by nearly 50% compared to the Stent A because of much higher stress concentration than that of Stent B. The 3D model can provide a convenient design and testing tool for novel magnesium alloy stents.     

Finite element calculations on detailed 3D models for the superferric main magnets of the FAIR SIS100 synchrotron

The synchrotron SIS100 is one of the two basic accelerators of the future Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt. This accelerator should provide high intensity U28+ and proton beams with a pulse repetition rate of 1 Hz (i.e. a ramp rate of 4 T/s). The magnetic system of the accelerator uses superferric 2.1 T dipoles of about 3 m length and 32 T/m quadrupoles of about 1 m length. The magnet coils are made of a hollow tube cable wrapped with Cu/NbTi composite wire cooled with two phase helium flow at 4.5 K. The bore dimensions were defined to 130 × 60 mm for the dipole and 135 × 65 mm for the quadrupole. We present the developed ANSYS models for different important aspects: AC loss, magnetic field quality and mechanical stability. Preliminary studies verified the approaches and these models were applied to calculate the effects for the coil, the yoke and the beam pipe structures. We outline further steps to fully describe the SIS100 magnets including mechanical and thermal properties.