Finite Element Modelling and the Experimental Verification of Superplastic Forming

FEM analysis has proved to be a powerful investigative tool capable of encompassing all the aspects that characterise an SPF process. However, despite the high potential of FEM programs they do not allow one to directly and suitably obtain the thickness of a sheet product for high deformation values, as commonly occurs in SPF processes. Many papers have been published on finite element analysis of S.P.F. process but the question of calculus accuracy in thicknesses of a sheet product has not been directly investigated. This problem has been already considered by the authors in a previous study which proposed an algorithm to determine thicknesses for a specific application. The software set up starts out with the results of the FEM modelling, keeps track of the deformation undergone by each element of the mesh and calculates to a good approximation the thicknesses at the end of the forming. Although the original version of the algorithm could only be used for the application studied an updated version is introduced in this study that can be used for any case. In other words, the software generates the thickness profile at the end of the analysis independently of technological set up, item shape and type of simulation (3D and 2D). The proposed algorithm was tested with reference to the superplastic forming of an item of simple geometry beginning with a thin circular plate blocked at the edges and put under constant hydrostatic pressure on one side. The test material, made superplastic by means of a series of repeated laminations, was characterised using an alternative method to the traditional tension test. The results of the experiments are in good accordance with the numerical predictions both in terms of thickness distribution and forming times.     

折叠式托盘箱货架弯曲的有限元分析及试验验证

目的市场上的托盘箱普遍根据经验设计,其设计周期长,成本高。拟研究利用有限元模拟托盘箱性能的可行性。方法先利用三维软件Solidwokrs完成托盘箱的建模,再导入有限元分析软件Workbench模拟其货架弯曲性能,根据模拟结果修改模型,直至满足要求后进行打样制造,然后进行实际托盘箱样品的实验。结果托盘箱货架弯曲的实验结果和模拟结果总体上吻合度较高,托盘上5个试验位置挠度的相对误差随着载荷的增大而逐渐减小,并趋于稳定。结论使用有限元软件Workbench来进行托盘箱结构的设计和性能模拟分析是可行且有效的。     

自由阻尼处理结构的有限元建模及声辐射分析

用整体划分单元法建立了一种四节点20个自由度自由阻尼处理薄板结构的有限元模型，用能量法推导了单元的刚度和质量矩阵。在用有限元法计算结构的动态响应特性的基础上，将每个单元划分为很多个微元，利用有限元分析得到结构表面振动速度，通过单元的形函数，求出微元上几个点的平均速度，作为微元的振动速度。以每个微元为一单位，分别计算声压和声功率之后叠加起来，即得整个结构的声辐射。算例表明，用此方法分析计算表面阻尼处理结构的动态特性和声辐射是可行的。     

Finite Element Assisted Modelling of the Microscopic Impregnation Process in Thermoplastic Preforms

Fibre reinforced composite materials incorporating thermoplastic matrices are gaining increasing popularity in many industrial applications. One of the potential preforms for the manufacture of technical components is commingled yarn composed of reinforcement and matrix in fibre form. These are often employed in the pultrusion process. Another innovative preform consists of polymer powder preimpregnated sheath surrounding fibre bundles. To achieve adequate mechanical properties of the final product it is essential, when producing laminates by a process such as pultrusion with both types of preform, that sufficient matrix impregnation is achieved. The prevention of voids and dry-spots in the laminate requires a theoretical understanding of the mechanisms involved. On a microscopic scale, several finite element (FE) models can be used to simulate the progress of the matrix flow into the interstitial spaces between the single reinforcement fibres. In the present simulations, a hexagonal and a square arrangement account for two of the various fibre packings occurring in a laminate. It permits an estimation of the impregnation performance of commingled and powder impregnated yarns. For each preform the shear rate, to which the polymer matrix is subjected during the impregnation and consolidation process, can be predicted.     

A Method to Improve Experimental Validation of Finite‐Element Models of Long Bones

Abstract: Finite‐element (FE) simulations are extremely sensitive to boundary conditions, including the position of applied forces. This is particularly critical for FE models of bones, where the lack of a univocal reference system makes identifying the boundary conditions difficult. The aims of this work were to design a transducer (FP‐transducer) to accurately determine the position of the resultant joint force during in vitro tests, and to assess its accuracy for future application in validating numerical models of long bones. A strain gauge‐based transducer was designed to indirectly measure the position of the force applied to the long bones during in vitro tests, by measuring the reaction moments about two perpendicular axes, generated by the force applied. Validation tests were performed to quantify the intrinsic precision of the FP‐transducer (by applying calibrated forces at known locations), and the overall accuracy when the FP‐transducer was included in a typical set‐up for long bone testing. The intrinsic accuracy of the FP‐transducer when used to calculate the position of an offset force was satisfactory (0.66 mm). The overall accuracy of the FP‐transducer in measuring the position of the applied force, when included in a typical set‐up for long bone testing was 0.85 mm. In vitro validation of FE models of long bones may, therefore, be improved, thanks to a more accurate determination of the force application point.     

Finite Element Analysis for the Treatment of Proximal Femoral Fracture

Dynamic hip screw and gamma nail have been widely used to treat the patients with proximal femoral fractures, but clinical failures of those implants are still to be found. This study developed three-dimensional finite element models to investigate the biomechanical performances of the implants. Two kinds of commercially available implants (dynamic hip screw and gamma nail) and one newly designed implant (double screw nail) under three kinds of the proximal femoral fractures (neck fracture, subtrochanteric fracture, and subtrochanteric fracture with gap) were evaluated. Double screw nail showed better biomechanical performances than dynamic hip screw and gamma nail. Two commercially available implants might provide good biomechanical performances if their designs were modified by using the suggestions of the reports. The finite element models developed in this study could provide the selection information of those implants to surgeons and offer the improved implant designs to engineers.     

Kriging响应面代理模型在有限元模型确认中的应用

结合Kriging理论,实现Kriging响应面代理模型在有限元模型确认过程中响应预测的应用。讨论模型验证与确认的基本思想,初步提出有限元模型确认流程;以Garteur benchmark飞机结构瞬态响应仿真为例,建立加速度响应最大值Kriging响应面,通过蒙特卡洛方法,实现有限元模型参数不确定性正向传递;采用核密度估计建立加速度响应最大值概率分布,计算响应量置信区间上下限。结果表明,Kriging响应面能准确对有限元模型响应进行预测,可为有限元模型确认过程提供很大便利。     

鸡蛋品质特性的有限元分析方法

目的研究鸡蛋品质物性参数与结构动力学响应特征参数间的关联特性,构建鸡蛋品质检测的动力学相关性模型。方法以敲击响应检测技术为基础,引入结构动力学分析方法,应用有限元仿真技术定量分析鸡蛋品质物性参数(蛋形参数、蛋壳厚度、蛋壳刚度、蛋液密度)与其一阶共振频率间的对应变化规律,获取鸡蛋品质相关的动力学特征参数。结果鸡蛋品质物性参数中蛋形参数、蛋壳厚度、蛋壳刚度、蛋液密度与其结构一阶共振频率关联性显著;蛋壳厚度与蛋体结构一阶共振频率间符合较好的线性规律。相较而言,蛋壳密度、气室高度对结构一阶共振频率的影响较小。结论鸡蛋品质特性相关参数(蛋形参数、蛋壳厚度、蛋壳密度和蛋液密度)与其结构动力学响应特性具有较强的关联性。     

用不完全模态测量数据修正有限元分析模型

提出一种基于不完全模态测量数据同时修正有限元质量矩阵与刚度矩阵的有效数值方法。运用代数特征值反问题的理论与方法，得到了满足正交关系及特征方程的最逼近有限元质量矩阵及刚度矩阵的唯一的修正质量矩阵与刚度矩阵（最优修正矩阵）。该方法有一个简洁的表达式，修正过程简单而且容易实现。数值算例表明，修正模型与模态试验数据具有非常好的一致性。     

胶印机整机有限元建模与综合分析

为了从整体上获取胶印机的性能数据,以某型单张纸四色胶印机的印刷单元为研究对象,综合运用多种有限元建模技术,建立了胶印机单色组整机有限元模型。在整体建模的基础上,对胶印机有限元模型进行了静力分析、模态分析和谐响应分析,获得了胶印机的静态、动态综合性能数据。分析结果表明,该型胶印机整体动态性能欠佳,有必要进行胶印机结构的动态优化。     

基于建模误差位置识别的有限元模型修正方法

提出了一种修正有限元模型的方法。将模型修正分为两步，首先用矩阵型方法求出系统质量、刚度矩阵的误差矩阵，通过定义的误差百分比确定建模误差位置；然后针对建模误差比较大的单元（子结构）依据特征方程和固有振型对质量矩阵的加权正交条件建立参数修正方程组，方程求解采用奇异值分解法。算例表明它能有效地避免先前方法中参数修正的盲目性，修改结果物理意义明确，精度较好。     

气泡在聚合物内长大过程的等温有限元模拟

针对气泡在聚合物熔体内的等温长大过程,建立了其几何模型和有限元模型;采用幂律型流体本构关系描述聚合物流变性质;对控制方程进行无量纲化处理,采用Galerkin方法对对流扩散有限元控制方程进行数值求解;采用隐式差分法对扩散方程中的时间导数项进行离散,并在每个时间步进行网格重划分,确保计算结果的可靠性。计算获得了聚合物内发泡剂浓度分布规律及不同的特征无量纲量对气泡长大过程的影响。     

有限元热分析中空气夹层传热处理方法及其验证

以传热学理论为基础,考虑夹层空气的热传导、对流和辐射,确定夹层空气传热的处理原则。对于较薄空气夹层,在考虑导热和辐射传热的基础上,作等效导热处理;对于较厚和厚空气夹层,则在考虑边界对流、辐射传热的基础上,引入中间节点,处理夹层空气与两壁间的传热。在结构有限元热分析中,用此方法处理空气夹层,温度值计算分析结果与实验实测温度值比较,相符较好。     

扭力梁热成形模拟仿真分析

目的研究扭力梁热成形工艺。方法利用有限元分析软件,对扭力梁热成形进行模拟仿真,分析管坯的初始温度、冲压速度和摩擦因数对扭力梁热成形质量的影响。结果当管坯的初始温度为800℃,冲压速度为100 mm/s,摩擦因数为0.45时,减薄率达到最低,马氏体含量达到最高,热成形质量最优。结论利用有限元进行热成形分析的结果符合热成形规律,对该工艺的实际生产具有一定的指导意义。     

基于ANSYS的新型瓦楞纸板结构的有限元分析

借助有限元分析软件ANYSYS10.0,对传统V型瓦楞纸板在静定载荷作用下的力学性能进行了数值模拟,结合U型、UV型瓦楞芯纸结构,设计了O型和不倒翁型两种新型瓦楞芯纸结构,并对所有5种结构纸板的力学性能进行了对比模拟实验。结果表明:V型纸板具有很好的抗压性能,且抗压强度与V形夹角有关;不倒翁型结构瓦楞纸板同时具有良好的抗静压强度和抗冲击性能;各种纸板应力较大区域都集中在各层的粘接处,表现为纸板的应力集中点。     

斜拉桥有限元建模与模型修正

以圆弧桥面、单偏置斜塔的Safti斜拉桥为对象，研究了斜拉桥的有限元建模技术和基于敏感度分析的有限元模型修正技术及其对该桥的应用。基于该桥现场测量的模态数据，修正后的有限元模型获得了较好的改善。     

Structure Design and Finite Element Analysis of a Connection Assembly Program

The new connection assembly program contains four cone-shapes of fixed welders and four bolts.It is used for connecting the cover assembly of a Down-The-Hole( DTH) drill rig and its chassis.The design feasibility and reliability are evaluated according to the mechanical calculation and finite element method.     

颗粒增强金属基复合材料力学行为有限元模拟研究现状

从细观尺度和宏观尺度两个方面分析总结了国内外颗粒增强金属基复合材料有限元模拟研究现状.介绍了基于几何建模的周期性单胞模型、基于实际微观结构的有限元模型及宏观尺度模拟几个方面的内容,并对目前该领域存在的问题及今后的研究方向进行了分析总结.