膜基反射镜的非线性有限元挠度分析

介绍一种获得较精确的膜基反射镜挠度数值解的方法。通过非线性有限元分析,对三种有限元网格划分方法进行研究比较,建立符合实际情况的有限元模型,给出薄膜分析中施加预应力的方法,分析研究膜基反射镜的挠度特性。首先在简易边界条件下,验证有限元分析结果符合固定支撑圆板挠度弯曲问题的理论值;然后运用此方法分析复杂边界条件下膜基反射镜的表面位移情况,获得膜基反射镜面形特征数据。获得的挠度值相对误差小于0.04%,为深入研究膜基反射镜成型及面形控制做了准备。     

Effect of bone material properties on the initial stability of a cementless hip stem: a finite element study

In previous finite element studies of cementless hip stems reported in the literature, the effect of bone quality on the initial micromotion and interface bone strain has been rarely reported. In this study, the effect of varying cortical and cancellous bone modulus on initial stem micromotion and interface bone strain was examined and the potential consequence of these changes on bone ingrowth and implant migration was reported. A finite element (FE) model of a total hip replacement (THR) was created and the Young's moduli of cortical and cancellous bone were systematically varied to study the relative effect of the quality of both types of bone on the initial stability of a cementless THR. It was found that the initial micromotion and interface bone strain in a THR was significantly affected by the overall stiffness of the femur. In other words, both the reduction of the modulus of cortical and cancellous bone caused an increase in the initial micromotion and interface bone strain. This suggests that for FE studies to be truly predictive, a range of bone quality must be examined to study the performance envelope of a particular stem and to allow comparison with clinical results.     

Wear analysis of a ceramic on ceramic hip endoprosthesis

The authors have analyzed the wear of a ceramic-on-ceramic hip joint prosthesis retrieved after 25 years of use. Severe wear and flattening of the femoral head was revealed, while the acetabular component was less worn. Three wear zones can be seen on the femoral head depending on surface topography. The wear patterns of the ceramic components of the prosthetic head indicate the role of microseparation that occurs during implant functioning.     

A mixed-hybrid finite element for three-dimensional isotropic helical beam analysis

This paper presents a two node finite element with six degrees of freedom per node, able to model the behaviour of a three-dimensional isotropic helical beam with two constant radii of curvature (curvature and torsion radii). The formulation, which includes the shear strain effects, is based on the assumed resultant forces hybrid approach. The resulting forces approximation verifies exactly the equilibrium equations. Numerical results of samples and distribution of generalized forces along the helical beam are presented. Comparison with other models indicates that the presented element gives exact solutions.     

工业构件塑变校正的非线性有限元分析

采用非线性有限元法,研究了杆类零件和板簧的塑性矫直过程,计算结果表明,对被矫直的工件施加合理的载荷,可以获得较高的矫直精度。     

Non-linear finite element analysis of formation and treatment of intervertebral disc herniae.

A biomechanical model of the spine motion segment L2/L3 consisting of the truncated vertebrae, endplates, intervertebral disc and pieces of anterior and posterior longitudinal ligaments has been used for a computer simulation study. A non-linear finite element analysis has shown that small loads compressing the spine, not greater than those occurring in everyday life, cause loss of stability of an intervertebral disc, resulting in lateral dislocation of its nucleus pulposus. This could be a potential cause of discopathy. The model indicates that conservative therapy of herniated disc by the traction method may result in retraction of hernia by about 40 per cent.     

Non-linear optimization of a new robotic induction process for local heat treatment using thermal finite element analysis

Performing high-quality repair on aging hydro power equipment is a challenging issue for utilities. Weld repair deteriorates the mechanical properties of the base metal in and around the heat-affected zone. For martensitic stainless steel runners, there is no way to perform post-weld heat treatment (PWHT) on site to restore those properties without dismantling, a very expensive job for such large components, typical of power utilities. To perform in situ high-quality repairs on such components, a new robotic heat treatment process is developed. Heat is generated and controlled using a flat spiral coil mounted on a compact, portable robot and moved over the area needing heat treatment. Unlike conventional induction heating, which requires a customized coil, this new approach combines a universal coil and a flexible robot to heat a broad range of complex shapes. One critical aspect is to set heating and path parameters in order to generate a target spatial and temporal temperature field. This paper proposes a numerical method combining thermal finite element analysis and a non-linear optimization algorithm to set these parameters. The temperature resulting from the electromagnetic field induced by the coil is modeled using an average heat input source to improve computation speed. Good agreement is obtained between numerical and experimental results for PWHT under laboratory conditions.     

A three-dimensional rigid-plastic finite element analysis of bevel gear forging by using a remeshing technique

A three-dimensional remeshing scheme implemented by using a modular concept is proposed for the finite element analysis of a complicated forging process. In order to show the effectiveness of the scheme, forging of a bevel gear is simulated by using several basic modules in the general rigid-plastic finite element code (Yoon and Yang, Int. J. Mech. Sci.30, 887, 1988; Yang et al., Int. J. Mech. Sci.31, 145, 1989) developed for cold forging. Criteria for remeshing as well as a scheme for the mapping of state variables are proposed for three-dimensional remeshing. The computational results are compared with experimental data in order to check the validity of the simulation. The computational results show that the computation can be effectively carried out by using the proposed remeshing scheme and that it can be extended to other more complicated product geometry.     

Temperature prediction in a finite element model for sliding contact analysis of total hip prosthesis

A finite-element model for sliding contact in total hip joint prosthesis is presented in this paper. The hip prosthesis studied consists of an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup articulating against cobalt-chrome and alumina-ceramic femoral heads. Various aspects of prosthesis operation were analysed using the finite-element model. For example, bulk material and surface stresses were analysed under varying conditions of elastic modulus, friction coefficient, sliding speed, and radial clearance. The resulting variations of temperature were also recorded. The results obtained from the model are useful in understanding the operating conditions and the causes of wear in the hip prosthesis.     

万向联轴器十字轴强度三维有限元分析

在对５３０轧机轧制扭矩的现场实测基础上,建立了十字轴的三维有限元计算模型,驼用ＳＡＰ５程序分析了十字轴的应力轴,找出了十字轴的危险截面,分析了十字轴发生断裂的原因,提出了在十字轴结构设计时应采取的措施。     

A three-dimensional finite element method for plate bending

A three-dimensional finite element method is proposed for plate bending. The displacement function is assumed to have a particular form with respect to the thickness variable.The assumed displacement function is substituted into the three-dimensional potential energy functional and a two-dimensional variational problem emerges.The two-dimensional problem is treated by the finite element method and it is seen that for conforming solutions the only requirement is continuity of the basis functions.The method includes transverse shear and thickness effects and may be used for both thin and moderately thick shells.To illustrate the method and to compare it with other results, the problems of a square plate under point and distributed loads and with simply supported and clamped boundary are treated numerically.     

A finite element methodology for wear–fatigue analysis for modular hip implants

Fretting of the stem-head joint in a prosthetic hip implant is investigated experimentally and computationally. An FE-based methodology for fretting wear-fatigue prediction in a prosthetic hip implant is developed. Tribological and profilometry tests are performed for two head/stem material combinations: Co–28Cr–6Mo/DMLS Ti–6Al–4V and Co–28Cr–6Mo/forged Ti–6Al–4V. The hardness and wear resistance of DMLS Ti–6Al–4V are shown to be superior to those of forged Ti–6Al–4V. The significance of wear in a hip joint for 10 years of service in a normal weight person for moderately intense exercise is predicted for both material combinations. Both material combination joints are shown to have excellent wear resistance which suggests that the wear debris emission will not be significant.     

Thermo-mechanical finite element analysis of a rail wheel

The rail wheel, which is acted upon by mechanical forces also experiences thermal stresses due to braking, during service. The coupled nature of these forces is analysed using a three-dimensional elasto-plastic finite element model. Contact stresses at the rail–wheel interaction location are analysed using a global–local approach on a three-dimensional elasto-plastic finite element model. The paper also brings out the size and shape of the plastic zone at the contact region. Commercial finite element code ABAQUS has been used for the analysis and SDRC’s I-DEAS has been used for modelling. American Association of Railroad’s standards, available for the purpose of analytical evaluation of the rail wheel, has also been critically evaluated in this work.     

Biomechanical finite element analysis of bone cemented hip crack initiation according to stem design

The purpose of this investigation was to determine the specific fracture mechanics response of cracks that initiate at the stem-cement interface and propagate into the cement mantle. Two-dimensional finite element models of idealized stem-cement-bone cross-sections from the proximal femur were developed for this study. Two general stem types were considered; Rectangular shape and Charnley type stem designs. The FE results showed that the highest principal stress in the cement mantle for each case occurred in the upper left and lower right regions adjacent to the stem-cement interface. There was also a general decrease in maximum tensile stress with increasing cement mantle thickness for both Rectangular and Charnley-type stem designs. The cement thickness is found to be one of the important fatigue failure parameters which affect the longevity of cemented femoral components, in which the thinner cement was significantly associated with early mechanical failure for shot-time period.     

三维有限元后处理图形程序设计

讨论了三雏有限元后处理图形程序的实现过程，同时以钢管斜轧穿孔过程为例，给出了变形区构形以及等效应变率、等效应变、等效应力的云图。结果表明，所开发的图形程序简洁、精确、便于实际应用。     

A three-dimensional finite element model from computed tomography data: a semi-automated method

Three-dimensional finite element analysis is one of the best ways to assess stress and strain distributions in complex bone structures. However, accuracy in the results may be achieved only when accurate input information is given. A semi-automated method to generate a finite element (FE) model using data retrieved from computed tomography (CT) was developed. Due to its complex and irregular shape, the glenoid part of a left embalmed scapula bone was chosen as working material. CT data were retrieved using a standard clinical CT scanner (Siemens Somatom Plus 2, Siemens AG, Germany). This was done to produce a method that could later be utilized to generate a patient-specific FE model. Different methods of converting Hounsfield unit (HU) values to apparent densities and subsequently to Young's moduli were tested. All the models obtained were loaded using three-dimensional loading conditions taken from literature, corresponding to an arm abduction of 90 degrees. Additional models with different amounts of elements were generated to verify convergence. Direct comparison between the models showed that the best method to convert HU values directly to apparent densities was to use different equations for cancellous and cortical bone. In this study, a reliable method of determining both geometrical data and bone properties from patient CT scans for the semi-automated generation of an FE model is presented.     

Development and experimental validation of a three-dimensional finite element model of the human scapula

A new modelling approach, using a combination of shell and solid elements, has been adopted to develop a realistic three-dimensional finite element (FE) model of the human scapula. Shell elements were used to represent a part of the compact bone layer (i.e. the outer cortical layer) and the very thin and rather flat part of the scapula--infraspinous fossa and supraspinous fossa respectively. Solid elements were used to model the remaining part of the compact bone and the trabecular bone. The FE model results in proper element shapes without distortion. The geometry, material properties and thickness were taken from quantitative computed tomography (CT) data. A thorough experimental set-up for strain gauge measurement on a fresh bone serves as a reference to assess the accuracy of FE predictions. A fresh cadaveric scapula with 18 strain gauges fixed at various locations and orientations was loaded in a mechanical testing machine and supported at three locations by linkage mechanisms interconnected by ball joints. This new experimental set-up was developed to impose bending and deflection of the scapula in all directions unambiguously, in response to applied loads at various locations. The measured strains (experimental) were compared to numerical (FE) strains, corresponding to several load cases, to validate the proposed FE modelling approach. Linear regression analysis was used to assess the accuracy of the results. The percentage error in the regression slope varies between 9 and 23 per cent. It appears, as a whole, that the two variables (measured and calculated strains) strongly depend on each other with a confidence level of more than 95 per cent. Considering the complicated testing procedure on a fresh sample of scapula, the high correlation coefficients (0.89-0.97), the low standard errors (29-105 micro epsilon) and percentage errors in the regression slope, as compared to other studies, strongly suggest that the strains calculated by the FE model can be used as a valid predictor of the actual measured strain. The model is therefore an alternative to a rigorous three-dimensional model based on solid elements only, which might often be too expensive in terms of computing time.     

Enriched finite element method for three-dimensional viscoelastic interface crack problems

The enriched finite element method is developed for three-dimensional problems of an interface crack between elastic and viscoelastic (including dissimilar viscoelastic) materials. According to the displacement fields of elastic interface crack, the displacement fields of viscoelastic interface crack are derived through the correspondence principle. By incorporating the displacement expressions into the displacement model of regular element, the incremental formulations of enriched element are derived. The stress intensity factors and strain energy release rates can be solved based on the enriched degree of freedoms. A 3-D through interface crack at the center of jointed dissimilar viscoelastic plate subjected to remote tension and a quarter-circular viscoelastic interface corner crack subjected to uniform thermal loading was investigated using the enriched finite element method. It is shown that the present solutions are consistent with the analytical solutions, which indicates the present method is correct and efficient.

     

A three-dimensional or penalty finite element method for plate bending

This paper, a sequel to an earlier paper by the same authors, uses a three dimensional or penalty function approach to obtain finite element solutions for plate bending problems. The advantage in using this approach is that the finite element subspaces need only be continuous; the disadvantages are that more functions are needed.In our previous paper, we used piecewise quadratic and linear functions, in the present paper we use piecewise cubic and quadratic functions with a resultant reduction of the discretization error. We also suggest an interpolation method or an a priori choice of the thickness to length ratio which are appropriate for thin or moderately thick plates. Numerical results are given for clamped and simply supported plates with point and distributed loads.     

无人机机翼主翼梁三维有限元分析及试验研究

建立了某无人机主翼梁的三维有限元模型,应用多点约束模拟主翼梁外梁和中梁的连接,基于ANSYS软件,计算得到主翼梁应力分布和变形量,并与试验结果进行对比,吻合较好;分析结果表明:主翼梁强度满足设计要求,最大应力位于外梁和中梁的对接区周围,并且在此区域存在一个高应力梯度区域,该分析结果为机翼及主翼梁的优化设计提供了理论依据;这种有限元分析与试验验证相结合的思路,可为无人机(UAV)其他结构分析提供借鉴.