Engineering aspect of alumina on alumina hip prosthesis

Alumina on the alumina sliding system in a total hip replacement is recognized as a breakthrough in orthopaedic surgery. Advantages and problems with this material are explained and discussed in the light of 36 years of clinical application. Laboratory data as well as clinical ones are summarized.     

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.     

A preliminary dual-energy X-ray absorptiometry-based finite element model for assessing osteoporotic hip fracture risk

To more accurately assess osteoporotic hip fracture risk in a specific patient, a dual-energy X-ray absorptiometry (DXA)-based finite element model was constructed from the patient's femur DXA image. The outermost contour of the femur bone segmented from the DXA image was used to generate a finite element mesh. Bone mechanical properties, such as Young's modulus, are correlated with areal bone mineral density (BMD) captured in the DXA image. A quasi-static loading condition representing a sideway fall was applied to the finite element model. Three fracture risk indices were introduced and expressed as ratios of internal forces caused by impact forces occurring in sideway fall to bone ultimate cross-section strength at the three critical locations, i.e. the femoral neck, the intertrochanteric region, and the subtrochanteric region. The proposed finite element modelling procedure was validated against six representative clinical cases extracted from the Manitoba BMD database, where initial and follow-up DXA images have been taken to monitor longitudinal variation of areal BMD in individual patients. It was found from the clinical validation that variations in the proposed fracture risk indices have the same trends as those indicated by the conventional areal BMD and T-score. In addition, by the three proposed fracture risk indices it is possible to further identify the specific fracture location. It was also found that for the same subject, the variations in the three fracture risk indices have quite different magnitudes, with intertrochanteric region the largest and subtrochanteric region the smallest, which is probably owing to the different content of trabecular and cortical bones in the three regions. With further development, it is promising that the proposed DXA-based finite element model will be a useful tool for accurate assessment of osteoporosis development and for treatment monitoring.     

Design optimization of hip prosthesis of thick laminated composites by developing finite element method and sensitivity analysis

An investigation has been performed to develop a finite element method for the analysis of the behavior of complicated three-dimensional thick laminated composite structure, and the method has been applied to the design of hip prosthesis with nonuniform cross-sections. The developed method can accomodate the varying material properties layered within the element and allow the ply-drop-off along the element edges. The numerical results are compared with the analytical solution, and the results show that the number of elements can be reduced up to 80% within 5% error bounds by using the ply-drop-off element. A method of design sensitivity analysis has also been developed to find the optimal ply angles minimizing the deflection of thick laminated composite structures. The developed finited element method together with the design sensitivity analysis has been applied to design of hip stem, and a procedure for calculating the optimum ply angle is proposed to minimize the rotational micromotion which is one of causes of patients’ pain.     

A finite element model for rolling contact fatigue of refurbished bearings

Bearing refurbishing has become a popular method of extending the life of rolling element bearings. In the refurbishing process the raceways of the bearing may be ground to remove any surface damage prior to repolishing and reassembly with larger sized rolling elements. In the current study a continuum damage mechanics finite element model was developed to quantify the damage in original and refurbished bearings. After calculating the damage accumulation for a set number of contact cycles with the original bearing geometry, refurbishing is simulated by removing a layer of the original surface. The refurbished microstructural model is then subjected to additional computational contact cycles until a fatigue crack reaches the surface, signifying failure. This model preserves the fatigue damage accumulated prior to refurbishing and evaluates its influence on the refurbished bearing fatigue life. All refurbished bearing surfaces showed a significant amount of life after refurbishing with L₁₀ lives from the point of refurbishment, varying from 20% to 94% of the original L₁₀ life. The results indicate that the remaining life of the refurbished bearing population is inversely related to the time before refurbishing and is proportional to the depth of the regrinding. Results obtained from this investigation are in good agreement when compared to the Lundberg-Palmgren bearing life equation modified for analyzing the life of a refurbished bearing.     

各向同性热解石墨的纳米压痕试验与有限元仿真研究

通过对各向同性热解石墨进行了纳米压痕试验,得到了其材料的载荷-位移曲线.并根据Olive和Pharr理论算出了其硬度与弹性模量值,得到了主要的材料性能.在纳米压痕试验的基础上,通过有限元单元法建立了纳米压痕试验的数值模型,通过比较有限元所拟合的载荷一位移曲线和实际纳米压痕试验所得到的曲线,进行相应的修正,最后得到了该材料的塑性性能,也证明了有限元仿真的可行性.     

Near net shape processing of a sintered alumina component: adjustment of pressing parameters through finite element simulation

Near net shape forming of alumina powder by cold die pressing and pressureless sintering was investigated. From experimental data of triaxial compression test of alumina powder, a hyperbolic cap model with a critical state line was proposed for densification of alumina powder at room temperature. For pressureless sintering, the phenomenological model for densification and viscous behavior of alumina powder proposed by Kim and co-workers was used. The constitutive models were implemented into a finite element program (ABAQUS) to simulate densification of alumina powder under cold die pressing and pressureless sintering. Finite element results were compared with experimental data for density distribution and deformation of an alumina powder compact under cold die pressing and pressureless sintering. New conditions of compaction were then proposed to reduce the distortion of the sintered part.     

Curvilinear finite element mesh generation for electron gun simulation

Mesh generation is an integral part of the finite element simulation of electron guns. This paper shows that curvilinear meshes are the ideal type of mesh to use, both in terms of accuracy and speed of computation, and presents a numerical method to generate quasi-curvilinear meshes for a wide variety of electron gun structures.     

汽车钢圈疲劳寿命的有限元分析

钢圈是位于轮胎和车轿之间承受负荷的旋转部件,其作用是安装轮胎,承受轮胎与车轿之间各种作用力和力矩,对汽车行驶的安全性、稳定性、平顺性和牵引性均起着重要的作用。基于名义应力法的分析过程及有限元分析软件,探讨了钢圈弯曲工况下结构强度及疲劳寿命预估的方法。通过理论计算、实际使用情况及弯曲疲劳试验的结果验证了所提方法的正确性,所提方法可在产品设计阶段就预测设计产品的使用寿命及结构特点,为钢圈的设计及优化提供依据。     

An alternative finite element model for simulation of frictional gap

This study is an attempt to modeling a frictional gap in a crack closure process under compressive loading conditions in which the crack surfaces are in touch and the effects of friction between them are significant. An iterative finite element (FE) solution is developed to model a finite crack in an interfacial layer with varying material properties. A mere application of a Lagrange multiplier formulation (node-to-node, NTN, or node-to-segment, NTS) in a developed FE framework to fulfill the contact constraints between contacting surfaces is discussed which improves the penalty formulation used in ANSYS. We then argue that the penalty formulation allows for a certain amount of crack surface interpenetration whereas the Lagrange multiplier formulation fulfils the contact constraints more accurately. This technique is easy to implement and offers higher accuracy than the equivalent FE solution, available in commercial FE software such as ANSYS 9.0, to the same system.     

采用ANSYS的橡胶弹簧的有限元建模与仿真

建立 AD250铰接式自卸车前悬架橡胶弹簧的参数化非线性有限元接触模型,比较橡胶弹簧实体建模与平面建模的计算精度,并分析大载荷下橡胶弹簧内部应力的分布,得到的结果与试验结果有很好的一致性.此模型可为橡胶弹簧结构的参数优化提供理论支持.     

磁流变抛光磁路的结构设计及有限元仿真

合理的磁路结构及磁场强度是决定磁流变抛光效果的关键所在。根据磁流变抛光要求设计了电磁铁磁路结构,建立了磁路结构和磁场强度分析模型。通过静态磁路理论和标量磁位分析,获得了相应磁路结构的磁场强度分布状况,并采用有限元分析软件ANSYS进行仿真,进而验证了磁路结构对磁流变抛光工艺的适应性和有效性。     

手机静态机械特性的有限元仿真

采用有限元技术对手机的静态机械特性进行仿真试验分析。仿真建模采用I-DEAS软件,用分组的方式建立装配 模型。单元划分采取划分子区域的方法。仿真结果与实物试验相吻合。     

旋转直线永磁电动机有限元仿真

设计一种可以同时实现旋转运动和直线运动的新型两自由度永磁电动机,给出轴向绕组和径向绕组的分布示意图,描述旋转磁场的形成和直线(轴向)运动原理.具体介绍设计中所使用的永磁材料和铁心材料.使用ANSYS建立电动机的有限元模型,给出有限元基本参数,具体描述前处理、材料定义、网格划分和边界条件的设定.仿真结果表明,这种两自由度永磁电动机的设计是可行的.     

汽车碰撞过程并行有限元仿真技术

根据显式有限元的计算特点和神威超级计算机的体系结构,设计了基于消息传递和区域分割的动态显式有 限元的并行算法,给出了基于汽车结构和材料特征的并行化分区算法,提出的算法应用在自行开发的GEFEP-P汽 车碰撞的并行化有限元分析软件,并成功移植到神威Ⅰ超级计算机。算例计算结果表明:采用并行有限元计算,可 以大大提高汽车碰撞过程的仿真计算效率。     

膜片联轴器多体接触有限元数值模拟

考虑膜片联轴器实际工作状态下的螺栓预紧力、离心力、扭矩等载荷工况,建立了膜片联轴器的整体有限元模型,采用ANSYS软件对其进行接触有限元分析,得到膜片联轴器的综合位移和等效应力云图,以及膜片组的接触应力分布曲线。通过对存在轴向偏离、径向不对中、角向不对中等安装误差的膜片联轴器的多体接触有限元仿真及对比分析,得出各种安装误差对膜片联轴器力学性能的影响规律。     

Non-linear three-dimensional finite element analysis of a cementless hip endoprosthesis

In this finite element study the stresses between a stem component of a cementless hip endoprosthesis (Young modulus of Co-Cr-Mo) and the human femur were calculated for two different loading types. Linear and non-linear models were used to simulate the interface implant bone. Two models, a stem with a porous coated surface over the entire length and a stem with a porous coated surface in the proximal region were compared regarding the load transmission to the femur. An additional calculation of an 'isoelastic' stem (Young modulus of cortical bone) was done to show the influence of the stem stiffness. A porous coated surface over the entire length causes principal shear stresses up to 2.75 MPa in the distal-medial region during level walking. The highest compressive stresses were calculated in the proximal-lateral region as 1.5 MPa in cancellous bone. A more physiological load transmission is obtained by limiting the coated area to the proximal region. All stresses in the two models are lower than experimentally evaluated strengths in the interface between implant and bone. A strong influence of the Young modulus of the stem material on the interface stresses was found. An 'isoelastic' stem causes compressive stresses in the proximal-lateral region whose values exceed the experimental strength of cancellous bone.     

静电涂油机涂油室的有限元仿真分析

根据电磁场基本原理和有限元数值计算方法,利用ANSOFT Maxwell软件对静电涂油机的涂油室进行静电场仿真分析,模拟了涂油室电势和电场强度的矢量分布,分析了最大场强与刀梁长度、涂油室宽度、外加电压和刀梁与钢板距离等参数的变化规律.研究发现,随着涂油室中场强的增大,油液雾化的效果越好,因此从理论上验证了油液在静电场中的雾化规律,为深入研究静电涂油机的雾化机理提供了参考依据.     

三轴转台运动学仿真与结构有限元分析

利用Pro/E软件对三轴转台进行了三维实体建模,实现了转台零部件的装配,同时对转台进行了运动学仿真,分析了各部件运动时的干涉情况,并获得了被测试件在三轴一定运动条件下的位置和速度曲线.根据对三轴转台机械结构特点进行分析,考虑到计算速度和准确度,对转台各结构部件进行了合理的简化和等效处理,采用有限元分析软件ANSYS建立了转台的有限元模型,对转台进行了静力计算和模态分析.结果表明,三轴转台的结构设计满足指标要求.     

Thermo-mechanical finite element simulation and validation of rubber curing process

Journal of Mechanical Science and Technology - Vulcanization, or curing, is a very important process in producing useful rubber products. The curing process takes place when heat is transferred to...