Friction in orthopaedic zirconia taper assemblies

The torque resistance of zirconia ceramic heads/titanium taper trunnion junctions was tested in accordance with ISO 7206-9:1994(E); using twelve modified heads of 32 mm diameter under representative physiological conditions. Test parameters studied included assembly force, vertical load during test (test load) and head length. Mean torque resistances measured were 8.9 N m for a 1 kN test load and 15 N m at 4 kN test load. Coefficients of friction calculated for the torsional stability ranged from 0.06 to greater than 1.0. Multiple regression analysis confirmed that the failure torques measured were significantly dependent on test load (beta = 0.77; P < 0.001) whereas assembly force and head length played a lesser, insignificant, part in the variation. Data from push-on/pull-off tests were used to calculate coefficients of friction under axial loading, which were significantly correlated with taper angle and material. Torque testing shows greater variability than push-on/pull-off tests for similar combinations, and for zirconia heads on other tapers. The coefficients of friction measured (0.16-0.31) are significantly different from values typically used in stress analyses.     

Subcapital fracture in a femoral prosthesis: brief report

Stem fractures in prosthetic femoral components are a well recognized problem. More recently neck fractures have been described. An unusual case of a 'sub-capital fracture' in a femoral component is described.     

Friction and prow formation in a scratch process of copper by a diamond cone

A deformation process of flat copper surfaces scratched by diamond conical riders was observed by a metallographic technique and scanning electron microscopy. The geometric shape and the size of prows formed by material pile-up in front of the rider were examined and their influence on friction was investigated. It was found that, taking into account the actual shape of the prow, the friction force can be obtained theoretically for any cone angle.     

Biotribology: Friction,wear, and lubrication of natural synovial joints

Studies have been carried out over the past several years to explore possible interconnections between tribology — the study of friction, wear, and lubrication — and arthrology, more specifically, mechanisms of synovial joint lubrication and degeneration. The focus of this paper is on the tribological behaviour of natural and so-called ‘normal’ synovial joints. A separate paper deals with possible connections between tribology and degenerative joint disease (e.g., osteoarthritis). The purpose of this paper is fourfold: (1) to present a summary of salient work on mechanisms of synovial joint lubrication; (2) to review the key findings of our in vitro wear studies made with bovine articular cartilage; (3) to discuss the significance of the cartilage wear studies in relation to existing joint lubrication theories; and (4) to describe a new device being used for studies of cartilage-on-cartilage deformation, friction, wear and damage under in vitro conditions.     

Friction and wear mechanisms in hip prosthesis: Comparison of joint materials behaviour in several lubricants

In this work, the most commonly used joint materials for substitution of hip joints, ultra high molecular weight polyethylene (UHMWPE) for the cup, and alumina, stainless steel or CoCrMo alloy for the head, were submitted to pin-on-disk tribological tests. The interfacial behaviour prosthetic material/lubricant was investigated through wettability measurements. Four lubricants were used: Hanks’ balanced salt solution (HBSS) and solutions of bovine serum albumin (BSA), of hyaluronic acid (HA) and of both components (BSA + HA) in HBSS. It was observed that the friction coefficient increased significantly with time, in a random way, when the lubricant did not contain albumin. The addition of HA induced a slight reduction in the initial value of the friction coefficient but did not affect qualitatively its behaviour for longer times. Observation of the worn metallic surfaces revealed parallel grooves typical of abrasive wear and also lumpy transfer film of UHMWPE, while the transfer of polymer to alumina was incipient. Wear was particularly intense on the steel surface where delamination and fatigue wear mechanisms were also found. In the presence of albumin, the friction coefficient remained constant and small for the metallic surfaces and increased in the case of alumina. The observation of the worn surfaces showed that the presence of albumin in the lubricant avoided the transfer of polymer for the metallic surfaces but not for the alumina surfaces. These results, together with the wettability measurements, strongly indicate that the presence of albumin in the lubricant avoids the adhesion and transfer of UHMWPE only for the least hydrophilic surfaces, which are the metallic ones.     

Fretting corrosion damage of total hip prosthesis: Friction coefficient and damage rate constant approach

This paper analyzes friction coefficient evolution between materials related to total hip prosthesis. Fretting corrosion tests were conducted with stainless steel and poly(methyl methacrylate) interacting surfaces. In the course of fretting corrosion tests, the Coulomb friction coefficient is determined as a function of the number of cycles. It was found that the friction coefficient growth rate can be expressed as a power-law function. The influences of ionic strength, applied potential, pH, and albumin content on fretting corrosion were then investigated on the basis of the evolution of the friction coefficient. Finally, we identify the damage rate constant as being relevant for linking the mechanical and chemical parameters in the evolution of damage.     

模型分割制造中相似形联接键生成算法

对于超出现有设备加工范围的大尺寸模型,可将其分割成多个带有联接键的小尺寸子模型来进行加工和装配.为了提高子模型联接键的生成效率和装配精度,提出一种在子模型装配面上快速生成相似形联接键的新方法.相似形联接键的轮廓直接由切割面轮廓通过偏移获得,省去了二次建模和模型间的布尔操作;联接键的最大深度通过轮廓投影法确定,保证了装配深度的合理性.子模型切割面的闭合与相似形联接键的构成同步进行,确保了装配面的三角化一致性,进而提高了公母子模型的装配精度.     

A comparative study of the performance of metallic and ceramic femoral head components in total replacement hip joints

Arthroplasty represents an outstanding twentieth century achievement in orthopaedic surgery. However, in recent years polyethylene wear debris has been linked to the loosening process in implants and there is considerable interest in reducing the severity of wear through the introduction of improved materials and alternative designs of total replacements joints. During the past twenty years or so, ceramic components have been introduced, either as ceramic-on-ceramic or as ceramic-on-polymer combinations of sliding pairs of materials and in this paper a tribological appraisal is made of the performance of the latter combination in relation to the long established metal-on-polymer arrangement. The basic mechanisms of wear in total replacement joints are considered and attention is drawn to the role of creep in determining the initial penetration of the femoral head into the polyethylene acetabular cup. Laboratory and clinical studies of the tribological characteristics of current forms of implants are then reviewed.     

圆锥球头立铣刀的CNC磨削模型及工艺

复杂形状刀具结构上的复杂性导致了磨削加工的复杂性。利用圆锥球头立铣刀这一典型复杂形状刀具,对其圆锥部分和球头部分的刀刃曲线的连续性进行了分析,然后对刀刃结构和加工特性进行研究,再利用Frenet标架来确定砂轮的摆放姿态,实现利用活动坐标系控制机床坐标的插补进给,并通过磨削实例验证。     

用中心投影法作直齿圆锥齿轮的仿真模型及其数据库

为了建立直齿圆锥齿轮的草图和仿真模型数据库,研究用中心投影法把形成圆锥齿轮齿廓的球面渐开线近似投影成圆的渐开线,根据机械设计的原理,作出圆锥直齿轮的草图,然后把上千个设计齿轮的数据用方程式关联到草图中,在草图中只要改变圆锥直齿轮的当量齿数、大端模数、分度圆圆锥角和齿宽等主要数据,就可以得到不同的新数据下的圆锥直齿轮的草图和仿真图形。研究结果表明建立这样的数据库能在很大程度上方便直齿圆锥齿轮的设计和加工,同时对于齿轮的教学培训也有很有帮助,相应的图块和方程式也可以做Solidworks软件的插件使用。     

Coupling of dynamics and contact mechanics of artificial hip joints in a pendulum model

To date, fully coupled dynamics and contact mechanics analysis is still limited by expensive computational cost and long computing time and has not been addressed comprehensively, particularly in the hip joint. To understand the influence of different parameters on the biomechanics of the total hip replacement (THR) and improve its design, two numerical approaches were developed and implemented in finite element models to investigate the coupling between the dynamics response and the contact mechanics for three different THR configurations, metal-on-polyethylene (MOP), metal-on-metal (MOM), and ceramic-on-ceramic (COC). The dynamic force and the contact pressure distribution at the bearing surfaces from the two methods were predicted and compared. The influences of various parameters (motion angle, load applied in the pendulum, friction coefficient, geometry, and material properties) were subsequently investigated. From the comparisons, the decoupled method, based on the rigid-body dynamics and the quasi-static elastic contact mechanics, was adequate to predict the performance of the THRs efficiently. The load had the greatest influence on the dynamics/contact mechanics among other factors.     

摩擦圆辊直径与摩擦包角对板成形摩擦系数测量的影响

基于Duncan方法设计了一种板料成形摩擦系数测试装置,用以考察摩擦圆辊的直径和摩擦包角对摩擦系数计算的影响。正交试验分析表明:随着摩擦圆辊直径和摩擦包角的增大,由板料弯曲和包角边界造成的摩擦系数计算干扰效应将逐级减小,进而计算摩擦系数也逐步减小,并且最终趋向真实摩擦系数。基于最终试验分析结果,得出包角在90°,圆辊直径在30 mm左右时,测得的摩擦系数可以忽略弯曲效应和包角边界效应,能反映真实摩擦状态,可以用于后续的金属板料成形有限元模拟。     

A flexible multi-body dynamic model for analyzing the hysteretic characteristics and the dynamic stress of a taper leaf spring

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of 1–2 mm/sec and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.     

Experimental and mechanical model for predicting the behaviour of minor axis beam-to-column semi-rigid joints

This paper describes a series of experimental tests followed by finite element simulations produced to enable the prediction of moment resistance and rotation capacity of minor axis beam-to-column semi-rigid connections. These investigations motivated the development of a mechanical model to assess the connection's structural response. The mechanical model is based on the component method of design, in accordance with the Eurocode 3 specification. This philosophy implies that each joint component is represented by a spring possessing a non-linear force versus displacement (F-Δ) curve. The model was subsequently calibrated against experimental and finite element results previously performed.     

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.     

SiO2填充聚四氟乙烯复合材料的摩擦学行为研究

用机械共混和冷压成型、热烧结的方法制备了琐体积含量不同粒径的SiO2填充PTFE样品，用M-2000摩擦磨损试验机评价了不同样品在干摩擦下的摩擦学性能；用X射线能量损失谱（EDS）观察分析了摩前后Si元素在样品表面的分布情况，结果表明：在本实验所采用的实验条件下，SiO2/PTFE复合材料的摩擦系数随SiO2体积含量的增加而增大，抗磨损能力则有一个最佳含量；填料粒径不同其体积填充分数对复合材料摩擦磨损性能的作用规律不同，在相同的体积分数下，粗SiO2填充PTFE的摩擦系数小于细SiO2填充PTFE的摩擦系数，且其随SiO2填充分数增加而增大的趋势远小于细SiO2填充PTFE；其具有最好抗磨能力的最佳体积填充含量也大于细SiO2的体积填充含量，SiO2这种填充作用规律可由其在PTFE基体中的形态结构特征来解释。     

含复铰平面运动链型综合中消极子链的识别方法

提出了在运动链中识别消极子链的生成树—基本回路法。通过能够反映复铰和多副杆等结构特点的构件邻接矩阵,得到运动链的广度优先生成树。由生成树的弦将运动链分解成为数目确定的基本回路。利用基本回路或基本回路的并所形成子链的活动度识别消极子链。研究表明,该方法适用于无复铰和含复铰平面运动链,并且具有运动链分解形式选择唯一、简单、可靠及便于用计算机处理等特点。