Influence of contaminants in the stem-ball interface on the static fracture load of ceramic hip joint ball heads

The probability of in-vivo failure of ceramic hip joint implants is very low (0.05-0.004 per cent). Besides material flaws and overloading, improper handling during implantation may induce fractures of the ceramic ball head in the long term. This study focuses on the influence of contaminants located in the stem-ball interface and on the use of damaged metal tapers on the strength of ceramic ball heads. Mechanical tests on alumina ball heads according to the standard ISO 7206-10 were performed to identify their effect on the static fracture load. A decrease of up to 90 per cent with respect to the reference static fracture load was found when contaminants such as bone chips, soft tissue, or blood were present. Reductions of 57 per cent and 27 per cent were observed for deformed stem cross-sections (from circular to elliptical) and for flattened stems respectively, making deformed stems another influential parameter. Since any alteration of the interface between the metal taper and the ceramic ball head yields a nonuniform load introduction and hence results in stress concentrations, its presence has to be avoided.     

混合式陶瓷轴承沟道结构参数的简化算法

以目前钢轴承的结构参数合理正确和轴承滚动体与内外圈滚道在相同的接触应力及接触面积作用下具有相近的接触疲劳寿命及发热为前提 ,以相同负荷作用下 ,混合式陶瓷球轴承与相应钢轴承的接触应力和接触面积相等为依据 ,给出了混合式陶瓷球轴承内外圈沟道结构参数的简化计算方法。以 6 2 0 9深沟球轴承为例 ,对相应的混合式陶瓷球轴承的沟道曲率半径进行了计算 ,以计算结果制造的混合式陶瓷球轴承的运转性能完全能够满足使用要求     

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.     

不同轴向载荷下氮化硅全陶瓷轴承润滑特性

全陶瓷球轴承广泛应用在航天航空领域、燃气发动机和极端工况下,然而针对全陶瓷轴承油润滑特性的研究比较少见。以氮化硅6206全陶瓷深沟球轴承作为研究对象,在轴承测振仪上开展陶瓷轴承润滑特性实验研究,采用拟静力学和最小油膜厚度理论通过MatLab的牛顿迭代法得到比较精确的数值解,分析陶瓷轴承的接触载荷、轴向载荷、离心力、最小油膜厚度之间的关系,并通过改变供油量和轴向载荷得到陶瓷轴承在不同工况下的振动规律。实验结果表明：在轴向载荷相同条件下球与外圈之间的接触载荷比球与内圈之间的接触载荷大,轴向位移随着轴向载荷增加呈递增趋势;在轴向载荷一定时,存在一个最佳供油量使轴承振动最小,在干摩擦条件下轴承振动随着轴向载荷增加呈先减少后增大的趋势。     

Longevity enhancement of bolted joints for aircrafts

New designs of bolted joints with bolt countersunk heads having high longevity in comparison with the used ones were proposed. One type of joint has the bolt heads with the reduced surface taper of the bolt head and in a joined part. Two other types have a spherical head surface, which is in contact with a tapered countersink surface. The rise in the fatigue life is achieved owing to the balance of the radial tension along the contact surfaces of the head and the countersink. Designs of a washer from the direction of a nut are proposed. These washers have ring bulges of wedge-shaped cross section that form areas of plastic deformations around a bolt body during the bolt tightening and reduce the concentration of contact stresses close to an edge of the contact surfaces of the bolt and joined parts. Procedures of fatigue tests were developed. Results of tests of the proposed bolted joints supporting their high longevity are presented. Findings of experimental investigations verify the efficiency of the application of proposed types of bolted joints in the designs of aircrafts.     

Scratch and wear performance of prosthetic femoral head components against crosslinked UHMWPE sockets

Total hip arthroplasty is a highly successful procedure where the hip joint is replaced by an artificial ball and socket joint. Bearing wear continues to be a contributing factor to implant failure. Prosthetic femoral heads roughen in vivo which leads to increased wear. Along with the introduction of improved polyethylene which reduces wear by up to 99%, improved femoral head materials have been introduced to improve resistance to abrasion. The abrasion resistance of two of these improved femoral heads was assessed in this study and compared to a cobalt chromium (CoCr) femoral head. The resulting wear performance against a polyethylene acetabular component was assessed. The bulk ceramic (zirconia toughened alumina) femoral head exhibited superior abrasion resistance compared to CoCr (97% reduction in damage) as well as reduced wear after abrasion (97% reduction in wear). The oxide coated zirconium niobium femoral head showed inferior abrasion resistance compared to CoCr (99% increase in damage) as well as increased wear after abrasion (161% increase in wear). Both femoral head surfaces utilize hard ceramic materials, however, the thin ceramic coating on top of a softer metallic substrate of the oxide coated bearing was unable to withstand aggressive abrasion.     

高水头水轮机球阀压力试验封头受力分析

以某高水头水轮机球阀压力试验封头结构为研究对象,介绍了球壳与锥壳组焊式压力试验封头的各组成部分,并利用有限元方法对其进行受力分析。利用应力线性化方法,提取了高应力区域组焊钢板的最大平均应力,并依据相应的应力考核标准对结果进行考核。     

A laboratory study of friction in hip implants

One of the most promising methods of reducing wear and extending the useful life of artificial joints is by regular microrelief treatment, a novel finishing technology based on the formation of a system of fine grooves by means of plastic deformation of surfaces with a ball-tipped diamond. Laboratory friction testing of treated joint prostheses is an essential component in the developmental process of this application. In order to evaluate the friction characteristics of hip prostheses made up of metal ball heads treated with regular microrelief, a computer-monitored friction tester was developed. The ball head was pressed against the cup by a load. The friction torque was measured by means of a load cell. Distilled water was used as the lubricant. Before the friction test, all balls were tested in a specially developed wetting ability tester, to evaluate the effect of regular microrelief treatment on the wetting behaviour of the head surface in water. The results obtained showed that the wetting ability of balls treated with regular microrelief was higher by 30% as compared with non-treated hip heads. The articulating pairs with heads treated with regular microrelief showed a 25–35% reduction in the friction torque, when compared with conventional, non-treated joints.     

轿车轮辐侧孔冲模结构设计

轮辐是组合式车轮的主要组成部分,它的质量直接影响整个车轮在运行过程中的性能。在冲轮辐侧壁8个出水孔时由于有较大的侧向应力存在、且受力方向与竖直方向形成的夹角,容易使已经加工好的中心孔和预加工的螺栓孔产生严重变形,影响车辆在行驶时的稳定性、平顺性及配套轮胎的使用寿命,所以应把冲侧孔这道工序安排在冲中心孔和加工螺栓孔之前。采用整体冲模一次成形的方案,并设计了一套完整的侧孔整体冲模,采用的下冲倾斜斜楔结构可预防凸模受弯扭而损坏并且提高斜楔机构的效率,同时对模具的主要参数进行了选取,增加了强迫复位装置以使斜楔复位。     

无垫片焊唇密封法兰螺栓载荷的分析与计算

分析了无垫片焊唇密封元件---焊环在承受介质压力载荷时的受力及径向位移状况;指出现行设计规定的螺栓载荷不能约束焊环的径向位移,焊环与法兰的连接焊缝承受了焊环的径向拉力;提出了由螺栓载荷平衡焊环与法兰之间静摩擦力和介质的压力载荷;并给出了螺栓载荷的计算方法。此外,还分析了高温下焊环与法兰存在热膨胀差时,焊环的受力及径向位移状况,提出了采用热当量压力计算螺栓载荷的方法。     

纯滚动状态下氮化硅陶瓷球临界应力分析

氮化硅陶瓷球临界应力在很大程度上决定其滚动接触疲劳和磨损寿命.由于陶瓷材料的抗拉能力较弱,所以设想其滚动接触疲劳失效的临界应力为最大主拉应力.应用弹性接触力学和赫兹理论分析纯滚动条件下陶瓷球表面层接触应力,得到表面层最大主拉应力.针对理论计算值,设计相应的纯滚动接触疲劳实验.分析表明,理论值与实验结果趋于一致,从而证实最大主拉应力为氮化硅陶瓷球滚动接触疲劳失效的临界应力.计算结果为陶瓷球的滚动接触疲劳寿命分析提供理论基础.     

螺栓法兰连接的失效案例分析及有关进展的讨论

根据2010年在英国机械工程师学会专题讨论会上介绍的法兰失效案例,简要讨论了螺栓法兰连接设计中应注意的问题,并介绍近期紧凑法兰和螺栓法兰连接标准的一些进展。为了防止法兰密封面泄漏,对重要法兰应进行实际螺栓载荷下的整体塑性变形分析。     

陶瓷球轴承的热弹流润滑分析

建立陶瓷球轴承热弹流润滑的数学模型,利用多重网格法和逐列扫描法,得到陶瓷球轴承的点接触热弹性流体动力润滑完全数值解,并与普通轴承计算结果进行比较。结果表明:转速与载荷会对陶瓷轴承的接触区的压力、膜厚、温度产生影响,其中随着转速的增加,最小膜厚增加,摩擦因数减小,滚动体表面温度下降,而随着载荷的增加,最小膜厚减小,摩擦因数增大,滚动体表面温度上升;在相同的工况参数下,陶瓷球轴承的油膜压力低于普通轴承,膜厚高于普通轴承,轴承内圈、滚动体、中层油膜的温升小于钢质轴承,因而陶瓷轴承的润滑性能更好,使用寿命更长。     

全陶瓷球轴承油润滑特性及其对服役性能影响规律

相比于金属球轴承,全陶瓷球轴承在极端工况下的服役性能更加突出。为了揭示全陶瓷球轴承油润滑特性,提高全陶瓷球轴承的运转性能与使用寿命,以6208CE氮化硅全陶瓷深沟球轴承为例,对其在油润滑工况下所表现出的摩擦、振动、温升等特性进行试验研究,探讨供油量对全陶瓷球轴承润滑状态的影响,并对试验后的全陶瓷球轴承接触微区表层进行解析。研究发现：全陶瓷球轴承油润滑服役过程中,在某个特定工况下存在一个最佳供油量,使得轴承可实现全膜润滑,从而表现出最好的摩擦、振动、温升等特性;小于最佳供油量时,为乏油状态,轴承接触微区存在油-固混合润滑状态;大于最佳供油量时,过多润滑油液会产生的黏滞阻力;相比于载荷,轴承的转速对最佳供油量的取值具有决定性影响。研究成果对于揭示全陶瓷球轴承油润滑特性,丰富其润滑理论与方法具有一定指导意义。     

1000m^3液氨球罐地震失效分析

对5·12汶川地震中一台被震裂的1000m^3液氨球罐进行了应力计算和失效分析。利用有限元法计算了地震时球罐整体结构、支柱、拉杆、液氨出口管线的应力水平,研究销子、地脚螺栓、拉杆、液氨出口管线断裂的可能先后秩序。结果表明,地震时拉杆和销子首先发生断裂失效,随后致使地脚螺栓和液氨出口管线破裂,并g】发液氨介质泄漏。基于此,提出了球罐的支柱、耳板、底板、拉杆、销子、地脚螺栓等设计改进建议,以加强球罐抗震能力。     

Pre-clinical evaluation of ceramic femoral head resurfacing prostheses using computational models and mechanical testing

Ceramic-on-ceramic hip resurfacing can potentially offer the bone-conserving advantages of resurfacing while eliminating metal ion release. Thin-walled ceramic resurfacing heads are conceivable following developments in the strength and reliability of ceramic materials, but verification of new designs is required. The present study aimed to develop a mechanical pre-clinical analysis verification process for ceramic resurfacing heads, using the DeltaSurf prosthesis design as a case study. Finite element analysis of a range of in vivo scenarios was used to design a series of physiologically representative mechanical tests, which were conducted to verify the strength of the prosthesis. Tests were designed to simulate ideal and worst-case in vivo loading and support, or to allow comparison with a clinically successful metallic device. In tests simulating ideal loading and support, the prosthesis sustained a minimum load of 39 kN before fracture, and survived 10 000 000 fatigue cycles of 0.534 kN to 5.34 kN. In worst-case tests representing a complete lack of superior femoral head bone support or pure cantilever loading of the prosthesis stem, the design demonstrated strength comparable to that of the equivalent metal device. The developed mechanical verification test programme represents an improvement in the state of the art where international test standards refer largely to total hip replacement prostheses. The case study's novel prosthesis design performed with considerable safety margins compared with extreme in vivo loads, providing evidence that the proposed ceramic resurfacing heads should have sufficient strength to perform safely in vivo. Similar verification tests should be designed and conducted for novel ceramic prosthesis designs in the future, leading the way to clinical evaluation.     

Design aspects and clinical performance of the thrust plate hip prosthesis

The thrust plate hip prosthesis (TPP) was conceived to maintain the physiological stress distribution in the proximal femur so as to prevent bone atrophy in this region, often encountered after implantation of conventional stem-type prostheses. A thrust plate of TiAlNb is firmly fixed to the neck of the femur by means of a forged CoCrMo bolt introduced through the lateral cortex, just below the greater trochanter, and through the metaphysis. A boss that contains the bolt head rests on the lateral cortex. A proximal extension from the thrust plate terminates in the ball head of the hip joint. Bone remodelling causes the initial prestressing of the structure (primary stability) to decline, but full integration of the thrust plate with the underlying host bone affords secondary stability. A total of 102 TPPs were implanted in the Cantonal Hospital, Chur, Switzerland, from 1992 to 1999 in 84 patients. The TPP was selected particularly for patients of the younger age group (26-76). Through its ability to load the medial cortex of the proximal femur in a physiological manner, the cortical bone in this region is preserved. The mean Harris hip score is 97 points and the survival rate 98 per cent, 144 months post-operatively.     

基于ANSYS／LS—DYNA的陶瓷球轴承仿真与分析

陶瓷球轴承以其自身特点广泛应用于机械、机床、精密仪器、船舶、航空等方面,为了更好的发挥陶瓷球轴承特性．以B7005C滚动轴承为例,运用ANSYS／LS—DYNA软件,建立了陶瓷球轴承的实物模型与有限元模型,实现了陶瓷球轴承的试算与相关参数的显示运动学仿真,分析了陶瓷球轴承运动过程中的转速、载荷、时间与应力、应变、加速度、载荷、振动之间的关系,结果表明,与已有的滚动轴承运动的理论和实际情况基本吻合。     

The Performance of a Hybrid Ceramic Ball Bearing Under High Speed Conditions with the Under-Race Lubrication Method

Large bore (150 mm) hybrid ceramic ball bearings and all-M50 steel bearings were tested with under-race lubrication to compare the heat generation and the temperature rise at speeds up to 2.25 million DN. Furthermore, oil shut-off tests were carried out with both bearings over 2.25 million DN.

The experimental results of the heat generation for both bearings were nearly the same at an axial load of 19.6 kN. at 34.3 kN, the heat generation of the hybrid bearing was lower than that of the M50 steel bearing at low speed. The heat generation of both bearings gradually approached each other with increasing speed and became nearly equal at a speed of 15,000 rpm. The survivability of the hybrid bearing in the oil shut-off test was superior to that of the M50 bearing. These experimental results were explained by the calculation results using a computer analysis software which simulates the kinematics and the performance of ball bearings.     

前稳定杆拉杆球头螺栓断裂问题的分析与解决

为解决道路耐久试验中轿车前稳定杆拉杆球头螺栓断裂问题,对球头螺栓进行了有限元分析.首先由ADAMS/Car悬架多体动力学仿真模型计算得到球头螺栓的载荷,然后使用ABAQUS有限元分析软件计算球头螺栓的应力,仿真结果显示的最大应力位置与实车样件断裂位置基本一致.基于仿真分析结果,对球头螺栓进行结构改进并进行耐久试验验证,试验结果表明,改进设计的球头螺栓是有效和可靠的.