THREE-DIMENSIONAL FINITE ELEMENT SIMULATION OF TOTAL KNEE JOINT IN GAIT CYCLE

Based on CT scanning pictures from a volunteer＇s knee joint, a three-dimensional finite element model of the healthy human knee joint is constructed including complete femur, tibia, fibular, patellar and the main cartilage and ligaments. This model was validated using experimental and numerical results obtained from other authors. The pressure distribution of contact surfaces of knee joint are calculated and analyzed under the load action of ‘heel strike＇, ‘single limb stance＇ and ‘toe-off＇. The results of the gait cycle are that the contact areas of medial cartilage are larger than that of lateral cartilage; the contact force and contact areas would grow larger with the load increasing; the pressure of lateral meniscus is steady, relative to the significant variation of peak pressure in medial meniscus; and the peak value of contact pressure on all components are usually found at about 4570 of the gait cycle.

Investigation of contact behavior on a model of the dual-mobility artificial hip joint for Asians in different inner liner thicknesses

BACKGROUND The four components that make up the current dual-mobility artificial hip joint design are the femoral head,the inner liner,the outer liner as a metal cover to prevent wear,and the acetabular cup.The acetabular cup and the outer liner were constructed of 316L stainless steel.At the same time,the inner liner was made of ultra-high-molecular-weight polyethylene(UHMWPE).As this new dual-mobility artificial hip joint has not been researched extensively,more tribological research is needed to predict wear.The thickness of the inner liner is a significant component to consider when calculating the contact pressure.AIM To make use of finite element analysis to gain a better understanding of the contact behavior in various inner liner thicknesses on a new model of a dual-mobility artificial hip joint,with the ultimate objective of determining the inner liner thickness that was most suitable for this particular type of dual-mobility artificial hip joint.METHODS In this study,the size of the femoral head was compared between two diameters(28 mm and 36 mm)and eight inner liner thicknesses ranging from 5 mm to 12 mm.Using the finite element method,the contact parameters,including the maximum contact pressure and contact area,have been evaluated in light of the Hertzian contact theory.The simulation was performed statically with dissipated energy and asymmetric behavior.The types of interaction were surface-to-surface contact and normal contact behavior.RESULTS The maximum contact pressures in the inner liner(UHMWPE)at a head diameter of 28 mm and 36 mm are between 3.7-13.5 MPa and 2.7-10.4 MPa,respectively.The maximum von Mises of the inner liner,outer liner,and acetabular cup are 2.4–11.4 MPa,15.7–44.3 MPa,and 3.7–12.6 MPa,respectively,for 28 mm head.Then the maximum von Mises stresses of the 36 mm head are 1.9-8.9 MPa for the inner liner,9.9-32.8 MPa for the outer liner,and 2.6-9.9 MPa for the acetabular cup.A head with a diameter of 28 mm should have an inner liner with a thickness of 12 mm.Whereas the head diameter was 36 mm,an inner liner thickness of 8 mm was suitable.CONCLUSION The contact pressures and von Mises stresses generated during this research can potentially be exploited in estimating the wear of dual-mobility artificial hip joints in general.Contact pressure and von Mises stress reduce with an increasing head diameter and inner liner’s thickness.Present findings would become one of the references for orthopedic surgery for choosing suitable bearing geometric parameter of hip implant.

A research on the contact stress of roller bearing based on crowning analysis

According to elastic contact theory, contact model between roller and race is established. Compared with the Hertz results, the results are proved, based on which contact stress distribution of different crowning and initial contact length is given, then the appropriate value is derived. On the basis, inertia force and different radial force is given into consideration. Via analysis, it con- cludes that under balanced pure radial load condition the largest contact stress between roller and race increases along with crowning value increasing. With the same crowning value, the largest contact stress between roller and race decreases in the first and increases at the end along with initial contact length increasing. Contact stress between roller and outer race increases along with revolution speed increasing.

Finite element analysis of tibio-femoral contact mechanics of a customised knee spacer

With one-third of patients having osteoarthritis predominantly in one compartment of the knee,unicompartmental knee spacers have been introduced as a less invasive alternative to total knee replacement.However,patients with the knee spacer implanted were seen to have persistent pain,resulting in high revision rates.A static finite element model of the knee and its interaction with a knee spacer implant at full extension and 90°flexion was used to investigate the tibio-femoral contact mechanics of the knee joint after a knee spacer surgery.Three different knee spacer designs(contoured,flat and C-shaped)were modelled and prescribed with cobalt-chrome,ultra-high molecular polyethylene and polyurethane material properties.The results suggested that a softer spacer is generally preferred as this helps in the conformity of knee spacer to the condyle,effectively distributing the load subjected to the implant.Flat spacers that result in high stresses resulting from lower contact areas should be avoided.

Finite-Element Analysis of Parts Stress State of Tight Joint Assembled by Press Fitting

This paper includes descriptions of the stress distribution regularities in the tight joint parts, regularities of the stress state changes in the contact region along coupling length, stress concentration factors, levels of additional stresses caused by press fitting. Distributions of stress intensity, axial stress, contact pressure, tangent stress in parts and in contact zone along coupling length are considered. Calculation results obtained by three approaches: Lame relationships, FEM without considering assembly method, FEM with considering press fitting process are analyzed and compared. The adequacy of research carried out is confirmed.

Numerical analysis of stress distribution in the upper arm tissues under an inflatable cuff：Implications for noninvasive blood pressure measurement

An inflatable cuff wrapped around the upper arm is widely used in noninvasive blood pressure measurement.However, the mechanical interaction between cuff and arm tissues, a factor that potentially affects the accuracy of noninvasive blood pressure measurement, remains rarely addressed. In the present study, finite element（FE） models were constructed to quantify intra-arm stresses generated by cuff compression, aiming to provide some theoretical evidence for identifying factors of importance for blood pressure measurement or explaining clinical observations. Obtained results showed that the simulated tissue stresses were highly sensitive to the distribution of cuff pressure on the arm surface and the contact condition between muscle and bone. In contrast, the magnitude of cuff pressure and small variations in elastic properties of arm soft tissues had little influence on the efficiency of pressure transmission in arm tissues. In particular, it was found that a thickened subcutaneous fat layer in obese subjects significantly reduced the effective pressure transmitted to the brachial artery, which may explain why blood pressure overestimation occurs more frequently in obese subjects in noninvasive blood pressure measurement.

A modified logarithmic spiral method for determining passive earth pressure

In this study, a modified logarithmic spiral method is proposed to determine the passive earth pressure and failure surface of cohesionless sloping backfill, with presence of wallesoil interface friction. The proposed method is based on a limit equilibrium analysis wherein the assumed profile of the backfill failure surface is a composite of logarithmic spiral and its tangent. If the wallesoil interface is smooth, a straight line does not need to be assumed for the failure surface. The geometry of the failure surface is determined using the Mohr circle analysis of the soil. The resultant passive earth thrust is computed considering equilibrium of moments. The passive earth pressure coefficients are calculated with varied values of soil internal friction angle and cohesion, wall friction angle and inclination angle, and sloping backfill angle. This method is verified with the finite element method(FEM) by comparing the horizontal passive earth pressure and failure surface. The results agree well with other solutions, particularly with those obtained by the FEM. The implementation of the present method is efficient. The logarithmic spiral theory is rigorous and self-explanatory for the geotechnical engineer.

非均布压力作用下纯弯曲孔道预应力摩阻损失

为获得更准确的孔道预应力摩阻损失计算方法,保证桥梁结构设计的有效预应力和桥梁结构的安全运行。根据赫兹接触理论,综合考虑摩擦力、接触压力与张拉力间的相互作用,导出了纯弯曲孔道在非均匀压力作用下摩阻损失公式。通过有限元软件分析不同参数对摩阻损失计算值的影响。通过实际工程的摩阻试验探究纯弯曲孔道在非均匀压力下预应力摩阻损失的具体分布规律,并通过规范公式、推导公式的理论计算值与现场实测数据的偏差,验证公式的合理性。结果表明:弯曲角度小于120°、摩擦系数为0.2~0.4范围内,推导公式计算值更接近实际情况;随着张拉应力和弯曲角度的增加,利用推导公式计算得到的摩阻损失值更接近实测结果。

矿用重载轮胎接地印痕的研究

以14.00R25宽体自卸车轮胎为例,通过轮胎使用情况调研,结合实验室测试和轮胎有限元仿真,研究矿用重载轮胎接地印痕及接地压力分布。结果表明:宽体自卸车轮胎接地印痕形状应接近矩形且接地压力分布均匀;影响轮胎接地印痕及接地压力分布的主要因素为断面高宽比、胎冠弧半径和弧度高、带束层角度和宽度、花纹沟壁角度和花纹沟宽度等。通过有限元仿真优化设计可避免轮胎出现花纹掉块和非均匀磨损等问题,提高设计效率。

新型弧形板簧支撑非充气轮胎的有限元分析

设计一种以弧形等厚板簧为主要承载部件的新型非充气轮胎,建立其有限元模型,仿真模拟静态径向加载与稳态纯滚动工况,得出轮胎径向刚度和径向力,对接地压力参数进行评价,计算出轮胎有效滚动半径。结果表明:在静态径向加载条件下,轮胎径向力与径向位移近似线性正相关,径向刚度和径向力随板簧厚度增大而增大;轮胎接地印痕中心出现应力集中现象,板簧越厚则平均接地压力越大,胎面不均匀磨损程度越高;轮胎有效滚动半径随径向负荷增大线性减小。本研究可为非充气轮胎性能分析或者结构优化提供参考。

湿热耦合条件下混凝土墙内的孔隙压力研究

基于高温下混凝土的湿热本构模型对火灾下混凝土墙内孔隙压力的发展及其影响因素进行研究.主要采用ABAQUS对墙体进行热分析,并在分析步中调用子程序进行湿热耦合,求解墙体内部孔隙压力的分布.在该计算模型中,考虑了高温下混凝土内部孔隙中水的相态转变及质量守恒、水泥浆体的脱水、混凝土的高温热损伤等因素.在与试验结果对比验证模型的有效性与准确性后,给出了一个案例研究以对火灾下混凝土墙内孔隙压力的发展进行分析,并评估了由孔隙压力导致混凝土发生爆裂的可能,最后探讨了升温制度、混凝土骨料类型、初始渗透率、初始孔隙率等因素对火灾下混凝土墙内孔隙压力的影响.研究结果表明:混凝土墙体受火后,其内部的孔隙压力会在较短的时间内迅速上升,这导致墙体在火灾前期可能出现较大的剥落风险;受火后墙体在厚度方向上往往存在着两处可能由孔隙压力触发墙体剥落的点.研究结果还表明火灾作用下混凝土墙体的孔隙压力发展受升温制度的影响显著,在升温速率最快的炔类火作用下的混凝土墙体最快到达了孔隙压力峰值,且相较于ASTM-E119和ISO-834升温制度,炔类火灾作用下混凝土墙内的孔隙压力峰值分别提高了16.82%和5.81%;混凝土骨料类型对混凝土墙内的孔隙压力发展的影响相对较小;采用硅质骨料的混凝土墙体内部产生的孔隙压力峰值仅高出钙质骨料混凝土3.14%;混凝土初始渗透率同样对混凝土墙内孔隙压力的发展影响显著,混凝土初始渗透率越小,墙体内部产生的孔隙压力越大;混凝土的内部初始孔隙率对受热后墙体内部孔隙压力发展的存在次要影响,随着初始孔隙率的增大,墙体的孔隙压力呈现非线性下降趋势.

不同耦连比的联肢钢板仓组合剪力墙抗震性能有限元分析

耦连比是影响联肢剪力墙结构抗震性能的重要参数。为研究联肢体系下新型钢板仓组合剪力墙的抗震性能和破坏特征,并确定该种结构较为适宜的设计耦连比取值范围,借助ABAQUS软件建立了10个不同耦连比的联肢钢板仓组合剪力墙有限元分析模型,并进行了单调推覆和循环往复加载。结果表明,不同耦连比下,联肢钢板仓组合剪力墙的抗震性能以及破坏特征存在明显差异。耦连比过小,钢连梁将首先破坏并造成联肢体系失效;耦连比过大,组合墙肢将在钢连梁耗能不充分的情况下提前破坏。因此,建议将塑性耦连比的取值范围控制在45%~50%之间,并将其与弹性耦连比的比值限制在90%以下,以确保钢连梁先于组合墙肢屈服,从而提高结构的抗震性能。

芯轴式套管悬挂器金属密封设计及性能分析

为了避免芯轴式套管悬挂器密封失效,根据芯轴式套管悬挂器的结构及密封工作原理,设计了一种新型的金属密封结构。建立了芯轴式悬挂器密封性能有限元模型,研究了不同顶丝压力和套管悬重对密封锥面变形及接触压力的影响。结果表明:随顶丝推力的增加,上、下密封锥面上平均接触压力都增加,有利于实现密封;随套管悬重的增加,上密封锥平均接触压力增加,下密封锥平均接触压力减小,除下内锥面外,均能满足密封要求。研究结果可为芯轴式悬挂器密封部位的结构设计提供参考。

石墨填料垫片变形特性研究

针对石墨填料垫片会在使用过程中发生边角撕裂的问题,本文基于密封试验台结构及材料的弹塑性,建立了垫片系统的有限元模型,模拟了垫片的压缩回弹过程,并通过压缩回弹实验验证了模型的准确性。通过分析石墨填料垫片在不同尺寸、压缩率及侧面间隙的条件下,加卸载过程中的压缩回弹曲线变化,验证了石墨填料垫片边角应力集中现象。通过分析上密封面和侧密封面的应力分布,阐述了石墨填料垫片边角撕裂是由于上表面两侧过大的应力峰值导致的,且包边结构能明显改善垫片压缩后的边角撕裂问题。

压接式IGBT组件的压力均匀性仿真分析

针对压力不均会导致压接式IGBT模块不同区域的接触电阻和接触热阻不同,进而导致芯片局部温度过高和使用寿命降低等问题,本论文采用有限元方法建立压接式IGBT组件在接触条件下的有限元模型,对比分析实际结构与理想条件的接触压强,并提出改进方案。结果表明:原始方案的中心区域芯片接触压强可达44.96MPa,是理想条件接触压强的1.98倍,压力分布不均问题可以从均匀化轴向载荷和增加散热器四周刚度两个方向解决;加工散热器拱度的改进方案可以降低中心区域芯片的接触压强,但四周的芯片总是承受较大的轴向载荷;增加散热器厚度的改进方案可使四周的芯片保持接触,但会增加散热器的重量与热阻;增加支撑环的改进方案可使芯片接触压强降低44%,达到与理想条件接近的受力状态。利用接触压强的仿真分析方法可为压接式IGBT组件结构优化设计提供依据。

筒承式风机基础设计分析

山区复杂地形风电场工程,在保证边坡稳定和风机运行安全的前提条件下,为减少开挖工程量,实现对环境的最少破坏,提出了筒承式这一新型风机基础结构形式。本文研究了筒承式风机基础概念设计与受力特点,基于CFD技术精细化分析了筒承式风机基础上侧边坡高差影响,研究了筒承式风机基础主要控制标准及荷载,采用有限元分析方法进行结构承载力分析,提出了施工期间按基础强度分段施工的方法。按照强度折减系数法等方法研究基础与岩土地基协同作用与变形。经对比分析,筒承式风机基础和风机平台综合效益明显。

子午线轮胎静态力学特性的有限元仿真

以205/55R18子午线轮胎为例,采用有限元仿真方法分析子午线轮胎的静态力学特性。建立有限元模型,并验证该模型的可靠性,在此基础上分析径向负荷、充气压力和接地摩擦因数对轮胎接地压力、纵向刚度和横向刚度的影响。结果表明:轮胎的径向负荷增大时,轮胎的接地压力、纵向刚度和横向刚度相应增大;轮胎的充气压力增大时,轮胎的接地面积减小,接地压力和刚度增大;通过增大摩擦因数可以提高轮胎的接地性能和操控性能,但摩擦因数的影响程度相比于径向负荷和充气压力较小。

外侧楔形鞋垫对足踝生物力学影响的有限元分析

目的 探究外侧楔形鞋垫对足踝内部组织(包括足骨、关节和韧带)的生物力学影响。方法 建立并验证足踝-鞋垫-地面三维有限元模型,探究步态3个关键瞬间赤足模型和鞋垫干预模型的足底压力分布、关节接触压力、跖骨及主要韧带的应力。结果 5°外侧楔形鞋垫模型足底峰值压力比赤足模型减小65.8%。鞋垫干预使楔舟关节处峰值接触压力减小;距下关节处峰值接触压力和第4、5跖骨处峰值应力增大。结论 本研究量化评估了外侧楔形鞋垫对足踝各部分的生物力学影响,提出了可适当减小外侧楔形鞋垫第4、5跖骨处倾斜角度的设计建议。

基于有限元的防蠕变O形圈预紧力研究

针对伺服电机浮动端轴承出现的跑外圈问题,通常采用增加橡胶O形圈来进行相应处理。由于O形圈的尺寸规格,以及O形圈的开槽尺寸和公差,直接会影响到防跑圈力矩,在选用O形圈规格和设计O形圈槽的尺寸时需要核算相关内容。采用有限元法,对不同硬度和不同沟槽尺寸下O形圈提供的预紧力和防跑圈力矩进行分析计算,该计算方法对O形圈的选型和O形圈沟槽的设计具有一定的指导意义。

薄壁复合材料耐压筒在水下潜器中的应用研究

围绕国家海洋战略规划,为解决水下无人潜航器对轻量化、高强度、高稳定性耐压结构关键部件的迫切需求,本文通过对碳纤维复合材料进行优化选材,研制不同长度的薄壁复合材料满足深海耐压需求。采用ANSYS建立有限元模型,对薄壁耐压筒进行结构设计及强度、稳定性计算。并通过深海压力模拟测试装置对1000 mm和500 mm耐压筒开展静水压力试验,验证其结构稳定性。有限元分析表明,各向应力均有1.6倍以上安全系数可满足强度要求;在补强后1000 mm和500 mm复合材料耐压筒在外压作用下屈曲系数分别为1.95和2.0,大于1.8要求值,可满足刚度使用需求。随后在深海压力模拟测试装置对耐压筒进行2 MPa外压测试下,1000 mm和500 mm耐压筒均具有耐压生存能力。本文研制的不同长度的薄壁复合材料满足技术要求,为无人潜水器重要组成部件提供了一种有效的解决方案。