腰椎椎间植骨融合有限元分析

为了评估植骨融合术对腰椎运动和应力分布的影响, 利用影像诊断技术(CT扫描) 和CAD三维重建技术获得人体腰椎三维模型, 椎间盘纤维环采用各向异 性纤维加强超弹性本构模型, 建立了包括椎体、椎间盘和韧带的正常有限元模型以 及L3-L4融合的腰椎L2-L4节段有限元模型, 并通过对比模拟和实验结果验证其有效 性. 利用商业有限元软件ABAQUS/Standard 进行前屈、后伸和轴向旋转载荷情况下 的模拟分析, 对比两种模型在不同状态下的运动范围及应力分布情况. 模拟结果显 示: 在相同的载荷情况下, 融合模型的运动范围和正常模型相比明显偏小; 相邻椎 体的应力分布与正常模型明显不同, 但植骨融合对相邻椎间盘的影响相对较小. 此 外, 小关节对维持脊椎正常生理功能起着重要作用, 小关节功能丧失会使相应节 段的椎间盘髓核压力增大.     

低频振动作用下人体椎间盘多孔弹性单元的研究

建立了 L4/L5段人体腰椎关节的非线性多孔弹性单元有限元模型，并对该模型进行了轴向静力（0Hz)和低频(0.01 Hz、0.1 Hz、0.5 Hz、1 Hz)振动作用各1小时的仿真研究，对比了在不同频率振动作用下人体脊椎组织的多孔弹性单元力学特性。结果表明：在相同振幅和时间内，与低频(0.01Hz、0.1Hz)相比，相对较高频率(0.5 Hz、1 Hz)作用下的椎间盘组织产生的轴向位移较大，髓核和纤维环的孔压应力均呈现逐渐上升的趋势；与此同时，髓核的有效应力逐渐增加，而纤维环的有效应力却逐渐减少；在相对较低频率(0.01Hz、0.1Hz)作用下的各项力学特性指标与静力作用下的相比，差值均在3%以下；加载时间超过600s 后，振动频率的增加更容易使椎间盘轴向位移增大；相对较高频率(0.5 Hz、1 Hz)振动作用下髓核和纤维环内的孔压值逐渐升高，而静力压缩和相对较低频率(0.01 Hz、0.1 Hz)振动作用下孔压值却逐渐降低；不断增加的孔压应力使椎间盘内的体液流失速率变大，导致椎间盘退化。     

基于多孔弹性模型的脊椎关节生物力学特性和体液流动特性研究

建立了L4/L5段人体腰椎关节的非线性多孔弹性有限元模型,并对其施加1000N振动载荷1h,考察在不同的振动频率(1Hz、4Hz、8Hz、11.5Hz、15Hz)下腰椎关节的变形、应力分布和体液流动情况;并对不同频率作用下脊椎组织的生物力学特性进行了对比分析。结果表明,在不同频率振动载荷下,脊椎模型的应力分配、体液流量都呈现与振动载荷不同的周期性波动变化。振动载荷频率等于腰椎关节的固有频率11.5Hz时,椎间盘应力分配和体液流量波动的幅值最短;而振动频率为4Hz、8Hz、15Hz时各项指标波动的幅值比11.5Hz时小。振动过程中,椎间盘内外压力梯度的变化引起体液的流动,振动时间越长,总流失量越大。     

旋转中心刚体-FGM梁刚柔热耦合动力学特性研究

对旋转中心刚体-功能梯度材料(functionally graded material,FGM)梁刚柔热耦合动力学特性进行研究.FGM梁为物理性能参数沿厚度方向呈幂律分布的欧拉伯努利梁.考虑柔性梁的横向弯曲变形和轴向拉伸变形, 并计入横向弯曲变形引起的纵向缩短,即非线性耦合变形量.考虑变截面空心梁在外部高温、内冷通道冷却情况下的热力耦合对系统动力学特性的影响,求解得到FGM梁沿厚度方向分布的温度场, 进而在本构关系中计入热应变.采用假设模态法对柔性梁变形场进行离散,运用第二类拉格朗日方程推导得到系统的刚柔热耦合动力学方程,并编制动力学仿真软件, 然后通过仿真算例对系统的动力学问题进行研究.结果表明:不同截面梁动力学响应差异较大, 因此需对实际系统合理建模;大范围运动已知时, 考虑热冲击载荷的FGM梁将有效抑制横向弯曲变形,而大范围运动恒定时随热冲击的叠加会出现高频振荡; 大范围运动未知时,外力矩和热冲击载荷相互作用产生热力耦合效应, 导致系统呈现高频振荡,同时与中心刚体大范围旋转运动产生刚柔热耦合效应.      

DP钢板应变路径多步演变下的弹塑性力学行为

针对DP高强双相钢板在复杂载荷作用下的弹塑性力学特征,提出利用三步拉伸力学实验,对比分析单轴循环加载和非等轴加载下材料的各向异性硬化、永久软化和弹性模量衰减特性等力学行为,揭示应变路径多步演变下的弹塑性力学特性.研究结果表明:材料再加载初期的瞬态行为与应变路径有关,在初期瞬态阶段显示出明显的各向异性,且再加载角度、预应...     

考虑热流固耦合作用的多孔介质孔隙尺度两相流动模拟

为了研究深层油气资源在岩石多孔介质内的运移过程, 使用一种基于Darcy-Brinkman-Biot的流固耦合数值方法, 结合传热模型, 完成了Duhamel-Neumann热弹性应力的计算, 实现了在孔隙模拟多孔介质内的考虑热流固耦合作用的两相流动过程. 模型通过求解Navier-Stokes方程完成对孔隙空间内多相流体的计算, 通过求解Darcy方程完成流体在岩石固体颗粒内的计算, 二者通过以动能方式耦合的形式, 计算出岩石固体颗粒质点的位移, 从而实现了流固耦合计算. 在此基础上, 加入传热模型考虑温度场对两相渗流过程的影响. 温度场通过以产生热弹性应力的形式作用于岩石固体颗粒, 总体上实现热流固耦合过程. 基于数值模型, 模拟油水两相流体在二维多孔介质模型内受热流固耦合作用的流动过程. 研究结果表明: 热应力与流固耦合作用产生的应力方向相反, 使得总应力比单独考虑流固耦合作用下的应力小; 温度的增加使得模型孔隙度增加, 但当注入温差达到150 K后, 孔隙度不再有明显增加; 温度的增加使得水相的相对渗流能力增加, 等渗点左移.      

一种新的振动叠加气动耦合加载技术

飞机机动飞行时,机体结构受到随机振动叠加气动的耦合载荷作用,有可能迅速产生破坏。为了考核在这种振动环境下飞机的结构强度及使用寿命能否达到设计要求,需要提供有效的地面试验验证手段和可靠的试验数据。本文研究了一种振动叠加气动的耦合载荷加载技术,通过液压球头传递振动载荷,同时通过气囊施加气动载荷,并设计进行了原理性验证试验。试验结果表明,这种耦合载荷加载技术可以避免过多改变试件自身的振动特性,同时可精确实现振动叠加气动的耦合载荷加载,真实模拟试验件的振动工作环境。此项技术可应用于现代战机的地面结构强度研究。     

航空铆钉动态加载失效实验

为研究航空铆钉连接元件在动态加载下的失效模式,依托高速液压伺服材料试验机,通过特殊设计的实验夹具,进行了6类航空铆钉在不同加载速度和不同加载模式下的动态失效实验,获得了铆钉元件在纯拉伸加载、纯剪切加载、30°拉-剪耦合加载和60°拉-剪耦合加载状态下的失效实验数据。实验结果表明,铆钉元件的失效模式和失效载荷与加载速度、载荷的作用形式密切相关,并基于实验结果拟合得到铆钉元件的失效本构参数,获得了可表征铆钉在一般情形下失效的本构方程。     

航空发动机叶片-机匣碰摩热-结构耦合仿真

针对转静子碰摩过程中的摩擦热效应现象,建立了叶片-机匣的碰摩热-结构耦合模型。采用热-结构耦合单元,对航空发动机叶片-机匣进行了碰摩热效应特性研究。考虑摩擦因数及旋转过程中的离心力作用,对瞬态-热结构耦合场进行了有限元分析,研究了结构在温度场作用下的热-结构耦合应力和温度分布。与纯机械载荷下的应力分布对比,发现了碰摩热效应在叶片与机匣上的扩散规律。研究结果表明,考虑摩擦热效应时由于热应力的作用,导致结构的总应力水平升高进而产生热变形,从而使故障进一步恶化。由此可见,碰摩热效应的影响在实际航空发动机振动分析中不能忽视。     

拉扭耦合作用下柱形纤维与基底的界面黏附性能研究

受壁虎刚毛可逆黏附性能的启发,本文建立了单根弹性圆柱纤维与刚性基底黏附接触的理论和数值模型,同时考虑了拉伸和扭转载荷的耦合作用及纤维半径对界面黏附性能的影响.研究发现耦合载荷作用下柱形纤维同样存在一个临界半径,当纤维半径小于该临界尺寸时,界面应力达到均匀的理论强度分布,接触边界应力集中消失,出现缺陷不敏感现象;当纤维半径大于该临界尺寸时,界面以裂纹扩展而失效.在耦合载荷作用下纤维的临界半径小于纯拉伸而大于纯扭转时的临界尺寸,且该临界半径随着施加扭转载荷的增大而减小.表明在纯拉伸载荷下使界面黏附强度达到最优的柱形纤维,在拉伸和扭转载荷耦合作用下,由于界面失效形式的转变使界面易发生脱黏,并且界面脱黏时的拉脱力随着扭转载荷的增大而减小,理论和数值结果一致.本文结果进一步应用揭示了壁虎可以通过调控施加在其最小黏附单元上的载荷形式实现纯拉伸载荷下强黏附及耦合载荷下易脱黏的力学机制.     

Deduction of Spinal Loading from Vertebral Body Surface Strain Measurements

The lumbar intervertebral disc, the apparent nexus of low back pain, undergoes biomechanical changes during its degeneration which are as yet poorly understood. In an effort to ultimately examine in vivo daily activity loads across intervertebral discs, we engaged in the following methodological study. The aim of this research was to correlate vertebral body surface strains with the loads across a lumbar spine segment. Rosette strain gages were affixed anterolaterally on L4 and L5 in a macaque monkey model. These tissues were loaded axially and with sagittal plane moments and the principal strains were compared with the applied loads. Predictable axial and sagittal plane loading profiles were found for similar strain measurements and the system was found to be robust through freezing and thawing. These results support future research aimed at quantifying the in vivo disc mechanics of healthy and degenerate tissues in an attempt to develop prevention or intervention strategies to ease those afflicted with low back pain.     

Biomechanical analysis of lumbar interbody fusion with an anisotropic hyperelastic model for annulus fibrosis

Based on computed tomography scanning images, this paper developed a detailed finite element model for the human L2–L4 lumbar spine segment with or without L3–L4 fusion. The model included vertebrae, intervertebral disc, facet articulating surfaces and various ligaments. A previously developed hyperelastic fibre-reinforced constitutive model was used to characterize the material property of annulus fibrosus. Numerical results of L3–L4 motion unit such as load–displacement curves and nucleus pressure were compared with experimental data to validate the FE model. The normal and fused lumbar spine segments under various loading conditions, such as flexion, extension and axial rotation, were analysed. The motion range and stress distribution of the L2–L4 models under different loading conditions were then obtained to investigate the effect of lumbar fusion operation. It was shown that under the same loading condition, the fused model had a much smaller body motion range. Interbody fusion brought out obviously different stress distribution in adjacent intervertebral disc annulus fibrosus. And it also increased the intradiscal pressure of adjacent intervertebral disc significantly.     

人体腰椎生物力学的某些基本问题

本文就人体腰段脊柱生物力学的某些基本问题的研究现状与进展进行述评。介绍了腰椎各组成部分包括椎体、椎间盘、椎弓、韧带以及脊髓的力学性能,对其运动学和运动力学进行了讨论,最后就腰椎的力学模型主要是有限元模型的研究作了简单的回顾。      

A semi-experimental stress analysis of the human intervertebral disk in compression

The intervertebral disk is a heavily loaded component of the human body. In the lumbar region, in vivo measurements by Nachemson (1966, 1970)^4–5 show compressive loads in the range of 1000–3000 Newton under normal living conditions. Determination of stresses in intervertebral disks is, thus, a relevant biomechanical problem that has been studied experimentally and from a clinical point of view by Nachemson (1960, 1963, 1966, 1970).^2–5 Galante (1967)¹ investigated tensile properties of the lumbar annulus fibrosus. Nachemson found the state of stress in the nucleus pulposus to be hydrostatic, and Galante's investigation revealed a considerable inhomogeneity of the material in the annulus fibrosus. In this paper, the effect of material inhomogeneity on the distribution of stress in annulus fibrosus is studied. On the basis of previous experimental findings and complementary measurements of the lateral pressure distribution through the disk, the tangenital and radial stress distributions are determined theoretically. The results of the theoretical analysis show that inhomogeneity influences the distribution of tangential stress considerably, whereas only heavy lateral pressure gradients disturb this same stress distribution to any significant extent. Experimental results show that high pressure gradients may well be present in annulus. Only pure compression of the disk is considered.     

Simulating the sensitivity of cell nutritive environment to composition changes within the intervertebral disc

Altered nutrition in the intervertebral disc affects cell viability and can generate catabolic cascades contributing to extracellular matrix (ECM) degradation. Such degradation is expected to affect couplings between disc mechanics and nutrition, contributing to accelerate degenerative processes. However, the relation of ECM changes to major biophysical events within the loaded disc remains unclear. A L4-L5 disc finite element model including the nucleus (NP), annulus (AF) and endplates was used and coupled to a transport-cell viability model. Solute concentrations and cell viability were evaluated along the mid-sagittal plane path. A design of experiment (DOE) was performed. DOE parameters corresponded to AF and NP biochemical tissue measurements in discs with different degeneration grades. Cell viability was not affected by any parameter combinations defined. Nonetheless, the initial water content was the parameter that affected the most the solute contents, especially glucose. Calculations showed that altered NP composition could negatively affect AF cell nutrition. Results suggested that AF and NP tissue degeneration are not critical to nutrition-related cell viability at early-stage of disc degeneration. However, small ECM degenerative changes may alter significantly disc nutrition under mechanical loads. Coupling disc mechano-transport simulations and enzyme expression studies could allow identifying spatiotemporal sequences related to tissue catabolism.     

A non-linear finite element model of human L4-L5 lumbar spinal segment with three-dimensional solid element ligaments

This paper establishes a non-linear finite element model (NFEM) of L4-L5 lumbar spinal segment with accurate three-dimensional solid ligaments and intervertebral disc. For the purpose, the intervertebral disc and surrounding ligaments are modeled with four-nodal three-dimensional tetrahedral elements with hyper-elastic material properties. Pure moment of 10 N·m without preload is applied to the upper vertebral body under the loading conditions of lateral bending, backward extension, torsion, and forward flexion, respectively. The simulate relationship curves between generalized forces and generalized displacement of the NFEM are compared with the in vitro experimental result curves to verify NFEM. The verified results show that: (1) The range of simulated motion is a good agreement with the in vitro experimental data; (2) The NFEM can more effectively reflect the actual mechanical properties than the FE model using cable and spring elements ligaments; (3) The NFEM can be used as the basis for further research on lumbar degenerative diseases.     

基于Hangmann骨折的植骨融合钢板内固定术有限元稳定性分析

Hangmann骨折是近年来发病率逐渐上升的上部颈椎损伤之一。植骨融合钢板内固定术作为一种较新的手术方案刚刚开始在国内采用。本文采用基于医学影像的快速自动三维有限元模型的构建方法,建立了上颈椎C2～C4两个运动节段的三维有限元模型,对上颈椎正常状态、植骨融合钢板系统内固定术方案在模拟生理荷载下的三维六自由度的稳定性、内固定器植入后的应力情况进行了计算和比较分析,并通过实验验证了内固定手术对上颈椎的生物力学稳定性和内固定器的力学疗效特征。本文结果显示：对Hangmann骨折治疗,植骨融合钢板系统内固定技术是一个较好的可供选择的措施之一。     

基于双向流固耦合的超空泡射弹入水研究

超空泡射弹通过超空泡减阻技术在水下高速长距离航行, 是对抗水下近距离威胁的有效手段. 为了扩大防御范围、增加杀伤力, 超空泡射弹具有很高的发射速度. 高速超空泡射弹在入水时中受到极大的冲击载荷, 发生显著的结构变形, 结构变形与流场之间存在相互影响和作用, 常规的基于刚体假设的仿真研究方法不再适用. 为了研究高速超空泡射弹入水过程中的结构变形及其对流体动力特性的影响, 通过耦合流体力学求解器和结构动力学求解器, 建立了射弹高速入水双向流固耦合仿真模型, 并通过与文献中的试验结果进行对比验证了该模型空泡形态计算方法和耦合方法的准确性. 使用双向流固耦合的方法对高速射弹在不同初始攻角入水过程中的超空泡流动特性及结构变形特性进行了数值模拟研究, 通过对比流固耦合模型与刚体模型的计算结果, 得到了超空泡射弹的结构弯曲变形对流体动力载荷的影响. 研究结果表明: 高速射弹入水过程中流固耦合效应对超空泡流型及流体动力载荷的计算结果有显著影响; 本文所研究的射弹在考虑流固耦合效应, 带攻角垂直入水两倍弹长的范围内, 超空泡射弹的流体动力载荷与弯曲变形之间形成正反馈; 高速超空泡射弹在入水过程中受到的流体动力载荷及弹体应力应变随入水初始攻角的增加显著增大, 研究对象在初速1400m/s的条件下入水时, 当初始攻角不超过2°时不存在结构安全性问题.