基于可行方向法的脂肪组织本构模型参数反求优化

目的研究脂肪组织在中等应变率下本构模型及其参数反求。方法基于脂肪组织力学性能实验,通过有限元方法重构脂肪组织压缩实验,并对常见表征脂肪组织的本构模型进行参数筛选。结合最优化方法中的可行方向法(method of feasible direction,MFD),进行中应变率下脂肪组织本构模型相关参数的反求。结果中应变率(260 s~(-1))下黏弹性本构模型相比Ogden本构模型更适合表征脂肪组织的力学响应,并反求得到适用于仿真的本构模型参数。结论中等应变率下黏弹性本构模型更适合表征脂肪组织力学响应。研究结果为汽车碰撞有限元仿真中探究人体脂肪组织对人体损伤的影响提供参考。     

后碰撞中人体颈椎骨的有限元分析

对建立并验证的全颈椎有限元模型进行仿真以分析后碰撞中颈部的响应及其损伤机制.模型包括C1-T1的8块椎骨以及椎间盘、韧带和肌肉等软组织,共35 042个节点和22 618个单元.运用后碰撞志愿者实验数据对模型进行仿真,得到各椎骨间相对转角、各椎骨应力、应变曲线及应力云图.颈部S形曲线、C形曲线得到体现;最大应力、应变主要发生在颈部过度伸展过程中,上位颈椎中C2应力、应变较大,而下位颈椎中T1数值最大,受力较大值发生在椎体上下表面及其关节突关节面上,易产生多部位骨折.分析结果可为人体颈部损伤的预防、诊断和治疗提供理论依据.     

坐姿下不同组织压力性损伤生物力学研究

目的 探讨坐姿下臀部压力性损伤易发部位以及不同软组织的生物力学响应,为有效预防深层组织压力性损伤提供参考。 方法 基于臀部 CT 扫描数据,建立坐位臀部有限元模型,包括骨骼、肌肉、脂肪和皮肤组织及坐垫模型,利用生死单元模拟组织损伤。 对比实验坐垫界面压力测量数据与有限元模拟结果,验证模型有效性。 模拟坐位力学状态,研究软组织的应力、应变情况,分析不同软组织中的压应力及超出极限值后可能造成的损伤情况。结果 通过对比坐垫模型仿真结果与实验界面压力测量结果,证明模型有效。 坐位时坐骨结节下方软组织区域出现应力集中现象。 其中,臀大肌组织中的横向压应力峰值约为 38 kPa,剪切应力峰值约为 3. 4 MPa;而脂肪组织中的最大压应力与剪切应力峰值分别为 22 kPa 与 4. 5 MPa,均未出现在坐骨结节正下方。 结论 软组织受到一定时间和大小的压力载荷作用,可能出现深层组织损伤。 当保持坐姿一定时间后,应及时变换体位,以降低压力性损伤出现的概率。 研究结果为预防压力性损伤提供生物力学依据,具有重要的临床研究价值。     

人体脊椎骨粘弹性实验研究

本文通过对人体椎骨进行粘弹性实验研究。定量地给出脊椎骨应力、应变和时间相关的不同效应。根据线性粘弹性理论拟合了实验曲线。并给出了人体椎骨的应力松驰和蠕变方     

脑组织压缩力学性能和本构模型

目的 研究脑组织在不同应变率下的压缩力学性能和本构模型。方法 使用电子万能试验机对猪脑组织白质和灰质开展准静态压缩和中速压缩试验,获得脑组织不同应变率下的应力-应变曲线。采用Ogden本构模型对试验曲线进行拟合,确定本构模型参数,并在有限元软件中进行仿真验证。结果 脑组织应力-应变曲线呈现非线性特征,具有较强的应变率相关性和敏感性。压缩至0.6应变时,在5×10-4~5×10-2 s-1应变率下,白质和灰质的应力分别增加102%和129%,在1~1.5 s-1应变率下则分别增加50.7%和54.6%;1.5 s-1应变率下白质、灰质应力比5×10-4 s-1应变率下分别增加347%、413%。Ogden模型拟合下的R2>0.99,仿真结果与试验结果误差在15%以内,验证了模型的有效性。结论 研究结果有助于实现对脑组织变形的预测,为建立更加科学合理的人体模拟靶标以及在设计和改进颅脑防护装备上提供准确的理论依据。     

拦阻着舰过程中飞行员头颈部的动力学响应

目的分析航母舰载机拦阻着舰过程中飞行员在佩戴和不佩戴头盔时的头颈部动力学响应以及主要肌肉应变量。方法建立包括头部、7个颈椎和2个胸椎共10个刚体的人体头颈部的多体动力学模型;采用集总参数法描述韧带、椎间盘等软组织的力学特性;应用非线性应力-应变关系描述人体头颈部15组肌肉的力学特性。采用多组汽车碰撞过程人体头颈部动力学响应实验数据对模型进行验证。结果获取了拦阻着舰过程飞行员头部的过载曲线和15组肌肉的应变,结果表明颈夹肌拉伸程度最大,在不佩戴头盔时其应变可达50%,佩戴2.7 kg头盔时其应变可达56%。结论佩戴防护头盔会增加飞行员在拦阻着舰过程的颈部肌肉拉伸,仿真结果可用于进一步的损伤评估。     

弹道明胶力学性能测试

目的研究弹道明胶力学性能,进而建立动态本构模型,为采用数值计算方法开展创伤弹道学相关研究奠定基础。方法首先制备出10℃下20%弹道明胶试件,随后采用万能材料试验机和铝制霍普金森杆测试弹道明胶的准静态和动态压缩力学性能。结果获得10℃下20%弹道明胶准静态和动态压缩应力-应变曲线;当应变为0.45时,7组应变率(10~(-3)、10~(-2)、10~(-1)、5 800、7 900、10 400、13 000 s~(-1))下的真实应力分别为0.041、0.083、0.194、14.515、31.496、55.597、96.678 MPa。当应变率为13 000 s~(-1)、应变从0.4增加到0.5时,应力从53.558 MPa迅速上升到164.417 MPa,增大了3.07倍。结论弹道明胶在低应变率和高应变率范围内都有着明显的应变率效应;基于试验数据,建立形如σ=k_ε~(·m)ε_n的含应变率本构模型,并给出20%弹道明胶的材料常数。     

单轴压缩下松质骨的应力率和蠕变性能北大核心

背景:松质骨是一种多孔、非均质、各向异性和具有黏弹性的结构,是骨的重要组成部分。它在负载传输和能量吸收方面起着十分重要的作用。所以对松质骨的力学行为进行研究具有重要意义。目的:探讨单轴压缩实验中应力率对松质骨性能的影响以及不同应力值下松质骨的蠕变行为。方法:以新鲜的猪股骨松质骨为实验材料,施加不同的应力率,至试样的压缩应变达到5%卸载;在松质骨表面施加恒定的应力水平,并保持7 200 s,以便观察其蠕变应变变化。结果与结论:(1)单轴压缩实验中,在同一应变条件下,随着应力率的增加,应力值、杨氏模量也增加;(2)在不同的加载率作用下,松质骨的压缩应力-应变曲线不重合,说明松质骨的压缩力学性能具有率相关性;(3)在蠕变实验中,蠕变应变随着压缩的应力的增加而增加,蠕变柔量随着应力的增加反而减少;(4)轴压缩和蠕变实验结果说明,应力率和恒定应力水平对松质骨的力学性能影响很大,以上结果可以为如何避免松质骨损伤提供参考依据。     

脂肪组织压缩实验中摩擦系数对力学响应的影响

目的针对当前摩擦力对脂肪组织无约束压缩实验结果影响的不确定性,研究压缩实验中合适的摩擦系数设置及适用于模拟脂肪组织生物力学响应的材料本构模型。方法构建低应变率(0.2s^-1)和中应变率(20s^-1)下的脂肪组织有限元模型,分别应用LS-DYNA中常用于模拟脂肪组织的线性黏弹性材料本构、Mooney-Rivlin超弹性材料本构、Ogden超弹性材料本构、软组织材料本构,在不同摩擦系数下进行无约束压缩实验,分析不同摩擦系数及本构模型对接触力大小的影响。结果4种材料本构模型在低、中应变率下,输出的接触力均与摩擦系数呈正相关,有摩擦时的接触力比无摩擦时的接触力大50%左右。中应变率下脂肪组织的力学响应对摩擦系数的灵敏度比低应变率下的更高,且不同材料本构模型输出的接触力差异显著。结论在脂肪组织无约束压缩实验中,静摩擦系数取0.1,动摩擦系数取0.05是合理的,在低、中应变率下Ogden超弹性材料本构能够良好地反映脂肪组织的生物力学响应。     

基于不同应变判定准则模拟皮质骨断裂的准确性

文题释义：基于等效应变断裂模拟：即在大鼠股骨皮质骨断裂模拟过程中，应用皮质骨有限元模型在外部载荷作用下所产生的等效应变数值，与皮质骨组织的失效应变进行对比，当等效应变数值大于皮质骨组织失效应变时，有限元模型内的单元便发生失效，直至失效单元达到一定数量，模型便发生整体失效，此过程为基于等效应变的断裂模拟。 基于主应变断裂模拟：即在大鼠股骨皮质骨断裂模拟过程中，应用皮质骨有限元模型在外部载荷作用下所产生的主应变数值，与皮质骨组织的失效应变进行对比，当主应变数值大于皮质骨组织失效应变时，有限元模型内的单元便发生失效，直至失效单元达到一定数量，模型便发生整体失效，此过程为基于主应变的断裂模拟。 背景：由于意外碰撞等外力因素所产生的皮质骨裂纹是引起骨折的重要原因之一，要防止此类骨折发生，首先需弄清不同载荷作用下皮质骨裂纹的产生与扩展机制。由于实验分析对样本具有破坏性，难以同时了解骨结构在断裂前后的内部力学状态，找到一种能够准确模拟皮质骨从裂纹产生、扩展，直至断裂过程的有限元方法就显得尤为重要。当前模拟方法主要应用主应变或等效应变判定模型单元力学状态，继而进行断裂模拟，却鲜有关于这2种应变进行模拟准确性的探究。 目的：验证应用主应变与等效应变进行皮质骨断裂模拟的准确程度。 方法：结合实验与仿真分析，应用主应变与等效应变进行皮质骨断裂模拟，将仿真与实验结果进行对比，确定应用哪种应变进行模拟更加准确。 结果与结论：①应用主应变模拟的皮质骨断裂时间要明显晚于应用等效应变；②通过与实验对比发现，相比主应变，应用等效应变进行仿真所得结果与实验值更为接近；③因此，应用等效应变进行皮质骨断裂模拟相对更加准确。 ORCID: 0000-0003-0313-1359(王伟军) 中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程     

A method for a mechanical characterisation of human gluteal tissue.

The most common complication associated with immobilization is pressure sores caused by sustained localized tissue strain and stress. Computational simulations have provided insight into tissue stress-strain distribution, subject to loading conditions. In the simulation process, adequate soft tissue material parameters are indispensable. An in vivo procedure to characterise material parameters of human gluteal skin/fat and muscle tissue has been developed. It employs a magnetic resonance imaging (MRI) device together with an MRI compatible loading device. Using the derived data as constraints in an iterative optimization process the inverse finite element (FE) method was applied. FE-models were built and the material constants describing skin/fat and muscle tissue were parameterized and optimized. Separate parameter sets for human gluteal skin/fat and muscle were established. The long-term shear modulus for human gluteal skin/fat was G_{infinity, S/F}= 1182 Pa and for muscle G_{infinity, M} = 1025 Pa. The Ogden form for slightly compressible materials was chosen to define passive human gluteal soft tissue material behaviour. To verify the approach, the human skin/fat-muscle tissue compound was simulated using the derived material parameter sets and the simulation result was compared to empirical values. A correlation factor of R;{2} = 0.997 was achieved.     

Investigation on the load-displacement curves of a human healthy heel pad: In vivo compression data compared to numerical results

The aims of the present work were to build a 3D subject-specific heel pad model based on the anatomy revealed by MR imaging of a subject's heel pad, and to compare the load-displacement responses obtained from this model with those obtained from a compression device used on the subject's heel pad. A 30 year-old European healthy female (mass=54kg, height=165cm) was enrolled in this study. Her left foot underwent both MRI and compression tests. A numerical model of the heel region was developed based on a 3D CAD solid model obtained by MR images. The calcaneal fat pad tissue was described with a visco-hyperelastic model, while a fiber-reinforced hyperelastic model was formulated for the skin. Numerical analyses were performed to interpret the mechanical response of heel tissues. Different loading conditions were assumed according to experimental tests. The heel tissues showed a non-linear visco-elastic behavior and the load-displacement curves followed a characteristic hysteresis form. The energy dissipation ratios measured by experimental tests (0.25±0.02 at low strain rate and 0.26±0.03 at high strain rate) were comparable with those evaluated by finite element analyses (0.23±0.01 at low strain rate and 0.25±0.01 at high strain rate). The validity and efficacy of the investigation performed was confirmed by the interpretation of the mechanical response of the heel tissues under different strain rates. The mean absolute percentage error between experimental data and model results was 0.39% at low strain rate and 0.28% at high strain rate.     

兔髌韧带压缩力学性能

目的 研究不同应变率下韧带的压缩应力-应变关系,并构建本构模型,为韧带的损伤预估及替代材料的研 发提供参考。 方法 通过万能拉伸试验机测试兔髌韧带在不同应变率(0. 001、0. 01、0. 1、1 s-1 )下的压缩力学性能 和压缩松弛响应,并构建相应的本构方程。 结果 单轴无侧限压缩实验表明,随着应变率增加,30% 、40% 应变下的 应力和切线模量均明显增大。 相比于 Gent 模型,Fung 和 Ogden 模型更适用于拟合韧带压缩曲线(R2 >0. 99);采用 4 项 Prony 级数更适用于拟合韧带的松弛曲线(R2>0. 99)。 结论 兔髌韧带的压缩力学性能有显著的黏弹性响应, Fung 和 Ogden 模型可用于拟合韧带的压缩响应,4 项 Prony 级数可用于拟合兔髌韧带的压缩松弛响应。     

基于病理切片延髓-上颈髓三维有限元模型的建立及其损伤生物力学分析

目的 基于标本病理切片数据,建立延髓-上颈髓三维实体模型,通过有限元分析获得延髓-上颈髓受齿状突压迫情况下应力、应变水平,为临床研究提供参考.方法 运用Mimics对切片数据进行处理,建立点云模型;运用SolidWorks对点云模型进行定位、编辑、优化,建立三维实体模型;运用HyperMesh建立有限元模型并运用ANS...     

A numerical model for investigating the mechanics of calcaneal fat pad region

The present paper pertains to the definition of a numerical model of the calcaneal fat pad region, considering a structure composed of adipose and connective tissues organized in fibrous septae and adipose chambers. The mechanical response is strongly influenced by the structural conformation, as the dimension of adipose chambers, the thickness of connective septae walls and the mechanical properties of the different soft tissues. In order to define the constitutive formulation of adipose tissues, experimental data from pig specimens are considered, according to the functional similarity, while the mechanical response of connective tissue septae is assumed with regard to the mechanical behaviour that characterize ligaments. Different numerical models are provided accounting for the variation of chambers dimensions, septae wall thickness and tissues characteristics. The spiral angles of collagen fibres within the septae influence the capability of the structure to withstand the bulging of chambers. The analysis considers different orientation of the fibres. The response of calcaneal fat pad region is evaluated in comparison with experimental data from unconfined compression tests. The present work provides a preliminary approach to enhance the correlation between the structural conformation and tissues mechanical properties towards the biomechanical response of overall heel pad region.     

Evaluation of a new set of calibration standards for the measurement of fat content via DPA and DXA.

A simulation study was performed to evaluate a new set of calibration standards for estimating the fat content of the body via dual-photon absorptiometry (DPA) and dual-energy x-ray absorptiometry (DXA). The standards, proposed by Nord and Payne [presented at the 2nd meeting of The Bath Conference on Bone Mineral Measurement (1990)] consist of stearic acid (100% fat) and 0.6% NaCl in water (100% lean). They were compared with other standards consisting of average composition adipose/muscle tissues and fatty adipose/lean muscle tissues. Source and detector properties of a Gd-153 DPA system and three commercial DXA systems were modeled. For each system and calibration set, rms errors in the calculated fat contents of simulated tissues having fat mass percentages that ranged from about 4%-44% and thicknesses that ranged from 5-20 cm were determined. Beam hardening errors for the systems were evaluated as was a calibration technique employed by one of the manufacturers to correct for such errors. In general, the smallest rms errors (2% or less when the calibration standards and tissues were of equal thickness) were obtained with the average adipose/muscle standards. Equivalent results were obtained with standards consisting of stearic acid and 0.8% NaCl. The latter is a higher salt content than proposed by Nord and Payne and results from differences in the x-ray attenuation coefficients that were employed in calculating the fat equivalence of water. Other, more convenient standards, such as lucite and water may be employed by using appropriate fat equivalences (approximately 69% for lucite and approximately 10% for water). Beam hardening errors for the DXA systems are considerable, and the simulated correction technique was shown to be effective.     

Combined compression and elongation experiments and non-linear modelling of liver tissue for surgical simulation

Uniaxial stress-strain data were obtained from in vitro experiments on 20 porcine livers for compressions, elongations and cycles of compression and then elongation. There were about 70 cylindrical samples, with diameter 7 mm and varying height (4–11 mm). The combined compression and elongation test provide a unified framework for both compression and elongation for applications such as computer-aided surgical simulation. It enable the zero stress state of the experimental liver sample to be precisely determined. A new equation that combined both logarithmic and polynomial strain energy forms was proposed in modelling these experimental data. The assumption of incompressibility was justified from a preliminary Poisson's ratio for elongation and compression at 0.43±0.16 and 0.47±0.15, respectively. This equation provided a good fit for the observed mechanical properties of liver during compression-elongation cycles and for separate compressions or elongations. The root mean square errors were 91.92±17.43 Pa, 57.55±13.23 Pa and 29.78±17.67 Pa, respectively. In comparison with existing strain energy functions, this combined model was the better constitutive equation. Application of this theoretical model to small liver samples and other tissues demonstrated its suitability as the material model of choice for soft tissue.     

前交叉韧带力学特性差异对膝关节有限元仿真结果的影响

目的研究不同前交叉韧带力学特性对膝关节有限元模拟结果产生的影响。方法基于医学图像数据重建包含主要解剖结构在内的膝关节三维有限元模型,并考虑韧带的横观各向同性特性;用同一种韧带本构方程对3种不同前交叉韧带应力应变力学实验曲线进行参数拟合,对比不同的前交叉韧带力学参数对膝关节运动学和生物力学性能的影响。结果不同的前交叉韧带力学特性会得到不同的膝关节位移结果,前交叉韧带内的应力及应变大小有很大变化,但分布的趋势基本相同。结论选取不同前交叉韧带力学特性曲线会影响膝关节有限元分析的仿真结果,今后在关节组织力学性能的设置、模型的构建及验证中要足够重视。