牛湿密质骨的粘塑性实验分析

本文用一维拉伸试验研究了牛湿密度质骨在应变率为３×１０－６～１×１０－２ｓ－１范围内屈服后的力学行为，共试验１５０个试件，其中９０个做拉断试验，其余６０个做蠕变试验。结果表明，牛湿密质骨的屈服应力σｙ和极限应力σｕ都与应变率高度相关（Ｐ＜０．０１）；其次，屈服后的应力与应变率的关系可用马尔文（Ｍａｌｖｅｒｎ）模型来描述，并拟合出几种形式的粘塑性本构关系     

骨粘弹性解析和微压痕硬度测试

本文用一维三元模型描述密质骨的粘弹性,首先建立该系统的微分方程,对应力和应变解微分方程,由边界条件说明密质骨粘弹性。蠕变现象和应力松弛试验图(1)、(2)与理论分析一致。模型与实验观察到的应变率随模量增加相符图(4)所示。骨的微压痕硬度试验,在加载过程中可以连续观察压印的形态和大小,微压痕仪测试时间一般调节在约15—20秒钟之间,时间不宜过长,抬高压痕器后,压痕成四角星形状,其对角线立即减到有负荷时的80%。在60秒钟内维持原形态,以后压痕大小又慢慢不规则的恢复。图(五)表示兔胫骨加载和卸载过程的硬度,在加载时,硬度出现较小的变化系数,湿骨样品卸载后在不同位置硬度值相差较大。图(六)(a)表示不同材料的微压痕比较一骨、铅(塑性)、有机玻璃(粘弹性)。     

人湿尺骨对冲击载荷的响应

本文采用分离式Ｈｏｐｋｉｎｓｏｎ压杆（ＳＨＰＢ）技术对人湿润尺骨密质骨进行了应变率在ε＝１．２×１０３Ｓ－１条件下的冲击压缩试验，得到了不同纵向位置尺骨的极限强度、极限应变和压缩模量。实验结果表明，尺骨密质骨的力学响应随其纵向位置变化，呈现中间强两端弱的分布规律，最强的位置约在距近端１／３处，且近端强于远端；与静态结果的比较表明，尺骨密质骨对应变率有较大的依赖性。     

密质骨的滑动界面细观力学模型

本文将粘合线作为骨单元和间板之间的粘弹性界面,建立了密质骨的细观力学模型,并给出了该模型在滑骨的轴线方向载荷作用下的应力响应和某些密质骨的宏观等效模量。还发现骨单元和间板的泊松比之差对密质骨的等效模量和内部横向应力的分布具有重要影响。     

人密质骨动态力学性能及莫电效应

本实验建立起用Ｈｏｐｋｉｎｓｏｎ压杆技术，测量骨动态力学性能及骨应变源电动势的实验方法，对新鲜人股骨密质进行测试。①低应变率下（２ｘ１０－３／ｓ）骨弹性模量值为１３．６ＧＰａ，与高应变率（６ｘ１０２／ｓ）下骨弹性模量值１８．３ＧＰａ之间差别显著，表明骨是一种粘弹性材料。②结合骨断面扫描电镜图象，讨论了静、动载荷下骨创伤发生的机制，证实骨单位粘合线处是密质骨力学性能薄弱点，骨单位断裂前发生骨板相对滑动。③湿骨试件应变源电动势（ＳＧＰｓ）峰值较干骨试件大，且时相滞后于骨应变时相约４４μｓ，干骨试件ＳＧＰｓ无明显滞后。④提出压电效应和流动电动势分别是干、湿骨试件ＳＧＰｓ产生的机制。实验结果为新型骨生物材料研制，临床骨伤病电刺激疗法的应用，以及骨折愈合质量的评价等，提供了理论依据。     

动脉壁非线性弹性的理论和实验研究

在理论方面,作者提出了一个三维理论模型分析动脉壁的非线性力学性质。该模型假设动脉壁是各向异性、局部正交对称、不可压缩和非线性弹性的。引进了一个含有七个物理参数的三维指数型应变能函数,并由该函数详细地推导了动脉壁非线性弹性本构方程及增量形式的应力和应变关系。在实验方面,本文讨论了研究大血管力学特性的实验方法,对六只狗的胸主动脉离体血管段进行了测量研究,得出了主动脉的应力和应变关系曲线及七个参数的值,并由这些参数,根据本文的理论计算出主动脉的增量弹性模量。结果比较表明,本文理论模型是能很好地描述动脉壁的力学行为。     

前交叉韧带粘弹性特性的实验研究

目的 探讨前交叉韧带的力学性能和粘弹性行为与时间的变化规律，为研究人工韧带提供生物力学参数。方法 对正常国人新鲜尸体膝关节前交叉韧带进行系统的拉伸、应力松驰、蠕变实验，得出最大载荷、强度极限、最大应变、弹性模量等；还得出了应力松驰、蠕变实验数据和曲线，归一化应力松驰函数、蠕变函数数据和曲线。并得到7200s时的蠕变量和应力松驰量。结果 ①前交叉韧带在实验中表现出典型的松弛、蠕变现象，说明其粘弹性性质在膝关节运动中起着重要的缓冲作用。②最初600s时应力应变的变化幅度较大，之后应力缓慢下降，应变缓慢上升，前交叉韧带7200s时应力松弛量1．05Mp，蠕变量为6．82％。结论 前交叉韧带具有良好的粘弹性力学性质。其粘弹性力学行为是为了适应其所在解剖部位的功能需要。     

非线性模型在椎间盘黏弹性特性分析中的应用

目的 构建变参数非线性模型,研究人体椎间盘在循环应变状态下的应力松弛特性。方法 采用变参数非线性模型结合椎间盘应力松弛和蠕变反应的实验数据,研究循环应变状态下椎间盘的应力松弛特性,比较线性与非线性模型在循环状态下椎间盘黏弹性特性的差异。结果 采用变参数非线性模型得出的循环模量和松弛系数在0.01Hz循环状态下与实验模型非常接近,得出的循环模量在0.1和1 Hz下也与实验值相近,但是得出的松弛系数在0.1和1 Hz下失真严重。结论 在压缩应变作用下椎间盘经历的是一个非线性的应力行为,非线性变参数模型更符合研究在循环应变下椎间盘应力松弛反应的需要。     

考虑粘弹性性能的密质骨损伤本构模型的研究

本研究考虑密质骨的粘弹性性能,在连续损伤力学的框架范围内研究了密质骨的本构模型,分别就细观结构强度服从均匀分布和非均匀分布两种情况进行了讨论。实验研究表明,该损伤模型是可取的。     

同种异体骨移植的动态粘弹性分析研究

本文在同种异体ＡＡＡ骨片植入羊肱骨的实验基础上，应用稳态拉伸疲劳试验，测试分析了移植９、１２个月的植骨和正常密质骨动态粘弹性性质。结果表明，植骨的动态粘弹性力学性质（损失正切ｔａｎ（δ）、储存弹性模量Ｅ１、损失弹性模量Ｅ２）在植入初期与正常密质骨相比有显著的差异，随着植入时间为增加，ｔａｎ（δ）、Ｅ１、Ｅ２逐渐趋于正常值。表明临床应用的可行性。     

皮持骨在拉伸型,剪切型和撕裂型加载条件下的断裂韧性——纵向断裂…

对以质骨在拉伸、剪切和撕裂型载荷下的裂纹启裂韧性进行了研究。总数为１３０个紧凑拉式样,紧凑剪切试样和三腿型试样分别用于测量骨的拉伸型、剪切型和撕裂型启裂韧性。多试样柔度法用来测定当ａ／Ｗ＝０．５５（１,裂纹长度,Ｗ,试样宽度）时的临界能量释放率。临界应力强度因子由ａ／Ｗ＝０．５５的试样在试验中得到的临界载荷来计算。为了考察骨力学 各是性对于它的剪切型和撕裂裂纹启裂韧性的影响,对骨试样的裂纹扩展方向     

In vitro biomechanical evaluation of antegrade femoral nailing at early and late postoperative stages

The present study addresses the question of evaluating, by combining both experimental and numerical methods, the stress/strain distribution within a standardized composite femur implanted with an anterograde intramedullary nail. A transverse diaphyseal fracture has been introduced in order to evaluate the implant response in the early postoperative clinical stage. By comparing these experimental data with those obtained in the fully healed stage, in which the bone continuity had been recovered, it was possible to get information on load sharing between the bone and the intramedullary nail, location of high strain concentrations, bone relative motion at the fracture site, and stiffness reduction caused by bone discontinuity. Experimental data were correlated with those predicted by a validated 3D finite element model of the complete implant/femur assembly to investigate the full field stress distribution either in the cortical bone, in the nail or in the locking screws. The obtained results suggest that full weight bearing in the immediate post-operating stage should not be allowed since high stress levels are generated in the outer shell of the cortical bone either around the proximal screw hole or the upper locking screw hole. Long-term implant reliability should be guaranteed instead, since after fracture consolidation equivalent von Mises stresses never exceed critical levels neither in the bone nor in the implant.     

Effect of Fatiguing Exercise on Longitudinal Bone Strain as Related to Stress Fracture in Humans

Muscular fatigue in the training athlete or military recruit has been hypothesized to cause increased bone strain that may contribute to the development of a stress fracture. Under normal circumstances, muscles exert a protective effect by contracting to reduce bending strains on cortical bone surfaces. In vivo strain studies in dogs show that muscle fatigue following strenuous exercise elevates bone strain and changes strain distribution. However, a similar experiment has yet to be performed in humans. The purpose of this work was to test the hypothesis in humans that strenuous fatiguing exercise causes an elevation in bone strain. It was also hypothesized that this elevation is greater in younger people than in older people due to the decline in muscle strength and endurance that normally occurs with age. To test these hypotheses, strain in the tibiae of seven human volunteers was measured during walking before and after a period of fatiguing exercise. Neither hypothesis was sustained. Post-hoc analysis of the strain data suggests that strain rate increases after fatigue with a greater increase in younger as opposed to older persons. Although not conclusive, this suggests that it is strain rate, rather than strain magnitude, that may be causal for stress fracture. © 1998 Biomedical Engineering Society. PAC98: 8745Dr, 8745Bp, 0180+b     

皮质骨中骨单元应力集中效应的有限元分析

目的建立包含骨单元的皮质骨三维实体模型,通过有限元分析验证骨单元的应力集中效应,并对应力集中位置进行疲劳仿真和预测。方法利用Pro/E wildfire 5.0和ANSYS 12.0软件建立包含骨单元的皮质骨三维实体模型,在不同轴向压缩载荷条件下计算分析皮质骨中局部应力和应变分布情况;选取关键位置进行疲劳仿真,预测不同疲劳载荷强度下骨组织的疲劳状态。结果轴向压缩载荷作用下,骨单元附近会出现明显的应力集中效应,随着压缩载荷的增加,模型内部病理性局部应变的比例逐渐增大;关键位置的疲劳仿真结果证明了骨组织生理强度运动时的低疲劳风险,也预测了高强度运动或训练时骨组织疲劳骨折的高风险。结论成功建立了包含骨单元的皮质骨三维实体模型,验证了骨单元的应力集中效应,预测了高强度运动训练条件下骨组织的疲劳损伤位置和风险,实验结果可为部队新兵或中长跑运动员运动训练计划的制定以及运动疲劳损伤的预防提供参考。     

X-Ray Image Review of the Bone Remodeling Around an Osseointegrated Trans-femoral Implant and a Finite Element Simulation Case Study

The insertion of an implant into a bone leads to stress/strain redistribution, hence bone remodeling occurs adjacent to the implant. The study of the bone remodeling around the osseointegration implants can predict the long-term clinical success of the implant. The clinical medial–lateral X-rays of 11 patients were reviewed. To eliminate geometrical distortion of different X-rays, they were converted into a digital format and geometrical correction was carried out. Furthermore, the finite element (FE) method was used to investigate how the bone remodeling was affected by the stress/strain distribution in the femur. The review of clinical X-rays showed cortical bone growth around the proximal end of the implant and absorbtion at the distal end of the femur. The FE simulation revealed the stress/strain distribution in the femur of a selected patient. This provided a biomechanical interpretation of the bone remodeling. The existing bone remodeling theories such as minimal strain and strain rate theories were unable to offer satisfactory explanation for the cortical bone growth at the implant side of the proximal femur, where the stress/strain level was much lower than the one in the intact side of the femur. The study established the correlation between stress/strain distribution obtained from FE simulations and the bone remodeling of the clinical review. The cortical bone growth was initiated by the stress/strain gradient in the bone. Through the review of clinical X-rays and FE simulations, the study confirmed that the bone remodeling in a femur with an implant was influenced by the stress/strain redistribution. The strain level and stress gradient hypothesis is presented to offer an explanation for the implanted cortical bone remodeling observed in this study.     

The effect of strain rate on fracture toughness of human cortical bone: a finite element study

Evaluating the mechanical response of bone under high loading rates is crucial to understanding fractures in traumatic accidents or falls. In the current study, a computational approach based on cohesive finite element modeling was employed to evaluate the effect of strain rate on fracture toughness of human cortical bone. Two-dimensional compact tension specimen models were simulated to evaluate the change in initiation and propagation fracture toughness with increasing strain rate (range: 0.08–18 s⁻¹). In addition, the effect of porosity in combination with strain rate was assessed using three-dimensional models of micro-computed tomography-based compact tension specimens. The simulation results showed that bone’s resistance against the propagation of a crack decreased sharply with increase in strain rates up to 1 s⁻¹ and attained an almost constant value for strain rates larger than 1 s⁻¹. On the other hand, initiation fracture toughness exhibited a more gradual decrease throughout the strain rates. There was a significant positive correlation between the experimentally measured number of microcracks and the fracture toughness found in the simulations. Furthermore, the simulation results showed that the amount of porosity did not affect the way initiation fracture toughness decreased with increasing strain rates, whereas it exacerbated the same strain rate effect when propagation fracture toughness was considered. These results suggest that strain rates associated with falls lead to a dramatic reduction in bone’s resistance against crack propagation. The compromised fracture resistance of bone at loads exceeding normal activities indicates a sharp reduction and/or absence of toughening mechanisms in bone during high strain conditions associated with traumatic fracture.     

Similar damage initiation but different failure behavior in trabecular and cortical bone tissue

The mechanical properties of bone tissue are reflected in its micro- and nanostructure as well as in its composition. Numerous studies have compared the elastic mechanical properties of cortical and trabecular bone tissue and concluded that cortical bone tissue is stiffer than trabecular bone tissue. This study compared the progression of microdamage leading to fracture and the related local strains during this process in trabecular and cortical bone tissue. Unmachined single bovine trabeculae and similarly-sized cortical bovine bone samples were mechanically tested in three-point bending and concomitantly imaged to assess local strains using a digital image correlation technique. The bone whitening effect was used to detect microdamage formation and propagation. This study found that cortical bone tissue exhibits significantly lower maximum strains (trabecular 36.6%±14% vs. cortical 22.9%±7.4%) and less accumulated damage (trabecular 16100±8800 pix/mm2 vs. cortical 8000±3400 pix/mm2) at failure. However, no difference was detected for the maximum local strain at whitening onset (trabecular 5.8%±2.6% vs. cortical 7.2%±3.1%). The differences in elastic modulus and mineral distribution in the two tissues were investigated, using nanoindentation and micro-Raman imaging, to explain the different mechanical properties found. While cortical bone was found to be overall stiffer and more highly mineralized, no apparent differences were noted in the distribution of modulus values or mineral density along the specimen diameter. Therefore, differences in the mechanical behavior of trabecular and cortical bone tissue are likely to be in large part due to microstructural (i.e. orientation and distribution of cement lines) and collagen related compositional differences.     

压缩载荷下不同应变判定皮质骨断裂准确性分析

目的 寻找适合压缩断裂工况下的应变判据。方法 基于连续损伤力学理论进行皮质骨在压缩载荷下的断裂模拟。分别将等效应变与主应变设置为有限元模型单元损伤与失效判据进行断裂模拟,通过对比两种预测结果与动物实验数据,探究应用两种应变判据进行断裂模拟的准确性。结果 应用等效应变判据模拟的断裂时间晚于应用主应变模拟;相比等效应变,应用主应变进行仿真所得结果与动物实验结果更为接近。结论 压缩载荷下,应用主应变判定皮质骨单元力学状态进行断裂模拟较为准确。通过对比分析找到准确模拟皮质骨在压缩载荷下断裂的数值方法,能够为临床中提高骨折预测精度提供理论基础。     

Calibration of the mechanical properties in a finite element model of a lumbar vertebra under dynamic compression up to failure

Finite element models (FEM) dedicated to vertebral fracture simulations rarely take into account the rate dependency of the bone material properties due to limited available data. This study aims to calibrate the mechanical properties of a vertebral body FEM using an inverse method based on experiments performed at slow and fast dynamic loading conditions. A detailed FEM of a human lumbar vertebral body (23,394 elements) was developed and tested under compression at 2,500 and 10 mm s⁻¹. A central composite design was used to adjust the mechanical properties (Young modulus, yield stress, and yield strain) while optimizing four criteria (ultimate strain and stress of cortical and trabecular bone) until the failure load and energy at failure reached experimental results from the literature. At 2,500 mm s⁻¹, results from the calibrated simulation were in good agreement with the average experimental data (1.5% difference for the failure load and 0.1% for the energy). At 10 mm s⁻¹, they were in good agreement with the average experimental failure load (0.6% difference), and within one standard deviation of the reported range of energy to failure. The proposed method provides a relevant mean to identify the mechanical properties of the vertebral body in dynamic loadings.