Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire LE11 3TU, UK.
J Mech Behav Biomed Mater. 2011 Jul;4(5):807-20. doi: 10.1016/j.jmbbm.2010.10.001. Epub 2010 Oct 17.
Bone fractures affect the health of many people and have a significant social and economic effect. Often, bones fracture due to impacts, sudden falls or trauma. In order to numerically model the fracture of a cortical bone tissue caused by an impact it is important to know parameters characterising its viscoelastoplastic behaviour. These parameters should be measured for various orientations in a bone tissue to assess bone's anisotropy linked to its microstructure. So, the first part of this study was focused on quantification of elastic-plastic behaviour of cortical bone using specimens cut along different directions with regard to the bone axis-longitudinal (axial) and transverse. Due to pronounced non-linearity of the elastic-plastic behaviour of the tissue, cyclic loading-unloading uniaxial tension tests were performed to obtain the magnitudes of elastic moduli not only from the initial loading part of the cycle but also from its unloading part. Additional tests were performed with different deformation rates to study the bone's strain-rate sensitivity. The second part of this study covered creep and relaxation properties of cortical bone for two directions and four different anatomical positions-anterior, posterior, medial and lateral-to study the variability of bone's properties. Since viscoelastoplasticity of cortical bone affects its damping properties due to energy dissipation, the Dynamic Mechanical Analysis (DMA) technique was used in the last part of our study to obtain magnitudes of storage and loss moduli for various frequencies. Based on analysis of elastic-plastic behaviour of the bovine cortical bone tissue, it was found that magnitudes of the longitudinal Young's modulus for four cortical positions were in the range of 15-24 GPa, while the transversal modulus was lower--between 10 and 15 GPa. Axial strength for various anatomical positions was also higher than transversal strength with significant differences in magnitudes for those positions. Quantitative data obtained in creep and relaxation tests exhibited no significant position-specific differences. DMA results demonstrated relatively low energy-loss capability due to viscosity of bovine cortical bone that has a loss factor in the range of 0.035-0.1.
骨骨折影响许多人的健康，对社会和经济有重大影响。通常，骨头会因撞击、突然摔倒或外伤而骨折。为了数值模拟由于冲击引起的皮质骨组织的骨折，重要的是要知道其粘弹塑性行为的特征参数。应该为骨骼组织中的各个方向测量这些参数，以评估与微观结构相关的骨骼各向异性。因此，本研究的第一部分集中于使用沿骨骼轴（轴向）和横向的不同方向切割的标本来量化皮质骨的弹塑性行为。由于组织的弹塑性行为具有明显的非线性，因此进行了循环加载-卸载单轴拉伸试验，以获得弹性模量值，不仅来自循环的初始加载部分，还来自其卸载部分。进行了不同变形速率的附加测试，以研究骨骼的应变率敏感性。本研究的第二部分涵盖了皮质骨的蠕变和松弛特性，用于两个方向和四个不同的解剖位置（前、后、内和外），以研究骨骼特性的可变性。由于皮质骨的粘弹塑性会由于能量耗散而影响其阻尼特性，因此在我们研究的最后一部分中使用动态机械分析（DMA）技术来获得各种频率下的存储和损耗模量值。基于对牛皮质骨组织的弹塑性行为的分析，发现四个皮质位置的纵向杨氏模量值在 15-24 GPa 范围内，而横向模量较低-在 10-15 GPa 之间。各种解剖位置的轴向强度也高于横向强度，这些位置的强度差异显著。蠕变和松弛测试中获得的定量数据没有表现出位置特异性差异。DMA 结果表明，由于牛皮质骨的粘性，能量损耗能力相对较低，其损耗因子在 0.035-0.1 范围内。
