Fondrk M T, Bahniuk E H, Davy D T
Department of Mechanical & Aerospace Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.
J Biomech Eng. 1999 Dec;121(6):616-21. doi: 10.1115/1.2800862.
An experimental study examined the tensile stress-strain behavior of cortical bone during rapid load cycles to high strain amplitudes. Machined bovine and human cortical bone samples were subjected to loading cycles at a nominal load/unload rate of +/- 420 MPa/s. Loads were reversed at pre selected strain levels such that load cycles were typically completed in 0.5-0.7 seconds. Axial strain behavior demonstrated considerable nonlinearity in the first load cycle, while transverse strain behavior was essentially linear. For the human bone 29.1 percent (S.D. = 4.7 percent), and for the bovine bone 35.1 percent (S.D. = 10.8 percent) of the maximum nonlinear strain accumulated after load reversal, where nonlinear strain was defined as the difference between total strain and strain corresponding to linear elastic behavior. Average residual axial strain on unloading was 35.4 percent (S.D. = 1.2 percent) for human bone and 35.1 percent (S.D. = 2.9 percent) of maximum nonlinear strain. Corresponding significant volumetric strains and residual volumetric strains were found. The results support the conclusions that the nonlinear stress-strain behavior observed during creep loading also occurs during transient loading at physiological rates. The volume increases suggest that damage accumulation, i.e., new internal surfaces and voids, plays a major role in this behavior. The residual volume increases and associated disruptions in the internal structure of bone provide a potential stimulus for a biological repair response.
一项实验研究考察了皮质骨在快速加载至高应变幅值的循环载荷下的拉伸应力-应变行为。对加工好的牛和人皮质骨样本，以名义加载/卸载速率±420 MPa/s进行加载循环。在预先选定的应变水平下使载荷反向，使得加载循环通常在0.5 - 0.7秒内完成。轴向应变行为在第一个加载循环中表现出相当大的非线性，而横向应变行为基本呈线性。对于人骨，在载荷反向后累积的最大非线性应变中，有29.1%（标准差 = 4.7%）；对于牛骨，这一比例为35.1%（标准差 = 10.8%），其中非线性应变定义为总应变与对应线弹性行为的应变之差。人骨卸载时的平均残余轴向应变为最大非线性应变的35.4%（标准差 = 1.2%），牛骨为35.1%（标准差 = 2.9%）。还发现了相应的显著体积应变和残余体积应变。结果支持了以下结论：在蠕变加载过程中观察到的非线性应力-应变行为在生理速率的瞬态加载过程中也会出现。体积增加表明损伤积累，即新的内表面和空隙，在这种行为中起主要作用。残余体积增加以及骨内部结构的相关破坏为生物修复反应提供了潜在刺激。
