Hoffseth Kevin, Randall Connor, Hansma Paul, Yang Henry T Y
Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
Department of Mechanical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106, USA.
J Mech Behav Biomed Mater. 2015 Feb;42:282-91. doi: 10.1016/j.jmbbm.2014.11.020. Epub 2014 Nov 29.
In an attempt to study the mechanical behavior of bone under indentation, methods of analyses and experimental validations have been developed, with a selected test material. The test material chosen is from an equine cortical bone. Stress-strain relationships are first obtained from conventional mechanical property tests. A finite element simulation procedure is developed for indentation analyses. The simulation results are experimentally validated by determining (1) the maximum depth of indentation with a single cycle type of reference point indentation, and (2) the profile and depth of the unloaded, permanent indentation with atomic force microscopy. The advantage of incorporating in the simulation a yield criterion calibrated by tested mechanical properties, with different values in tension and compression, is demonstrated. In addition, the benefit of including damage through a reduction in Young's modulus is shown in predicting the permanent indentation after unloading and recovery. The expected differences in response between two indenter tips with different sharpness are predicted and experimentally observed. Results show predicted indentation depths agree with experimental data. Thus, finite element simulation methods with experimental validation, and with damage approximation by a reduction of Young's modulus, may provide a good approach for analysis of indentation of cortical bone. These methods reveal that multiple factors affect measured indentation depth and that the shape of the permanent indentation contains useful information about bone material properties. Only further work can determine if these methods or extensions to these methods can give useful insights into bone pathology, for example the bone fragility of thoroughbred racehorses.
为了研究骨在压痕作用下的力学行为，已经开发了分析方法和实验验证方法，并选用了一种测试材料。所选测试材料来自马的皮质骨。首先通过常规力学性能测试获得应力 - 应变关系。开发了一种用于压痕分析的有限元模拟程序。通过确定（1）单循环型参考点压痕的最大压痕深度，以及（2）用原子力显微镜观察卸载后的永久压痕的轮廓和深度，对模拟结果进行了实验验证。展示了在模拟中纳入通过测试力学性能校准的屈服准则（拉伸和压缩时具有不同值）的优势。此外，通过降低杨氏模量来考虑损伤在预测卸载和恢复后的永久压痕方面的益处也得到了体现。预测并通过实验观察了两种不同尖锐度的压头尖端在响应上的预期差异。结果表明预测的压痕深度与实验数据相符。因此，经过实验验证且通过降低杨氏模量来近似损伤的有限元模拟方法，可能为皮质骨压痕分析提供一种良好的方法。这些方法表明，多种因素会影响测量的压痕深度，并且永久压痕的形状包含有关骨材料特性的有用信息。只有进一步的研究才能确定这些方法或其扩展是否能为骨病理学提供有用的见解，例如纯种赛马的骨脆性。
