The true toughness of human cortical bone measured with realistically short cracks
The true toughness of human cortical bone measured with realistically short cracks
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DOI：
10.1038/nmat2221
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发表时间：
2008-08-01
期刊：
影响因子：
41.2
通讯作者：
Ritchie, R. O.
中科院分区：
文献类型：
--
作者：
Koester, K. J.;Ager, J. W., III;Ritchie, R. O.
骨头比劈骨更难折断。虽然这是众所周知的，而且已经有许多关于骨中长裂纹行为的研究，但仍然需要关于人类皮质骨的定向相关的裂纹扩展抵抗行为的数据，以准确地评估其在适当大小尺度下的韧性。在这里，我们使用原位力学测试来研究生理上相关的短(600微米)裂纹是如何在皮质骨的横向和纵向上扩展的，同时使用裂纹偏转/扭转力学和非线性弹性断裂力学来确定裂纹阻力曲线。我们发现，在仅500亩长的裂缝后，由于主要的裂缝偏转/扭曲，横向(断裂)方向的裂缝扩展驱动力比纵向(劈裂)方向的裂缝扩展驱动力大5倍以上，主要是在水泥环。事实上，我们的结果表明，皮质骨的真正横向韧性远远高于先前报道的水平。然而，在这些小裂纹尺寸下，纵向方向的韧性(裂纹倾向于沿着水泥线)相当低；只有当裂纹变得几毫米长时，桥接机制才能充分发展，从而产生通常引用的(较大裂纹)骨骼的韧性。
Bone is more difficult to break than to split. Although this is well known, and many studies exist on the behaviour of long cracks in bone, there is a need for data on the orientation-dependent crack-growth resistance behaviour of human cortical bone that accurately assesses its toughness at appropriate size scales. Here, we use in situ mechanical testing to examine how physiologically pertinent short (< 600 mu m) cracks propagate in both the transverse and longitudinal orientations in cortical bone, using both crack-deflection/twist mechanics and nonlinear-elastic fracture mechanics to determine crack-resistance curves. We find that after only 500 mu m of cracking, the driving force for crack propagation was more than five times higher in the transverse (breaking) direction than in the longitudinal (splitting) direction owing to major crack deflections/twists, principally at cement sheaths. Indeed, our results show that the true transverse toughness of cortical bone is far higher than previously reported. However, the toughness in the longitudinal orientation, where cracks tend to follow the cement lines, is quite low at these small crack sizes; it is only when cracks become several millimetres in length that bridging mechanisms can fully develop leading to the (larger-crack) toughnesses generally quoted for bone.