Hazenberg Jan G, Taylor David, Lee T Clive
Department of Anatomy, Royal College of Surgeons in Ireland, Dublin, Ireland.
Technol Health Care. 2006;14(4-5):393-402.
It is well known for almost half a century that bones contain microcracks. Very little is known about the crack growth behaviour of very small cracks, e.g. the stage before they become macroscopically long. The aim of this work was to investigate the dynamic crack growth behaviour of sub-millimetre microcracks in cortical bone. It was found that slow stable crack growth occurs in specimens subjected to static loading conditions. Crack growth direction was dominated by the local fibre orientation of the bones. Crack angles varied between 10 and 36 degrees of the long axis of the bone. Short cracks were found to show periods of rapid growth followed by intervals of temporary crack arrest. Histological analysis showed that crack arrest occurred due to vascular canals in the bone. During these periods of crack arrest, crack opening displacements increased until the local strain was sufficient to overcome these features. These observations indicate a mechanism for growth of small cracks in bone at constant stress, involving microstructural barriers, time-dependent deformation of material near the crack tip and strain-controlled propagation.
近半个世纪以来，人们都知道骨骼中存在微裂纹。对于非常小的裂纹，例如在它们变得宏观上很长之前的阶段，其裂纹扩展行为却知之甚少。这项工作的目的是研究皮质骨中亚毫米级微裂纹的动态裂纹扩展行为。研究发现，在承受静态载荷条件的标本中会出现缓慢稳定的裂纹扩展。裂纹扩展方向由骨骼的局部纤维取向主导。裂纹角度在与骨长轴成10度至36度之间变化。发现短裂纹会出现快速扩展期，随后是暂时裂纹停止的间隔期。组织学分析表明，裂纹停止是由于骨中的血管通道。在这些裂纹停止期间，裂纹张开位移增加，直到局部应变足以克服这些特征。这些观察结果表明了一种在恒定应力下骨中小裂纹扩展的机制，该机制涉及微观结构障碍、裂纹尖端附近材料的时间依赖性变形以及应变控制的扩展。
