Physics Department, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
J Mech Behav Biomed Mater. 2011 May;4(4):523-34. doi: 10.1016/j.jmbbm.2010.12.009. Epub 2010 Dec 24.
The use of bone mineral density as a surrogate to diagnose bone fracture risk in individuals is of limited value. However, there is growing evidence that information on trabecular microarchitecture can improve the assessment of fracture risk. One current strategy is to exploit finite element analysis (FEA) applied to 3D image data of several mm-sized trabecular bone structures obtained from non-invasive imaging modalities for the prediction of apparent mechanical properties. However, there is a lack of FE damage models, based on solid experimental facts, which are needed to validate such approaches and to provide criteria marking elastic-plastic deformation transitions as well as microdamage initiation and accumulation. In this communication, we present a strategy that could elegantly lead to future damage models for FEA: direct measurements of local strains involved in microdamage initiation and plastic deformation in single trabeculae. We use digital image correlation to link stress whitening in bone, reported to be correlated to microdamage, to quantitative local strain values. Our results show that the whitening zones, i.e. damage formation, in the presented loading case of a three-point bending test correlate best with areas of elevated tensile strains oriented parallel to the long axis of the samples. The average local strains along this axis were determined to be (1.6±0.9)% at whitening onset and (12±4)% just prior to failure. Overall, our data suggest that damage initiation in trabecular bone is asymmetric in tension and compression, with failure originating and propagating over a large range of tensile strains.
使用骨密度作为个体骨折风险诊断的替代指标的价值有限。然而，越来越多的证据表明，有关小梁微结构的信息可以改善骨折风险的评估。目前的一种策略是利用有限元分析（FEA）应用于从非侵入性成像方式获得的几个毫米大小的小梁骨结构的 3D 图像数据，以预测表观力学性能。然而，缺乏基于坚实实验事实的 FEA 损伤模型，这些模型需要验证这些方法，并提供标记弹塑性变形转变以及微损伤起始和累积的标准。在本通讯中，我们提出了一种策略，该策略可以为未来的 FEA 损伤模型提供优雅的解决方案：直接测量涉及单小梁微损伤起始和塑性变形的局部应变。我们使用数字图像相关将骨中的应力白化与微损伤相关联，据报道，骨中的应力白化与微损伤相关联。我们的结果表明，在三点弯曲试验的呈现加载情况下，发白区域（即损伤形成）与沿样品长轴平行的拉伸应变升高区域相关性最好。在发白开始时，沿该轴的平均局部应变确定为（1.6±0.9）%，在失效之前为（12±4）%。总体而言，我们的数据表明，小梁骨中的损伤起始在拉伸和压缩时是不对称的，在很大的拉伸应变范围内起源和传播。
