HISTOLOGIC MICROCRACKS AND FATIGUE OF CORTICAL BONE

这是一个项目的竞争性续订提案，该项目 研究皮质骨的疲劳损伤如何依赖于应用 应力范围和应用的循环次数。我们对这两个都感兴趣 微裂纹损伤和以机械损伤形式减少的损伤 属性。我们还开发了一个机械理论模型 将这两种损害联系起来。这一模式在以下方面取得了成功 预测疲劳寿命和模数随温度变化的函数 应用的周期数，N。该理论基于这样的概念 骨质骨是一种纤维-基质复合材料，其中次级骨细胞 纤维、初级组织和骨组织碎片是基质。它是 还根据观察到不同种类的基质和纤维 当人类皮质骨承受张力和压力时，就会发生损伤 压缩。由此产生的纤维-基质损伤理论成功 对Pattin等人的E-N曲线进行建模。(1996)用于单轴拉伸 和人体股骨的压缩，我们已经初步确认 人体股骨的弯曲疲劳数据。 最初，我们提出在四点弯曲中使用疲劳 标本取自马的第三掌骨，作为我们的 实验模型，这就是我们大部分研究的内容， 在第一次赠与期间。然而，我们发现马匹 骨骼不会表现出与人类相同类型的微裂纹损伤 皮质骨。因此，我们建议将重点转移到人 在下一次授权期内提供股骨头。我们这项工作的目标是 严格检验并推广纤维-基质损伤理论 通过与Continue合作的实验计划 分析性发展。特别是，我们希望更充分地开发 关于剪应力损伤的理论，骨骼的局部变异 结构和双峰加载方式。

This is a competing continuation proposal for a project which is studying how fatigue damage in cortical bone depends on the applied stress range and the number of cycles applied. We are interested in both microcrack damage and damage in the form of diminished mechanical properties. We have also developed a mechanistic theoretical model for relating these two kinds of damage. This model has been successful in predicting fatigue life and reduction of modulus as a function of the number of cycles applied, N. The theory is based on the concept that osteonal bone is a fiber-matrix composite in which secondary osteons are the fibers and primary tissue and osteon fragments are the matrix. It is also based on the observation that different kinds of matrix and fiber damage occur when human cortical bone is loaded in tension and compression. The resulting fiber-matrix damage theory successfully models the E vs. N curves of Pattin et al. (1996) for uniaxial tension and compression of human femoral bone and we have preliminary validation data for flexural fatigue of human femoral bone as well. Originally, we proposed to use fatigue in four-point bending of specimens machined from equine third metacarpal bones as our experimental model, and this is what we have studied, for the most part, during the first grant period. However, we have found that the equine bone does not exhibit the same kinds of microcrack damage as human cortical bone. Therefore, we propose to shift our emphasis to human femoral bone during the next grant period. Our goals for this work are to rigorously test, and to extend, the fiber-matrix damage theory through a program of experimentation in concert with continued analytical development. In particular, we want to more fully develop the theory in terms of shear stress damage, local variations in bone structure, and bimodal modes of loading.