HISTOLOGIC MICROCRACKS AND FATIGUE OF CORTICAL BONE

这是一个项目的竞争性延续提案， 研究皮质骨的疲劳损伤如何取决于应用的 应力范围和施加的循环次数。我们对两者都感兴趣 微裂纹损伤和机械损伤 特性.我们还开发了一个机械理论模型， 把这两种伤害联系起来。这种模式在 预测疲劳寿命和模量的减少作为一个函数， 应用的循环次数，N。这个理论是基于这样一个概念， 骨单位骨是纤维基质复合物，其中次级骨单位 纤维和初级组织以及骨单位碎片是基质。是 还基于观察到不同种类的基质和纤维 当人类皮质骨承受张力时会发生损伤， 压缩由此产生的纤维-基体损伤理论成功地 对Pattin等人（1996）的单轴拉伸的E与N曲线进行建模 和人类股骨的压缩，我们已经初步验证了 人股骨的弯曲疲劳数据。 最初，我们建议在四点弯曲中使用疲劳， 标本加工从马第三掌骨作为我们的 实验模型，这是我们研究的，在很大程度上， 在第一个赠款期间。然而，我们发现马 骨不表现出与人类相同的微裂纹损伤 皮质骨因此，我们建议将重点转移到人类 在下一个资助期内的股骨。我们这项工作的目标是 严格测试和扩展纤维-基体损伤理论 通过一个实验计划， 分析发展。特别是，我们希望更充分地发展 剪切应力损伤理论，骨局部变化 结构和双峰加载模式。

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.