Taylor D
Mechanical Engineering Department, Trinity College, Dublin, Ireland.
J Orthop Res. 1998 Mar;16(2):163-9. doi: 10.1002/jor.1100160203.
The measured fatigue strength of a material can be affected by specimen size:tests using a large stressed volume may show a low fatigue strength due to the increased probability of finding weak regions. A Weibull analysis revealed an important size effect in bone and predicted this effect with an accuracy of 12%. This approach also explained apparent inconsistencies in the published data and made it possible to separate and quantify the effects of frequency, loading mode, and material source. The effect of frequency is the same for human and bovine bone, and the differences between different types of loading (tension, compression, and bending) are small (maximum: 12%). By extrapolating to the volume of whole bones, it is concluded that large bones will have a fatigue strength much lower, by a factor of 2-3, than that measured by conventional tests. Failure within 10(5) cycles is expected to occur at cyclic stresses of 23-30 MPa in human long bones and of 32-43 MPa in bovine bones. Repair is therefore needed to prevent failure at physiological stress levels.
使用较大应力体积的测试可能会显示出较低的疲劳强度，这是因为发现薄弱区域的概率增加了。威布尔分析揭示了骨骼中重要的尺寸效应，并以12%的准确度预测了这种效应。这种方法还解释了已发表数据中明显的不一致之处，并使得分离和量化频率、加载模式及材料来源的影响成为可能。频率对人体骨骼和牛骨的影响是相同的，不同加载类型（拉伸、压缩和弯曲）之间的差异很小（最大为12%）。通过外推至整个骨骼的体积，得出的结论是，大骨骼的疲劳强度比传统测试所测得的疲劳强度低2至3倍。预计在10⁵次循环内失效会发生在人体长骨23至30兆帕的循环应力下以及牛骨32至43兆帕的循环应力下。因此需要进行修复以防止在生理应力水平下发生失效。
