Materials Science & Engineering Program, University of California-San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0418, USA.
J Mech Behav Biomed Mater. 2011 Jan;4(1):57-75. doi: 10.1016/j.jmbbm.2010.09.006. Epub 2010 Sep 21.
Although clinical bone fractures occur predominantly under impact loading (as occurs during sporting accidents, falls, high-speed impacts or other catastrophic events), experimentally validated studies on the dynamic fracture behavior of bone, at the loading rates associated with such events, remain limited. In this study, a series of tests were performed on femoral specimens obtained post-mortem from equine donors ranging in age from 6 months to 28 years. Fracture toughness and compressive tests were performed under both quasi-static and dynamic loading conditions in order to determine the effects of loading rate and age on the mechanical behavior of the cortical bone. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack initiation between dynamic and quasi-static experiments. Compressive properties were measured on bone loaded parallel and transverse to the osteonal growth direction. Fracture propagation was then analyzed using scanning electron and scanning confocal microscopy to observe the effects of microstructural toughening mechanisms at different strain rates. Specimens from each horse were also analyzed for dry, wet and mineral densities, as well as weight percent mineral, in order to investigate possible influences of composition on mechanical behavior. Results indicate that bone has a higher compressive strength, but lower fracture toughness when tested dynamically as compared to quasi-static experiments. Fracture toughness also tends to decrease with age when measured quasi-statically, but shows little change with age under dynamic loading conditions, where brittle "cleavage-like" fracture behavior dominates.
尽管临床骨骨折主要发生在冲击载荷下（如运动事故、跌倒、高速冲击或其他灾难性事件中发生），但与这些事件相关的加载速率下骨的动态断裂行为的实验验证研究仍然有限。在这项研究中，对从年龄在 6 个月至 28 岁的马供体死后获得的股骨标本进行了一系列测试。在准静态和动态加载条件下进行了断裂韧性和压缩测试，以确定加载速率和年龄对皮质骨机械性能的影响。使用四点弯曲几何形状在单和双缺口试样上进行了断裂韧性实验，以测量断裂韧性，并观察动态和准静态实验中裂纹起始的差异。在与骨单元生长方向平行和垂直的方向上对骨进行了压缩性能测量。然后使用扫描电子显微镜和扫描共聚焦显微镜分析断裂扩展，以观察不同应变速率下微观结构增韧机制的影响。还对每匹马的标本进行了干燥、湿润和矿物质密度以及矿物质重量百分比的分析，以研究组成对机械性能的可能影响。结果表明，与准静态实验相比，骨在动态测试时具有更高的抗压强度，但断裂韧性较低。准静态测量时，断裂韧性随年龄的增长而降低，但在动态加载条件下随年龄的变化很小，脆性“类似劈裂”的断裂行为占主导地位。
