Fatihhi S J, Rabiatul A A R, Harun M N, Kadir Mohammed Rafiq Abdul, Kamarul T, Syahrom Ardiyansyah
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor, Malaysia.
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Johor, Malaysia; Sport Innovation and Technology Centre (SITC), Institute Human Centred Engineering (IHCE), Universiti Teknologi Malaysia, Johor, Malaysia.
J Mech Behav Biomed Mater. 2016 Feb;54:21-32. doi: 10.1016/j.jmbbm.2015.09.006. Epub 2015 Sep 14.
The present study reports the effects of combined torsional and compressive cyclic loading on trabecular bone in order to mimic true physiological conditions and thereby provides improved data that represents clinical and real life conditions. However, only compressive behaviour is evaluated in most previous studies of bone mechanics. From the monotonic evaluation, it is observed that lower stress is needed for the onset of microcrack in the sample under torsional loading, compared to the stress needed in compression. Trabecular bone samples were subjected to a combination of torsion and compression fatigue at different stress levels during which they were compared to compressive axial fatigue. The stress levels were determined by considering the monotonic strength at 25-50% for both compressive and shear stresses. Significant decrease in fatigue lifetime is observed in between samples of pure compression fatigue and those with superpositioned torsional loading (p<0.05). The reduction in fatigue lifetime became more evident at a high torsional stress level. In this case, the failure of the sample is said to be 'torsional dominant'. Fatigue behaviour of bovine trabecular bone begins with plastic deformation, followed by strain accumulation and modulus reduction. As the strain rate increases, more energy dissipates and the sample finally failed. Further, the analysis of fractograph revealed something on the trabeculae by bending in sample with superpositioned torsional loading. In conclusion, torsional loading decreases the quality of the trabecular properties in terms of stiffness, life and structural integrity. It is hoped that results from this study will improve the understanding of the behaviour of trabecular bone under combined fatigue and help to develop future assessments of trabecular failure.
本研究报告了扭转和压缩循环加载联合作用对松质骨的影响，以模拟真实的生理条件，从而提供更能代表临床和现实生活状况的改进数据。然而，在以往大多数骨力学研究中仅评估了压缩行为。从单调评估中可以观察到，与压缩时所需的应力相比，扭转加载下样品中微裂纹起始所需的应力更低。对松质骨样品在不同应力水平下进行扭转和压缩疲劳的联合作用，在此期间将它们与压缩轴向疲劳进行比较。应力水平是通过考虑压缩和剪切应力在25% - 50%时的单调强度来确定的。在纯压缩疲劳样品和叠加扭转加载的样品之间观察到疲劳寿命显著降低（p<0.05）。在高扭转应力水平下，疲劳寿命的降低变得更加明显。在这种情况下，样品的失效被称为“扭转主导”。牛松质骨的疲劳行为始于塑性变形，随后是应变积累和模量降低。随着应变率增加，更多能量耗散，样品最终失效。此外，断口分析揭示了叠加扭转加载样品中骨小梁弯曲的情况。总之，扭转加载在刚度、寿命和结构完整性方面降低了松质骨特性的质量。希望本研究结果能增进对松质骨在联合疲劳作用下行为的理解，并有助于开展未来松质骨失效的评估。
