Department of Mechanical Engineering, University of Birmingham, B15 2TT, UK.
Department of Mechanical Engineering, University of Birmingham, B15 2TT, UK.
J Mech Behav Biomed Mater. 2018 Jan;77:40-46. doi: 10.1016/j.jmbbm.2017.08.036. Epub 2017 Sep 1.
Cracks can occur in the articular cartilage surface due to the mechanical loading of the synovial joint, trauma or wear and tear. However, the propagation of such cracks under different frequencies of loading is unknown. The objective of this study was to determine the effect of frequency of loading on the growth of a pre-existing crack in cartilage specimens subjected to cyclic tensile strain. A 2.26mm crack was introduced into cartilage specimens and crack growth was achieved by applying a sinusoidally varying tensile strain at frequencies of 1, 10 and 100Hz (i.e. corresponding to normal, above normal and up to rapid heel-strike rise times, respectively). These frequencies were applied with a strain of between 10-20% and the crack length was measured at 0, 20, 50, 100, 500, 1000, 5000 and 10,000 cycles of strain. Crack growth increased with increasing number of cycles. The maximum crack growth was 0.6 ± 0.3 (mean ± standard deviation), 0.8 ± 0.2 and 1.1 ± 0.4mm at frequencies of 1, 10 and 100Hz, respectively following 10,000 cycles. Mean crack growth were 0.3 ± 0.2 and 0.4 ± 0.2 at frequencies of 1 and 10Hz, respectively. However, this value increased up to 0.6 ± 0.4mm at a frequency of 100Hz. This study demonstrates that crack growth was greater at higher frequencies. The findings of this study may have implications in the early onset of osteoarthritis. This is because rapid heel-strike rise times have been implicated in the early onset of osteoarthritis.
关节软骨表面会由于滑膜关节的机械载荷、创伤或磨损而出现裂纹。然而，在不同的载荷频率下，这些裂纹的扩展情况尚不清楚。本研究的目的是确定载荷频率对软骨标本中已有裂纹在循环拉伸应变下生长的影响。在软骨标本中引入 2.26mm 的裂纹，通过在 1Hz、10Hz 和 100Hz 频率下施加正弦变化的拉伸应变来实现裂纹扩展（分别对应于正常、高于正常和达到快速足跟冲击上升时间）。这些频率的应变幅度在 10-20%之间，在 0、20、50、100、500、1000、5000 和 10000 个应变循环时测量裂纹长度。随着循环次数的增加，裂纹扩展增加。在 10000 个循环后，频率为 1、10 和 100Hz 时的最大裂纹扩展分别为 0.6±0.3（平均值±标准差）、0.8±0.2 和 1.1±0.4mm。频率为 1 和 10Hz 时的平均裂纹扩展分别为 0.3±0.2 和 0.4±0.2，但在 100Hz 时增加到 0.6±0.4mm。本研究表明，裂纹扩展在较高频率时更大。本研究的结果可能对骨关节炎的早期发病有影响。这是因为快速足跟冲击上升时间与骨关节炎的早期发病有关。
