Ligaments are dense fibrous tissues that connect bones across a joint and are exposed daily to creep and fatigue loading. Ligaments are tensile load-bearing tissues; therefore, fatigue loading will have a component of time-dependent damage from the non-zero mean stress and cycle-dependent damage from the oscillating stress. If time-dependent damage is not sufficient to completely predict the fatigue response, then cycle-dependent damage could be an important contributor. Using data from normal ligaments (current study and Thornton et al., Clin. Biomech. 22:932-940, 2007a) and healing ligaments (Thornton and Bailey, J. Biomech. Eng. 135:091004-1-091004-6, 2013), creep data was used to predict the fatigue response considering time-dependent damage. Relationships between creep lifetime and test stress or initial strain were modelled using exponential or power-law regression. In order to predict fatigue lifetimes, constant rates of damage were assumed and time-varying stresses were introduced into the expressions for time-dependent damage from creep. Then, the predictions of fatigue lifetime were compared with curvefits to the fatigue data where exponential or power-law regressions were used to determine the relationship between fatigue lifetime and test stress or initial strain. The fatigue prediction based on time-dependent damage alone greatly overestimated fatigue lifetime suggesting that time-dependent damage alone cannot account for all of the damage accumulated during fatigue and that cycle-dependent damage has an important role. At lower stress and strain, time-dependent damage was a greater relative contributor for normal ligaments than healing ligaments; however, cycle-dependent damage was a greater relative contributor with incremental increases in stress or strain for normal ligaments than healing ligaments.

中文翻译：

---

预测正常韧带和愈合韧带疲劳行为的时间依赖性损伤。

韧带是致密的纤维组织，其通过关节连接骨骼，每天暴露于蠕变和疲劳负荷下。韧带是承受张力的组织。因此，疲劳载荷将具有由非零平均应力引起的时间相关损伤和由振荡应力引起的周期相关损伤。如果与时间有关的损害不足以完全预测疲劳响应，那么与周期有关的损害可能是重要的因素。使用正常韧带的数据（当前研究和Thornton等人，Clin。Biomech。22：932-940，2007a）和愈合韧带的数据（Thornton和Bailey，J。Biomech。Eng。135：091004-1-091004-6， 2013），蠕变数据用于考虑时间相关损伤的预测疲劳响应。蠕变寿命与测试应力或初始应变之间的关系使用指数或幂律回归模型化。为了预测疲劳寿命，假定了恒定的破坏率，并且将随时间变化的应力引入了蠕变随时间变化的破坏表达式中。然后，将疲劳寿命的预测与疲劳数据的曲线拟合进行比较，其中使用指数或幂律回归确定疲劳寿命与测试应力或初始应变之间的关系。仅基于时间相关损害的疲劳预测大大高估了疲劳寿命，这表明仅基于时间的损害无法解决疲劳期间累积的所有损害，而基于周期的损害具有重要作用。在较低的应力和应变下 时间依赖性损伤对正常韧带的影响大于对愈合韧带的影响；然而，与正常韧带相比，与周期有关的损伤是相对更大的相关因素，其对正常韧带的压力或劳损的增加与愈合韧带的增加有关。