Department of Mechanical & Biomedical Engineering, Boise State University, Boise, ID, USA.
Department of Mechanical Engineering, University of Zaragoza, Zaragoza, Spain; CIBER-BBN, Biomedical Research Networking Center in Bioengineering, Biomaterials and Nanomedicina, Zaragoza, Spain.
J Mech Behav Biomed Mater. 2023 Aug;144:105968. doi: 10.1016/j.jmbbm.2023.105968. Epub 2023 Jun 8.
Soft tissue is susceptible to injury from single high-magnitude static loads and from repetitive low-magnitude fatigue loads. While many constitutive formulations have been developed and validated to model static failure in soft tissue, a modeling framework is not well-established for fatigue failure. Here we determined the feasibility of using a visco-hyperelastic damage model with discontinuous damage (strain energy-based damage criterion) to simulate low- and high-cycle fatigue failure in soft fibrous tissue. Cyclic creep data from six uniaxial tensile fatigue experiments of human medial meniscus were used to calibrate the specimen-specific material parameters. The model was able to successfully simulate all three characteristic stages of cyclic creep, and predict the number of cycles until tissue rupture. Mathematically, damage propagated under constant cyclic stress due to time-dependent viscoelastic increases in tensile stretch that in turn increased strain energy. Our results implicate solid viscoelasticity as a fundamental regulator of fatigue failure in soft tissue, where tissue with slow stress relaxation times will be more resistant to fatigue injury. In a validation study, the visco-hyperelastic damage model was able to simulate characteristic stress-strain curves of pull to failure experiments (static failure) when using material parameters curve fit to the fatigue experiments. For the first time, we've shown that a visco-hyperelastic discontinuous damage framework can model cyclic creep and predict material rupture in soft tissue, and may enable the reliable simulation of both fatigue and static failure behavior from a single constitutive formulation.
软组织容易受到单一高幅度静态负荷和重复低幅度疲劳负荷的损伤。虽然已经开发和验证了许多本构公式来模拟软组织的静态失效，但疲劳失效的建模框架还没有很好地建立。在这里，我们确定了使用具有不连续损伤（基于应变能的损伤准则）的粘弹性损伤模型来模拟软纤维组织的低周和高周疲劳失效的可行性。使用来自六个人体内侧半月板单轴拉伸疲劳实验的循环蠕变数据来校准特定于样本的材料参数。该模型能够成功模拟循环蠕变的所有三个特征阶段，并预测组织破裂前的循环次数。从数学上讲，由于拉伸延伸的粘弹性随时间增加而导致的恒定循环应力下的损伤传播，从而增加了应变能。我们的结果表明，固体粘弹性是软组织疲劳失效的基本调节剂，其中具有较慢应力松弛时间的组织将更能抵抗疲劳损伤。在验证研究中，当使用拟合疲劳实验的材料参数来模拟拉断实验（静态失效）的特征应力-应变曲线时，粘弹性损伤模型能够模拟。这是第一次，我们表明粘弹性不连续损伤框架可以模拟循环蠕变并预测软组织中的材料破裂，并且可以从单个本构公式中可靠地模拟疲劳和静态失效行为。
