Provenzano P, Lakes R, Keenan T, Vanderby R
Department of Biomedical Engineering, University of Wisconsin-Madison, 53792-3228, USA.
Ann Biomed Eng. 2001 Oct;29(10):908-14. doi: 10.1114/1.1408926.
Ligaments display time-dependent behavior, characteristic of a viscoelastic solid, and are nonlinear in their stress-strain response. Recent experiments (25) reveal that stress relaxation proceeds more rapidly than creep in medial collateral ligaments, a fact not explained by linear viscoelastic theory but shown by Lakes and Vanderby (17) to be consistent with nonlinear theory. This study tests the following hypothesis: nonlinear viscoelasticity of ligament requires a description more general than the separable quasilinear viscoelasticity (QLV) formulation commonly used. The experimental test for this hypothesis involves performing both creep and relaxation studies at various loads and deformations below the damage threshold. Freshly harvested, rat medial collateral ligaments (MCLs) were used as a model. Results consistently show a nonlinear behavior in which the rate of creep is dependent upon stress level and the rate of relaxation is dependent upon strain level. Furthermore, relaxation proceeds faster than creep; consistent with the experimental observations of Thornton et al. (25) The above results from rat MCLs are not consistent with a separable QLV theory. Inclusion of these nonlinearities would require a more general formulation.
韧带表现出与时间相关的行为，这是粘弹性固体的特征，并且其应力应变响应是非线性的。最近的实验（25）表明，内侧副韧带中的应力松弛比蠕变进行得更快，这一事实无法用线性粘弹性理论解释，但莱克斯和范德比（17）表明这与非线性理论一致。本研究检验以下假设：韧带的非线性粘弹性需要比常用的可分离准线性粘弹性（QLV）公式更通用的描述。对该假设的实验测试包括在低于损伤阈值的各种载荷和变形下进行蠕变和松弛研究。刚摘取的大鼠内侧副韧带（MCL）被用作模型。结果一致显示出非线性行为，其中蠕变速率取决于应力水平，松弛速率取决于应变水平。此外，松弛比蠕变进行得更快；这与桑顿等人（25） 的实验观察结果一致。大鼠MCL的上述结果与可分离QLV理论不一致。纳入这些非线性需要更通用的公式。
