Giles Julie M, Black Amanda E, Bischoff Jeffrey E
Department of Mechanical Engineering, 300 Main Street, Room A219, University of South Carolina, Columbia, SC 29208, USA.
J Biomech. 2007;40(4):777-85. doi: 10.1016/j.jbiomech.2006.03.017. Epub 2006 May 30.
It has been observed in load controlled laboratory tests of myocardium and skin that the tissues can exhibit a decrease in nonlinear stiffness with an increase in loading rate: the faster a test is performed, the more compliant is the preconditioned material behavior. This response seems to conflict with what is generally expected of soft tissues based on stretch or strain controlled tests, in which an increased rate of deformation results in a stiffer material response. It is hypothesized that this anomalous behavior has not been observed previously due to the small number of cyclic load controlled mechanical characterization tests that are geared specifically towards viscoelastic tissue response. The goal of this paper is to examine the preconditioned response of soft tissue to load controlled deformation using nonlinear viscoelastic material models including quasi-linear viscoelasticity, and to determine under what conditions this anomalous behavior becomes apparent. Results from this study suggest that this behavior is a true phenomenon unique to load controlled deformations that results from the interplay of nonlinear effects and creep behavior. These results call for increased attention to experimental parameters when testing and modeling nonlinear viscoelastic material behavior.
在对心肌和皮肤进行的载荷控制实验室测试中观察到，随着加载速率的增加，组织的非线性刚度会降低：测试进行得越快，预处理后的材料行为就越柔顺。这种反应似乎与基于拉伸或应变控制测试对软组织的一般预期相冲突，在拉伸或应变控制测试中，变形速率的增加会导致材料反应更硬。据推测，由于专门针对粘弹性组织反应的循环载荷控制力学特性测试数量较少，这种异常行为以前未被观察到。本文的目的是使用包括准线性粘弹性在内的非线性粘弹性材料模型，研究软组织对载荷控制变形的预处理反应，并确定在何种条件下这种异常行为会变得明显。这项研究的结果表明，这种行为是载荷控制变形所特有的真实现象，是由非线性效应和蠕变行为的相互作用导致的。这些结果要求在测试和模拟非线性粘弹性材料行为时，更多地关注实验参数。
