Kim Wonsuk, Argento Alan, Rozsa Frank W, Mallett Kaitlyn
Department of Mechanical Engineering, University of Michigan-Dearborn, Dearborn, MI 48128, USA.
J Biomech Eng. 2012 Jun;134(6):061002. doi: 10.1115/1.4006847.
The constitutive behavior of bovine scleral and corneal tissues is measured in tension and compression, at quasi-static and moderate strain rates. Experiments are conducted at strain rates up to about 50 strain per second by a pneumatic testing system developed to overcome noise and measurement difficulties associated with the time dependent test of low impedance materials. Results for the tissues at room and the natural bovine body temperatures are similar and indicate that ocular tissue exhibits nonlinear stiffening for increasing strain rates, a phenomena termed rate hardening. For example, at a tensile strain rate of 29/s, corneal tissue is found to develop 10 times the stress that it does quasi-statically at the same strain. Thus, conventional constitutive models will grossly underpredict stresses occurring in the corneo-scleral shell due to moderate dynamic events. This has implication to the accuracy of ocular injury models, the study of the stress field in the corneo-scleral shell for glaucoma research and tonometry measurements. The measured data at various strain rates is represented using the general framework of a constitutive model that has been used to represent biological tissue mechanical data. Here it is extended to represent the measured data of the ocular tissues over the range of tested strain rates. Its form allows for straightforward incorporation in various numerical codes. The experimental and analytical methods developed here are felt to be applicable to the test of human ocular tissue.
在准静态和中等应变率下，对牛巩膜和角膜组织的本构行为进行拉伸和压缩测量。通过开发的气动测试系统在高达约每秒50应变的应变率下进行实验，以克服与低阻抗材料的时间相关测试相关的噪声和测量困难。在室温和牛体自然温度下组织的结果相似，表明眼组织在应变率增加时表现出非线性硬化，这种现象称为速率硬化。例如，在拉伸应变率为29/s时，发现角膜组织产生的应力是在相同应变下准静态时的10倍。因此，传统的本构模型将严重低估由于中等动态事件在角膜巩膜壳中产生的应力。这对眼损伤模型的准确性、青光眼研究中角膜巩膜壳应力场的研究以及眼压测量都有影响。使用已用于表示生物组织力学数据的本构模型的一般框架来表示在各种应变率下测量的数据。在此将其扩展以表示在测试应变率范围内眼组织的测量数据。其形式允许直接纳入各种数值代码。此处开发的实验和分析方法被认为适用于人体眼组织的测试。
