The normal stress effect and equilibrium friction coefficient of articular cartilage under steady frictional shear.
The normal stress effect and equilibrium friction coefficient of articular cartilage under steady frictional shear.
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DOI：
10.1016/s0021-9290(97)00031-6
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发表时间：
1997-08
影响因子：
2.4
通讯作者：
H. Wang;G. Ateshian
中科院分区：
文献类型：
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作者：
H. Wang;G. Ateshian
在蠕变或应力松弛期间，关节软骨表现出时间依赖性摩擦系数，随着组织变形平衡，该摩擦系数已被证明达到平衡值μeq。本研究探讨关节软骨组织块在应力松弛平衡状态下，在稳态摩擦剪应力及恒压应变作用下的摩擦特性。测量的两个参数是法向力和摩擦扭矩，然后从中计算摩擦系数。实验结果表明：（1）在规定的无限小压应变下，软骨在稳态剪切下比在无摩擦剪切下承受更大的压正应力。此外，正应力随着滑动速度的增加而增加，导致μeq的值依赖于速度。所观察到的法向应力有效地增加了软骨的压缩刚度的一个因素高达3.1。(2)在规定的稳定摩擦剪切下，法向应力和摩擦剪应力都随着压缩应变的增加而增加，但不是成比例的，从而产生减小的摩擦系数。(3)这种速度依赖性的正常应力效应也被证明是导致，至少部分地，从软骨的内在属性。关节软骨的正应力效应以前没有报道过，代表了一种在固体中不常见的有趣的机械反应，尽管在非牛顿流体中很常见。
During creep or stress relaxation, articular cartilage exhibits a time-dependent friction coefficient which has been shown to reach an equilibrium value, μeq, as the tissue deformation equilibrates. This study investigates the frictional properties of articular cartilage explants under steady frictional shear and constant compressive strain after the tissue reaches stress-relaxation equilibrium. The two parameters measured are the normal force and frictional torque, from which the friction coefficient was then calculated. It is shown in this experimental study that: (1) Under a prescribed infinitesimal compressive strain, cartilage supports higher compressive normal stress under steady shear than it does in the absence of frictional shear. Furthermore, the normal stress increases with increasing sliding velocity, resulting in a velocity-dependent value of μeq. The observed normal stress effectively increases the compressive stiffness of cartilage by a factor up to 3.1. (2) Under a prescribed steady frictional shear both the normal stress and frictional shear stress increase, though not proportionally, with increasing compressive strain, producing a decreasing friction coefficient. (3) This velocity-dependent normal stress effect is also shown to result, at least partly, from intrinsic properties of cartilage. The normal stress effect has not been previously reported for articular cartilage, and represents an intriguing mechanical response not commonly encountered in solids, though common in non-Newtonian fluids.