Skin is a highly non-linear, anisotropic, rate dependent inelastic, and nearly incompressible material which exhibits substantial hysteresis even under very slow (quasistatic) loading conditions. In this paper, a series of uniaxial cyclic loading tests of porcine and rat skin at different strain rates and with samples oriented in different directions (with respect to the spine) were conducted to study the effect of strain rate and samples orientations with respect to spine on Mullins-type softening and skin inelastic response. A noteworthy feature of skin is that, similar to certain filled rubbers, its mechanical response shifts after the first extension and exhibits softening and hysteresis when loaded under cyclic tension and Mullins-type softening is observed. The results of these strain-controlled cyclic loading tests also indicated that the extent of softening is different for different strain rates and orientations. Also, a substantial hysteresis persists even at very low strain rates indicating inelastic behavior beyond the rate sensitive viscoelastic response. Through this series of experiments, by investigating the effect of strain rate on pig skin and rat skin, we conclude that the skin response is rate dependent but inelastic and shows irreversible changes in fiber orientation which are observed in histology results. Also, skin shows persistent deformation that is only partially recovered even after a long period of unloading.

中文翻译：

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单轴循环机械载荷下猪和大鼠皮肤非弹性响应的实验研究

皮肤是一种高度非线性、各向异性、速率相关的非弹性材料，并且几乎不可压缩，即使在非常缓慢（准静态）加载条件下也表现出明显的滞后。在本文中，对猪和大鼠皮肤在不同应变率和不同方向（相对于脊柱）的样品进行了一系列单轴循环加载试验，以研究应变率和样品相对于脊柱的方向的影响。关于穆林斯型软化和皮肤无弹性反应。表皮的一个值得注意的特征是，类似于某些填充橡胶，它的机械响应在第一次拉伸后发生变化，并在循环张力下加载时表现出软化和滞后现象，并观察到穆林斯型软化。这些应变控制循环加载试验的结果还表明，不同应变率和取向的软化程度不同。此外，即使在非常低的应变率下，显着的滞后也持续存在，表明超出了速率敏感的粘弹性响应的非弹性行为。通过这一系列实验，通过研究应变速率对猪皮肤和大鼠皮肤的影响，我们得出结论，皮肤反应是速率依赖性的，但没有弹性，并且在组织学结果中观察到纤维取向的不可逆变化。此外，皮肤显示出持久的变形，即使在长时间卸载后也只能部分恢复。即使在非常低的应变率下，显着的滞后仍然存在，表明超出了速率敏感的粘弹性响应的非弹性行为。通过这一系列实验，通过研究应变速率对猪皮肤和大鼠皮肤的影响，我们得出结论，皮肤反应是速率依赖性的，但没有弹性，并且在组织学结果中观察到纤维取向的不可逆变化。此外，皮肤显示出持久的变形，即使在长时间卸载后也只能部分恢复。即使在非常低的应变率下，显着的滞后仍然存在，表明超出了速率敏感的粘弹性响应的非弹性行为。通过这一系列实验，通过研究应变速率对猪皮肤和大鼠皮肤的影响，我们得出结论，皮肤反应是速率依赖性的，但没有弹性，并且在组织学结果中观察到纤维取向的不可逆变化。此外，皮肤显示出持久的变形，即使在长时间卸载后也只能部分恢复。