Université François Rabelais, Inserm UMR 930 Imagerie et Cerveau, Équipe 5 Imagerie et Ultrasons, 2 Bd Tonnellé, 37044 Tours Cedex 9, France; INSA Centre Val de Loire, Laboratoire de Mécanique et Rhéologie, Université François Rabelais Tours, 3, Rue de la Chocolaterie CS 23410, F-41034 Blois Cedex, France.
INSA Centre Val de Loire, Laboratoire de Mécanique et Rhéologie, Université François Rabelais Tours, 3, Rue de la Chocolaterie CS 23410, F-41034 Blois Cedex, France.
J Mech Behav Biomed Mater. 2018 Jan;77:242-249. doi: 10.1016/j.jmbbm.2017.09.009. Epub 2017 Sep 11.
When a living tissue is subjected to cyclic stretching, the stress-strain curves show a shift down with the increase in the number of cycles until stabilization. This phenomenon is referred to in the literature as a preconditioning and is performed to obtain repeatable and predictable measurements. Preconditioning has been routinely performed in skin tissue tests; however, its effects on the mechanical properties of the material such as viscoelastic response, tangent modulus, sensitivity to strain rate, the stress relaxation rate, etc….remain unclear. In addition, various physical interpretations of this phenomenon have been proposed and there is no general agreement on its origin at the microscopic or mesoscopic scales. The purpose of this study was to investigate the effect of the cyclical stretching and the stress-relaxation tests on the mechanical properties of the porcine skin. Cyclic uniaxial tensile tests at large and constant strain were performed on different skin samples. The change in the reaction force, and skin's tangent modulus as a function of the number of cycles, as well as the strain rate effect on the mechanical behavior of skin samples after cycling were investigated. Stress-relaxation tests were also performed on skin samples. The change in the reaction force as a function of relaxation time and the strain rate effect on the mechanical behavior of skin samples after the stress-relaxation were investigated. The mechanical behavior of a skin sample under stress-relaxation test was modeled using a combination of hyperelasticity and viscoelasticity. Overall, the results showed that the mechanical behavior of the skin was strongly influenced by cycling and stress relaxation tests. Indeed, it was observed that the skin's resistance decreased by about half for two hours of cycling; the tangent modulus degraded by nearly 30% and skin samples became insensitive to the strain rates and accumulated progressively an inelastic deformation over time during cycling. Finally, the hysteresis loops became very narrow at the end of cycling and after relaxation process.
当活组织受到循环拉伸时，随着循环次数的增加，应力-应变曲线会向下移动，直到稳定。这种现象在文献中被称为预处理，目的是获得可重复和可预测的测量结果。预处理已在皮肤组织测试中常规进行；然而，其对材料力学性能的影响，如粘弹性响应、切变模量、应变率敏感性、应力松弛率等，仍不清楚。此外，已经提出了这种现象的各种物理解释，并且在微观或介观尺度上，对于其起源没有达成普遍共识。本研究的目的是研究循环拉伸和应力松弛测试对猪皮力学性能的影响。在不同的皮肤样本上进行了大应变和恒应变的循环单轴拉伸测试。研究了在循环过程中，反作用力的变化和皮肤的切变模量随循环次数的变化，以及应变率对皮肤样本力学行为的影响。还对皮肤样本进行了应力松弛测试。研究了在松弛过程中，反作用力随松弛时间的变化，以及应变率对皮肤样本力学行为的影响。使用超弹性和粘弹性的组合对皮肤样本在应力松弛测试下的力学行为进行建模。总的来说，结果表明，皮肤的力学行为受到循环和应力松弛测试的强烈影响。实际上，观察到在两小时的循环过程中，皮肤的阻力降低了约一半；切变模量下降了近 30%，皮肤样本对应变率变得不敏感，并且随着时间的推移，在循环过程中逐渐积累了不可恢复的变形。最后，在循环结束和松弛过程之后，滞后环变得非常狭窄。
