Farran L, Ennos A R, Starkie M, Eichhorn S J
Materials Science Centre, School of Materials, Grosvenor Street, University of Manchester, Manchester, United Kingdom.
J Biomech. 2009 Jun 19;42(9):1230-5. doi: 10.1016/j.jbiomech.2009.03.020. Epub 2009 Apr 19.
The mechanical properties of fingernails are important because of their impact in preventing damage and in maintaining their appearance. In particular, knowing the effect of local environmental conditions can tell us how they might best be protected. In order to better understand this, tensile tests were carried out to characterise the properties of fingernails at different relative humidities. Cyclic tests were also conducted to investigate the ability of the structure to recover deformation at different moisture contents. Torsional tests were performed to determine the shear modulus of the keratinous matrix material which binds together the fibrous components of the fingernails. This enabled an analysis of how the material may resist bending, torsion and permanent deformation in a natural environment. In particular, it is shown that at low relative humidity the nails are more brittle, and at high moisture contents they are more flexible. Increasing relative humidity lowers torsional stiffness much more than tensile stiffness, suggesting that moisture plasticises the matrix rather than affecting the fibres. The twist to bend ratio is minimised at 55% RH, close to the natural condition of nails which should minimise susceptibility to torsional damage due to plasticisation and a disruption of the matrix material binding the keratin fibres.
指甲的机械性能很重要，因为它们对防止损伤和保持外观有影响。特别是，了解局部环境条件的影响可以告诉我们如何最好地保护它们。为了更好地理解这一点，进行了拉伸试验以表征不同相对湿度下指甲的性能。还进行了循环试验，以研究结构在不同含水量下恢复变形的能力。进行扭转试验以确定将指甲的纤维成分结合在一起的角蛋白基质材料的剪切模量。这使得能够分析材料在自然环境中如何抵抗弯曲、扭转和永久变形。特别是，结果表明，在低相对湿度下指甲更脆，而在高含水量下它们更灵活。相对湿度的增加使扭转刚度降低的幅度远大于拉伸刚度，这表明水分使基质增塑而不是影响纤维。扭转与弯曲比在55%相对湿度下最小化，接近指甲的自然状态，这应使由于增塑和结合角蛋白纤维的基质材料破坏而导致的扭转损伤敏感性最小化。
