The relationship between the geometric and mechanical profiles of hair fibers has been studied, with special focus on curly samples. Incidental observations pointed to a significantly different viscoelastic character with varying curliness. Further investigations confirmed initial observations, showing an initial distinct toe region behavior for curly fibers on the stress-strain plot, which is absent for straight fibers. This behavior suggested a difference in the viscoelastic nature of the curly fiber that is linked to mechanical energy stored in the fiber. Results also suggest that the strength of hair depends on two main components, and further pointed out that de facto methods of tensile testing may erode curly fiber strength during preparation. The main outcome of this study is that the tensile strength (σT) of hair fibers is composed of two (rather than one main) components, namely the toe region (σt) and the elastic region (σε), so that: σT=σt+σε. For noncurly fibers, the greatest part of fiber strength is derived from σε, while σt ≈ 0. For curly fibers, σt (i.e., springiness) adds significantly to the overall strength, even though σε remains the major contributor. Although these results require validation in larger studies, they are significant in the current understanding of curly hair. Also, they may represent a fundamental shift from the current understanding of tensile testing of human hair in general.

中文翻译：

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了解卷发力学：纤维强度。

已经研究了毛发纤维的几何和机械轮廓之间的关系，特别关注卷曲的样品。偶然的观察指出，具有不同的卷曲度的显着不同的粘弹性特征。进一步的研究证实了初步的观察结果，在应力-应变曲线上显示了卷曲纤维的初始明显的脚趾区域行为，而对于直纤维则没有。这种行为表明，卷曲纤维的粘弹性性质有所不同，这与存储在纤维中的机械能有关。结果还表明，头发的强度取决于两个主要成分，并进一步指出，事实上的拉伸测试方法可能会在制备过程中侵蚀卷曲纤维的强度。这项研究的主要结果是，头发纤维的拉伸强度（σT）由两个（而不是一个主要）组成，即脚趾区域（σt）和弹性区域（σε），因此：σT=σt +σε。对于非卷曲纤维，纤维强度的最大部分来自σε，而σt≈0。对于卷曲纤维，尽管σε仍然是主要贡献者，但σt（即弹性）显着增加了整体强度。尽管这些结果需要在较大的研究中进行验证，但它们在当前对卷发的理解中具有重要意义。同样，它们可能代表了从目前对人发拉伸测试的总体理解上的根本转变。纤维强度的最大部分来自σε，而σt≈0。对于卷曲纤维，尽管σε仍然是主要贡献者，但σt（即弹性）显着增加了整体强度。尽管这些结果需要在较大的研究中进行验证，但它们在当前对卷发的理解中具有重要意义。同样，它们可能代表了从目前对人发拉伸测试的总体理解上的根本转变。纤维强度的最大部分来自σε，而σt≈0。对于卷曲纤维，尽管σε仍然是主要贡献者，但σt（即弹性）显着增加了整体强度。尽管这些结果需要在较大的研究中进行验证，但它们在当前对卷发的理解中具有重要意义。同样，它们可能代表了从目前对人发拉伸测试的总体理解上的根本转变。