Viscoelastic shear properties of human vocal fold tissues were previously quantified by the shear moduli (G' and G″). Yet these small-strain linear measures were unable to describe any nonlinear tissue behavior. This study attempted to characterize the nonlinear viscoelastic response of the vocal fold lamina propria under large-amplitude oscillatory shear (LAOS) with a stress decomposition approach. Human vocal fold cover and vocal ligament specimens from eight subjects were subjected to LAOS rheometric testing with a simple-shear rheometer. The empirical total stress response was decomposed into elastic and viscous stress components, based on odd-integer harmonic decomposition approach with Fourier transform. Nonlinear viscoelastic measures derived from the decomposition were plotted in Pipkin space and as rheological fingerprints to observe the onset of nonlinearity and the type of nonlinear behavior. Results showed that both the vocal fold cover and the vocal ligament experienced intercycle strain softening, intracycle strain stiffening, as well as shear thinning both intercycle and intracycle. The vocal ligament appeared to demonstrate an earlier onset of nonlinearity at phonatory frequencies, and higher sensitivity to changes in frequency and strain. In summary, the stress decomposition approach provided much better insights into the nonlinear viscoelastic behavior of the vocal fold lamina propria than the traditional linear measures.

中文翻译：

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大振幅振荡剪切 (LAOS) 下人类声带组织的非线性粘弹性表征

人类声带组织的粘弹性剪切特性先前通过剪切模量（G' 和 G”）量化。然而，这些小应变线性测量无法描述任何非线性组织行为。本研究试图用应力分解方法表征声带固有层在大振幅振荡剪切 (LAOS) 下的非线性粘弹性响应。使用简单剪切流变仪对来自八名受试者的人类声带盖和声带韧带标本进行了 LAOS 流变测试。基于傅里叶变换的奇整数谐波分解方法，经验总应力响应被分解为弹性和粘性应力分量。从分解得到的非线性粘弹性测量被绘制在皮普金空间中，并作为流变指纹来观察非线性的开始和非线性行为的类型。结果表明，声带盖和声带韧带都经历了周间应变软化、周内应变硬化以及周间和周内的剪切变薄。声带似乎在发声频率上表现出更早的非线性，并且对频率和应变的变化具有更高的敏感性。总之，与传统的线性测量相比，应力分解方法对声带固有层的非线性粘弹性行为提供了更好的洞察。结果表明，声带盖和声带韧带都经历了周间应变软化、周内应变硬化以及周间和周内的剪切变薄。声带似乎在发声频率上表现出更早的非线性，并且对频率和应变的变化具有更高的敏感性。总之，与传统的线性测量相比，应力分解方法对声带固有层的非线性粘弹性行为提供了更好的洞察。结果表明，声带盖和声带韧带都经历了周间应变软化、周内应变硬化以及周间和周内的剪切变薄。声带似乎在发声频率上表现出更早的非线性，并且对频率和应变的变化具有更高的敏感性。总之，与传统的线性测量相比，应力分解方法对声带固有层的非线性粘弹性行为提供了更好的洞察。