Dynamic oscillatory shear flow has been widely used to investigate viscoelastic material functions. In particular, small amplitude oscillatory shear (SAOS) tests have become the canonical method for characterizing the linear viscoelastic properties of complex fluids based on strong theoretical background and plenty of experimental results. Recently, there has been increasing interest in the use of large amplitude oscillatory shear (LAOS) tests for the characterization of complex fluids. However, it is difficult to define material functions in LAOS regime due to an infinite number of higher harmonic contributions. For this reason, many recent studies have focused on intrinsic nonlinearities obtained in medium amplitude oscillatory shear (MAOS) regime, which is a subdivision of the full LAOS regime. In this study, we reviewed recent experimental and theoretical results of nonlinear material functions in the MAOS regime, which contain four MAOS moduli (two first-harmonic moduli and two third-harmonic moduli) from Fourier and power series of shear stress, and a nonlinear material function Q₀ and its elastic and viscous parts from Fourier-transform rheology (FT rheology). Furthermore, to identify linear-to-nonlinear transitions in stress response of model polystyrene (PS) solutions, we presented Pipkin diagrams in frequency ranges from the rubbery plateau region to the terminal region.

中文翻译：

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中振幅振荡剪切（MAOS）流下的非线性材料功能

动态振荡剪切流已被广泛用于研究粘弹性材料的功能。特别是，基于强大的理论背景和大量实验结果，小振幅振荡剪切（SAOS）测试已成为表征复杂流体的线性粘弹性特性的规范方法。近来，人们越来越关注使用大振幅振荡剪切（LAOS）测试来表征复杂流体。但是，由于无限数量的高次谐波贡献，很难在LAOS制度中定义物质功能。因此，许多最新研究集中在中振幅振荡剪切（MAOS）方案中获得的固有非线性上，该振幅是完整LAOS方案的细分。在这个研究中，Q ₀及其弹性和粘性部分来自傅立叶变换流变学（FT流变学）。此外，为了识别模型聚苯乙烯（PS）解决方案的应力响应中的线性到非线性转变，我们在从橡胶高原区域到末端区域的频率范围内提供了皮普金图。