We present a theoretical and computational study of thixotropic yield-stress materials in cylindrical Couette flows using a novel fluidity-based constitutive model introduced by de Souza Mendes et al. [J. Nonnewtion. Fluid Mech. 261, 1–8 (2018)]. The model relies on measurable rheological properties to couple the equations of motion with an additional equation for the evolution of the material fluidity (i.e., the reciprocal of viscosity). The fluidity itself is used as a structure parameter to assess the material structuring state without the introduction of phenomenological functions or additional parameters. Our simulations parallel rheological tests with a stress-controlled rheometer and are carried out with the material properties obtained experimentally for the laponite suspension from which the model was originally developed. The results reveal that the processes of breakdown and buildup of the microstructure as well as the position of the yield surface in the flow essentially depend on the applied stress and on two material properties associated with distinct thixotropic time scales, namely, the avalanche time and the construction time. The model predictions also capture many features observed in the flow of yield-stress materials with thixotropy, such as the avalanche effect and transient shear banding. We also show that the steady-state flow is uniquely determined by the imposed stress and does not depend on the material initial structuring state. This contrasts with previous reports for nonthixotropic elastoviscoplastic materials, suggesting that nonunique steady flows of structured materials are probably associated with the transient evolution of elastic stresses from a given initial condition.

中文翻译：

---

触变性屈服应力材料的库埃特流动：一种基于流动性的新型本构模型的性能

我们使用 de Souza Mendes 等人引入的基于流动性的新型本构模型，对圆柱形 Couette 流中的触变屈服应力材料进行了理论和计算研究。[J. 无新意。流体机械 261, 1–8 (2018)]。该模型依赖于可测量的流变特性，将运动方程与材料流动性演变的附加方程（即粘度的倒数）相结合。流动性本身被用作结构参数来评估材料结构状态，而无需引入现象学函数或附加参数。我们的模拟与应力控制流变仪并行流变测试，并使用实验获得的材料特性进行，该材料特性用于最初开发模型的锂皂石悬浮液。结果表明，微观结构的分解和建立过程以及屈服面在流动中的位置基本上取决于施加的应力和与不同触变时间尺度相关的两种材料特性，即雪崩时间和施工时间。模型预测还捕获了在具有触变性的屈服应力材料流动中观察到的许多特征，例如雪崩效应和瞬态剪切带。我们还表明，稳态流动是由施加的应力唯一决定的，不依赖于材料的初始结构状态。这与之前关于非触变性弹粘塑性材料的报道形成对比，