标题： 通过挤压流动实验的数值模拟表征一种触变半固体浆料的流变特性 显示英文标题

标题： Rheological characterization of a thixotropic semisolid slurry by means of numerical simulations of squeeze flow experiments

摘要： 我们提出了一种利用实验挤压流动数据表征半固态金属浆料流变特性的方法。 该浆料被建模为一种结构性触变粘塑性材料，遵循正则化的Herschel-Bulkley本构方程。 所有流变参数都假定随受控于一级反应动力学的结构参数变化，该反应动力学考虑了材料结构的破坏和重建。 使用拉格朗日框架中的有限元法模拟挤压流动。 研究了宾汉数、雷诺数、幂律指数以及结构参数的动力学参数广泛范围内的样品高度演化。 与半固态铝合金（A356）的现有实验数据进行了系统比较，在该实验中，样品在582℃下从顶部以80%应变压缩，而底部固定不动。 只要在实验初始阶段（直到0.01秒），施加的载荷远高于名义实验载荷，并且屈服应力和幂律指数随结构参数线性变化，则可以与实验数据取得极好的一致性。 第一个假设意味着在实验初期需要采用不同的模型，例如弹粘塑性模型。 至于第二个假设，通过允许屈服应力从0（无结构）到最大名义值（完全结构），以及幂律指数从0.2到1.4变化（即从剪切稀化到剪切增稠区域），可以重现样品高度的变化。 这些变化与已知半固态浆料内部微观结构的变化模式一致。 显示英文摘要

摘要： We propose a methodology for the rheological characterization of a semisolid metal slurry using experimental squeeze flow data. The slurry is modeled as a structural thixotropic viscoplastic material, obeying the regularized Herschel-Bulkley constitutive equation. All rheological parameters are assumed to vary with the structure parameter that is governed by a first-order kinetics accounting for the material structure breakdown and build-up. The squeeze flow is simulated using finite elements in a Lagrangian framework. The evolution of the sample height has been studied for wide ranges of the Bingham and Reynolds numbers, the power-law exponent as well as the kinetics parameters of the structure parameter. Systematic comparisons have been carried out with available experimental data on a semisolid aluminium alloy (A356), where the sample is compressed from its topside under a specified strain of 80% at a temperature of 582 oC while the bottom side remains fixed. Excellent agreement with the experimental data could be achieved provided that at the initial instances (up to 0.01s) of the experiment the applied load is much higher than the nominal experimental load and that the yield stress and the power-law exponent vary linearly with the structure parameter. The first assumption implies that a different model, such as an elastoviscoplastic one, needs to be employed during the initial stages of the experiment. As for the second one, the evolution of the sample height can be reproduced allowing the yield stress to vary from 0 (no structure) to a maximum nominal value (full structure) and the power-law exponent from 0.2 to 1.4, i.e., from the shear-thinning to the shear-thickening regime. These variations are consistent with the internal microstructure variation pattern known to be exhibited by semisolid slurries.