In this work, the effect of rigid rods on the discontinuous shear thickening (DST) transition in mixtures of smaller isotropic-shaped (calcium carbonate—CC) and larger rod-like (polyamide or glass) particles dispersed in water is experimentally established. The CC suspension in water is considered as a shear thickening matrix filling the pores of the fiber network. The DST in the matrix originates from the competition between the applied shear stress and the steric repulsion between adsorbed superplasticizer molecules. It is characterized by a typical S-shape of the flow curves, irregular oscillations of the shear rate in response to the applied shear stress, and some thixotropy. An addition of rods shifts the DST transition to lower critical shear rates, as explained by an increase in the suspension viscosity such that the shear rate to reach the onset stress of DST decreases. This behavior is satisfactorily reproduced by the reduced shear rate approach of Ohl and Gleissle [J. Rheol. 37, 381–406 (1993)] and, to a lesser extent, by the homogenization approach of Chateau et al. [J. Rheol. 52, 489–506 (2008)], both assuming random rod orientation. At fiber volume fractions, φ f ≥ 0.04, the mixture undergoes jamming, which is likely associated with the percolation threshold of the fiber network, nearly independent of the CC particle concentration. This idea is qualitatively supported by a modified homogenization approach, assuming that viscous dissipation mostly occurs in the vicinity of the contacts between fibers. The results of this work are believed to be useful for optimal formulations of fiber-reinforced cementitious materials.

中文翻译：

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通过混合器型流变仪测试各向同性和棒状颗粒的浓缩混合物中的不连续剪切增稠

在这项工作中，通过实验确定了刚性棒对分散在水中的较小的各向同性（碳酸钙-CC）和较大的棒状（聚酰胺或玻璃）颗粒的混合物中的不连续剪切增稠 (DST) 转变的影响。CC 在水中的悬浮液被认为是填充纤维网络孔隙的剪切增稠基质。基质中的 DST 源于施加的剪切应力和吸附的超塑化剂分子之间的空间排斥之间的竞争。它的特点是流动曲线呈典型的 S 形，剪切速率响应于所施加的剪切应力而发生不规则振荡，并且具有一定的触变性。添加棒将 DST 转变转移到较低的临界剪切速率，正如悬浮液粘度的增加所解释的那样，达到 DST 起始应力的剪切速率降低。Ohl 和 Gleissle 的降低剪切速率方法令人满意地再现了这种行为 [J. 流变。37, 381–406 (1993)] 以及在较小程度上通过 Chateau 等人的同质化方法。[J. 流变。52, 489–506 (2008)]，均假设杆方向随机。在纤维体积分数 φ f ≥ 0.04 时，混合物发生堵塞，这可能与纤维网络的渗透阈值有关，几乎与 CC 颗粒浓度无关。这个想法得到了改进的均质化方法的定性支持，假设粘性耗散主要发生在纤维之间的接触附近。