We analyze different flow regimes of a filament formed by extrusion of a material through a cylindrical die. We deduce that the elongational yield stress of a simple yield stress fluid (i.e., with negligible thixotropy effects) can be determined from the mass of the droplet after filament breakage and an estimation of the critical radius at pinch-off at the solid-liquid regime transition. We demonstrate that such a simple characterization is relevant in a relatively wide range of extrusion velocities, i.e., this velocity slightly affects the drop mass in this range. For the simple yield stress fluids used, Carbopol gel, clay-water paste at different concentrations, and emulsion, covering a large range of yield stress values (50–1000 Pa), the elongational yield stress appears to be equal to the simple shear yield stress times a factor equal to about $1.5\sqrt{3}$. As a consequence, this simple test may be used to obtain, almost instantaneously and without sophisticated apparatus (a syringe and a balance are sufficient), a good estimate of the shear yield stress of simple yield stress fluids. In that case, the main source of uncertainty (up to about 20%) is the value of the critical radius at the solid-liquid transition. Finally, we review the operating conditions (material properties and extrusion characteristics) for which we can expect this approach to be valid.

中文翻译：

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从落下的液滴尺寸测量即时屈服应力：“注射器测试”

我们分析了通过圆柱形模具挤压材料形成的细丝的不同流动状态。我们推断，简单屈服应力流体（即，触变效应可忽略不计）的伸长屈服应力可以根据细丝断裂后的液滴质量和固液状态下夹断临界半径的估计来确定过渡。我们证明了这种简单的表征与相对较宽范围的挤压速度相关，即该速度略微影响该范围内的液滴质量。对于使用的简单屈服应力流体、Carbopol 凝胶、不同浓度的粘土水糊和乳液，涵盖了很大范围的屈服应力值 (50–1000 Pa)，$1.5\sqrt{\mathrm{3个}}$. 因此，这个简单的测试可以用来获得，几乎瞬间并且不需要复杂的设备（注射器和天平就足够了），对简单屈服应力流体的剪切屈服应力的良好估计。在这种情况下，不确定性的主要来源（高达约 20%）是固液转变时的临界半径值。最后，我们回顾了我们可以预期此方法有效的操作条件（材料特性和挤压特性）。