<p>Yielding pastes are a class of soft materials that have the ability to mechanically transition between solid-like deformation and fluid-like flow based on the level of mechanical loading. This phenomenology, particularly when it is reversible, makes them ideal for use in additive manufacturing processes such as direct-ink-writing (DIW) 3D printing. To optimize materials for such applications, robust characterization of the flow behavior of these materials is needed. The most common means of doing this is the collection of a steady-shear flow curve, which consists of a series of constant shear rate tests across the desired deformation range, tracking the stress required for the deformation in each. The exact means by which this is accomplished, however, varies quite widely, with literature implementing tests with a variety of collection orders, preshear protocols, and end-of-test conditions. As many yielding pastes exhibit complex shear history, this variation in testing procedures creates a potential obstacle for obtaining reproducible results. To address this, we compare the flow curves of model yielding pastes as the order of measurements is changed. We also examine the impact of material conditioning on these changes by contrasting between a conventional shear-ramping preconditioning and a novel oscillatory/forced-recovery preshear. By examining the effect that the measurement collection order has on collected flow curves of multiple model yielding pastes, we determine the inclusion of an oscillatory preshear containing a forced-recovery step in-between successive measurements allows for a minimization of the path-dependence caused by material shear history.</p>

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Path-independent flow characterization of model yielding pastes

  • Gavin J. Donley,
  • Nicos Martys,
  • Emanuela Del Gado,
  • Kenneth Snyder

摘要

Yielding pastes are a class of soft materials that have the ability to mechanically transition between solid-like deformation and fluid-like flow based on the level of mechanical loading. This phenomenology, particularly when it is reversible, makes them ideal for use in additive manufacturing processes such as direct-ink-writing (DIW) 3D printing. To optimize materials for such applications, robust characterization of the flow behavior of these materials is needed. The most common means of doing this is the collection of a steady-shear flow curve, which consists of a series of constant shear rate tests across the desired deformation range, tracking the stress required for the deformation in each. The exact means by which this is accomplished, however, varies quite widely, with literature implementing tests with a variety of collection orders, preshear protocols, and end-of-test conditions. As many yielding pastes exhibit complex shear history, this variation in testing procedures creates a potential obstacle for obtaining reproducible results. To address this, we compare the flow curves of model yielding pastes as the order of measurements is changed. We also examine the impact of material conditioning on these changes by contrasting between a conventional shear-ramping preconditioning and a novel oscillatory/forced-recovery preshear. By examining the effect that the measurement collection order has on collected flow curves of multiple model yielding pastes, we determine the inclusion of an oscillatory preshear containing a forced-recovery step in-between successive measurements allows for a minimization of the path-dependence caused by material shear history.