We study the viscoelastic solid properties of cohesive particulate suspensions using creep and constant rate tests in a vane-in-large-cup geometry. A cup-to-vane diameter ratio larger than 4 is used to ensure that wall effects are minimized. In both the creep and constant rate tests, the modulus becomes nonlinear at strains consistent with scaled interparticle bond distances. Yielding and subsequent flow do not occur until strains of order 1, corresponding to a cage melting or particle crowding failure mechanism. In between the bond and cage melting strains, the modulus shows power-law softening with an index of approximately −0.8, corresponding to progressive bond breakage. The observed behavior in creep correlates with constant rate experiments and demonstrates that strain softening of the modulus prior to yielding is an important component of the rheology of particulate gels and suspensions. The assumption of linear behavior up to yielding appears to be inappropriate. We observe that the transient creep behavior initially shows power-law or Andrade creep that transforms to an exponential decay at long times. For creep stresses that show time-dependent yield, the break time decreases exponentially with stress.

中文翻译：

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浓缩粘性内聚颗粒悬浮液的应变软化，然后进行屈服

我们使用大杯形叶片中的蠕变和恒定速率测试研究粘性颗粒悬浮液的粘弹性固体性质。杯与叶片的直径比大于4，可确保将壁效应最小化。在蠕变和恒定速率测试中，模量在与按比例缩放的粒子间键合距离一致的应变下变为非线性。直到发生1级应变（对应于笼式熔化或颗粒拥挤破坏机制）后，屈服和随后的流动才发生。在键和保持架熔化应变之间，模量显示出幂律软化，其折射率约为-0.8，对应于渐进的键断裂。蠕变中观察到的行为与恒定速率实验相关，并表明屈服之前模量的应变软化是颗粒凝胶和悬浮液流变学的重要组成部分。线性行为直到屈服的假设似乎是不合适的。我们观察到，瞬态蠕变行为最初显示出幂律蠕变或Andrade蠕变，在很长一段时间内会转变为指数衰减。对于表现出随时间变化的屈服应力的蠕变应力，断裂时间随应力的增加呈指数下降。