Pre-shearing is widely recognized as a necessary step to guarantee repeatability in rheological studies of thixotropic or aging soft materials. When one-directional pre-shear protocols are used, unrecovered elastic strain which leads to biased material states that are not always relaxed because of the build-up of structure during the relaxation process. We propose a way of guaranteeing unbiased material states by incorporating recovery steps, consisting of steps of strain opposing the initial direction of shearing, into any pre-shear protocol. Using such a multi-step pre-shear protocol, we show that it is possible to produce identical results from shearing in the positive and negative directions for the same magnitude of rate after pre-shearing. We further show how this idea of unbiased material states can be used to obtain unbiased results for other fundamental rheological experiments such as flow curves and frequency sweeps. By performing the new pre-shear protocol for every single measurement point of a flow curve or frequency sweep, it is possible to obtain data which is not affected by previous data collection, which leads to material responses with simple and clear shear histories.

中文翻译：

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预剪切触变或老化软材料的最佳条件

预剪切被广泛认为是保证触变性或老化软材料流变学研究可重复性的必要步骤。当使用单向预剪切协议时，未恢复的弹性应变会导致偏置材料状态，由于在松弛过程中结构的积累，这些状态并不总是松弛。我们提出了一种通过将恢复步骤（包括与初始剪切方向相反的应变步骤）合并到任何预剪切协议中来保证无偏材料状态的方法。使用这种多步预剪切协议，我们表明可以在预剪切后以相同幅度的速率从正方向和负方向剪切产生相同的结果。我们进一步展示了如何使用这种无偏材料状态的想法来获得其他基本流变学实验（例如流动曲线和频率扫描）的无偏结果。通过对流量曲线或频率扫描的每个测量点执行新的预剪切协议，可以获得不受先前数据收集影响的数据，这导致材料响应具有简单而清晰的剪切历史。