ISO 20844:2015规定了一种评估矿物油、合成油和其他含有聚合物的流体在通过指定的柴油喷射器喷嘴时对剪切应力的抵抗力的方法。剪切稳定性通过受试流体的粘度变化来测量，所述粘度变化是由应力期间聚合物降解引起的。在正常情况下，本国际标准适用于ISO 6743中定义的HR和HV类液压油？4[1]和ISO 11158[2]中规定，但它也可应用于HFA、HFB、HFC和HFD类别内的耐火液压油，条件如ISO 12922[3]中规定。 使用本国际标准中描述的程序获得的粘度损失或不存在粘度损失与实际使用中的油和流体的粘度损失之间没有正式的相关性。然而，它为在最小化的热和氧化应力下评估聚合物稳定性提供了标准化条件。它通常被流体和添加剂制造商以及用户用作对现有和潜在配方进行排名的手段。 注:一些规范中规定了粘度以外的性质的变化，但这些变化不在本国际标准中规定的程序中。

ISO 20844:2015 specifies a method to assess the resistance to shear stresses applied to mineral oils, synthetic oils, and other fluids containing polymers, when passed through a specified diesel injector nozzle. The shear stability is measured by the change in viscosity of the fluid under test, brought about by the polymer degradation during stress. Under normal circumstances, this International Standard is applied to hydraulic fluids of categories HR and HV as defined in ISO 6743？4^[1] and specified in ISO 11158 ^[2], but it may also be applied to fire-resistant hydraulic fluids within categories HFA, HFB, HFC, and HFD, with modified conditions as specified in ISO 12922^[3]. No formal correlation has been established between the viscosity loss, or the absence of viscosity loss, obtained using the procedures described in this International Standard and that of oils and fluids in actual service. However, it provides standardized conditions for the evaluation of polymer stability under minimized thermal and oxidative stresses. It is normally used by manufacturers of fluids and additives, and users, as a means of ranking existing and potential formulations. NOTE Changes to properties other than viscosity are specified in some specifications, but these are not covered by the procedures specified in this International Standard.