A Brief History of the Yield Stress

This short article is a summary of a recently published, lengthy review [1] in which the author challenges the often-accepted view that materials have yield stresses, below which no flow takes place. However, following the introduction of the new generation of controlled-stress rheometers it is shown that when careful measurements are made below the supposed ’yield stress‘, flow does actually take place. The argument for the nonexistence of the yield stress as a physical entity now seems insuperable. However, in spite of this, it is nevertheless accepted that an apparent yield stress is a useful mathematical abbreviated description of limited data over a given range of flow conditions. This yield stress parameter can be used effectively for predicting flow, but only within the region of the original measurement that furnished the yield stress