yield value

The yield value is the amount of push a material can withstand before it gives in and starts to flow. Below this threshold it holds its shape like a solid; above it, it flows like a thick liquid. The everyday test is whether a blob of toothpaste or mayonnaise sits in a peak without slumping: the higher the yield value, the steeper a peak it can hold.

Formally, the yield value is the minimum shear stress that must be applied to initiate flow in a plastic material, with units of pascals. On a rheogram it appears as the point where the flow curve intercepts the shear-stress axis: no flow occurs at any stress below that intercept. It arises from an internal structure, typically a network of flocculated particles or a gel matrix, that must be ruptured before the material can move.

Controlling the yield value is central to designing many semisolids and structured suspensions. A high enough yield value keeps suspended particles from settling and lets a topical product cling to vertical skin without dripping, while a yield value that is too high makes the product hard to pour, extrude, or rub in. Real materials often show a slightly fuzzy onset of flow rather than a sharp single point, so extrapolated and dynamic-measured yield values may differ.