Yield, Creep And Recovery - Why Are They Important?

By Robert G. McGregor, General Manager – Global Marketing, Brookfield Engineering Laboratories, Inc.

Material flow behavior may include the phenomenon called “creep” which applies to various liquids and semi-solids, like gels and lotions that continue to move slightly even after placement on the skin. R&D’s intent when formulating the substance is to minimize movement because the medicinal effect is best accomplished by keeping the material in the original position where it is applied. Laws pertaining to the effect of gravity and what happens to materials in motion require that flow behavior continue until the lowest energy state is achieved. Simply put, R&D needs to know how much force is needed to initiate flow of a material, how long the movement of the material will continue once flow has commenced, and the potential displacement or deformation of the material relative to its initial position.