A property involving a combination of elastic and viscous behavior in the application of which a material is considered to combine the features of a perfectly elastic solid and a perfect fluid. The property of resistance to flow exhibited within the body of a material, expressed in terms of relationship between applied shearing stress and resulting rate of strain in shear. Viscosity is usually taken to mean Newtonian viscosity, in which case the ration of shearing stress to the rate of shearing strain is constant. In non-Newtonian behavior, which is the usually case with plastics, the ratio varies with the shearing stress. Such ratios are often called the apparent viscosities at the corresponding shearing stresses.
Viscosity is measured in terms of flow with water as the base standard.
The higher the number, the less flow. Index voids Air or gas that has been trapped and cured into a laminate. Porosity is an aggregation of microvoids. Voids are essentially incapable of transmitting structural stresses or nonradiative energy fields. The percent of volatiles that are driven off as a vapor from a plastic or an impregnated reinforcement.