What is rule of mixture?

Rule of mixture refers to a mathematical formula used to calculate the properties of a composite material, which is made up of two or more different constituents. The rule of mixture has two variations i.e., Voigt's rule and Reuss' rule. Voigt's rule assumes that the two constituents of the composite remain separated and are parallel to each other. Reuss' rule, on the other hand, assumes that the two constituents of the composite are mixed together randomly. The rule of mixture is used to calculate the composite material's properties, such as thermal conductivity, mechanical properties, and electrical conductivity, by taking into account the properties of each constituent and their volume fractions in the composite material. The rule of mixture provides an approximation of the composite material's properties, but actual results may deviate from the calculated values due to factors such as the size, shape, and orientation of the constituents within the composite material.