For two porous components A and B in welded contact, the volume fractions of the components vA, vB satisfy
v_A + v_B = 1, while the overall porosity is given by
= v_A_A + v_B_B, where are respectively the porosities of the porous constituents A and B. The fractions of the total volume occupied by the solid components are and , respectively. The solid components in A and B are individually pure, so that each porous constituent may be thought of as a microhomogeneous (or Gassmann) material.