The present paper focuses on the discussion of a set of rational crite
ria for the selection of the damage parameter. The paper considers sca
lar, second-, fourth-, and six-order tenser representations of damage
and evaluates the accuracy with which they approximate exact, micromec
hanical solutions. Considerations of geometrical, stiffness and failur
e criteria favor the selection of effective stiffness as being the mos
t appropriate choice for the damage parameter.