In this paper, it has been pointed out that material laws and constitutive
theories are the fundamental bases for describing the mechanical behaviour
of materials under multiaxial states of stress involving actual boundary co
nditions and considering the micro structure of the material, the anisotrop
y, and, furthermore, both physical and geometrical non linearities. In solv
ing such complex problems, the tensor function theory has become a powerful
tool as illustrated in this paper.