Anisotropy

Abstract

In the preceding chapters, the constitutive law developed for poroelastic materials assumes that the materials do not exhibit directional properties at the macroscopic level, and are isotropic. Geomaterials however are often anisotropic due to the existence of bedding surfaces in sedimentary rocks, foliations in metamorphic rocks, and microcracks aligned in the direction of stresses. Biomaterials such as cortical and trabecular bones are also anisotropic, due to their growth oriented in the direction of the physiological load (Yoon and Cowin, Biomech Model Mechanobiol 7(1):13–26, 2008). In this chapter we shall develop the constitutive laws for the general material anisotropy, which are also simplified to special cases.

The passive strength of the materials employed in the mechanical arts depends on the cohesive and repulsive forces of their particles, and on the rigidity of their structure. The consideration of the intimate nature of these forces belongs to the discussion of the physical properties of matter; but the estimation of their magnitude, and of their relative value in various circumstances, is of undeniable importance to practical mechanics, …The principal effects of any force acting on a solid body may be reduced to seven denominations; extension, compression, detrusion, flexure, torsion, a1teration, and fracture.

—Thomas Young (1845)