ABSTRACT
This chapter looks at representing stresses and strains in volumetric and deviatoric form. Deviatoric stresses play an important role in metal plasticity. The chapter discusses an alternative form of stress invariants that is useful in the modeling of frictional materials. Most constitutive models of material behavior, such as plasticity models, are defined in terms of stress invariants. The volumetric and deviatoric stress–strain relations are uncoupled for isotropic elastic materials. The chapter also considers a Cartesian coordinate system oriented in the principal stress directions. In a uniaxial test, a sample of the material is subjected to a single component of stress along the axis of the sample. In an isotropic compression test, usually done on geomaterials, the stresses applied on the sample are the same in all directions. Triaxial tests are usually performed on geomaterials such as soils, rocks, and concrete. A triaxial testing apparatus generally consists of a pressure chamber, together with an axial loading device.
