In this study, a simple approach is proposed for the formulation of a rock failure criterion based on octahedral shear stress theory, while maintaining and modifying some of the given restrictions.

The equation is also valid if one assumes failure to be a function of octahedral shear stress.

The modification of the octahedral shear stress failure criterion represented by 2[[sigma].

The motivation for the combined compression-and-shear plate-impact experiments stems from the fact that in classical metal plasticity based on dislocation mechanisms, the volumetric and shear behaviors are typically considered uncoupled: the classical plasticity theory addresses shear only, and the von Mises criterion leads to a convenient unifying constitutive description that is independent of the deformation rates in terms of the

octahedral shear stress.

sigma]] and the octahedral shear stress [tau], to be defined below.

The scalar octahedral shear stress [tau] used in (Eq.

sigma]] Mean stress [tau] Scalar octahedral shear stress [tau] Stress deviator tensor [SIGMA] Stress tensor

supo] are the critical octahedral shear stress and shear stress under zero pressure, respectively.

7 and 10 to all available yield data expressed in terms of their octahedral shear stress or maximum shear stress as a function of hydrostatic mean stress (Table 2).

Sweeney and Ward [12] showed that in PVC above the glass transition temperature, the different modes of uniaxial, planar, and equibiaxial tensile deformation are comparable provided the results are expressed in terms of the

octahedral shear stress and strains.

Conversion from axial stress to

octahedral shear stress could also be made easily, but since data is plotted here as principal stresses such a conversion was not made.

According to their analysis the maximum

octahedral shear stress and principal stress are 141% and 35.