Institute of Fundamental Technological Research

Yielding and failure of oriented solids is studied within the framework of tensor representations. Transversely isotropic materials are considered. Using the information available regarding the tensor generators and the set of independent stress and mixed stress-material orientation invariants the general form of constitutive relation for incipient plastic motion of transversely isotropic solid is given and the yield condition is discussed. Specific forms of yield criteria for cohesive materials as well as for materials with internal friction are developed and compared with experimental information. A novel approach to flow and failure of oriented solid is thus explained on example of stratified material, starting with experimental motivation, passing through theoretical development and terminating on comparisons with experiments.

Flow, hardening and failure of a soft orthotropic rock is studied under isotropic pressure. A theory employing the tensor functions representation is outlined. Experimental data regarding deformation modes, volume changes and yielding are presented. Anisotropic deformation of a stratified rock (diatomite) subjected to a sequence of isotropic pressures is demonstrated in the permanent deformation range. Originally circular cylindrical specimens are shown to deform to elliptic inclined cylinders depending on the orientation of privileged directions of anisotropy to the cylinder generator. Experiments disclose essential features of mechanical anisotropy in the irreversible deformation range.