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We present a generalization of a scalar nonlinear damage rheology model of a brittle solid to the case of a tensor damage parameter. The main values of damage tensor describe the reduction in the cross-sectional area of the material in three orthogonal directions. The introduced damage tensor allows decribing the orthotropy of the elastic properties of the material caused by the development of microfractures during the deformation. For the case of traditional triaxial compression, two general problems are considered: the orientation of damage (microfractures) in the entire material and the orientation of the localized damage zone, ensuring the maximum rate of its growth. The solution of the first problem shows that, the degree of disorientation of the original fracturing and the growth rate of new fracturing depend on the damage anisotropy parameter. The solution of the second problem demonstrates that the optimal angle of inclination of the localized damage zone is the Mohr-Coulomb angle with microfractures inside the zone oriented either strictly vertically or at an angle close to the Mohr-Coulomb angle. [ABSTRACT FROM AUTHOR]

The growth of CdTe buffer layers on (211)B GaAs substrates by organometallic vapor phase epitaxy (OMVPE) was studied, and it was found that, depending on the growth conditions, either the (211) or (133) epitaxial orientation could be formed. In some cases, an epilayer showing a mixed (211) and (133) orientation was also observed. The influence of several growth parameters on the orientation of the CdTe layer was investigated, and it was found that the Te/Cd ratio, together with the growth temperature, have the most significant effect in determining the epilayer orientation. From these results, it was then possible to select nominally optimized growth conditions for CdTe buffer layers of both orientations. (Hg,Cd)Te layers of the same orientations could then be grown and characterized. Although double crystal x-ray diffraction measurements indicated a somewhat better crystalline perfection in the (133) (Hg,Cd)Te layers, these layers showed a poor surface morphology compared to the (211) orientation. Measurement of etch pit densities also indicated defect densities to be typically half an order of magnitude higher in the (133) orientation. Diodes were formed by ion implantation in both orientations and significantly better results were obtained on the (211) (Hg,Cd)Te layers. [ABSTRACT FROM AUTHOR]

Bone, dentine and enamel samples were treated with a gas-propelled jet of an abrasive, NaHCO, which is physically much softer than any of these tissues in their fully mineralised condition. It was nevertheless found that they are all eroded by this treatment, which can therefore be used as a new kind of qualitative test of physical properties relating to wear resistance. General correlations were found between both degree of mineralisation and between structure orientation and erosion rate, surface-parallel-feature zones being worn more rapidly. Bone domains with surface-parallel collagen were eroded faster than those with perpendicular lamellae even if they were more densely mineralised. Rates of dentine wear depended on both density and tubule orientation, with peritubular zones and better mineralised incremental layers being more resistant. Enamel tufts wear more rapidly than the surrounding well mineralised regions. Enamel diazones wear less than parazones (areas with surface parallel prisms). At the prism scale, enamel is removed more rapidly near prism boundary discontinuities and in tubular enamel, at tubule walls. As regards the common orientation dependent effects seen in these three tissues, a cohesive explanation would be that structure discontinuities can be better exploited in a wear process if they allow cleavage from the surface; which tendency will increase with parallelism to the surface. [ABSTRACT FROM AUTHOR]