Properties, anisotropic failure

Isotropic carbon is obtained by the pyrolysis of a hydrocarbon, usually methane, at high temperature (1200-1500°C) in a fluidized bed on a graphite substrate.Under these conditions, a turbostratic structure is obtained which is characterized by very little ordering and an essentially random orientation of small crystallites. In contrast to graphite which is highly anisotropic, such a structure has isotropic properties (see Ch. 7). Isotropic carbon is completely inert biologically. Its properties are compared to alumina, another common implant material, in Table 17.8. Notable is its high strain to failure. 

The structural soft rock is due to dense structure surface, or weakly cemented micro-structure which make it easy to deform and failure. Layered, sheet-hke rock is a kind of structure soft rock. Schist, carbonaceous slate with directional arrangement of flaky minerals are typical structural soft rock, which is very easy to be sphtted into thin shces by any shght mechanical and hydrauhc disturbance, resulting strong anisotropic and soft property. 

The indentation confidence depth was determined to be a function of the coating to substrate yield strength ratio for three different substrate configurations. Tilbrook et al. (2007) incorporated microstructural failure mechanisms into finite element simulations of nanoindentation of TiN thin films on elastic—plastic substrates. Intergranular sliding that occurs as a result of the columnar grain structure is incorporated into the model via anisotropic property definitions and nodal coupling. 

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