Constrained indentation

The broad band at 1110 cm (Fig. 42b) has also been repeatedly observed in the Raman spectra of indentations in diamond. It was initially assigned to amorphous diamond [4, 196]. However, both the experimental Raman spectra of sp -bonded amorphous films [203] and the calculated vibrational density of states of an amorphous carbon network constrained to be fully -bonded [204] show a strong peak at 1200 cm. In contrast, the vibrational density of states of tetrahedral amorphous carbon (ta-C) features a broad peak centered at 1100 cm [205], which is quite similar to that observed in Figure 42b. The ta-C networks should not be confused with amorphous diamond because they contain some portion of aromatically bonded sp carbon. 

H is the Vickers hardness, E is the Young s modulus, 2a = d is the diagonal of the indentation, (f> is the constrained factor and 1 is the crack length. As is clear from many hardness indentations on ceramics, Palmqvist cracks are observed at the ends of the diagonals of the indentations. The criteria for such cracks are given as ... 

---