ANISOTROPY OF YOUNG MODULUS AND POISSON RATIO IN DIAMOND

The elastic modulus E of diamond is often set equal to 1/s11 = 1050 GPa, which assumes that it does not vary much with orientation, and many authors use nu = 0.2 as an appropriate average value of Poisson's ratio, which is incorrect. In this paper, we show that, since the elastic constants of diamond are known with great accuracy, it is a straightforward matter to derive exact numbers for E and nu that take into consideration the stress direction, the intrinsic anisotropy, as well as the crystalline configuration. For textured CVD diamond deposits, we find that, in a first approximation, the Hershey-Kroner-Eshelby averaging procedure yields acceptable numbers, EBAR = 1143 GPa and nuBAR = 0.0691, which are quite compatible with available experimental evidence; this confirms that high-quality deposits have elastic constants similar to those of single-crystal natural diamond.