Strength and fracture properties of diamond

Abstract

Abstract The strength of diamond is usually measured using an indentation technique. It is shown that the values obtained by previous workers for good quality diamond are reasonably consistent if they are all calculated with the same chosen values of modulus and Poisson ratio. By monitoring the extent of crack growth from beneath a loaded indenter it has been possible to measure the fracture surface energy, γ, of diamond (5·50 ± 0·15 Jm−2) and from this calculate the critical stress intensity factor KIC (3·4MN m−3/2). The significance of the measured γ compared with the theoretical value for the surface energy of 5·3 J m−2 for (111) cleavage is discussed. The strengths of various types of diamond grit particle have been measured by loading single particles between hard anvils. It is shown that there is a strength/size effect with smaller particles giving higher strengths. A linear relation between load and particle diameter suggests that Auerbach's Law holds for diamond in the size range covered. Some syn...