A computer-aided design study of the behaviour of diamond anvils under stress

The aims were to understand and to learn how to control potentially destructive stresses which limit the performance of anvils in high pressure optical and X-ray cells. The calculations show that the largest compressive and shear stresses are near the working face of the anvil and, hence, that plastic flow will begin there, as has been observed. The largest tensile stresses are at the base, above the unsupported light port. Since diamond, a brittle material, is liable to failure in tension, these stresses are potentially destructive. The largest principal tensile stress is in a hoop direction: consequently diamond anvils are liable to basal failure by radial cracking, with ring cracking from tensile radial stresses important also. This type of failure has been observed in diamond anvil cells. In the light of these results, mechanisms of anvil failure are discussed and illustrated with photographs. Attention is drawn to the importance of fatigue as a cause of failure in diamond.