Mode-I Fracture Toughness Prediction of Diamond at the Nanoscale

Abstract

In this paper, the fracture process of nanoscale diamond is analyzed using atomistic simulations and fracture toughness obtained using four different continuum fracture-mechanics theories. In particular, the authors have used (1) the Griffith’s energy release rate (Irwin modified), (2) crack-tip-opening displacement (CTOD) method, (3) Irwin’s K-based method, and (4) the modified crack closure method. Three different nanosized cracks have been considered: 5a0, 7a0, and 9a0, where a0=0.357 nm as diamond’s lattice constant. For applying the CTOD and the Griffith’s methods, molecular dynamics (MD) simulation is sufficient to obtain fracture toughness values. In addition to MD simulation, the other two methods need supplementary finite-element analysis. The authors evaluated fracture toughness of diamond in terms of critical stress-intensity factors (KIC) and critical energy release rate (GIC) using the four methods and found consistent fracture toughness values (approximately 8.85 MPa·m0.5) for diamond regardless of methods and crack lengths considered.