Mode-I fracture toughness prediction of diamond at the nanoscale

In this paper, the fracture process of nanoscale diamond is analyzed using atomistic simulations and fracture toughnessobtained using four different continuum fracture-mechanics theories. In particular, the authors have used (1) the Griffith's energyrelease rate (Irwin modified), (2) crack-tip-opening displacement (CTOD) method, (3) Irwin's K-based method, and (4) themodified crack closure method. Three different nanosized cracks have been considered: 5a₀, 7a₀, and 9a₀, where a₀= 0.357 nmas diamond's lattice constant. For applying the CTOD and the Griffith's methods, molecular dynamics (MD) simulation is sufficientto 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 (K_IC) and critical energy releaserate (G_IC) using the four methods and found consistent fracture toughness values (approximately 8.85 MPa · m^0.5) for diamond regardlessof methods and crack lengths considered.