Quantitative prediction of the fracture toughness of amorphous carbon from atomic-scale simulations

SM Khosrownejad and JR Kermode and L Pastewka, PHYSICAL REVIEW MATERIALS, 5, 023602 (2021).

DOI: 10.1103/PhysRevMaterials.5.023602

Fracture is the ultimate source of failure of amorphous carbon (a-C) films; however, it is challenging to measure fracture properties of a-C from nanoindentation tests, and results of reported experiments are not consistent. Here, we use atomic-scale simulations to make quantitative and mechanistic predictions of fracture of a-C. Systematic large-scale K-field controlled atomic-scale simulations of crack propagation are performed for a-C samples with densities of rho = 2.5, 3.0, and 3.5 g/cm(3) created by liquid quenches for a range of quench rates T-q = 10-1000 K/ps. The simulations show that the crack propagates by nucleation, growth, and coalescence of voids. Distances of approximate to 1 nm between nucleated voids result in a brittlelike fracture toughness. We use a crack growth criterion proposed by Drugan, Rice, and Sham J. Mech. Phys. Solids 30. 447 (1982) to estimate steady-state fracture toughness based on our short crack-length fracture simulations. Fracture toughness values of 2.4-6.0 MPa root m for initiation and 3-10 MPa root m for the steady-state crack growth are within the experimentally reported range. These findings demonstrate that atomic- scale simulations can provide quantitatively predictive results even for fracture of materials with a ductile crack propagation mechanism.

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