Ab initiodynamics of rapid fracture

Abstract

As our title implies, we consider materials failure at the fundamental level of atomic bond breaking and motion. Using computational molecular dynamics, scalable parallel computers and visualization, we are studying the failure of notched solids under tension using in excess of 10 8 atoms. In rapid brittle fracture, two of the most intriguing features are the roughening of a crack's surface with increasing speed and the terminal crack speed which is much less than the theoretical prediction. Our two-dimensional simulations show conclusively that a dynamic instability of the crack motion occurs as it approaches one-third of the surface sound speed. This discovery provides an explanation for the crack's surface roughening and limiting speed. For three-dimensional slabs, we find that an intrinsically ductile FCC crystal can experience brittle failure for certain crack orientations. A dynamic instability also occurs, but brittle failure is not maintained. The instability is immediately followed by a brittle-to-ductile transition and plasticity. Hyperelasticity, or the elasticity near failure, governs many of the failure processes observed in our simulations and its many roles are elucidated. 'Refrain from immediately resorting to a jackhammer to break open a hazelnut without first checking for an incipient crack on the surface of the shell.' P-G de Gennes ¶ 'You may think I have used a hammer to crack eggs, but I have cracked eggs.' S Chandrasekhar + * Based on Plenary Talk given at PC'97 by FFA.

Crack tip blunting and cleavage under dynamic conditions

“…Atomistic simulations have therefore become increasingly popular for studying crack tip deformation mechanisms and their implications for ductility [16], both in quasi-static [17][18][19][20] and dynamic [21][22][23][24] conditions. In the latter case, model interatomic potentials have found great utility in molecular dynamics simulations [12,13,[25][26][27][28][29]. Although such potentials do not correspond to any specific real material, they help to elucidate the general principles governing crack tip behavior and fracture, such as "hyperelasticity" [12,13].…”

Experimental and numerical studies on dynamic crack growth in layered slate rock under wedge impact loads: part II – non‐plane strain problem

“…Failure of materials at the fundamental level of atomic bonds was examined numerically by Abraham et al 13 …”

“…They are making it more versatile by incorporating possible evaluation rules, based on experimental observations and existing failure theories, which allow for generalized crack growth trajectories. 12 Failure of materials at the fundamental level of atomic bonds was examined numerically by Abraham et al 13 ; the element size was equal to that of an atom. The study used computational molecular dynamics, scalable parallel computers and visualization for examining the rapid brittle fracture of notched solids under tension.…”

On the application of the method of difference potentials to linear elastic fracture mechanics

“…This equation will be referred to as the Boundary Equation with Projection (BEP). Substituting our expression for the potential 0 N D D P N D (10) into the inhomogeneous Green's formula (8) gives:…”