1. Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 1-272, Cambridge, Massachusetts 02139, USA
2. Max Planck Institute for Metals Research, Heisenbergstrasse 3, D-70569 Stuttgart, Germany
3. *These authors contributed equally to this work

Correspondence to: Markus J. Buehler^1,3 Correspondence and requests for materials should be addressed to M.J.B. (Email: mbuehler@MIT.EDU).

As the speed of a crack propagating through a brittle material increases, a dynamical instability leads to an increased roughening of the fracture surface. Cracks moving at low speeds create atomically flat mirror-like surfaces; at higher speeds, rougher, less reflective ('mist') and finally very rough, irregularly faceted ('hackle') surfaces^{1, 2, 3, 4, 5} are formed. The behaviour is observed in many different brittle materials, but the underlying physical principles, though extensively debated, remain unresolved^{1, 2, 3, 4}. Most existing theories of fracture^{6, 7, 8, 9, 10, 11, 12} assume a linear elastic stress–strain law. However, the relation between stress and strain in real solids is strongly nonlinear due to large deformations near a moving crack tip, a phenomenon referred to as hyperelasticity^{13, 14, 15, 16, 17}. Here we use massively parallel large-scale atomistic simulations—employing a simple atomistic material model that allows a systematic transition from linear elastic to strongly nonlinear behaviour—to show that hyperelasticity plays a governing role in the onset of the instability. We report a generalized model that describes the onset of instability as a competition between different mechanisms controlled by the local stress field^{6, 7, 8} and local energy flow^{13, 14} near the crack tip. Our results indicate that such instabilities are intrinsic to dynamical fracture and they help to explain a range of controversial experimental^{1, 2, 3, 4, 5, 18} and computational^{19, 20, 21, 22, 23, 24, 25, 26} results.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.