Self-emitted surface corrugations in dynamic fracture of silicon single crystal

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 29; pp. 16872 - 16879
• Main Authors: Wang, Meng, Fourmeau, Marion, Zhao, Lv, Legrand, Franck, Nélias, Daniel
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 21-07-2020
• Subjects: Asperity; Crack propagation; Crystal structure; Crystallinity; Elastic waves; Engineering Sciences; Fracture surfaces; Frequency dependence; Mechanics; Mechanics of materials; Morphology; Oscillations; Physical Sciences; Propagation modes; Silicon; Single crystals; Solitary waves; Wave propagation; silicon single crystal; corrugation waves; solitary waves; crack front kink; dynamic fracture
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1916805117

When a dynamic crack front travels through material heterogeneities, elastic waves are emitted, which perturb the crack and change the morphology of the fracture surface. For asperity-free crystalline materials, crack propagation along preferential cleavage planes is expected to present a smooth crack front and form a mirror-like fracture surface. Surprisingly, we show here that in single crystalline silicon without material asperities, the crack front presents a local kink during high-speed crack propagation. Meanwhile, local oscillations of the crack front, which can move along the crack front, emerge at the front kink position and generate periodic fracture surface corrugations. They grow from angstrom amplitude to a few hundred nanometers and propagate with a long lifetime at a frequency-dependent speed, while keeping a scale-independent shape. In particular, the local front oscillations collide in a particle-like manner rather than proceeding with a linear superposition upon interaction, which presents the characteristic of solitary waves. We propose that such a propagating mode of the crack front, which results from the fracture energy fluctuation at a critical crack speed in the silicon crystal, can be considered as nonlinear elastic waves that we call “corrugation waves.”