Berlin 2018 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 17: Topical Session (Symposium MM): Fundamentals of Fracture

MM 17.5: Topical Talk

Monday, March 12, 2018, 18:30–19:00, TC 006

Crack dynamics in brittle crystals: the varying cleavage energies. — •Dov Sherman and Merna Shaheen Mualim — School of Mechanical Engineering, Tel-Aviv University, Tel-Aviv, Israel

We investigated cracks dynamics in quasi-statically loaded silicon crystal on two low energy cleavage systems,(110)[1-10] and (111)[11-2]. The experiments were performed in air and under Ar at atmospheric pressure (low oxygen) to imitate vacuum, at low and high driving forces. The experimental energy speed relationships were compared with Freund equation of motion to extract the varying cleavage energies. An important variable in these experiments was the gradient of the energy release rate, dG0/da, denoted Theta. We show that at low Theta(<0.5 J/m2/mm), the cleavage energy is environmental, cleavage system, and crack speed dependent. At high Theta (>0.5 J/m2/mm), however, the stress corrosion cracking mechanisms vanished for both cleavage systems. The cleavage energy at initiation and propagation remain the same, but linearly increases as Theta increasing. We also specified the range of crack speed where crack dynamics is governed by the Griffith barrier. We indicate on an important physical fact in this investigation, i.e., the curvature of the crack front that giving rise to bond breaking mechanisms in form of kinks along the crack front. Crack propagation by kinks is governed by Theta, with complex advance or formation energies that determines the macroscopic cleavage energy. We therefore connect between the macroscopic cleavage energy and the microscopic crack front bond breaking mechanisms.