School of Mechanical Engineering Mirna Shahin
School of Mechanical Engineering Seminar
Monday, May 22, 2017 at 14:00
Wolfson Building of Mechanical Engineering, Room 206
Critical aspects of crack dynamics in single crystals
PhD. Student of Prof, Dov Sherman
1Dept. of Materials Science and Engineering, Technion, Haifa, Israel
2School of Mechanical Engineering, Tel-Aviv University, Tel-Aviv, Israel
We investigated two critical aspects of the physics of fast crack propagation in ideal brittle crystals when loaded by time independent (quasi-static) loading. The first is a rate dependent cleavage energy, the second is the effect of reflected stress wave on crack speed with this type of materials and loading. Silicon crystal was used as a model material in this investigation.
It was found that the cleavage energy is crack extension dependent of the driving force, G0, namely, dG0/da. The dynamic cleavage energies at high of cracks propagating on two low energy cleavage systems of silicon crystal, (110)[1 0] and (111)[11 ], were evaluated using our Coefficient of Thermal Expansion Method (CTEM). Previous studies [1,2] showed that when is low, the cracks are subjected to stress corrosion cracking mechanisms. At high , however, these mechanisms are vanished, and higher energy than the theoretical Griffith barrier is required to initiate and propagate the crack. We suggest that this complex behavior is due kinking mechanisms along the propagating crack front, which are governed by various energies. 1 2
We further show that crack speed under time independent loading is only slightly affected by stress wave reflecting from the specimen boundary. The maximal speed reduction was estimated by comparing the experimental energy-speed relationship to that of Freund equation of motion. It was found to be less than 8.5% and occurred at speed above 2,500 m/sec in our specimens.
1. A. Gleizer, M. Shaheen-Mualim, D. Sherman. " cracks dynamics in silicon crystal at the low energy and speed: from macroscopic energy flow to atomistic kinks", Submitted (2017).
2. A. Gleizer, M. Shaheen-Mualim, D. Sherman. "Complex and divers dynamic stress corrosion cracking in silicon crystal", Submitted (2017).