Critical aspects of crack dynamics in single crystals

Seminars
11.05.2017
14:30
אודיטוריום ע"ש דיוויד וואנג, קומה 3, בנין דליה מידן
Merna Shaheen-Mualim, PhD Candidate

Merna Shaheen-Mualim, PhD Candidate

Department of Materials Science and Engineering, Technion, Haifa 3200003, 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 dynamic cleavage energy is rate dependent of the driving force, G0, namely, Q=dG0/da. The dynamic cleavage energies at high Q 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 Q is low, cracks in brittle crystals can propagate at energy comparable with Griffith barrier of 2gs, twice the free and relaxed surface energy and subjected to stress corrosion cracking mechanisms. At high Q, however, the energy required to break the bonds and propagate the crack is higher than 2gand varies during crack propagation. We suggest that this complex behavior is due kinking mechanisms along the propagating crack front, which are governed by various energies.

We further show that crack speed under time independent loading is only slightly affected by stress wave reflecting from the specimen boundary, and the maximal speed reduction was estimated by about 5% when 75% of the energy is reflected back.

Advisor: Prof. Dov Sherman, Tel Aviv University.

 

  1. 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. Gleizer, M. Shaheen-Mualim, D. Sherman. "Complex and divers dynamic stress corrosion cracking in silicon crystal", Submitted (2017).