Seminar Series - 1996-1997

Statistical Characteristics of Triple Junction Cracks in Random Polycrystals

Mingdong He
Department of Engineering Mechanics
University of Nebraska
Lincoln, NE
M.S. Advisor:  Dr. Mao S. Wu

Date:  Thursday, August 7, 1997
Time:  2:00 p.m.
Place:  306 Bancroft Hall


The statistical characteristics of cracks nucleated in a random polycrystal are investigated through the development of a crack nucleation model.  The physical mechanism of crack nucleation considered in the interactive pile-ups of extrinsic grain boundary dislocations (EGBDs) around triple junctions.  These pile-ups give rise to nonequilibrium grain boundaries in polycrystals.  The crack nucleation model is developed on the basis of (i) a micromechanical model that describes rigorously the interaction between a triple junction wedge crack and the pile-ups of EGBDs, and (ii) an energy description of the crack nucleation process.  Numerical results are obtained for the stress intensity factors and the dislocation populations on the concurrent grain boundaries  Furthermore, a random polycrystal is constructed and used to study crack nucleation in aluminum.  The statistical characteristics of the crack length, the crack orientation and the energy decrease during crack formation, are investigated in terms of their probability density functions.


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