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Title: Unsteady cleavage crack propagation in sodium chloride crystals
Author: Wainer, Lelia Schmirgeld de
ISNI:       0000 0001 3420 8924
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1976
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The knowledge of dislocation mechanisms by which plastic deformation may relax the stresses concentrated at the tip of a cleavage crack in crystals is of fundamental importance to control fracture in materials of technological application. A propagating crack leaves, on the cleavage surfaces, characteristic traces due to the multiplication and movement of dislocations nucleated ahead of the crack tip, as discussed in chapter 1. One of the purposes of this thesis is to make a comprehensive study of the changes in surface markings accompanying accelerations and decelerations of a propagating cleavage crack in alkali halides, and to relate the resulting plastic deformation with these surface structures. With this aim in mind, the regions limited by successive stopped crack fronts are studied by several techniques, described in chapters 2 and 5, These techniques comprise a wide range of magnification: from macramethods like optical microscopy to micromethods like electron microscopy of decorated replicas, which allow the observation of monoatomic structures. In this connexion a new technique, described in chapter 3, is developed which permits, in most cases, the determination of the sign of elementary steps. This technique constitutes an important advance since possible modifications of cleavage structures due to the heat-activated movement of dislocations are avoided and the resolution attainable by decoration is improved. The results of these complementary experiments are described in chapter lt. X-ray topography studies are particularly efficient to determine the slip systems activated by the propagating crack as discussed in chapter 5. Prom these chapters an integral picture of the phenomena accompanying unsteady crack propagation is envisaged. Dislocation mechanisms responsible for the formation of the cleavage structures are discussed in chapter 6. The possibility of quantitative measurements which would allow a theoretical analysis of the subject is discussed in chapter 7.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD Chemistry ; QE Geology