Plastic Flow and Fracture of Zinc Single Crystals

Citation

Stofel, Edwin Jule (1962) Plastic Flow and Fracture of Zinc Single Crystals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/EQK7-RS94. https://resolver.caltech.edu/CaltechETD:etd-07012004-154735

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Plastic flow and fracture of zinc single crystals subjected to tension parallel to the hexagonal crystallographic axis, torsion about that axis, and combinations of such tension and torsion have been investigated experimentally at 25[degrees]C and -77[degrees]C. The results show that under tension alone, cleavage fracture on the basal plane is preceded by plastic elongation in the direction of the hexagonal crystallographic axis. Some evidence is presented which indicates that this newly discovered mode of plastic deformation of zinc crystals probably occurs by slip on [...] planes in [...] directions. The temperature dependence of this mode of plastic deformation is anomalous. The tensile stress required to produce a given amount of plastic strain is greater at 25[degrees]C than at -77[degrees]C. The critical resolved shear stress for basal slip, as determined from the results of torsional tests, is increased markedly by prior tensile plastic deformation. The tensile stress-strain relation is raised moderately by prior basal slip. Fracture was always found to occur by cleavage on a basal plane. The observed combinations of tensile stress and shear stress on the basal plane at fracture are not consistent with predictions based upon current dislocation theories for the initiation of cleavage fracture in zinc. The present results indicate that dislocations having Burgers vectors that do not lie in the basal plane may be of crucial importance in the dislocation mechanism of cleavage fracture of zinc. Such dislocations have not been considered in previously proposed theories.

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