ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The extension of initial surface cracks by the focusing of the ionic current in beta alumina electrolytes (Mode I degradation) is discussed in terms of existing models. Focusing for an ion current impinging on an elliptic-cylindrical flaw is calculated by solving for the electric potential with suitable boundary conditions. The current density distribution along the crack is used to calculate the sodium flow velocity and Poiseuille pressure inside the flaw. Calculated critical current densities using aK lc criterion are several orders of magnitude higher than measured average critical current densities. This implies a lower effectiveK lc for electrolytic degradation than for mechanical testing. Current density enhancement around insulating barriers, such as non-wetted surface areas, is also calculated using elliptic-cylindrical coordinates. Significant current density enhancements are found, but they are localized in very small regions. Crack growth would occur within these regions, but should be arrested once the flaw extends past the high current density zone. A plausible mechanism for decreasingK lc in the electrolytic case is discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00591486
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