Factors Influencing Thermomechanical Failure of Face Seals.
Interim rept. 1 Dec 80-30 Nov 81,
THAYER SCHOOL OF ENGINEERING HANOVER N H
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A microscopic examination, an analytical study, and an experimental study were carried out to determine why and how thermocracking occurs in the mating ring of a mechanical face seal. Microscopic examination of the cobalt-based superalloy mating ring of a marine propeller shaft seal yielded a better understanding of the initiation and propagation of thermocracks in the seal ring and of the role played by second phase particles in thermocracking. An analysis of surface temperatures and stresses in the seal, using finite element techniques, showed that the dominant stresses in the seal components are thermal stresses. A thermocracking mechanism is proposed, based on the analytical study, which agrees well with all microscopic features. The analytical model assumed that thermoelastic instabilities cause concentrated contact patches to form at the seal interface prior to the onset of thermocracking. The presence of these contact patches was confirmed by use of a novel contact probe in the experimental study. Suggestions are made of steps that could be taken to alleviate the thermocracking problem and guidance is offered for the choice of future seal materials.