Abstract
When polycrystalline materials deform at elevated temperatures under low applied stresses by the stress directed migration of vacancies, specific features need consideration in the bending of thin beams since a relatively high stress variation may arise across individual planar grain boundaries in addition to the variation that exists between boundaries of differing inclination. The features depend on grain and beam geometry and expressions are derived for their effect on the rate of deflection of cantilevered beams. Experiments were carried out on beams of high purity copper 100 and 250 μm thick. The cantilever profiles supported the theoretical approach and showed creep rates linearly dependent on stress at rates in accord with predictions based on a diffusional creep process. A further indication of this process was the associated strain localization that resulted in fracture of 100 nm thick alumina coatings applied to some of the beams. The analysis shows how relationships change as the beam thickness approaches the grain size and permits an evaluation of the rate of beam deflection under small bending moments in terms of grain and beam dimensions.
Published Version
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