Edge instabilities in thin plates

Abstract

In this investigation, experimental results previously obtained from transmission electron microscopy (TEM) are used to construct a predictive model for the development of instabilities at the edges of thin solid foils at elevated temperature. The capabilities of the TEM have been used to reveal details of the morphological instability which previously had not been fully examined. In particular, the edge thickness variations can be directly studied and compared with the current models put forth to examine the formation and propagation of the edge instability. These models have assumed, either explicitly or implicitly, that the periodic edge undulations correspond to localized, periodic thinning in the edge of the thin film. This is in disagreement with what may be inferred from the TEM micrographs and optical micrographs in cited references, where edge blunting (thickening) is clearly indicated. The degree of edge blunting is an important parameter. This is apparent from the equations that have been proposed to model the propagation velocity, which depend on the inverse of the local edge thickness to the third power. The purpose here is to examine in a more quantitative way the details of the thickness variations which occur at single crystal edges. This will allow themore » development of a model which describes the edge morphology and the relationship with plate thickness in a manner consistent with experimental results.« less