Determination of Stress in Biaxially Strained, Free Standing Films

Abstract

A simple but versatile technique, the double ring technique, was developed to introduce biaxial strain in free standing films permitting the observation of films with pre-determined levels of biaxial stress under a variety of environmental conditions for both short and long durations. The method also permits the observation of films while the strain is being increased, which is of particular interest when defects are present.Furthermore, a method was developed to measure the stress in free standing films by observing the load versus displacement relationship under a centrally placed load. This allows measurements of stress relaxation and stress reduction or increase with solvent or water up-take, etc. The usefulness of the two methods is illustrated by measurements of long-term crack propagation, of stress relaxation by thermal annealing, and by stress measurements on films under a layer of water.