Computer‐aided photoelasticity used for stress measurements in polycrystal silicon ribbons

The brittleness of the polycrystal silicon ribbons is due to the residual stresses which appear in the material during the electron‐powder‐ribbon pulling process. We developed a new method for stress analysis based on combination of two techniques: classical infrared photoelasticity and modern digital image processing. The separation of principal stresses is achieved by means of a microcomputer: The sum of the principal stresses is determined which, combined with their differences, gives their values separately; by using these procedures it is possible to observe on a video analyzer the pseudocolor restoration of the stresses in the silicon ribbons. It may be noted that this method can be easily applied to other materials, such as InP for optoelectronic components.