Abstract: The method of determining the change in the spacing between two positions on a single object or a position on each of two objects, by affixing two linear scatterers at the two positions; illuminating the scatterers with coherent monochromatic light from a source such as a He-Ne laser and obtaining an indication of the relative movement from changes in the interference pattern.In one apparatus, linear scatterers are positioned on opposite sides of an adhesive in a lap joint. The scatterers are illuminated with light from a He-Ne laser to produce an interference pattern on a screen. Movement of a preselected fringe on the screen will provide an indication of strain in the adhesive lap joint.In another apparatus, fibers are attached to the ends of a standard bar specimen and a test bar specimen which are placed in a furnace. The fibers are then illuminated with light from a helium neon laser to produce an interference pattern.

Abstract: The method of determining the change in the spacing between two positions on a single object or a position on each of two objects, by affixing two linear scatterers at the two positions; illuminating the scatterers with coherent monochromatic light from a source such as a He-Ne laser and obtaining an indication of the relative movement from changes in the interference pattern.In one apparatus, linear scatterers are positioned on opposite sides of an adhesive in a lap joint. The scatterers are illuminated with light from a He-Ne laser to produce an interference pattern on a screen. Movement of a preselected fringe on the screen will provide an indication of strain in the adhesive lap joint.In another apparatus, fibers are attached to the ends of a standard bar specimen and a test bar specimen which are placed in a furnace. The fibers are then illuminated with light from a helium neon laser to produce an interference pattern.