The Problem: To Measure Strain and Thermal Expansion

The K100/SPC optical head using the HoloFringe300 interferometry program provides a speckle correlation system that measures displacements at right angles to the line of sight. The resulting fringes measure thermal expansion or unidirectional strain. Time-lapse recordings can be used to collect data for stress relaxation studies. Fringe patterns can be converted to data and data files can be added together to generate start-to-finish analyses.

4b

4a

4c

Figure 4. Thermal Expansion of a Glass Jar. Fig. 4a shows the deformation of a glass jar when partially filled with warm water. The fringes are the wrapped phase, and are displayed in real-time. The speckle correlation system is setup so that it is sensitive to horizontal displacements. Fig. 4b shows the fringe locus function extracted from the fringes of 4a by the unwrapping program. Fig. 4c shows the deformation as a 3D plot. The slope of the deformation plot is proportional to the thermal expansion even though the geometry of the jar is circular, a fact that makes thermal expansion measurements very easy.