Stress Moire interferometry

Moire interferometry is accomplished by first bonding a clear plastic film, marked with closely spaced lines, to the specimen. A second sheet, similarly marked, is then placed over the first but without bonding or electrostatic coupling. During incremental static loading, the bonded layer deforms while the second, unbonded layer, does not. Consequently, some lines will super-impose while others overlap (the so-called Moire effect). Lines of equal displacement appear which can be photographed or transformed to strains and stresses. The technique is inexpensive (less than 1000 for equipment and materials), but limited in application because significant curvature can not be accommodated. 

YB02CU3O, Shadow Moire interferometry Residual stress. Dependence on position Wu(1993)... 

There are different techniques to evaluate the quantitative stress level in prototype and production products. They can predict potential problems. Included is the use of electrical resistance strain gauges bonded on the surface of the product. This popular method identifies external and internal stresses. Their various configurations are made to identify stresses in different directions. This technique has been extensively used for over a half century on very small to very large products such as toys to airplanes. There is the optical strain measurement system that is based on the principles of optical interference. It uses Moire, laser, or holographic interferometry (2,3,20). 

Water uptake by polymers is accommodated largely by swelling. For uptakes of only a few mass per cent, volumetric swelling would be of a similar or lower order(98, 99), and barely measurable. Moire fringe interferometry has been used to quantify the swelling stresses developed in a layer of adhesive upon exposure to water(lOO), and Comyn(90) describes some other work related to calculations of the stresses induced in bonded joints by water sorption. 

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