Previous attempts (1-6) to measure residual stresses by laser annealing and electronic speckle pattern interferometry have been successful for moderate to high stress levels. The method uses an infrared laser for relieving stress in a small spot. A dab on temperature indicating paint is applied to the spot and a specklegram of the spot and the surrounding area is captured. THe paint is then heated with a laser until it melts. The heat is transferred from the paint into the metal resultign in a small amount of localized stress relief as the yield stress of the material drops below the stress levels surrounding the spot. Once the spot and area around it have cooled a second specklegram is captured and the images are processed to determine the in-plane strain. The amount of stress relief depends on the melting temperature of the paint since yield stress is a function of temperature.
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