A technique widely used for determining macroscopic, near-surface residual stresses is the hole drilling strain gage method. The relaxed surface strains are measured during drilling of a small hole into a component using a three-element strain gage rosette. The residual stress is estimated from the strain relief using various prediction models based on the theory of elasticity. An enhancement of the semi-destructive hole drilling technique towards optical measurement of the strain relaxations by electronic speckle pattern interferometry (ESPI) is promising.
Recording the in-plane displacement field around the drilling hole by a non-contacting optical method instead of the commonly used stain gage technique provides an increased amount of data, less instrumentation effort, and a reduction of systematic measurement errors, including the error of misalignment of the drilling axis to the strain gage centre.
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