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Position Indication:


Local Strain Measurement by Objective Laser Speckle Technique

Dipl.-Ing. Dr. Thomas Thurner

Dipl.-Ing. Dr. Thomas Thurner

Supervisory committee:

Univ.-Prof. Dipl.-Ing. Dr. Bernhard Zagar
Univ.-Prof. Dipl.-Ing. Dr.techn. Georg Brasseur

Final exam:

August 23, 2004

Measurement techniques based on objective laser speckle tracking allow for the measurement of strain within optically rough surfaces with high sensitivity. When compared to alternative techniques the speckle-based principle offers some great advantages, like its contactless character and its ability to operate locally and to measure surface strain directly. This thesis discusses in detail the theoretical basis of the sensor principle setting out from the optical basis - the coherent optics - continuing on with the digital signal processing part leading to a practical sensor design by focusing on novel theoretical investigations of decorrelation effects during measurement cycles and also on the consideration of practically relevant illuminating conditions in the theory. Valuable design parameters for a practical realization of the principle are obtained from theoretical derivations detailed in this work. The investigation of the speckle pattern acquisition by a camera device allows for a discussion of novel signal processing approaches utilizing image processing techniques. The implementation of a strain sensor based on objective speckle tracking is furthermore discussed for two different optical set-ups. Measurements of rigid body displacement and thermal expansion of an aluminum plate were carried out with a single-beam set-up. The obtained measurement results are shown to be in good agreement with the theoretical derivations obtained in the thesis.