24 February 2005 Evaluation and calibration methods for the application of a video-extensometer to tensile testing of polymer materials
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Abstract
This paper presents a digital image processing system for the measurement of the volumetric tensile properties of polymer materials. The standard measurement setup with a single camera system focussing the face of the samples under test is described. An algorithm for fitting parallel and/or orthogonal lines based on singular value decomposition is explained in detail. Applications where higher resolution and accuracy is desired, are addressed by extending the standard measurement setup to two camera systems, whose images can be acquired simultaneously. The non-overlapping fields of view require determination of the relative location of the camera systems. A calibration target and procedure is presented to solve this referencing task. Three-dimensional specimens are subject to motion in testing machines with flexible jaws. An extended hardware setup with two line-projecting lasers is introduced, that enables the measurement of the specimen motion and with this the elimination of the associated errors. In a calibration procedure, the relative locations of the lasers and the camera are determined. The image processing task is extended to calculate the three-dimensional specimen location in each step of the sequence based on the results of the calibration. As a consequence, deformations are determined on the specimen surface under the assumption that the material remains planar. Finally, a number of measurement results gained with the video-extensometer system at real experiments in a testing laboratory are presented and different evaluation algorithms are compared.
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Ewald Fauster, Ewald Fauster, Peter Schalk, Peter Schalk, Paul L. O'Leary, Paul L. O'Leary, } "Evaluation and calibration methods for the application of a video-extensometer to tensile testing of polymer materials", Proc. SPIE 5679, Machine Vision Applications in Industrial Inspection XIII, (24 February 2005); doi: 10.1117/12.586734; https://doi.org/10.1117/12.586734
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