A self-built laser projection system for optical transverse strain measurements in tensile testing is presented. The setup based on laser diode modules, charge-coupled device array detectors, and standard optomechanical components is proposed to be a low-cost system for testing polymer samples. The optical setup is mobile and can easily be mounted on a tensile test machine. Circular cross-sectional changes in polymer diameter were detected with 10-μm resolution and stress-strain curves obtained by a tensile test machine. The article describes signal processing using the open-source programming language R, and the transverse deformation of the polymer sample is evaluated in two perpendicular planes. The results obtained by the optical system may be used to accurately describe the models of energy-based mechanical properties of polymers for complex load conditions.
We propose a fast algorithm to extract the phase in the center of an interferogram with circular fringes obtained in a simple Michelson interferometer setup with one rough surface. The phase in the center is a linear function of the displacement of an object, which is very advantageous. It avoids the uncertainty in displacement associated with intensity measurements near a maximum or minimum. Also the direction of movement is always clear. The method used also overcomes the problems associated with speckle, unavoidable with a rough surface, common in industrial applications, when using laser as a light source. Using a large number of points in the interferogram to obtain one value largely reduces noise and also increases the accuracy. Displacement is measured with an accuracy <10 nm.
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