Using laser Doppler extensometry with polarization diversity to measure strain in high-speed tensile testing

Abstract High-speed tensile tests are widely used to generate materials data for crash simulation purposes. The measurement of strain is of particular interest in these experiments. Laser-Doppler technology enables accurate strain measurements without contact, but the laser speckle effect causes an increased noise level and so-called signal dropouts. Signal diversity reduces the negative effects of these laser speckles. We implemented polarization diversity, where two photodetectors detect the light of two orthogonal polarization states, in a laser-Doppler extensometer. In this paper, we build a mathematical model to describe the carrier-noise-ratio under the laser speckle effect. Our findings show that polarization diversity leads to greater improvement with two diversity channels instead of the other two diversities (angular and wavelength diversity). Furthermore, we introduce that our sensor can measure the strain in the high-speed tensile testing, where velocities of over 30 m/s occur. Finally, we estimate the measurement uncertainty of our laser-Doppler extensometer. The measurement data obtained shows that our sensor can accurately measure such fast tearing processes.