Dynamic deformation measurements at translucent high speed rotors

Glass fibre-reinforced composites are an attractive material for high speed rotors offering high stiffness to weight ratios. In order to understand their dynamic material behaviour, optical in-situ deformation measurements are required at high rotor speeds up to 300 m/s. One challenge is the translucence, since the main part of incoming light propagates into the material and is backscattered by inhomogenities inside the rotor. For this reason, the laser Doppler distance (LDD) sensor is proposed, which is a two-wavelength Mach-Zehnder interferometer that profits from speckle of rough surfaces, in contrast to the most optical sensors. The measurement volume of the LDD sensor inside the translucent rotor is investigated by simulations in dependency of its surface characteristics. As a result, the LDD sensors is not disturbed by backscattered laser light from the rotor volume. For validation, a multi-sensor system consisting of four LDD sensors is finally applied for deformation measurements of a translucent rotor exhibiting a shape accuracy in the micron range.