Strain/stress measurements using combined ESPI contouring and deformation measurements

Electronic Speckle-Pattern Interferometry (ESPI) is commonly used to measure down-to nanometers long deformations of optically rough surfaces [5]. Topography measurement is also possible with ESPI by changing the illumination conditions, either by sliding the light sources (translation technique) or by changing the wavelength of the light source (multiple wavelength technique) [1][2][3]. Adapting both techniques to the approach of coded light sectioning, makes it possible to describe discontinuous surfaces with high steps [4][8][9]. With adequate ESPI experimental set-ups, both shape and deformation measurements can be done and it becomes a strain and stress measuring technique able to compete to the wire resistance strain-gauges, one which measurement set-up is very time-consuming and returns just single point strain values, without lateral resolution. ESPI-methods extend this kind of metrology to a matrix of some thousands points even including sensitivity in the out-of-plane-direction. In this paper current work on the field of stress and strain measurements with ESPI stress sensor prototype is described. The experimental result of several technical applications is shown and compared to measurements with strain-gauges. Additionally experimental results using the multiple wavelength approach with tunable laser sources to perform the contouring measurements will be discussed.