Thermoelastic stress analysis of a 2D stress field using a single detector infrared scanner and lock-in filtering

Abstract

A low resolution, low cost, fast infrared scanner is used to acquire the temperature change along a line on the surface of cyclically loaded samples. The temperature signal is sampled versus time by exploiting the raster scanning movement of the thermocamera single detector. The temperature data is then post-processed by a Fast Fourier Transform based lockin algorithm implemented in MATLAB®, in order to filter out the thermoelastic effect induced temperature change. A procedure is also implemented in order to extend the data sampling time by opportunely synchronising successively grabbed data frames. The effectiveness of such synchronisation procedure is first demonstrated by performing the signal processing analysis on unidirectional tensile samples made of polycarbonate. The ability of the implemented onedimensional FFT lock-in algorithm to analyse also two-dimensional stress fields is then assessed by processing the temperature data acquired on a polycarbonate disc under cyclic compression loads