Using speckle interferometry under extreme conditions
Recording and processing of fringes
Two applications are described in this paper where speckle interferometry was used to study objects under extreme loading conditions. The first part will give details about the recording step, about the specific solutions necessary to overcome several disturbing influences. Both applications are related to temperature load of materials differing in the kind of extreme values reached: T=1 600 deg C for staticly loaded ceramic matrix composites (CMCs) and heating rates of 200 K/s for high temperature alloys, respectively. In any case, quantitative results are required to characterize materials behaviour. The desired strain values were obtained by automatic and interactive fringe analysis. Extreme loading conditions do not allow common phase shifting techniques and it will be demonstrated how alternative approaches can be used. The skeleton method and the Fourier transform technique will be discussed with emphasis put on fringe preprocessing. The paper shows, that the optimization of reco rding as well as of processing of fringe patterns provides a way to successful measurements and extends the range of application also under difficult conditions for interferometry.