Digital shearographic vibration analysis of harmonically excited components

This paper describes the further development of the digital shearography fo r vibration analysis, i.e. the evaluation of the real time observation by m eans of the time-averaged digital shearography on the basis of the permanen tly refreshed reference technique (qualitative vibration analysis) and by m eans of stroboscopic illumination applying the phase-shifting technique for the numerical evaluation of the digital shearogram (quantitative vibration analysis). Both methods are combined into one arrangement without the need Of changing the set-up. The positions in the zeroth fringe order can be de termined simply in the time-averaged shearogram; the permanently refreshed reference frame technique improves the fringe contrast and suppresses the l ow frequency ambient noise widely. For quantitative analysis, the strobosco pic technique in conjunction with the phase shifting method is applied so t hat the accurate phase distributions of the digital shearograms of the exci ted object can be obtained for discrete moments triggering. After demodulat ing the phase maps the sinusoidal graph of the deformation or the amplitude gradient, resp., is determined for different triggerpoints.