The temporal phase shifting method (TPS) is the most powerful technique in phase-shifting shearography. Numerous
different phase-shifting algorithms have been developed to determine phase distribution for different
applications. Most of them are applied with known phase shifts. In these cases, the accuracy of quantitative
measurement using phase-shifting technique depends strongly on the accuracy of the phase shifter e.g. a piezoelectric
transducer (PZT) which is responsible for generating the known phase shifts. Thus, phase shifter has
to be calibrated. A new calibration method based on the so-called advanced iterative algorithm which provides
stable convergence and accurate phase distribution with minimum three randomly shifted interferograms will
be proposed in this paper. A fully automatic calibration procedure for calibrating of desired phase shifts and
for evaluating the characteristic curve of phase shift over voltage change will also be presented.
Using the continuously refreshed reference frame in conjunction with the real-time subtraction allows time-averaged shearography to observe and to evaluate the vibrations in form of J02 -fringes in quasi real time. Since the fringe patterns are dependent on the vibration amplitudes, the resonance frequencies of the object can be detected due to the higher amplitudes in resonance. In this presentation a new technique is introduced to automatic detection of the natural frequencies without applying additional sensors by means of statistical method.
This method is suitable for the automatic identification of flaws as well. An experimental investigation shows the detection of defects in a CFR material in this publication.
One of the most interesting and useful applications of shearographic interferometry is the detection, visualisation and measurement of the mechanical vibration of opaque objects. Until now the time-average shearography is a qualitative interferometric method for determining the oscillating loadings. The detected gradient of the deformation can be determined by changing the shearing distance. The fringes of the moving object are often faded and become clearer by filtering with FFT and against an uniform background intensity. The fringes formed in time-average shearography of sinusoidal motions have an irradiance described by the Bessel function Jo2. Quantitative interpretation of the shearogram requires a more precise analysis. Such a technique for extending or decreasing the sensitivity of vibration measurements and for determining the relative phase of vibration across the object surface is the stroboscopic illumination. Stroboscopic shearographic interferometry is a technique which compensates the deficiencies of time-average shearography at the expense of some increase in experimental complexity. However more complex is the recording of stroboscopic shearograms by using two pulses from a double-pulse laser.
One of the most interesting and useful applications of shearographic interferometry is the detection, visualization and measurement of the mechanical vibration of opaque objects. Until now the time-average shearography is a qualitative interferometric method for determining the oscillating loadings. The detected gradient of the deformation can be determined by changing the shearing distance. The fringes of the moving object are often faded and become clearer by filtering with FFT and against an uniform background intensity. The fringes formed in time-average shearography of sinusoidal motions have an irradiance described by the Bessel function J02. Quantitative interpretation of the shearogram requires a more precise analysis. Such a technique for extending or decreasing the sensitivity of vibration measurements and for determining the relative phase of vibration across the object surface is the stroboscopic illumination. Stroboscopic shearographic interferometry is a technique which compensates the deficiencies of time-average shearography at the expense of some increase in experimental complexity. However more complex is the recording of stroboscopic shearograms by using two pulses from a double-pulse laser.
University of Kassel and isi-sys have extended the application of shearography to quantitative vibration analysis and developed a portable automatic controlled shearography system. The Vibrograph is already used for vibration measurements in industry for example of electronic boards typically in combination with laboratory shakers in harmonic excitation modes. Now a small portable piezo shaker permits local excitation of the defects such as delaminations and disbonds. Vibrating in their natural mode shapes the Vibrograph detects the location of the defects within the fiber structure.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.