Uniaxial compression loading of 220 kPa is simulated next. In this case and as shown in Fig. 20.5, the simulation results indicate that using our hybrid technique, combination of FEM and fringe prediction, inspectors can locate partial hole defect by laser shearography. 20.4.2 Experimental Results for Validating Fringe Prediction Results The corresponding experimental result of the acrylic plate sample under compression loading is shown in Fig. 20.6. The result validates that by using appropriate loading conditions predicted by FEM, the defect can be detected with shearographic imaging. 20.4.3 Projection of Shearographic Results on the Sample Visualization of the results generated by laser shearography can improve the identification of defects on surfaces under test [3]. As shown in Fig. 20.7, a multimedia projector has been introduced at the end of inspection process to project the shearographic results back onto the surface of the sample, so that the defect detection process becomes more evident. In this experiment, the optical head was located at a working distance of 1.8 m from the panel. A pulsed laser with pulse energy of 0.2 mJ with the wavelength of 532 nm and power of 50 mW is used for shearographic imaging. Fig. 20.4 Prediction of shearographic fringes corresponding to the first six modes of vibrations obtained from FEM analysis: (a) 205 Hz; (b) 332Hz; (c) 545Hz; (d) 735Hz; (e) 1,038 Hz; and (f) 1,085 Hz, respectively Fig. 20.5 Prediction of shearography fringes by FEM under compression loading: (a) wrapped optical phase; (b) corresponding shearography intensity fringes 20 Structural Health Monitoring by Laser Shearography: Experimental and Numerical Investigations 153
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