Structural health monitoring (SHM) systems generally install low cost excitation component and/or sensors to the machines or buildings permanently to monitor the health of it. Non Destructive Evaluation (NDE) systems use high cost sensors to perform the inspection of structures. It would be advantageous to inspect the some aerospace structures and parts in vacuum environment by using the remotely monitoring systems such as laser vibrometer. In this study, a scanning laser vibrometer is used to detect the location of the problem at the structure. For data collection and analysis recently, developed surface response to excitation (SuRE) method was used.
First the software of the scanning laser vibrometer was used to evaluate the capabilities of the system. The vibration of simple structures such as the cone of a speaker and a beam was tested when they were excited below 200 Hz and the mode shapes were studied. Later, the scanning laser vibrometer was used for implementation of the SuRE method. The surface vibration of beams and plates were monitored while their surfaces were excited at high frequencies with a piezoelectric exciter. External force was applied to one point of the surface of the considered structures. The scanning laser vibrometer evaluated the vibration of different points on the structure according to given program and obtained the frequency response before and after the external load was applied. The sum of the squares of the differences of the frequency responses were obtained for each point on the surface and presented with a contour plot.
Use of the scanning laser vibrometer was convenient at the test conditions. The calculated mode shapes were very similar to the expected ones when the simple structures were tested. The locations of the external forces were identified correctly when the beams and plates were tested. The study indicated that the scanning laser vibrometer and SuRE method may be used for identification of defects and/or loose fasteners.
