Digital speckle pattern interferometry (DSPI): A fast procedure to detect and measure vibration mode shapes

Digital Speckle Pattern Interferometry (DSPI) is an optical nondestructive testing method allowing the visualization of the defects or the deformations of an object submitted to static deformation or to vibration. This method can be applied to a lot of cases within a range of displacements between tens of nanometers and tens of micrometers. DSPI can be applied to detect the natural frequencies and to visualize the mode shapes of a vibrating object. It is very convenient to study small and weak objects because no contact is required compared to classical modal analysis using accelerometers. DSPI was successfully applied to study a cantilever aluminium plate (5 cm × 10 cm × 1 mm). The experimental isodisplacement fringe maps are compared to computational results using a finite element method.