Non contact excitation and image processing technique for damage detection : design and experiment

Vibration and modal analysis of a structure, is a vast area of research due to its importance in determining the mechanical and dynamic properties of a structure. Therefore, eliminating any kind of uncertainty in process and methodology of testing can dramatically improve the results. Excitation and measurement techniques are developed in recent decades but there are still uncertainty and limitation in terms of employing the traditional techniques. In traditional methods, the excitation is performed with interface with the structure such as electromagnetic shakers or hammer. Both method needs to have contact with the structure. However, if the structure is small or located in a compact zone, making a contact is difficult. Impact hammer can cause damage to the surface. Moreover, any type of attachment to the structure can cause undesired additional mass and stiffness which creates false results. The same scenario goes for the measurement via contact with surface. In order to overcome these limitation and uncertainties, one of the promising ideas in increasing the accuracy of the test is using contactless excitation and contactless measurement methods. This experimental research demonstrates a new technique for contactless vibration and measurement using electromagnetic excitation and image processing techniques respectively. Comparative analysis between different excitation methods are demonstrated and the credibility of non-contact excitation is verified through experiments. Then with the help of digital camera and edge detection algorithm, the mode shapes are reconstructed, This thesis illustrates that with the designed electromagnetic excitation system and digital image processing algorithm are both applicable in order to performing the modal analysis on a cantilever beam in noncontact fashion.