Modal testing of large structures using projected grid Moire

This paper describes a optical method for obtaining full-field dynamic displacement data from relatively large structures using the projected grid Moire technique with non-collimated illumination. The method is non-contacting and non-disturbing and may be implemented with a minimum of specialized equipment. It provides a real-time qualitative display of vibration patterns that is useful when conducting sine-sweep vibration tests to identify normal modes. Transient vibrations may also be studied by employing an appropriate recording device to capture the live display for later analysis. The results of an experimental investigation are presented that support the assumptions made in developing the theory and illustrate its application.