Grating speckle method for in-plane displacement measurement

A high sensitivity technique combining lensless speckle photography and a grid technique is proposed and demonstrated. A high frequency grid is applied to the specimen surface and contact specklegrams are made in white light before and after loading, in the double exposure mode. Subsequent optical processing yields the various components of in-plane displacement. The sensitivity can be chosen equivalent to the grid frequency or multiples thereof. The method is simple and gives low-noise fringe patterns with high contrast. It is suitable for application in the mechanical laboratory and field environments, because vibration isolation precautions are not necessary.