Measurement of cyclic strain using metal foil and laser speckle sensor

This paper presents a new method to measure cyclic strain with no contact using metal foil gauges and laser speckle sensor. When a metal foil (such as aluminum, copper, nickel etc.) is pasted on a specimen and the specimen is loaded cyclically, slipbands are produced on the foil surface by fatigue. The occurrence of the slipbands is dominated by the strain amplitude of the specimen surface and number of the loading cycles. Thus the fatigue strain of the base metal can be estimated by observing the surface change of the foil. The method in this study is based on observation of the change of laser speckle pattern depending on the surface property change of the foil caused by fatigue. This method is intended to make a non-contact strain measurement by the application of the laser speckle technique for the detection of the surface change.