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The Interferometric Strain/Displacement Gage (ISDG) is an established laser-based technique that measures the relative displacement between two gage points on a specimen surface. The gage points are reflective markers illuminated with a low-power He-Ne laser to form interference patterns that are monitored with a computer-controlled system. Features of the technique are short gage length (50 – 300 μm) and no mechanical contact. Two new applications of the ISDG are described in this paper. The first is the measurement of strain on metal microspecimens that are 3 mm long with cross-sections typically 0.3 mm square. Details of the test procedure and results from 52 tests conducted as part of an ASTM-sponsored cross-comparison test are summarized. The second is strain measurement on 3.5 μm thick polysilicon film specimens; this capability has enabled measurement of the Young's Modulus and the tensile strength of this material which is used in microelectromechanical systems (MEMS).
interferometry, lasers, microspecimens, polysilicon, thin films, weldments, MEMS
Decker Professor and ChairJohns Hopkins University, Baltimore, MD
Graduate Student, Johns Hopkins University, Baltimore, MD