A Moiré-deflectometry Based Bulge/Contact Test for Transparent Thin Films

Bulge tests have been widely used to characterize mechanical properties of thin films. In this technique, mechanical properties are extracted from the analytically or approximately obtained pressure-deflection response. The determination of the out-plane deflection is critical for bulge tests and to date, this has been implemented by using optical microscopy with a calibrated vertical displacement, laser interferometry and shadow moiré. All these techniques rely on reflected light from the bulged film surface, so films with relatively smooth and reflective surfaces are required. Consequently, these techniques are less applicable to transparent polymeric thin films.