A novel bulge-testing setup for rectangular free-standing thin films

Abstract

A newly designed bulge-testing apparatus for the mechanical testing of the tensile properties of free-standing thin films has been constructed and tested. With this instrument it is possible to measure the elastic modulus, tensile and compressive growth stress, and plain strain yield strength in thin films. The setup features a high strain resolution (4E-10), and a high stress resolution, e.g., >0.2 MPa for bulge heights larger than 10 μm. In our setup, thin films are stressed by a differential gas pressure across the film, while the deflection is measured by a scanning laser beam. The scanning laser beam measures the curvature of the bulge rather than the bulge height. This makes the setup insensitive to a possible initial nonflatness of the film. This also provides the possibility to measure the growth stress of films that were deposited under a compressive stress. We show the results of measurements of the plane strain modulus on thin tungsten films and on both flat and nonflat aluminum (alloy) film samples.

Bulge Testing Transparent Thin Films with Moiré Deflectometry

“…In bulge tests, the mechanical properties of the thin film are extracted from the relationship between the imposed uniform pressure and the corresponding out-of-plane deflection of the bulged film. The determination of the out-of-plane deflection has been implemented via optical microscopy with a calibrated vertical displacement [8], laser interferometry [9,10], position sensitive detectors (PSD) with scanning laser beams [11][12][13] and shadow moiré [14]. In all these techniques, the measured signals result from light beams that are reflected from the bulged film surface.…”

In situ bulge testing in an atomic force microscope: Microdeformation experiments of thin film membranes

“…A similar setup has been reported in Ref. 9. The pressure difference is detected by a pressure transducer which is thermostatically kept constant at 45°C to minimize thermal drift and a pressure resolution of 240 Pa at 240 kPa maximum detectable pressure is achieved with this system (Fig.…”

The Validity Range of Low Fidelity Structural Membrane Models

“…Similar video camera image analysis for displacement and stretch is discussed by Hsu et al [32] and Reuge et al [33], the latter using a magnetic probe for thickness measurements as well. Kalkmann et al [28] uses a scanning laser to measure bulge curvatures rather than direct height measurements, in order to negate errors due to initial non-flatness. Li et al [34], Mitchell et al [35], and Genovese et al [36] all use projection moiré interferometry to measure the transverse deformation of inflated polymer sheets.…”

“…Several outstanding issues exist within the setup, including fragile specimens, alignment problems, edge effects, slipping of the grips along the membrane perimeter, membrane damage from the grips, wrinkling, and initial non-flatness [28]. Early experimental work by Stevens [29] is used to validate Hencky's analytical solution for the deformed membrane shape, while larger membrane deformations are validated through the experiments of Treloar [30].…”