Mechanical Properties Measurement of Polymer Films by Bulge Test and Fringe Projection

Abstract

This paper aims at determining the mechanical properties such as Poisson ratio, biaxial modulus, and residual stress of polymer membranes using the bulge test and fringe projection. Under this idea, a bulge test apparatus has been developed for robust usage, under the room temperature, in industrial environments that are usually noisy and full of all kinds of vibrations. A setup of the bulge test, consisting of single chips and digital on-off valves, was used to achieve automatic precision control of pressure application to gas chamber with a circular polyimide (PI) test film fixed on the opening of it. A deformed image was then obtained via fringe projections with a series of optical apparatuses, and a 3D membrane deformation distribution was further achieved from this deformed image by some image processes that are chiefly through wavelet transformation and phase expansion. With the measurements of maximum membrane deformation versus applied pressure and given the Young’s modulus of test membrane, we could further calculate the Poisson ration (and then biaxial modulus) and residual stress of the film. Also, the measurements were validated to be highly accurate by comparison with a finite element analysis.

Fringe projection profilometry for recovering 2.5D shape of ancient coins

“…engineering surfaces [26]- [28]. The fringe can be generated by projecting parallel light through optical grating slides with various projecting patterns, such as sinusoidal-like modulation.…”

Estimation of the Elastic Properties of Polymer Plates Using a Structured Light Technique

“…As an alternative, the bulge test is used for determining the mechanical properties under biaxial tension conditions with small bending component [5]. Among the different test methods for Young's modulus determination, the bulge test has become popular for sheet metal [6][7][8][9], thin films [10][11][12][13], polymers [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], and biological materials [29]. In comparison to uniaxial tests, higher strain values can be achieved by bulge tests [7,16] and the maximum strain obtained in uniaxial tensile test before necking is relatively small [6].…”

“…The bulge test has been successfully applied [6,9,12,[15][16][17][18][19][20][21][22][23][24][26][27][28][29] and differences have been observed in comparison with uniaxial tests. This test is suitable for investigating polymer blends for large biaxial plastic deformation prior to failure [16].…”

“…This test is suitable for investigating polymer blends for large biaxial plastic deformation prior to failure [16]. Currently, it has been applied for determining stress-strain curves [9,16,29], pressure versus out-of-plane displacement curves [20,29], Young's modulus [28], changes of plate thickness [23,29], radius of curvature [29], hyperelastic model parameters [24], strain distribution [22], mechanism of bursting [26], transient surface shapes [19], anisotropy coefficients [6], thermally induced changes [14,25,27] and mechanical properties of biological tissues [30]. The results presented by many researchers show good agreement with theoretical values and with other methods of testing, such as biaxial extension and uniaxial tension.…”

“…Some applied measuring methods for out-of plane displacement in the bulge test are photogrammetry [9,17,18], digital image correlation [10,16,14,21], interferometry [12], laser triangulation [19], fringe projection [11,20], and stereo vision [24]. The most accurate measuring method is interferometry since the resolution is, at least, half of the laser wavelength.…”