Elastomer biaxial characterization using bubble inflation technique. I: Experimental investigations

The biaxial rheological behavior of materials such as elastomers or polymer s can be obtained using a bubble-inflation-technique. A circular membrane i s clamped at the rim and expanded under gas pressure. The inflation of the circular membrane is recorded using a CCD video camera and the blowing pres sure by a pressure sensor. Then, from elongation and curvature radius measu rements at the pole of the bubble, one can deduce equibiaxial stress-strain data. This study describes the optimization of a bubble-inflation rheomete r. The most sensitive point of the technique is the estimation of the elong ation at the bubble pole, deduced from video camera measurements. A direct measurement of the bubble thickness was performed using a magnetic probe in order to validate rheometer results. Such a validation has evidently never been carried out before. Results of quasi-static equibiaxial characterizat ion of elastomers are presented and analyzed.