ABSTRACT
Equibiaxial tension testing is essential for the materials characterization of rubber. Only the addition of equibiaxial testing data to uniaxial data will allow correct curve fitting to different non-linear material models. The correct determination of the parameters through the curve fitting process is essential to enable meaningful Finite Element Analysis (FEA). However, dedicated test equipment for biaxial testing is expensive. This paper describes a newly developed, cost efficient test rig for equibiaxial tension testing, designed to be used within a conventional uniaxial tensile tester. A novel, innovative specimen fixture design allows the use of up to 15mm thick specimen to be tested, while still enabling quick and easy specimen changes. The test system utilizes cross-shaped samples, with slotted load arms, cut from sheet material. FEA analysis shows, that this cross-shaped specimen produces a near perfect equibiaxial stress distribution throughout the whole test area. Physical tests also show, that within the test area, the strain state is nearly homogeneous with standard deviations smaller than 3 %. Four commercially available silicone rubber materials are tested using the system. Together with uniaxial and pure shear test data, the results are used to model the materials using a Mooney-Rivlin material model. With these parameter, FEA of the tests are conducted. The results are in good agreement with the physical tests indicating the feasibility of the proposed test rig for physical testing.
