Equibiaxial Planar Tension Test Method and the Simulation Analysis for Hyperelastic EAP Membrane

Abstract

The equibiaxial planar tension test is an important method for determining the mechanical properties of hyperplastic membranes, and it is also critical to designing an effective equibiaxial tension test rig to meet experimental accuracy requirements. However, any analysis addressing the accuracy of this test is not reported in the literature. In this paper, an equibiaxial planar tension apparatus is proposed for conducting single-corner-point tension tests on hyperelastic electroactive polymer (EAP) membranes. The experimental data were compared with those obtained from two-corner-point-fixed tension tests and fitted with nonlinear material models, and the model’s parameters were also evaluated. Finally, the widely-used finite element software ABAQUS was employed to simulate equibiaxial planar tension methods and investigate the impact of clamping mode and point number on test accuracy as well as the uniformity of overall deformation. The test results indicate that the stress-strain curves for the two tensions remain consistent across small stretch ratios. However, as the stretch ratio increases (about $\lambda >2.25$ ) in two-corner-point-fixed tension, stress shielding may lead to a degradation of strain uniformity and result in greater stresses than single-corner-point tension. Additionally, both the three-parameter Yeoh model and the four-parameter Ogden model can provide an accurate description of the EAP membrane material. The simulation results indicate that the axial strain variation amplitudes remain below 5% within a region spanning approximately 80% of the specimen’s overall length from its center to edge and even below 1% within a region spanning 85% in the single-corner-point tension; stress inaccuracies increase with stretch ratio, while the calculated error is about 2.1% when $\lambda =4$ in the single-corner-point tension test, which has the smallest stress error among the tests; when the number of tension points is increased, the overall deformation becomes more sufficient, and the test accuracy improves as well. The conclusions drawn from this paper will be beneficial in designing equibiaxial planar tension test rigs and analyzing their accuracy and uniformity of deformation.