Elastomer biaxial characterization using bubble inflation technique. II: Numerical investigation of some constitutive models

An elastomeric material was investigated with a bubble inflation rheometer, and its mechanical behavior was modeled as a rubber-like solid. Classical strain energy functions were considered and the hyper-elastic constants wer e calculated by a direct identification procedure from simple uniaxial and equibiaxial extension test data, and the results are compared against those obtained by an inverse method from bubble inflation test data. The latter amounted to minimizing a cost function and matching the measured response t o a finite element analysis solution, which depended on the unknown materia l parameters. The optimization employed the Levenberg-Marquardt algorithm a nd Abaqus software to compute the cost function and its gradients. The cons tants so obtained were further used in finite dement analysis, and the nume rical results were compared with experiments. This study showed that the in verse method, used to estimate the material parameters, is a good alternati ve to the direct identification, especially since the latter often requires homogeneous strain state, which is very difficult to obtain.