The virtual fields method for identifying viscoelastic properties based on stress-sensitivity virtual fields

An inverse analysis technique is proposed for identifying characteristics from experimental data using the virtual fields method with stress-sensitivity-based virtual fields. Two-dimensional digital image correlation is used to obtain the inplane displacement and strain distributions on the specimen surface. To determine the stress distributions under the plane-stress condition, the numerical Laplace transform is used to obtain the through-thickness strain from the inplane strains based on the correspondence principle. Using the virtual displacement fields based on the stress sensitivity, the bulk and shear relaxation moduli, which represent the viscoelastic characteristics, are simultaneously identified. The various stress states generated by the specimen shape and their time variation in a single test and the use of the stress-sensitivity-based virtual fields make it possible to simultaneously determine two independent viscoelastic material properties. Therefore, this method is expected to make a significant contribution to the mechanics of viscoelastic materials.