Virtual fields method coupled with moiré interferometry: Special considerations and application

Abstract

The virtual fields method (VFM) is a novel highly efficient non-iterative tool for the identification of the constitutive parameters of materials. The VFM can obtain several constitutive parameters based on the full-field deformation of the specimen measured in a single test. However, the available results demonstrate that the accuracy of the identification result is strongly dependent on the quality of the deformation field, which is generally measured using optical methods. Especially, in the case where a small deformation is applied under elastic loading, the image noise and measurement error will exhibit a significant influence on the identification results. By combining the VFM with moiré interferometry (MI), a MI-based VFM is used to identify the parameters of an orthotropic linear elastic material. A numerical experiment is conducted to examine the feasibility of this method. From the analysis results, we determine that two factors exhibit an influence on the identification accuracy. The reinforcement direction of the orthotropic material is one factor, and the other is the noise in the deformation field. This MI-based VFM is then applied to determine the mechanical parameters of a unidirectional carbon fiber composite material. In the measurement, a three-point bending load is applied to the specimens. A high density grating with a frequency of 1200line/mm grating is replicated on the specimen surface and used for measuring the in-plane deformation fields using a moiré interferometer. The obtained deformation fields are taken as the inputs of the VFM identification process, and the elastic properties of the materials are identified. The obtained results verify the advantage of the proposed method with respect to high accuracy and good noise immunity.