Characterization of Material Properties Under Finite Strain Using an Optical Method of Measurement

Abstract

Numerical simulations need a constitutive model suitable to represent the mechanical behavior of the materials. The material parameters for the model are obtained by means of a parametric identification procedure using data acquired in experimental tests and numeric simulation of the discretized specimen. Non-linear materials, like polymers, present a localized heterogeneous displacement fields under finite strain and then the use of non-contact measurement techniques are the most appropriated. The optical method Digital Image Correlation (DIC) has been demonstrated great acceptability in the material characterization due its capability to measure the entire displacement field over the specimen. The experimental data provided by the testing machine and the DIC method provide useful data for the parametric identification procedure of nonlinear materials under finite strain. A cost function of the minimization problem was constructed based on the weighted least squares of the differences between the experimental and numeric data. The cost function has a multi-objective characteristic since it relates experimental and numerical data of different quantity and magnitudes, i.e., forces and displacements. This work presents a characterization of the material parameters of the polymer Polyvinyl chloride (PVC). The material showed localized heterogeneous strain fields, where the DIC method was capable to obtain information regarding the mechanical behavior of necking to be used in the parametric identification. From the results of the sensibility analysis of this material only the experimental force obtained from a uniaxial test is not enough to find the material parameters, since that different combinations of the parameters can result in a numerical force equivalent to the experimental force but quite different with regard to the experimental and numerical transverse displacement.