Application of the Virtual Fields Method to High Strain Rate Testing

Abstract

The novel Virtual Fields Method (VFM) for dynamic material characterization, which uses only acceleration and strain fields obtained by a full field measurement was introduced in order to exclude the unreliable load information from the characterization.

The feasibly of the methodology was confirmed after applying it to the displacement fields from finite element (FE) dynamic tension simulations. Through the sensitivity study with the FE simulations, it was suggested that for the accurate characterization (i.e. the accurate identification of constitutive parameters) using the VFM, the acceleration magnitude should reach above a certain level and the longer duration of non-zero acceleration during the deformation is required.

In addition, the VFM application to actual high strain tension tests with DP780 steel sheets were studied using both servo-hydraulic tester and impact frame high speed tensile tester. The first identification trial with the VFM was not successful, and after comparing the experimental results with the FE simulation results, it was verified that the identification was disturbed by the experimental noise within acceleration and strain data. In order to reduce the noise, the uniform strain assumption up to small deformation was taken into account for the purpose of strain smoothing, and other smoothing methods such as Diffuse Approximation Method and Savitzky-Golay filtering were also applied to experimental data as well. The results of the VFM application were improved after the smoothing process, but the investigation of local experimental data showed that more advanced smoothing techniques and careful experimental approaches are necessary to reduce the experimental noise even further in order to get the accurate dynamic constitutive parameters with the use of the VFM.