The identification of viscoplastic material parameters is addressed using a new powerful method: the virtual fields method (VFM). Contrary to classical procedures that are statically determined, the VFM is applied to heterogeneous mechanical fields. Without any hypotheses of homogeneity required, the exploitation of tests with the VFM is not limited to small levels of strains anymore and it can be taken advantage of the large amount of information available thanks to full‐field measurements. In the case of viscoplastic models, the characterisation of strain‐rate sensitivity with the VFM is attempted in this paper using only one test under high‐speed loading conditions, whereas several tests performed at different constant strain‐rates are required for the classical procedures. This article focuses on the development of the VFM for the characterisation of Johnson–Cook's (JC) viscoplastic model. To his aim a return‐mapping algorithm was developed according to the JC's model with an implicit Euler scheme implemented to integrate the constitutive relations. The whole viscoplastic behaviour of a Titanium alloy (Ti6Al4V) is successfully characterised by the VFM using only two tensile tests on notched flat specimens, with full‐field strain measurements by digital image correlation.

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Rate-dependent behaviour characterization of metals at high strain rate remains challenging mainly because of the strong hypotheses when tests are processed with statically determinate approaches. As a non-standard methodology, Image-Based Inertial Impact (IBII) test has been proposed to take advantage of the dynamic Virtual Fields Method (VFM) which enables the identification of constitutive parameters with strain and acceleration fields. However, most of the test parameters (e.g. projectile velocity, specimen geometry) are not constrained. Therefore, an FE-based approach is addressed to optimize the identification over a wide range of strain and strain-rate, according to two design criteria: (1)-the characterized viscoplastic spectra (2)-the identifiability of the parameters. Whereas the first criterion is assessed by processing the FEA simulations, the second is rated extracting material parameters using synthetic images to input the VFM. Finally, uncertainties regarding the identification of material constants are quantified for each IBII test configuration and different camera performances.