Identification of Johnson-Cook's Viscoplastic Model Parameters Using the Virtual Fields Method: Application to Titanium Alloy Ti6Al4V
Résumé
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.