The knowledge of material mechanical behaviour in different physical conditions is necessary to accurately simulate structural response using finite element methods, especially when complex physical processes, such as strain-hardening, large strains etc., are involved. In this context, the material characterization at different temperatures and strain-rates is indispensable, but it is equally essential to properly transform the test data into efficient constitutive equations capable to accurately reproduce the material response. As an alternative to the conventional analytical approach of the stress–strain curve fitting, this investigation examines the adoption of an inverse method that exploits a FEM model to accurately keep account of the specimen stress, strain, and temperature fields. The material parameters of the selected constitutive model are then obtained by using an optimization algorithm that iteratively changes the parameter values to minimize a target function. The algorithm has been implemented in MATLAB using the LS-DYNA FEM solver. In the paper, this method has been applied to the experimental data produced in a test campaign (EU project LISSAC) for a ferritic steel normally employed in nuclear pressure vessels. These data refer to tensile testing under several strain-rate and temperature conditions and include both smooth and notched cylindrical specimens. The constitutive models of Johnson–Cook and Zerilli–Armstrong have been considered for the demonstration of the methodology. The efficiency of the approach in determining the model parameters is critically assessed.

This paper presents an overview of the developments performed at the European Laboratory for Structural Assessment (ELSA) of the Joint Research Centre of European Commission concerning the new generation of servo-hydraulic real-time digital controller/acquisition system adopted in large scale experiments. The hardware architecture is based on EtherCAT® modules that guarantee a versatile and modular system easily adaptable to changing requirements (a typical situation experienced at ELSA with custom adapted non-standardized large scale structural experiments). Other fundamental features of this system are that all the analog signals are digitalized in the proximity of the transducers reducing noise-to-signal ratio (a great advantage for Pseudo-dynamic tests but in general for all experimentation), and all the different slave controllers communicate at each time sampling through a deterministic robust digital bus. In addition to the increasing computer performances, the developed simplified software architecture does offer a substantial improvement of control quality in terms of speed, safety, and accuracy compared with conventional/commercial systems.