2017 GEORGE STEPHENSON GOLD MEDAL
Morgan Bertin, François Hild, Stéphane Roux, Florent Mathieu, Hugo Leclerc, and Patrick Aimedieu
For their paper: ‘Integrated digital image correlation applied to elastoplastic identification in a biaxial experiment’, published in the Journal of Strain Analysis 2016, Vol 51(2) 118-131. 
This paper tackles the relationship between stresses and strains of samples of material so that numerical (finite element) models can be constructed for components, structures and systems. For materials in their elastic regime, this is relatively straightforward. However, materials can be used beyond their elastic range; extreme events (such as forming, impact or explosion) need to be modelled, and some materials (e.g. steels) may not always be regarded as linearly elastic.
The starting point is to carry out measurements on a sample of material under representative loading conditions, but often there may only be a small amount of material available and the stress state may not simply be uniaxial.
This paper showed how loading a miniaturised testpiece could be used to investigate plastic hardening. Digital Image Correlation was used to measure the displacements of the specimen under load, and then an finite element (FE) model of the test could be created and the material parameters optimised by seamlessly coupling experimental data and FE simulations. The authors have demonstrated that this approach leads to improved determination of the material parameters.
The paper therefore represents a significant step forward in the use of DIC for identifying material performance and properties. It will be useful in academia and industry, particularly in situations where accurate models are required for material performance under challenging or extreme conditions.
The Stephenson Gold Medal is a fitting recognition of the work of the group as a whole, and the contribution that they have made to the field of experimental mechanics.
François Hild, a co-author of the paper, is thrilled to win the prize: “It is an important recognition of the work of our Eikology (the science of images) group that aims to bridge the gap between experimental and computational mechanics. The award-winning paper illustrates such integrated procedures.”
Find out more about the George Stephenson Gold Medal Award.