Charles Brugger

Experiments and Numerical Simulations of Interlocked Materials

Interlocked materials are new examples of “hybrid materials”, mixing materials and structures at a millimetric scale. They consist of periodic assemblies of elementary blocks with specific shapes, maintained in contact by compressive boundary conditions. These “pre-fragmented materials” can simultaneously fulfil antagonistic properties such as high strength together with good damage tolerance. We performed indentation tests on two different structures: (i) an assembly of osteomorphic ice blocks and (ii) an assembly of plaster made cubes. The tests being performed up to the failure, it is found that these structures dissipate much more mechanical energy than similar monolithic plates and preserve their integrity up to much larger deformation. A numerical modelling is then developed in order to reproduce this behaviour. Using finite elements, we simulated the friction contact between two elastic cubes or blocks, for a given lateral load and friction coefficient. The outputs are then introduced as local contact rules in a “Discrete Elements code” specially developed for this study. The discrete code is then used to model the elastic and damage behaviour of assemblies of cubes or osteomorphic blocks. The comparison with experimental results is satisfactory. Finally, the code is used to model larger assemblies of interlocked structures for which the force path is analysed.

Ductility of thin metallic films

Depending on the loading conditions, geometry and material characteristics, the ductility of thin metallic films is controlled either by the resistance to plastic localization or by the resistance to internal damage. New on-chip tensile tests performed on submicron aluminium films show significant strain hardening capacity leading to relatively good resistance to necking, while damage occurs through void nucleation at grain boundaries followed by their growth and coalescence. These results are discussed in the light of several other studies presented in the recent literature in order to unravel the origins of the frequently reported poor ductility of thin metallic films, and the various means existing to improve it.