Development and validation of a 3D computational tool to describe concrete behaviour at mesoscale. Application to the alkali-silica reaction

A finite element analysis of the large deformation of three-dimensional polycrystals is presented using pixel-based finite elements as well as finite elements conforming with grain boundaries. The macroscopic response is obtained through volume-averaging laws. A constitutive framework for elasto-viscoplastic response of single crystals is utilized along with a fully-implicit Lagrangian finite element algorithm for modeling microstructure evolution. The effect of grain size is included by considering a physically motivated measure of lattice incompatibility which provides an updated shearing resistance within grains. A domain decomposition approach is adopted for parallel computation to allow efficient large scale simulations. Conforming grids are adopted to simulate flexible and complex shapes of grains. The computed mechanical properties of polycrystals are shown to be consistent with experimental results for different grain sizes.     

Uniaxial alignment of nanoconfined columnar mesophases

By confining discotic phthalocyanines in a network of crisscrossed nanogrooves, we obtain a uniaxial alignment of the columnar mesophase. The alignment process is based on the anisotropy of interface tension between the mesophase and the nanogrooves' walls. Preferential mesophase alignment results from this nonhomogeneity combined with the anisotropy of the network cell dimensions. A simple model is proposed to explain the experimental observations.