Modeling step-strain filament-stretching (CaBER-type) using ALE techniques

This paper discusses the numerical modeling of capillary break-up extensional rheometer procedures (CaBER) using Arbitrary Lagrangian/Eulerian (ALE) methods. Different models, fluid viscosities and aspect-ratios are studied, employing a hybrid finite element/finite volume spatial approach. Finite element discretisation is employed for the momentum and continuity equation, whilst a pure-upwinding cell-vertex finite volume representation is utilised for the hyperbolic stress equation. The results are validated against equivalent experimental results from the literature. By employing various constitutive models, viscoelastic response has been studied for some strain-hardening fluids. Two different polymeric to solvent viscosity ratios are studied covering both high and low solvent fractions. The relaxation time and the apparent extensional viscosity are calculated for both viscosity ratios, from the evolution of the mid-filament diameter. For these viscoelastic solutions, the extensional viscosity increases with strain, and this trend, and its range of values in apparent extensional viscosity values agree well with the literature. Also, estimated relaxation times are found to lie in close agreement with the actual relaxation time data used for the fluids in question

Relevance of a mesoscopic modeling for the coupling between creep and damage in concrete

International audienceIn its service-life concrete is loaded and delayed strains appear due to creep phenomenon. Some theories suggest that micro-cracks nucleate and grow when concrete is submitted to a high sustained loading, thereby contributing to the weakening of concrete. Thus, it is important to understand the interaction between the viscoelastic deformation and damage in order to design reliable civil engineering structures. Several creep-damage theoretical models have been proposed in the literature. However, most of these models are based on empirical relations applied at the macroscopic scale. Coupling between creep and damage is mostly realized by adding some parameters to take into account the microstruc-ture effects. In the authors' opinion, the microstructure effects can be modeled by taking into account the effective interactions between the concrete matrix and the inclusions. In this paper, a viscoelastic model is combined with an isotropic damage model. The material volume is modeled by a Digital Concrete Model which takes into account the "real" aggregate size distribution of concrete. The results show that stresses are induced by strain incompatibilities between the matrix and aggregates at mesoscale under creep and lead to cracking