Towards gigantic RVE sizes for 3D stochastic fibrous networks

The size of representative volume element (RVE) for 3D stochastic fibrous media is investigated. A statistical RVE size determination method is applied to a specific model of random microstructure: Poisson fibers. The definition of RVE size is related to the concept of integral range. What happens in microstructures exhibiting an infinite integral range? Computational homogenization for thermal and elastic properties is performed through finite elements, over hundreds of realizations of the stochastic microstructural model, using uniform and mixed boundary conditions. The generated data undergoes statistical treatment, from which gigantic RVE sizes emerge. The method used for determining RVE sizes was found to be operational, even for pathological media, i.e., with infinite integral range, interconnected percolating porous phase and infinite contrast of propertie

From Architectured Materials to the Development of Large-scale Additive Manufacturing

Architectured materials are a rising class of materials that bring new possibilities in terms of functional properties, filling the gaps and pushing the limits of Ashby’s materials performance maps [1]. Capitalizing on the concepts of architectured materials, explorations of the potential applications of large-scale 3D printing techniques to civil engineering structures were recently implemented in the DEMOCRITE project

Elastoplasticity of auxetic materials

International audienceMaterials exhibiting a negative Poisson's ratio (auxetics) have drawn attention for the past two decades, especially in the field of lightweight composite structures and cellular media. Studies have shown that auxeticity may result in higher shear modulus, indentation toughness and acoustic damping. Although elastic properties of such materials have been extensively investigated, the effect of plasticity on auxetic behavior has not been discussed. In particular, does the auxetic character of the material remain while entering the plastic domain? The present work aims at modeling the nonlinear mechanical response of auxetics. Full-field simulations are performed using the finite element method with periodic boundary conditions. Macroscopic modeling of auxetics is attempted using an anisotropic compressible plasticity framework

Effective elastic properties of auxetic microstructures : anisotropy and structural applications

International audienceMaterials presenting a negative Poisson's ratio (auxetics) have drawn attention for the past two decades, especially in the field of lightweight composite structures and cellular media. Studies have shown that auxeticity may result in higher shear modulus, indentation toughness and acoustic damping. In this work, three auxetic periodic microstructures based on 2D geometries are considered for being used as sandwich-core materials. Elastic moduli are computed for each microstructure by using finite elements combined with periodic homogenization technique. Anisotropy of elastic properties is investigated in and out-of-plane. Comparison is made between auxetics and the classical honeycomb cell. A new 3D auxetic lattice is proposed for volumic applications. Cylindrical and spherical elastic indentation tests are simulated in order to conclude on the applicability of such materials to structures. Proof is made that under certain conditions, auxetics can be competitive with honeycomb cells in terms of indentation strength. Their relatively soft response in tension can be compensated, in some situations, by high shear moduli

Homogenization of periodic auxetic materials

International audienceMaterials presenting a negative Poisson's ratio (auxetics) have drawn attention for the past two decades, especially in the field of lightweight composite structures and cellular materials. Studies have shown that auxeticity may result in higher shear modulus, fracture toughness and acoustic damping. In this work, three auxetic periodic lattices are considered. Elastic moduli are computed and anisotropy is investigated by the use of finite element method combined with numerical homogenization technique

Self-Heating Measurements for a Dual-Phase Steel under Ultrasonic Fatigue Loading for stress amplitudes below the conventional fatigue limit

AbstractThe aim of the present research was to study the self-heating behavior of a dual-phase steel under ultrasonic fatigue loading for stress amplitudes lower than the conventional fatigue limit. The steel studied in this research was DP600 commercial dual phase steel. Fatigue tests were conducted for different values of stress amplitudes up to 107 cycles using an ultrasonic fatigue machine at a testing frequency of 20 kHz with flat specimens. An infrared camera was used to measure the mean temperature evolution during the tests. A specific form of heat diffusion equation was adopted in this work to calculate the intrinsic dissipation from temperature measurements. The variation of the dissipated energy versus stress amplitude under cyclic loading was also studied

Effective elastic properties of auxetic microstructures: anisotropy and structural applications

Abstract Materials presenting a negative Poisson's ratio (auxetics) have drawn attention for the past two decades, especially in the field of lightweight composite structures and cellular media. Studies have shown that auxeticity may result in higher shear modulus, indentation toughness and acoustic damping. In this work, three auxetic periodic microstructures based on 2D geometries are considered for being used as sandwich-core materials. Elastic moduli are computed for each microstructure by using finite elements combined with periodic homogenization technique. Anisotropy of elastic properties is investigated in and out-of-plane. Comparison is made between auxetics and the classical honeycomb cell. A new 3D auxetic lattice is proposed for volumic applications. Cylindrical and spherical elastic indentation tests are simulated in order to conclude on the applicability of such materials to structures. Proof is made that under certain conditions, auxetics can be competitive with honeycomb cells in terms of indentation strength. Their relatively soft response in tension can be compensated, in some situations, by high shear moduli

Classification of building systems for concrete 3D printing

In the present paper, a study is conducted on building systems associated with concrete extrusion-based additive manufacturing techniques. Specific parameters are highlighted - concerning scale, environment, support, and assembly strategies - and a classification method is introduced. The objective is to explicitly characterise construction systems based on such printing processes. A cartography of the different approaches and subsequent robotic complexity is proposed. The state of the art gathered from the literature is mapped thanks to this classification. It appears that the disruption potential brought by concrete 3D printing has not been fully embraced yet.LafargeHolci