A micro-model of the intra-laminar fracture in fiber-reinforced composites based on a discontinuous Galerkin/extrinsic cohesive law method

The hybrid discontinuous Galerkin (DG)/extrinsic cohesive law (ECL) method was recently proposed [1] to circumvent the drawbacks of the cohesive element methods. With the DG/ECL method, prior to fracture, the flux and stabilization terms arising from the DG formulation at interelement boundaries are enforced via interface elements in a way that guarantees consistency and stability, contrarily to traditional extrinsic cohesive zone methods. At the onset of fracture, the traction–separation law (TSL) governing the fracture process becomes operative without the need to modify the mesh topology since the cohesive elements required to integrate the TSL are already present. This DG/ECL method has been shown to be an efficient numerical framework that can easily be implement in parallel with excellent scalability properties to model fragmentation, dynamic crack propagation in brittle and small-scale yielding materials, both for 3D problems and for thin structures [1, 2]. In this work, following the developments in [3], the DG/ECL method is extended to the study of composite materials failures at the micro-scale. The method is applied to study the transverse traction of composite materials in characteristic micro-volumes of different sizes. The method captures the debonding process, assimilated to a damaging process before the strain softening onset. It is shown that the density of dissipated energy resulting from the damage (debonding) remains the same for the different studied cell sizes. During the strain softening phase, a micro-crack initiates and propagates, in agreement with experimental observations. After strain softening onset, the extracted macroscale cohesive law, obtained by the method proposed in [4], is ultimately shown to converge for the different cell sizes. The predicted behaviors are then compared to experimental results obtained from laminate tests, and are found to be in good agreement.SIMUCOMP The research has been funded by the Walloon Region under the agreement no 1017232 (CT-EUC 2010-10-12) in the context of the ERA-NET +, Matera + framework

An XFEM/CZM implementation for massively parallel simulations of composites fracture

Because of their widely generalized use in many industries, composites are the subject of many research campaigns. More particularly, the development of both accurate and flexible numerical models able to capture their intrinsically multiscale modes of failure is still a challenge. The standard finite element method typically requires intensive remeshing to adequately capture the geometry of the cracks and high accuracy is thus often sacrificed in favor of scalability, and vice versa. In an effort to preserve both properties, we present here an extended finite element method (XFEM) for large scale composite fracture simulations. In this formulation, the standard FEM formulation is partially enriched by use of shifted Heaviside functions with special attention paid to the scalability of the scheme. This enrichment technique offers several benefits since the interpolation property of the standard shape function still holds at the nodes. Those benefits include (i) no extra boundary condition for the enrichment degree of freedom, and (ii) no need for transition/blending regions; both of which contribute to maintaining the scalability of the code. Two different cohesive zone models (CZM) are then adopted to capture the physics of the crack propagation mechanisms. At the intralaminar level, an extrinsic CZM embedded in the XFEM formulation is used. At the interlaminar level, an intrinsic CZM is adopted for predicting the failure. The overall framework is implemented in ALYA, a mechanics code specifically developed for large scale, massively parallel simulations of coupled multi-physics problems. The implementation of both intrinsic and extrinsic CZM models within the code is such that it conserves the extremely efficient scalability of ALYA while providing accurate physical simulations of computationally expensive phenomena. The strong scalability provided by the proposed implementation is demonstrated. The model is ultimately validated against a full experimental campaign of loading tests and X-ray tomography analyzes.A.J., A.M., D.T., L.N. and L.W. acknowledge funding through the SIMUCOMP ERA-NET MATERA + project financed by the Fonds National de la Recherche (FNR) of Luxembourg, the Consejería de Educación y Empleo of the Comunidad de Madrid, the Walloon region (agreement no 1017232, CT-EUC 2010–10-12), and by the European Unions Seventh Framework Programme (FP7/2007–2013).Peer ReviewedPostprint (author's final draft

Review of state of the art of dowel laminated timber members and densified wood materials as sustainable engineered wood products for construction and building applications

Copyright © 2019 The Authors. Engineered Wood Products (EWPs) are increasingly being used as construction and building materials. However, the predominant use of petroleum-based adhesives in EWPs contributes to the release of toxic gases (e.g. Volatile Organic Compounds (VOCs) and formaldehyde) which are harmful to the environment. Also, the use of adhesives in EWPs affects their end-of-life disposal, reusability and recyclability. This paper focusses on dowel laminated timber members and densified wood materials, which are adhesive free and sustainable alternatives to commonly used EWPs (e.g. glulam and CLT). The improved mechanical properties and tight fitting due to spring-back of densified wood support their use as sustainable alternatives to hardwood fasteners to overcome their disadvantages such as loss of stiffness over time and dimensional instability. This approach would also contribute to the uptake of dowel laminated timber members and densified wood materials for more diverse and advanced structural applications and subsequently yield both environmental and economic benefits.Interreg North-West Europe (NWE) funded by the European Regional Development Fund (ERDF) supporting the project (Towards Adhesive Free Timber Buildings (AFTB) - 348)

Modeling the large inelastic deformation response of non-filled and silica filled SL5170 cured resin

In recent years, important efforts have been focused on rapid production of tools using Rapid Prototyping and Manufacturing (RP&M) technologies such as the Stereo-Lithography Apparatus (SLA). One of the applications is the development of rapid polymer tooling such as dies for injection molding. For these applications, optimal thermal as well as mechanical properties of final tools are of significance. In order to characterize the mechanical response of materials made by SLA, a standard set of material tests, including uniaxial tension and compression tests under different strain rates and different temperatures, was conducted for both silica filled and non-filled resin. In this paper, the mechanical response of the non-filled SL5170 cured resin is discussed in terms of an elastic-viscoplastic material model. Further, a new model for silica filled SL5170 cured resin was developed to estimate the stress-strain relationship of the composite. This composite model is an extension of the elastic-viscoplastic model for non-filled resin to include the elastic deformation of the silica particles. The stress-strain curves predicted by the models under homogeneous deformation show good agreement with the experimental results.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44781/1/10853_2005_Article_903.pd

Potentiels de muffin tin, déphasages et structure électronique pour l'interprétation de nos mesures de transport électronique dans les alliages métalliques liquides à base de germanium (Ge-Ag ; Ge-Zn ; Ge-Cd)

This work was devoted to the experimental measurement of electron transport properties of binary liquid metals alloys with germanium (Ge-Ag ; Ge-Zn ; Ge-Cd). One of the originality of this study is the difficulty to control the measurements on these alloys because of their high vapor pressure. The experimental results are interpreted and discussed in term of Faber Ziman extended formula depending on the phase shifts due to diffusion by the muffin-tin potential for pure metals. We made a critical analysis for different construction methods of the muffin-tin potentials. In these methods we proceed by a construction of an atomic potential using Herman-Skilman-Slater approach or an ionic screened potential using Ratti approach. We introduced in both the exchange correction of Robinson, and we use an self consistent determination of the Fermi energy by adjusting the muffin-tin zero potential on the conduction band energy bottom. The differents improvements of the theory led us to a satisfactory interpretation of the alloys studied in this workCe travail a été consacré à l'étude expérimentale des propriétés de transport électronique d'alliages métalliques liquides binaires à base de germanium (Ge-Ag ; Ge-Zn ; Ge-Cd). Il s'agit d'un ensemble de mesures originales sur des alliages difficiles à mesurer en raison de leur tension de vapeur élevée. Nous avons interprété théoriquement la résistivité et le pouvoir thermoélectrique absolu des métaux purs par la formule de Ziman étendu exprimée en fonction des déphasages dus à la diffusion par des potentiels muffin tin sur les métaux purs. Nous avons effectué une analyse critique sur les métaux purs par différentes méthode de construction des potentiels de muffin tin. Ceux-ci font intervenir la construction du potentiel atomique suivant l'approche de Herman-Skilmann-Slater ou celle d'un potentiel ionique écranté suivant l'approche de Ratti, en incluant dans les deux cas la corrélation de robinson. Nous avons introduit une détermination autocohérente de l'énergie de fermi en ajustant le potentiel de muffin tin zéro sur le fond de la bande de conduction. Les perfectionnements proposés permettent d'améliorer de manière satisfaisante les interprétations des systèmes étudié

A Reference Benchmark Solution for Free Convection in A Square Cavity Filled with A Heterogeneous Porous Medium

International audienceThe Fourier-Galerkin (FG) method is used to produce a highly accurate solution for free convection in a square cavity filled with heterogeneous porous medium. To this end, the governing equations are reformulated in terms of the temperature and the stream function. These unknowns are then expanded in infinite Fourier series truncated at given orders. The accuracy of the FG solution is investigated for different truncation orders and compared to the results of an advanced finite-element numerical model using fine-mesh discretization. The obtained results represent a set of high-quality data that can be used for benchmarking numerical models

Constitutive modeling of polymer materials at impact loading rates

Starting from physical basis, a robust three-dimensional constitutive model for the finite strain response of amorphous polymers is briefly presented. This model accounts for the high strain rate and temperature effect. Intramolecular as well as intermolecular interactions under large elastic-inelastic behavior are considered for the mechanisms of deformation and hardening. In particular, it is found that the secondary relaxations of polymer chains play an important role in the deformation process for the high strain rates and low temperatures. For a wide range of temperature and strain rate, the proposed constitutive model has been validated in compression for three amorphous polymers: polymethylmethacrylate (PMMA), polycarbonate (PC) and polyamideimide (PAI)

A new three-phase model to estimate the effective elastic properties of semi-crystalline polymers: Application to PET

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On the numerical investigation of cardiovascular balloon-expandable stent using finite element method

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