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

Constitutive model for high-density cellulose-based materials

QC 20160414</p

Modeling and experimental validation of the mechanical behavior of pressboard

High density (HD) pressboard is an essential element in power transformers combining good electrical insulation properties with effective mechanical characteristics that well suit design requirements of power transformers. In order to ensure a correctly functioning transformer, it is therefore very important to characterize and to understand the mechanical properties of pressboard under different operating conditions. Pressboard is composed of natural polymeric chains, whose mechanical properties are affected by moisture and temperature. Moreover, temperature and moisture conditions in power transformers vary throughout manufacturing process and service/operation life-time. An accurate definition of the mechanical properties is, therefore, necessary. The present article focuses on the effect of different combinations of temperature/moisture and mechanical load on the deformation behavior of HD pressboard samples. A mechanical constitutive model is developed for finite element (FEM) simulation based on a viscoelastic–viscoplastic material description. Special attention is given on the complex through-thickness deformation behavior of HD pressboard. Thorough analyses are performed based on the comparisons between the results of experimental characterization and FEM modeling and simulations. The good agreement between experimental and modeling results shows a great potential for application in mechanical design of transformer insulation.QC 20150413</p

Klímaváltozás és klímaadaptáció helyi léptékben: Egy kutatási projekt tapasztalatai a hazai társadalmi-gazdasági folyamatok modellezésében = Climate Change and Adaptation on a Local Scale: Results of a Research Project on Social and Economic Modelling

High density (HD) pressboard is an essential element in power transformers combining good electrical insulation properties with effective mechanical characteristics that well suit design requirements of power transformers. In order to ensure a correctly functioning transformer, it is therefore very important to characterize and to understand the mechanical properties of pressboard under different operating conditions. Pressboard is composed of natural polymeric chains, whose mechanical properties are affected by moisture and temperature. Moreover, temperature and moisture conditions in power transformers vary throughout manufacturing process and service/operation life-time. An accurate definition of the mechanical properties is, therefore, necessary. The present article focuses on the effect of different combinations of temperature/moisture and mechanical load on the deformation behavior of HD pressboard samples. A mechanical constitutive model is developed for finite element (FEM) simulation based on a viscoelastic–viscoplastic material description. Special attention is given on the complex through-thickness deformation behavior of HD pressboard. Thorough analyses are performed based on the comparisons between the results of experimental characterization and FEM modeling and simulations. The good agreement between experimental and modeling results shows a great potential for application in mechanical design of transformer insulation.QC 20150413</p

The use of satellite imagery and topographical information in predicting moorland bird distribution and abundance in the North Pennines

SIGLEAvailable from British Library Document Supply Centre- DSC:3490.375F(NCC-CSD-R--1027)(fiche) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Alya: Computational Solid Mechanics for Supercomputers

While solid mechanics codes are now conventional tools both in industry and research, the increasingly more exigent requirements of both sectors are fuelling the need for more computational power and more advanced algorithms. For obvious reasons, commercial codes are lagging behind academic codes often dedicated either to the implementation of one new technique, or the upscaling of current conventional codes to tackle massively large scale computational problems. Only in a few cases, both approaches have been followed simultaneously. In this article, a solid mechanics simulation strategy for parallel supercomputers based on a hybrid approach is presented. Hybrid parallelization exploits the thread-level parallelism of multicore architectures, combining MPI tasks with OpenMP threads. This paper describes the proposed strategy, programmed in Alya, a parallel multi-physics code. Hybrid parallelization is specially well suited for the current trend of supercomputers, namely large clusters of multicores. The strategy is assessed through transient non-linear solid mechanics problems, both for explicit and implicit schemes, running on thousands of cores. In order to demonstrate the flexibility of the proposed strategy under advance algorithmic evolution of computational mechanics, a non-local parallel overset meshes method (Chimera-like) is implemented and the conservation of the scalability is demonstrated.D.D.T and A.J acknowledge funding through SIMUCOMP and ERA-NET MATERA+ project financed by the Consejería de Educación y Empleo of the Comunidad de Madrid and by the European Union’s Seventh Framework Programme (FP7/2007-2013). Thisworkwas partially supported by the grant SEV-2011-00067, Severo Ochoa Program, awarded by the Spanish Government. The authors’ would like to acknowledge PRACE infrastructure support.Peer Reviewe

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 Reviewe