| 1. |
- Vigueras, G., et al.
(författare)
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An XFEM/CZM implementation for massively parallel simulations of composites fracture
- 2015
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Ingår i: Composite structures. - : Elsevier BV. - 0263-8223 .- 1879-1085. ; 125, s. 542-557
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Wu, L., et al.
(författare)
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A micro-meso-model of intra-laminar fracture in fiber-reinforced composites based on a discontinuous Galerkin/cohesive zone method
- 2013
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944 .- 1873-7315. ; 104, s. 162-183
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Tidskriftsartikel (refereegranskat)abstract
- The recently developed hybrid discontinuous Galerkin/extrinsic cohesive law framework is extended to the study of intra-laminar fracture of composite materials. Toward this end, micro-volumes of different sizes are studied. The method captures the debonding process, which is herein proposed to be assimilated to a damaging process, before the strain softening onset, and the density of dissipated energy resulting from the damage (debonding) remains the same for the different studied cell sizes. Finally, during the strain softening phase a micro-crack initiates and propagates in agreement with experimental observations. We thus extract a resulting mesoscale cohesive law, which is independent on the cell sizes, using literature methods.
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| 3. |
- Barba, D., et al.
(författare)
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A thermodynamically consistent constitutive model for diffusion-assisted plasticity in Ni-based superalloys
- 2018
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 105, s. 74-98
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Tidskriftsartikel (refereegranskat)abstract
- An elasto-viscoplastic thermodynamically consistent constitutive model for diffusion-assisted phase transformations is presented here. The model accounts for the different deformation mechanisms, their time dependence, the crystal rotations produced by microtwin propagation and the chemistry-plasticity coupling occurring at high temperature. It is applied to the study of the chemically assisted microtwinning observed in Ni-based superalloys in the temperature range of 600-800 degrees C. The model parameters are calibrated against multi-directional mechanical data from tensile creep tests of single crystal superalloy MD2. The constitutive model is then implemented into a crystal plasticity finite element code to study the activation of the different deformation mechanisms within single crystal and polycrystalline aggregates. Doing so, a relation between the rotations of the crystal and the creep life of the different crystal orientations is established. The results eventually reveal the critical role of the strong anisotropy of microtwin formation on the asymmetric behavior of the alloy and its relevant role on the mechanical performance.
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| 4. |
- Casoni, E., et al.
(författare)
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Alya : Computational Solid Mechanics for Supercomputers
- 2015
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Ingår i: Archives of Computational Methods in Engineering. - : Springer Science and Business Media LLC. - 1134-3060 .- 1886-1784. ; 22:4, s. 557-576
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Forskningsöversikt (refereegranskat)abstract
- 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.
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