References of "Bordas, Stéphane 50000969"
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See detailAn efficient goal-oriented sampling strategy using reduced basis method for parametrized elastodynamic problems
Hoang, K. C.; Kerfriden, P.; Khoo, B. C. et al

in Numerical Methods for Partial Differential Equations (2015), 31(2), 575-608

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See detailGradient Smoothing in Finite Elasticity: near-incompressibility
Lee, Chang-Kye; Bordas, Stéphane UL; Kerfriden, Pierre

Report (2015)

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See detailA meshless adaptive multiscale method for fracture
Yang, S.-W.; Budarapu, P. R.; Mahapatra, D. R. et al

in Computational Materials Science (2015), 96(PB), 382-395

The paper presents a multiscale method for crack propagation. The coarse region is modelled by the differential reproducing kernel particle method. Fracture in the coarse scale region is modelled with the ... [more ▼]

The paper presents a multiscale method for crack propagation. The coarse region is modelled by the differential reproducing kernel particle method. Fracture in the coarse scale region is modelled with the Phantom node method. A molecular statics approach is employed in the fine scale where crack propagation is modelled naturally by breaking of bonds. The triangular lattice corresponds to the lattice structure of the (1 1 1) plane of an FCC crystal in the fine scale region. The Lennard-Jones potential is used to model the atom-atom interactions. The coupling between the coarse scale and fine scale is realized through ghost atoms. The ghost atom positions are interpolated from the coarse scale solution and enforced as boundary conditions on the fine scale. The fine scale region is adaptively refined and coarsened as the crack propagates. The centro symmetry parameter is used to detect the crack tip location. The method is implemented in two dimensions. The results are compared to pure atomistic simulations and show excellent agreement. [less ▲]

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See detailError Controlled Adaptive Multiscale Method For Fracture Modelling in Polycrystalline materials
Akbari, Ahmad; Kerfriden, ierre; Bordas, Stéphane UL

in Philosophical Magazine (2015)

In this paper an adaptive multiscale method is presented in an attempt to address the lack of separation of scales in simulation of fracture. This method is set in the context of FE2 [20] for which ... [more ▼]

In this paper an adaptive multiscale method is presented in an attempt to address the lack of separation of scales in simulation of fracture. This method is set in the context of FE2 [20] for which computational homogenisation breaks down upon loss of material stability (softening). The lack of scale separation due to the coalescence of microscopic cracks in a certain zone is tackled by a full discretisation of the microstructure in this zone. Polycrystalline materials are considered with cohesive cracks along the grain boundaries as a model problem. Adaptive mesh refinement of the coarse region and adaptive initiation and growth of fully resolved regions are performed based on discretisation error and homogenisation error criteria, respectively. In order to follow sharp snap-backs in load-displacement paths, a local arc-length technique is developed for the adaptive multiscale method. The results are validated against direct numerical simulation. [less ▲]

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See detailNonlinear FEM code with Finite elasticity lecture note written by L.A. Mihai
Lee, Chang-Kye; Bordas, Stéphane UL

Learning material (2015)

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See detailInterfacial shear stress optimization in sandwich beams with polymeric core using non-uniform distribution of reinforcing ingredients
Ghasemi, Hamid; Kerfriden, Pierre; Muthu, Jacob et al

in Composite Structures (2015)

Core shearing and core/face debonding are two common failure states of sandwich beams which are mainly the result of excessive shear stresses in the core. Generally, the core made of homogeneous Fiber ... [more ▼]

Core shearing and core/face debonding are two common failure states of sandwich beams which are mainly the result of excessive shear stresses in the core. Generally, the core made of homogeneous Fiber Reinforced Polymer (FRP) shows better shear resistance in comparison with that made of pure polymer. Usually, this enhancement is however somewhat limited. This paper proposes a methodology to decrease interfacial stresses by presenting the optimal distribution of reinforcing ingredients in the polymeric matrix. For this purpose, a Non-Uniform Rational Bspline (NURBS) based reinforcement distribution optimizer is developed. This technique aims at the local stress minimization within any arbitrary zone of the design domain. In our methodology, optimization and model analysis (calculation of the objective function and the design constraints) have common data sets. The quadratic NURBS basis functions smoothly define the reinforcement distribution function as a NURBS surface. The core and face sheets are modeled as multi-patches and compatibility in the displacement field is enforced by the penalty method. An adjoint sensitivity method is devised to minimize the objective function within areas of interest defined over arbitrary regions in the design domain. It is also used for efficient updating of design variables through optimization iterations. The method is verified by several examples. [less ▲]

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See detailThree-Dimensional Crack Propagation with Global Enrichment XFEM and Vector Level Sets
Agathos, Konstantinos; Ventura, Giulio; Chatzi, Eleni et al

Scientific Conference (2015)

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See detailProbabilistic multiconstraints optimization of cooling channels in ceramic matrix composites
Ghasemi, Hamid; Kerfriden, Pierre; Bordas, Stéphane UL et al

in Composites. Part B, Engineering (2015), 81

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal ... [more ▼]

This paper presents a computational reliable optimization approach for internal cooling channels in Ceramic Matrix Composite (CMC) under thermal and mechanical loadings. The algorithm finds the optimal cooling capacity of all channels (which directly minimizes the amount of coolant needed). In the first step, available uncertainties in the constituent material properties, the applied mechanical load, the heat flux and the heat convection coefficient are considered. Using the Reliability Based Design Optimization (RBDO) approach, the probabilistic constraints ensure the failure due to excessive temperature and deflection will not happen. The deterministic constraints restrict the capacity of any arbitrary cooling channel between two extreme limits. A “series system” reliability concept is adopted as a union of mechanical and thermal failure subsets. Having the results of the first step for CMC with uniformly distributed carbon (C-) fibers, the algorithm presents the optimal layout for distribution of the C-fibers inside the ceramic matrix in order to enhance the target reliability of the component. A sequential approach and B-spline finite elements have overcome the cumbersome computational burden. Numerical results demonstrate that if the mechanical loading dominates the thermal loading, C-fibers distribution can play a considerable role towards increasing the reliability of the design. [less ▲]

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See detailA staggered cell-centered finite element method for compressible and nearly-incompressible linear elasticity on general meshes
Ong, Thanh Hai; Hoang, Thi Thao Phuong; Bordas, Stéphane UL et al

in SIAM Journal on Numerical Analysis (2015), 53(4), 2051-2073

We propose a new numerical method, namely, the staggered cell-centered finite element method for compressible and nearly incompressible linear elasticity problems. By building a dual mesh and its ... [more ▼]

We propose a new numerical method, namely, the staggered cell-centered finite element method for compressible and nearly incompressible linear elasticity problems. By building a dual mesh and its triangular submesh, the scheme can be constructed from a general mesh in which the displacement is approximated by piecewise linear (P1) functions on the dual submesh and, in the case of nearly incompressible problems, the pressure is approximated by piecewise constant (P0) functions on the dual mesh. The scheme is cell centered in the sense that the solution can be computed by cell unknowns of the primal mesh (for the displacement) and of the dual mesh (for the pressure). The method is presented within a rigorous theoretical framework to show stability and convergence. In particular, for the nearly incompressible case, stability is proved by using the macroelement technique. Numerical results show that the method, compared with other methods, is effective in terms of accuracy and computational cost. [less ▲]

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See detailShape optimisation with isogeometric boundary element methods
Lian, Haojie; Bordas, Stéphane UL; Kerfriden, Pierre

Presentation (2014, December)

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See detailAdvances in Applied Mechanics
Bordas, Stéphane UL

Book published by Elsevier (2014)

Advances in Applied Mechanics draws together recent significant advances in various topics in applied mechanics. Published since 1948, Advances in Applied Mechanics aims to provide authoritative review ... [more ▼]

Advances in Applied Mechanics draws together recent significant advances in various topics in applied mechanics. Published since 1948, Advances in Applied Mechanics aims to provide authoritative review articles on topics in the mechanical sciences, primarily of interest to scientists and engineers working in the various branches of mechanics, but also of interest to the many who use the results of investigations in mechanics in various application areas, such as aerospace, chemical, civil, environmental, mechanical and nuclear engineering. [less ▲]

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See detailIsogeometric locking-free plate element: a simple first order shear deformation theory for functionally graded plates
Shuohui, Yin; Hale, Jack UL; Yu, Tiantang et al

in Composite Structures (2014), 118

An effective, simple, robust and locking-free plate formulation is proposed to analyze the static bending, buckling, and free vibration of homogeneous and functionally graded plates. The simple first ... [more ▼]

An effective, simple, robust and locking-free plate formulation is proposed to analyze the static bending, buckling, and free vibration of homogeneous and functionally graded plates. The simple first-order shear deformation theory (S-FSDT), which was recently presented in Thai and Choi (2013) [11], is naturally free from shear-locking and captures the physics of the shear-deformation effect present in the original FSDT, whilst also being less computationally expensive due to having fewer unknowns. The S-FSDT requires C1-continuity that is simple to satisfy with the inherent high-order continuity of the non-uniform rational B-spline (NURBS) basis functions, which we use in the framework of isogeometric analysis (IGA). Numerical examples are solved and the results are compared with reference solutions to confirm the accuracy of the proposed method. Furthermore, the effects of boundary conditions, gradient index, and geometric shape on the mechanical response of functionally graded plates are investigated. [less ▲]

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See detailMultiscale computational mechanics: industrial applications
Bordas, Stéphane UL; Kerfriden, Pierre; Beex, Lars UL et al

Presentation (2014, November 25)

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See detailMultiscale fracture across scales and time
Bordas, Stéphane UL; Kerfriden, Pierre

Scientific Conference (2014, November 11)

Multi-scale Computational Mechanics in Aerospace Engineering Flying is today one of the safest ways to spend our time. In the United Kingdom, for example, it is 33,000 times more likely to die from a ... [more ▼]

Multi-scale Computational Mechanics in Aerospace Engineering Flying is today one of the safest ways to spend our time. In the United Kingdom, for example, it is 33,000 times more likely to die from a clinical error than from an air crash. This is probably the consequence of over a century of experience building, starting with the Wright brothers at the beginning of the 20th century to the most recent aerospace developments culminating in technological giants such as the Airbus A380 and the Boeing Dreamliner, through the enlightening catastrophic events of the "Comet Aircraft”, ``Liberty Ships'' and many others. Yet, with the increasing urge to increase flight efficiency, decrease costs and Carbon emissions, airlines have been pushed to drive down the weight of aircraft, whilst guaranteeing their safety. This push for lighter aircraft has progressively seen a reduction in the use of metallic components which have been slowly replaced by composite materials. Such composite materials are made up of two or more phases of which they exploit the mechanical complementarity. For some applications, such as thermal barrier coatings, thermal complementarity is also leveraged. Yet, these novel materials, and especially their failure mechanisms and durability have proven difficult to understand, both through physical and virtual, in silico, experiments. One of the reasons for this is the large ratio between the size of the smallest constituent relevant in the description of failure mechanisms (e.g. 5-10 micron diameter carbon fibres) and the size of the structure (79m wingspan A380). In this presentation, we will briefly review advances in modeling and simulation of failure across the scales. We will discuss non exhaustively some of the recent advances in this field, ranging from adaptive atomistic modeling of fracture to algebraic model reduction methods for severely non-linear problems, including homogenization. We will also discuss the relevance of such simulations in daily engineering practice and claim that devising interactive simula- tors able to let engineers interact with the composite structure of interest and thus develop intuition about these advanced and complex materials. We will conclude by making a parallel between the difficulties encountered in modeling complex aerospace components and those met in personalized medicine, by discussing briefly the concept of Digital Twin. [less ▲]

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See detailMultiscale Quasicontinuum Methods for Dissipative Truss Models and Beam Networks
Beex, Lars UL; Peerlings, Ron; Geers, Marc et al

Presentation (2014, November 05)

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See detailCardiff/Luxembourg Computational Mechanics Research Group
Bordas, Stéphane UL; Kerfriden, Pierre; Hale, Jack UL et al

Poster (2014, November)

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See detailDiscrete Multiscale Modelling and Future Research Plans concerning Metals
Beex, Lars UL; Bordas, Stéphane UL; Rappel, Hussein UL et al

Presentation (2014, October 14)

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See detailGeometry-Independent Field approximaTion: CAD-Analysis Integration, geometrical exactness and adaptivity
Xu, Gang; Atroshchenko, Elena; Ma, Weiyin et al

in Computer Methods in Applied Mechanics and Engineering (2014)

In isogeometric analysis (IGA), the same spline representation is employed for both the geometry of the domain and approximation of the unknown fields over this domain. This identity of the geometry and ... [more ▼]

In isogeometric analysis (IGA), the same spline representation is employed for both the geometry of the domain and approximation of the unknown fields over this domain. This identity of the geometry and field approximation spaces was put forward in the now classic 2005 paper [20] as a key advantage on the way to the integration of Computer Aided Design (CAD) and subsequent analysis in Computer Aided Engineering (CAE). [20] claims indeed that any change to the geometry of the domain is automatically inherited by the approximation of the field variables, without requiring the regeneration of the mesh at each change of the domain geometry. Yet, in Finite Element versions of IGA, a parameterization of the interior of the domain must still be constructed, since CAD only provides information about the boundary. The identity of the boundary and field representation decreases the flexibility in which this parameterization can be generated and somewhat constrains the modeling and simulation process, because an approximation able to represent the domain geometry accurately need not be adequate to also approximate the field variables accurately, in particular when the solution is not smooth. We propose here a new paradigm called Geometry-Independent Field approximaTion (GIFT) where the spline spaces used for the geometry and the field variables can be chosen and adapted independently while preserving geometric exactness and tight CAD integration. GIFT has the following features: (1) It is possible to flexibly choose between different spline spaces with different properties to better represent the solution of the problem, e.g. the continuity of the solution field, boundary layers, singularities, whilst retaining geometrical exactness of the domain boundary. (2) For multi-patch analysis, where the domain is composed of several spline patches, the continuity condition between neighboring patches on the solution field can be automatically guaranteed without additional constraints in the variational form. (3) Refinement operations by knot insertion and degree elevation are performed directly on the spline space of the solution field, independently of the spline space of the geometry of the domain, which makes the method versatile. GIFT with PHT-spline solution spaces and NURBS geometries is used to show the effectiveness of the proposed approach. Keywords : Super-parametric methods, Isogeometric analysis (IGA), Geometry-independent Spline Space, PHT-splines, local refinement, adaptivity [less ▲]

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See detailShape optimisation directly from CAD: an isogeometric boundary element approach
Lian, Haojie; Bordas, Stéphane UL; Kerfriden, Pierre

Report (2014)

Detailed reference viewed: 115 (4 UL)