References of "Pardoen, Thomas"
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See detailMultiscale modelling framework for the fracture of thin brittle polycrystalline films - Application to polysilicon
Mulay, Shantanu; Becker, Gauthier ULg; Vayrette, Renaud et al

in Computational Mechanics (in press)

Micro-electro-mechanical systems (MEMS) made of polycrystalline silicon are widely used in several engineering fields. The fracture properties of polycrystalline silicon directly affect their reliability ... [more ▼]

Micro-electro-mechanical systems (MEMS) made of polycrystalline silicon are widely used in several engineering fields. The fracture properties of polycrystalline silicon directly affect their reliability. The effect of the orientation of grains on the fracture behaviour of polycrystalline silicon is investigated out of the several factors. This is achieved, firstly, by identifying the statistical variation of the fracture strength and critical strain energy release rate, at the nanoscopic scale, over a thin freestanding polycrystalline silicon film, having mesoscopic scale dimensions. The fracture stress and strain at the mesoscopic level are found to be closely matching with uniaxial tension experimental results. Secondly, the polycrystalline silicon film is considered at the continuum MEMS scale, and its fracture behaviour is studied by incorporating the nanoscopic scale effect of grain orientation. The entire modelling and simulation of the thin film is achieved by combining the discontinuous Galerkin method and extrinsic cohesive law describing the fracture process. [less ▲]

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See detailOn the Elasto-viscoplastic behavior of the Ti5553 alloy
ben bettaieb, Mohamed; Van Hoof, Thibaut; Pardoen, thomas et al

in Materials Science & Engineering : A (2014), 617

The elastoviscoplastic behavior of the Ti533 alloy is characterized and compared to the classical Ti-6A14V alloy. The true stress-strain curves are determined based on tensile tests performes under ... [more ▼]

The elastoviscoplastic behavior of the Ti533 alloy is characterized and compared to the classical Ti-6A14V alloy. The true stress-strain curves are determined based on tensile tests performes under different strain rates at room temperature and at 150°C, from which the elastic constants and the parameters of a Norton-Hoff viscoplastic model are identified. The strength of the Ti5553 alloy is 20-40% higherthan the strength of the Ti-6A1-4V alloy. The Ti5553 alloy constitutes thus a promising candidate for advanced structural applications. In view of modeling structural applications of forming operations, the elastic and plastic initial anisotropy of the two alloys is investigated by combining compression on cylinders with elliptical sections, uniaxial tensile tests in different material directions , plane strain and shear tests. The initial anisotropy of the different alloys is very weak which justifies the modeling of the mechanical behavior with isotropic yield surface. The identified elastoviscoplastic model is validated by comparing experimental results with FE predictions both on cylindrical specimens subjected to tensile tests and on flat specimens subjected to plane strain conditions. [less ▲]

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See detailBauschinger effect in thin metallic films by Fem simulations
marandi, kianoosh; vayrette, renaud; Pardoen, Thomas et al

in XII International Conference on Computational Plasticity. Fundamentals and Application COMPLAS XII , Barcelone 3-5 septembre 2013 (2013, September)

Unpassivated free-standing gold and aluminium thin films, subjected to tensile tests show Bauschinger effect (BE) during unloading [1,2]. The focus of this work is to investigate the effect of ... [more ▼]

Unpassivated free-standing gold and aluminium thin films, subjected to tensile tests show Bauschinger effect (BE) during unloading [1,2]. The focus of this work is to investigate the effect of microsstructural heterogeneity such as grain sizes on the BE and the macroscopic deformation behavior in thin metallic films. The finite element code LAGAMINE is used to model the response of films involving sets of grains with different strenghts. The numerical results are compared with experimental results from tensile tests on aluminium thin films from the work of Rajagolapan, et al. [2] [less ▲]

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See detailPolymer/carbon based composites as electromagnetic interference (EMI) shielding materials
Thomassin, Jean-Michel ULg; Jérôme, Christine ULg; Pardoen, Thomas et al

in Materials Science & Engineering : R (2013), 74(7), 211-232

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of ... [more ▼]

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation. [less ▲]

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See detailThe fracture studies of polycrystalline silicon based MEMS
Mulay, Shantanu Shashikant ULg; Becker, Gauthier; Vayrette, Renaud et al

in EUROSIME 2013 (2013)

The advantages of micro-electro-mechanical systems (MEMS), such as low power requirement, miniaturized sizes and costs reduction, have already made significant impact in many technological fields. MEMS ... [more ▼]

The advantages of micro-electro-mechanical systems (MEMS), such as low power requirement, miniaturized sizes and costs reduction, have already made significant impact in many technological fields. MEMS are now widely used as accelerometers, pressure sensors, and resonators etc. However, the determination of the mechanical properties of MEMS devices with high accuracy is still a challenging task due to their small dimensions and often anisotropic behaviour. This paper focuses on the modelling and simulation of the fracture of a key MEMS component, which is a polycrystalline silicon beam, by discontinuous Galerkin (DG) formulation combined with an extrinsic cohesive law (ECL) to describe the fracture process. As the beam is modelled by plane-stress 2D elements, an analytical equation to compute the effective fracture strength and the effective critical strain energy release rate in terms of the through-the-thickness fracture mode and of the orientation of the facet with respect to the crystal is also developed. At the end, a model is simulated, and the results are verified as per the physics of the problem and experiments. [less ▲]

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See detailThe fracture studies of polycrystalline silicon based MEMS
Mulay, Shantanu Shashikant ULg; Becker, Gauthier; Vayrette, Renaud et al

Scientific conference (2012, November 24)

The advantages of micro-electro-mechanical system (MEMS), such as low power requirement, miniature sizes and costs reduction, has already made significant impact in many technological fields. MEMS are now ... [more ▼]

The advantages of micro-electro-mechanical system (MEMS), such as low power requirement, miniature sizes and costs reduction, has already made significant impact in many technological fields. MEMS are now widely used as accelerometers, pressure sensors, and resonators. However, the determination of mechanical properties of MEMS devices with high accuracy is still a challenging task due to their miniature size. For example, the crystal size and orientation may have a significant effect on the fracture strength of MEMS microstructure. Among several important materials used for the development of MEMS devices, polycrystalline silicon plays a key role in various applications. Thus, an understanding of the relationship between poly-silicon manufacturing processes, and the resulting mechanical behaviour and durability of micro-fabricated structures is needed to allow rational design of MEMS devices. This work focuses on the modelling and simulation of the fracture of MEMS, made up of polycrystalline silicon, by discontinuous Galerkin (DG) formulation combined with an extrinsic cohesive law. The problem is solved as plane-stress type. All the elements are discontinuous in the DG method, and inter-element continuity is weakly enforced by having recourse to interface elements. When a fracture criterion is reached, an extrinsic cohesive law is activated on the already existing interface elements. The cracks can be initiated, merged or propagated, in this method. The fracture properties of material can be considered different along crystal interfaces and inside crystal bulk, and can account for crystal orientation. Moreover this method avoid drawbacks of usual cohesive method (no modification of the structure stiffness and no complex implementation in parallel) allowing for accurate large scale simulation. Polycrystalline silicon is an orthotropic material, i.e., it has different material properties, such as Young’s modulus, Poisson’s ratio, fracture strength, along different crystal lattice planes. These properties are also symmetric for a cubic crystal, i.e., the lattice planes perpendicular to each other have similar properties. This symmetric nature is well captured in the proposed work by a new formulation to compute effective fracture strength along any plane of interest based on the known values of the same along (1 0 0), (1 1 0), and (1 1 1) lattice planes. The effect of thickness of MEMS is also included by computing the effective stress on interface elements at different vertical angles. These formulations are analyzed by sample simulation results. The efficiency and accuracy of the method are assessed by experiments involving on-chip fracture tests, providing the fracture stress, and supplemented by the characterization of the test specimen. The characterization consists of the measurement of grain size and crystallographic orientation by electron back scattering diffraction, and the determination of crack path. An important point is the analysis of the competition between inter-granular versus trans-granular crack path with respect to the grain orientation. [less ▲]

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See detailHybrid material for electromagnetic absorption
Detrembleur, Christophe ULg; Molenberg, Isabel; Huynen, Isabelle et al

Patent (2012)

The present invention relates to a hybrid material (10) for absorbing electromagnetic radiation (60) and a method for making such a material. The hybrid material (10) comprises at least one grid panel (20 ... [more ▼]

The present invention relates to a hybrid material (10) for absorbing electromagnetic radiation (60) and a method for making such a material. The hybrid material (10) comprises at least one grid panel (20) of thickness t 1 having holes (25) traversing said thickness t 1 , at least one polymer composite material (30) of thickness t 2 filling at least partially the holes (25) of the at least one grid panel (20), said at least one polymer composite material (30) including a polymer matrix (40) and conductive particles (50) dispersed into said polymer matrix (40), characterized in that the internal surface of the holes (25) of the at least one grid panel (20) is metallic. [less ▲]

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See detailHybrid material for electromagnetic absorption
Detrembleur, Christophe ULg; Huynen, Isabelle; Thomassin, Jean-Michel ULg et al

Patent (2012)

The present invention relates to a hybrid material (10) for absorbing electromagnetic radiation (60) and a method for making such a material. The hybrid material (10) comprises at least one grid panel (20 ... [more ▼]

The present invention relates to a hybrid material (10) for absorbing electromagnetic radiation (60) and a method for making such a material. The hybrid material (10) comprises at least one grid panel (20) of thickness t 1 having holes (25) traversing said thickness t 1 , at least one polymer composite material (30) of thickness t 2 filling at least partially the holes (25) of the at least one grid panel (20), said at least one polymer composite material (30) including a polymer matrix (40) and conductive particles (50) dispersed into said polymer matrix (40), characterized in that the internal surface of the holes (25) of the at least one grid panel (20) is metallic. [less ▲]

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See detailElectromagnetic absorption properties of carbon nanotube nanocomposite foam filling honeycomb waveguide structures
Quiévy, Nicolas; Bollen, Pierre; Thomassin, Jean-Michel ULg et al

in IEEE Transactions on Electromagnetic Compatibility (2012), 24(1), 43-51

Carbon nanotube reinforced polymer foams filling a metallic honeycomb were processed and characterized for the production of hybrid materials with high electromagnetic absorption potential ... [more ▼]

Carbon nanotube reinforced polymer foams filling a metallic honeycomb were processed and characterized for the production of hybrid materials with high electromagnetic absorption potential. Electromagnetic modeling and experimental characterization of the hybrids proved that the honeycomb, acting as a hexagonal waveguide, improves the absorption properties in the gigahertz range above the cutoff frequency. The electromagnetic absorption can be tuned by changing the hybrid material properties. The required levels of electrical conductivity are attained owing to the dispersion of low amounts (1–2 wt%) of carbon nanotubes inside the polymermatrix. The combination of the foam and honeycomb architecture contributes to decrease the real part of the relative effective permittivity Re{εr,eff }. Varying the cell shape of the honeycomb changes the frequency range for high absorption. An analytical model for the absorption has been developed, showing good agreement with the experimental results. [less ▲]

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See detailMultifunctional hybrids for electromagnetic absorption
Huynen, Isabelle; Quievy, N.; Bailly, Christian et al

in Acta Materialia (2011), 59(8), 3255-3266

Electromagnetic (EM) interferences are ubiquitous in modern technologies and impact on the reliability of electronic devices and on living cells. Shielding by EM absorption, which is preferable over ... [more ▼]

Electromagnetic (EM) interferences are ubiquitous in modern technologies and impact on the reliability of electronic devices and on living cells. Shielding by EM absorption, which is preferable over reflection in certain instances, requires combining a low dielectric constant with high electrical conductivity, which are antagonist properties in the world of materials. A novel class of hybrid materials for EM absorption in the gigahertz range has been developed based on a hierarchical architecture involving a metallic honeycomb filled with a carbon nanotube-reinforced polymer foam. The waveguide characteristics of the honeycomb combined with the performance of the foam lead to unexpectedly large EM power absorption over a wide frequency range, superior to any known material. The peak absorption frequency can be tuned by varying the shape of the honeycomb unit cell. A closed form model of the EM reflection and absorption provides a tool for the optimization of the hybrid. This designed material sets the stage for a new class of sandwich panels combining high EM absorption with mass efficiency, stiffness and thermal management. [less ▲]

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See detailFinite element simulations of nanoindentation in beta metastable Ti alloys
Gerday, Anne-Françoise ULg; Clement, N.; Jacques, P. J. et al

in Juster, Neal; Rosochowski, Andrzej (Eds.) Proceedings of the 9th International ESAFORM Conference on Material Forming (2006)

Nanoindentation is a versatile tool to probe local plastic properties of materials. Finite element (FE) modelling is currently used to identify material data from nanoindentation tests [1-4]. The general ... [more ▼]

Nanoindentation is a versatile tool to probe local plastic properties of materials. Finite element (FE) modelling is currently used to identify material data from nanoindentation tests [1-4]. The general ambition of this research is to extract the material parameters describing the response of a new Ti alloy, called Ti-555, in order to perform simulations on representative microscopic cells and guide the optimisation of this alloy. In this paper, the first steps of the identification of the macroscopic flow parameters of the β-phase are described. The nanoindentation tests using a pyramidal Berkovich diamond indenter are performed in the β-phase. The FEM results with different parameters of an isotropic and anisotropic elasto-plastic (EP) constitutive law are analyzed and the predicted shapes are compared to the final shape of the indented material. The FE results very much depend on physical model choices, and cannot rely on an automatic identification approach. [less ▲]

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