Magnetorheological Elastomers

National audienceMagnetorheological elastomers (MREs) are ferromagnetic particle impregnated rubbers whose mechanical properties are altered by the application of external magnetic fields. Due to their coupled magnetoelastic response, MREs are finding an increasing number of engineering applications. In this work, we present a combined experimental and theoretical study of the macroscopic response of a particular MRE consisting of a rubber matrix phase with spherical carbonyl iron particles. The MRE specimens used in this work are cured in the presence of strong magnetic fields leading to the formation of particle chain structures and thus to an overall transversely isotropic composite. The MRE samples are tested experimentally under uniaxial stresses as well as under simple shear in the absence or in the presence of magnetic fields and for different initial orientations of their particle chains with respect to the mechanical and magnetic loading direction. Using the theoretical framework for finitely strained MREs introduced earlier by the author, we propose a transversely isotropic energy density function that is able to reproduce the experimentally measured magnetization, magnetostriction and simple shear curves under different prestresses, initial particle chain orientations and magnetic fields. Microscopic mechanisms are also proposed to explain i) the counterintuitive effect of dilation under zero or compressive applied mechanical loads for the magnetostriction experiments and ii) the importance of a finite strain constitutive formulation even at small magnetostrictive strains. The model gives an excellent agreement with experiments for relatively moderate magnetic fields but has also been satisfactorily extended to include magnetic fields near saturation

Delayed neutrons measurement at the MEGAPIE target

In the framework of the Neutronic and Nuclear Assessment Task Group of the MEGAPIE experiment we measured the delayed neutron (DN) flux at the top of the target. The measurement was proposed mainly for radioprotection purposes since the DN flux at the top of the target has been estimated to be of the same order of magnitude as the prompt neutron flux. Given the strong model-dependence of DN predictions, the measurement of DN contribution to the total neutron activity at the top of the target was thus desired. Moreover, this measurement is complementary to the DN experiments performed at PNPI (Gatchina) on solid lead and bismuth targets. The DN measurement at MEGAPIE was performed during the start-up phase of the target. In this paper we present a detailed description of the experimental setup and some preliminary results on decay spectra.Comment: 4 pages, 4 figures, Proceedings of International Conference on Nuclear Data for Science and Technology (ND 2007), Nice, France, 22-27 Apr 200

Failure of elasto-plastic porous materials subjected to triaxial loading conditions

National audienceThis work makes use of the recently proposed second-order nonlinear homogenization model (SOM) for (visco)plastic porous materials [1] to study the influence of the Lode parameter and the stress triaxiality on the failure of metallic materials. This model is based on the "second-order" or "generalized secant" homogenization method [2] and is capable of handling general "ellipsoidal" microstructures (i.e., particulate microstructures with more general orthotropic overall anisotropy) and general three-dimensional loading conditions.See http://hal.archives-ouvertes.fr/docs/00/59/26/93/ANNEX/r_A1B5O25U.pd

Magnetorheological Elastomers: Experiments and Modeling

National audienceMagnetorheological elastomers (MREs) are ferromagnetic particle impregnated elastomers whose mechanical properties are altered by the application of external magnetic fields. Due to their magnetoelastic coupling response MREs are finding an increasing number of engineering applications. The objective of this work is : (a) the experimental study of transversely isotropic MREs (i.e., the particles form chains along a certain direction) that are subjected to prestressing and arbitrary magnetic fields and (b), the phenomenological modeling of these materials using transversely isotropic energy functions.See http://hal.archives-ouvertes.fr/docs/00/59/26/92/ANNEX/r_NHEKI0N4.pd

Enhanced local maximum-entropy approximation for stable meshfree simulations

We introduce an improved meshfree approximation scheme which is based on the local maximum-entropy strategy as a compromise between shape function locality and entropy in an information-theoretical sense. The improved version is specifically designed for severe, finite deformation and offers significantly enhanced stability as opposed to the original formulation. This is achieved by (i) formulating the quasistatic mechanical boundary value problem in a suitable updated-Lagrangian setting, (ii) introducing anisotropy in the shape function support to accommodate directional variations in nodal spacing with increasing deformation and eliminate tensile instability, (iii) spatially bounding and evolving shape function support to restrict the domain of influence and increase efficiency, (iv) truncating shape functions at interfaces in order to stably represent multi-component systems like composites or polycrystals. The new scheme is applied to benchmark problems of severe elastic and elastoplastic deformation that demonstrate its performance both in terms of accuracy (as compared to exact solutions and, where applicable, finite element simulations) and efficiency. Importantly, the presented formulation overcomes the classical tensile instability found in most meshfree interpolation schemes, as shown for stable simulations of, e.g., the inhomogeneous extension of a hyperelastic block up to 100% or the torsion of a hyperelastic cube by 200° –both in an updated Lagrangian setting and without the need for remeshing

State-of-the-art research : reflections on a concerted Nordic-Baltic nuclear energy effort

Quite a few hold the view that nuclear energy will have its renaissance in the not too distant future. Technology is, however, a necessary, but not sufficient condition. The needed prerequisites represent a complex issue. With increasing energy demand and depletion of non-renewable energy resources, nuclear will have to prove its role in an increasing energy mix, globally, regionally and often also nationally. Based on its history, experience with coordinated interplay in electricity production from a variety of energy sources, and science engagements, we argue for a future Nordic/Baltic SHOW CASE: A nuclear weapons free and proliferation safe nuclear energy supplier in the region, with a concerted role in competence building and in international ventures, and with focus on operation, safety economy and societal aspects

ANALISA POLA TINGKAH LAKU PERUBAHAN TEGANGAN PADA SINGLE MACHINE INFINITE BUS (SMIB) DENGAN METODA LINEAR QUADRATIC REGULATOR (LQR) (Studi Kasus : Sistem Kelistrikkan PT. PLN Wilayah Sumatera Barat)

ABSTRACT This study discusses the performance analysis, stability analysis and robustness analysis of a single machine infinite bus system ( SMIB ) electric system West Sumatra . SMIB system is an electrical power subsystem consisting of one or more generators are connected to an infinite bus. SMIB system is a subsystem that most affect the performance of the power system . The analysis includes performance analysis in the time domain, frequency domain analysis of the performance, stability analysis and robustness analysis. Performance, stability and robustness of a factor - an important factor that must be considered in the operation of a single machine infinite bus system (SMIB). Performance, stability and robustness of the power system will be disturbed if there is interference . There are 2 types of disturbances that often occur in the operation of electric power systems including transition disorders and minor annoyances . If these disorders continue to occur continuously at any time will result in a change in the parameters - parameters in the SMIB system , especially changes in voltage. Change parameter - these parameters can lead to SMIB will be disrupted and the resulting system can no longer operate normally after the crash. By using the method of Linear Quadratic Regulator ( LQR ), Linear Quadratic Regulator method with weight function on the output ( LQRy ) and the data - the data system of a single machine infinite bus (SMIB) electric system West Sumatra will be analyzed performance, stability and robustness. The analysis shows that the performance, stability and robustness of the system SMIB electric system West Sumatra using the method of Linear Quadratic Regulator (LQR) and Linear Quadratic Regulator methods with weight function on the output (LQRy) is better

Europe 1992 and the Rise of the Pacific Rim: Do Changing World Trading Patterns Require a Change in United States Shipping Laws?

This Article analyzes the significant issues facing the Presidential Advisory Commission on Ocean Conferences in Ocean Shipping. This Commission will assess the success of the Shipping Act of 1984 and will report to Congress on the need for changes in the 1984 Act and in United States regulatory policy regarding international ocean common carriers. Mr. Danas recommends that the Commission carefully examine the antitrust-exempt conferences, which international ocean common carriers have been organizing for over one hundred years for the purpose of self-regulation and rationalization. Mr. Danas suggests that the review of the continued existence of the liner conference system requires a recognition that the ocean transportation industry is changing into an international intermodal transportation industry that handles shipments in one continuous movement from origin to destination. The author emphasizes that the development of a post-1992 European Common Market and the adoption of Pacific Rim distribution techniques will further the trend towards integrated transportation companies and the use of full service logistics in international shipping. He suggests that the development of the international intermodal transportation company and the needs of shippers dealing with such companies must figure prominently in the Advisory Commission\u27s treatment of those issues that Congress has required it to address--tariff filing, antitrust immunity for ports, independent action on service contracts, and the existence of the conference system. Mr. Danas suggests a framework whereby the Commission may successfully integrate these issues into the task presently committed to it by Congress

The mixed metric dimension of flower snarks and wheels

New graph invariant, which is called mixed metric dimension, has been recently introduced. In this paper, exact results of mixed metric dimension on two special classes of graphs are found: flower snarks $J_n$ and wheels $W_n$. It is proved that mixed metric dimension for $J_5$ is equal to 5, while for higher dimensions it is constant and equal to 4. For $W_n$, its mixed metric dimension is not constant, but it is equal to $n$ when $n\geq 4$, while it is equal to 4, for $n=3$