Mr. Rouven O. Christen Profile

Rouven O. Christen

at EMPA

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Author

Publications (5)

Proceedings Article | 27 April 2007 Paper

A simple model for the prediction of the discrete stiffness states of a homogeneous electrostatically tunable multi-layer beam

A. Bergamini, R. Christen, M. Motavalli

Proceedings Volume 6525, 652514 (2007) https://doi.org/10.1117/12.714951

KEYWORDS: Interfaces, Dielectrics, Protactinium, Metamaterials, Systems modeling, Solids, Aerospace engineering, Modeling, Modulation, Computer simulations

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The adaptive modification of the mechanical properties of structures has been described as a key to a number of new or enhanced technologies, ranging from prosthetics to aerospace applications. Previous work reported the electrostatic tuning of the bending stiffness of simple sandwich structures by modifying the shear stress transfer parameters at the interface between faces and the compliant core of the sandwich. For this purpose, the choice of a sandwich structure presented considerable experimental advantages, such as the ability to obtain a large increase in stiffness by activating just two interfaces between the faces and the core of the beam. The hypothesis the development of structures with tunable bending stiffness is based on, is that by applying a normal stress at the interface between two layers of a multi-layer structure it is possible to transfer shear stresses from one layer to the other by means of adhesion or friction forces. The normal stresses needed to generate adhesion or friction can be generated by an electrostatic field across a dielectric layer interposed between the layers of a structure. The shear stress in the cross section of the structure (e.g. a beam) subjected to bending forces is transferred in full, if sufficiently large normal stresses and an adequate friction coefficient at the interface are given. Considering beams with a homogeneous cross-section, in which all layers are made of the same material and have the same width, eliminates the need to consider parameters such as the shear modulus of the material and the shear stiffness of the core, thus making the modelling work easier and the results more readily understood. The goal of the present work is to describe a numerical model of a homogeneous multi-layer beam. The model is validated against analytical solutions for the extreme cases of interaction at the interface (no friction and a high level of friction allowing for full shear stress transfer). The obtained model is used to better understand the processes taking place at the interfaces between layers, demonstrate the existence of discrete stiffness states and to find guidance for the selection of suitable dielectric layers for the generation of the electrostatic normal stresses needed for the shear stress transfer at the interface.

Proceedings Article | 19 April 2007 Paper

Filtering of NDT signals obtained from wrapped steel cables

R. Christen, A. Novakovic, A. Bergamini, M. Motavalli

Proceedings Volume 6531, 653110 (2007) https://doi.org/10.1117/12.715119

KEYWORDS: Magnetism, Sensors, Linear filtering, Electronic filtering, Nondestructive evaluation, Wavelets, Measurement devices, Bridges, Corrosion, Signal detection

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Proceedings Article | 15 March 2006 Paper

Electrostatic tuning of the bending stiffness of a large scale GFRP-CFRP beam

A. Bergamini, R. Christen, M. Motavalli

Proceedings Volume 6169, 616919 (2006) https://doi.org/10.1117/12.659207

KEYWORDS: Bridges, Fiber reinforced polymers, Chemical elements, Adhesives, Interfaces, Glasses, Carbon, Ferroelectric polymers, Dielectrics, Sensors

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Proceedings Article | 16 May 2005 Paper

Electrostatic tuning of the bending stiffness of simple slender multilayer composite structures

Andrea Bergamini, Rouven Christen, Masoud Motavalli

Proceedings Volume 5760, (2005) https://doi.org/10.1117/12.598748

KEYWORDS: Dielectrics, Interfaces, Composites, Ferroelectric polymers, Oscillators, Adhesives, Shape memory alloys, Bismuth, Silicon, Carbon

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Proceedings Article | 1 August 2003 Paper

A simple approach to the localization of flaws in large diameter steel cables

Andrea Bergamini, Rouven Christen

Proceedings Volume 5047, (2003) https://doi.org/10.1117/12.484145

KEYWORDS: Magnetism, Sensors, Inspection, Nondestructive evaluation, Bridges, Finite element methods, Inverse problems, Spherical lenses, Magnetic sensors, 3D modeling

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