References of "Collette, Jean-Paul"
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See detailMechanical behaviour of tape springs used in the deployment of reflectors around a solar panel
Dewalque, Florence ULg; Collette, Jean-Paul; Bruls, Olivier ULg

in Acta Astronautica (2016), 123

In order to increase the production of power on small satellites, solar panels are commonly deployed and, in some cases, reflectors are added to improve the concentration factor on solar cells. In this ... [more ▼]

In order to increase the production of power on small satellites, solar panels are commonly deployed and, in some cases, reflectors are added to improve the concentration factor on solar cells. In this work, reflectors are deployed by the means of compliant mechanisms known as tape springs. Their attractive characteristics are, among others, their passive behaviour, their self-locking capacity, their elastic deformations and their robustness. However, their mechanical behaviour is highly nonlinear and requires thorough analyses in order to develop predictive numerical models. It is shown here through parametric studies that the nonlinear behaviour of a tape spring is mainly governed by its geometry. Thus, for each specific application, its dimensions can be determined in order to minimise two critical features: the maximum stress affecting the structure and the maximum motion amplitude during deployment. In this paper, an optimisation procedure is proposed to meet these requirements. [less ▲]

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See detailSURFACE ENGINEERING FOR PARTS MADE BY ADDITIVE MANUFACTURING
Nutal, Nicolas; Rochus, Pierre ULg; Collette, Jean-Paul et al

in 66th International Astronautical Congress (2015, October)

the surface preparation of metal parts made by additive manufacturing (AM). AM is a technology of choice for manufacturing of parts with complex shapes (heat exchangers, RF supports, optical parts…) and ... [more ▼]

the surface preparation of metal parts made by additive manufacturing (AM). AM is a technology of choice for manufacturing of parts with complex shapes (heat exchangers, RF supports, optical parts…) and integrated functions such as conformal cooling channels, clips, hinges, etc. This opens the door for lightweight parts which are of prime importance for space applications. The potential of the AM technologies is however impeded by the quite rough surface finish that is observed on the as-manufactured parts. It is known that such a finish is likely to impact the performance of the parts. Several post-treatment techniques can be applied to improve the surface condition of the AM parts. However, so far, the influence of the successive post-processing steps on the final properties is not well established. Therefore, a better understanding of the impact of surface characteristics on the material behaviour is needed to expand the use of AM for high performance parts. The objective of this study, supported by ESA, is to propose and evaluate various surface finishing techniques for parts made by the AM technologies, in order to check their compatibility, evaluate their properties and derive guidelines for future applications. CRM is the prime proposer of this study and is in charge of the surface treatment and characterisations. Sirris additive manufacturing facilities are used to produce the parts. Thales Alenia Space and Walopt are included into the industrial team to provide concrete application cases. The study focuses on metals. Two metals under study are presented here: AlSi10Mg and Ti6Al4V. This paper is devoted to the early results of the first steps of surface preparation, namely material removal from the surface of the produced parts in order to improve their surface properties. As a first phase, tribo-finishing (TF) is tested on prototype parts to check its capabilities. Surface and volume parameters are analyzed, namely achieved roughness, material removal rate, location of removed material. The limitations in terms of geometry and applicability are discussed as well. These first observations should serve as guidelines for further application of AM for the design of parts used in space industry. [less ▲]

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See detailMechanical behaviour of tape springs used in the deployment of reflectors around a solar panel
Dewalque, Florence ULg; Collette, Jean-Paul; Bruls, Olivier ULg

in Proceedings of the 6th International Conference on Mechanics and Materials in Design (M2D) (2015)

In order to increase the production of power on small satellites, large solar panels are commonly deployed and, in some cases, reflectors are added to improve the concentration factor on solar cells. In ... [more ▼]

In order to increase the production of power on small satellites, large solar panels are commonly deployed and, in some cases, reflectors are added to improve the concentration factor on solar cells. In this work, reflectors are deployed by the means of compliant mechanisms known as tape springs. Their attractive characteristics are, among others, their passive behaviour, their self-locking capacity, their elastic deformations and their robustness. It is shown here through parametric studies that the behaviour of a tape spring is mainly governed by its geometry. Thus, for each specific application, its dimensions must be determined in order to minimise two critical features: the maximum stresses affecting the structure and the maximum amplitudes of motion during deployment. In this paper, an optimisation procedure is proposed to meet these requirements. [less ▲]

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See detailOptimisation par éléments finis d'une couronne d'éolienne
Saadi, Ismaïl ULg; Collette, Jean-Paul

in Revue scientifique des ISILF (2013), 27

The purpose of this paper is the study of the most adapted grade of steel that should be used for a ring gear of wind turbine gearboxes. The first step consists in determining a reliable load case in ... [more ▼]

The purpose of this paper is the study of the most adapted grade of steel that should be used for a ring gear of wind turbine gearboxes. The first step consists in determining a reliable load case in order to study the stress to which the part concerned is subjected. After that, a numerical model of the ring gear is designed in a CAD software and then analyzed to rate the stress by the finite element method thanks to ANSYS. In the end, the choice of the grade of steel can be made. [less ▲]

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See detailPrototyping of a Phase Change Material Heat Storage Device
Collette, Jean-Paul; Rochus, Pierre ULg; Peyrou-Lauga, Romain et al

in Proceedings of the 63rd International Astronautical Congress 1-5 Octobre 2012 (2012, October 05)

A new concept of Phase Change Materials (PCM) device has recently been developed to improve the thermal control of spacecraft. Two Phase Change Material candidates have been selected after extensive ... [more ▼]

A new concept of Phase Change Materials (PCM) device has recently been developed to improve the thermal control of spacecraft. Two Phase Change Material candidates have been selected after extensive testing of a set of available materials. Special attention has been paid to the hysteresis and ageing. In the design of the container, the thermal expansion of the PCM is a critical parameter that has been taken into consideration by two competing technologies. These designs have been tested: a prototype of PCM heat storage device has been effectively manufactured and tested under vacuum environment. 1D and 2D mathematical models have been developed. Conclusions are drawn to promote the use of PCM Heat Storage device in various space missions. [less ▲]

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See detailRoughness evolution of some X-UV reflective materials induced by low energy (< 1 keV) ion beam milling
Gailly, Patrick ULg; Jamar, Claude ULg; Fleury-Frenette, Karl ULg et al

in Nuclear Instruments & Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms (2004), 216

Ion beam figuring (IBF) is an advanced technique that is been used for more than 10 years as a final step in the manufacturing of optical elements. It makes use of ion sputtering to correct shape defects ... [more ▼]

Ion beam figuring (IBF) is an advanced technique that is been used for more than 10 years as a final step in the manufacturing of optical elements. It makes use of ion sputtering to correct shape defects but this process may eventually lead to the degradation of the surface roughness. In this study, the evolution of roughness for some optical materials subjected to the ion beam figuring process has been investigated by using optical profilometry and scanning electron microscopy. Emphasis has been made on electroplated nickel, PVD gold and CVD silicon carbide. These materials are often used for X-ray and UV applications but only limited data on their behavior under ion milling is currently available. Roughness measurements have been performed at different etching depths down to 5 mum which is representative of typical IBF treatments. The effects of using different inert gases (Ar, Kr and Xe) with ion energies ranging from 200 to 900 eV have been studied. The observed trends are an important increase of the roughness for electroplated nickel, a slight decrease for PVD gold and a slight increase for CVD silicon carbide. Results are discussed in relation to previous related works and within sputtering considerations. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailNew process for X-ray mirror image quality improvement
Gailly, Patrick ULg; de Chambure, Daniel; Collette, Jean-Paul et al

in Freund, Andreas K. (Ed.) X-Ray Mirrors, Crystals, and Multilayers II (Proceedings Volume) (2002, December 24)

A new technique to improve the image quality of Ni replicated X-ray mirror is presented. During the manufacturing of XMM Mirror Module between 1994 to 1999, the classical manufacturing process showed its ... [more ▼]

A new technique to improve the image quality of Ni replicated X-ray mirror is presented. During the manufacturing of XMM Mirror Module between 1994 to 1999, the classical manufacturing process showed its limits. In 1995, the XMM Mirror Module Qualification Model HEW was around 20 arcsec. In 1998, the fifth Flight Model Mirror Module reached 11 arcsec HEW, with a single mirror shell achieving 8 arcsec HEW. The performance of this technology is namely limited by the integration process of the shells. The new technique is based on the following philosophy : • Firstly, an accurate measurement of each mirror shell after integration. A dedicated metrology system has been built and allows a precise metrology of the actual surface. • Secondly, a modification of the mirror shell and of the support to transfer the stress to a non optical active area. • Finally, an ion figuring run to correct the residual shape error of the mirror. The control and evaluation of the process is assured by EUV PSF assessment achieved in the FOCAL X facility developed for XMM. The advantages of this new process are to shape the mirrors in their final hardware configuration and the versality of the process enabling improvement of other kinds of high accuracy mirrors. [less ▲]

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See detailFiguring sequences on a super-smooth sample
Tock, Jean-Philippe; Collette, Jean-Paul; Gailly, Patrick ULg et al

in Geyl, Roland; Maxwell, Jonathan (Eds.) Optical Fabrication and Testing, Proc. SPIE Volume: 3739 (1999, September 06)

An ion beam figuring facility is operational at the Centre Spatial de Liège since 1997. Its present capabilities are described. An extensive characterisation programme is running in order to determine the ... [more ▼]

An ion beam figuring facility is operational at the Centre Spatial de Liège since 1997. Its present capabilities are described. An extensive characterisation programme is running in order to determine the optimised parameters for various materials and operating conditions. In this frame, tests have been performed on a spherical gold-coated aluminium mirror plated in between with nickel. The nickel plating was used to be super-polished to a BRDF of 1 10-4 at 1 deg at 10 µm wavelength. Micro-roughness and etching rate measurements were realised and influence of ion bombardment on the coating has been established after removal of the gold coating. The gold coating removing was performed by using the ion beam flux. Finally, the mirror has been figured from the original sphere to a parabola. Surface characteristics evolution is also described in terms of micro-roughness and surface error. An overview of the research and development programmes related to this facility is given. Results of this technique and potential impact on optics fabrication are then briefly exposed. [less ▲]

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See detailIon beam figuring of small BK7 and Zerodur optics : thermal effects
Gailly, Patrick ULg; Collette, Jean-Paul; Renson, Luc et al

in Geyl, Roland; Maxwell, Jonathan (Eds.) Optical Fabrication and Testing, Proc. SPIE Volume: 3739 (1999, September 06)

optics these last years. One of the disadvantages of ion figuring is the high surface temperature of the workpiece. Temperature aspects have already been mentioned by some authors but are weakly detailed ... [more ▼]

optics these last years. One of the disadvantages of ion figuring is the high surface temperature of the workpiece. Temperature aspects have already been mentioned by some authors but are weakly detailed. Therefore thermal effects on BK7 and Zerodur, mainly surface figure distortions and surface temperature measurements, have been investigated here in more detail. Distortion of the optical figure due to high temperature and temperature gradients induced by ion figuring is described. High figure distortion has been observed on 10 cm diameter BK7 samples. Distortions can also be observed on Zerodur samples (although much weaker). Differences between BK7 and Zerodur distortions are discussed. In order to analyse the nonuniform heating of the workpiece during ion bombardment, the surface temperature has been monitored with an infrared camera. Furthermore, surface temperature measurements with respect to ion beam parameters have also been performed. All these measurements show the necessity to care about thermal aspects during ion beam figuring for some sensible materials like BK7, but even for low expansion material like Zerodur. [less ▲]

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See detailIon beam figuring of precision aspheric optical surfaces
Gailly, Patrick ULg; Collette, Jean-Paul; Tock, Jean-Philippe et al

Conference (1999)

An ion beam figuring facility is fully operational at the Centre Spatial de Liège since 1997. Ion beam figuring principle is briefly reminded and the present capabilities of the technique are described ... [more ▼]

An ion beam figuring facility is fully operational at the Centre Spatial de Liège since 1997. Ion beam figuring principle is briefly reminded and the present capabilities of the technique are described. An extensive characterisation programme is running in order to determine the optimised parameters for numerous materials and operating conditions. In this frame, tests have been performed on various optics to demonstrate the capability of the technique to figure aspheric shapes on glass or metallic substrates. At first, an aspherisation on a spherical gold-coated aluminium mirror plated in between with Nickel is presented. After removal of the gold coating with the ion beam, micro-roughness and etching rate measurements have been performed on the substrate material. Finally, the mirror has been figured from the original sphere to a parabola. The surface characteristics evolution is described in terms of micro-roughness and surface error. Other examples of complex aspherical figuring (polynomials of high order, ...) are shown. In conclusion, the potential impact and the results of this technique on optics fabrication, especially for exotic shapes, are exposed. The integration of the ion beam figuring process in a classical optics manufacturing sequence will be discussed, identifying the potential time and money savings. [less ▲]

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