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See detailExperimental validation of a thermal model of a LOx flooded ball bearing
Servais, Christophe ULg; Bozet, Jean-Luc ULg; Kreit, Patrick ULg et al

in Tribology International (2014), 80

Ball bearings of turbopumps of rocket engines work in very singular conditions; they are flooded into liquid oxygen or liquid hydrogen. Therefore, the use of any conventional lubricants (oil or grease) is ... [more ▼]

Ball bearings of turbopumps of rocket engines work in very singular conditions; they are flooded into liquid oxygen or liquid hydrogen. Therefore, the use of any conventional lubricants (oil or grease) is prescribed. Although cryogenic fluids can cool this kind of ball bearing, they cannot separate the surfaces in contact. As a result, there is a significant increase in frictional power losses. This paper presents tests performed on a cryotechnic ball bearing flooded in liquid oxygen. The test results showed that beyond a critical loading of the bearing, a sudden increase in temperature occurred. A thermal model is also put forward, in order to understand and anticipate especially the thermal instability described above. [less ▲]

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See detailA Micro Model for Elasto-Plastic Adhesive-Contact in Micro-Switches: Application to cyclic loading
Wu, Ling ULg; Golinval, Jean-Claude ULg; Noels, Ludovic ULg

in Tribology International (2013), 57

Stiction is a major failure mode in micro-electromechanical systems. In previous works, a statistical rough surfaces interaction model, for which only elastic adhesive contact has been considered, was ... [more ▼]

Stiction is a major failure mode in micro-electromechanical systems. In previous works, a statistical rough surfaces interaction model, for which only elastic adhesive contact has been considered, was developed for multiscale analyzes. However, during the impact between rough surfaces, plastic deformations of asperities cannot always be neglected. In the present work, the adhesion between rough surfaces is studied considering the elasto-plastic deformations of the asperities, and a model predicting the resulting micro adhesive-contact forces is derived. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. To determine the degree of plasticity involved, the impact energy of the movable electrode at pull-in is estimated. Thus the maximal adhesive force evolution during cyclic loading is predicted using the developed model. [less ▲]

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See detailModelling of friction and wear for designing cryogenic valves
Bozet, Jean-Luc ULg

in Tribology International (2001), 34(4), 207-215

From a tribological point of view, the selection of materials for seals for valves of cryogenic rocket engines is a critical issue for the designer. Due to the lack of comprehensive information on this ... [more ▼]

From a tribological point of view, the selection of materials for seals for valves of cryogenic rocket engines is a critical issue for the designer. Due to the lack of comprehensive information on this topic. data have been obtained in the framework of research programmes. In the first step, two polymers potentially usable for sealing cryogenic fluids were identified, They were submitted to general test conditions to gain some fundamental understanding of their tribological behaviour when immersed in a cryogenic fluid. This fundamental understanding proved to be helpful for an efficient technical approach. This approach with the test conditions as close as possible to those met in real valves has been used in the second step. In order to obtain the best information with the minimum number of tests, the statistical method of Doehlert has been adopted. The use of such a method led to the construction of surface response for modelling friction and wear. These surfaces and their associated equation are directly and easily usable by the designer, This way of treating technical tribological problem is illustrated by an example. (C) 2001 Elsevier Science Ltd. All rights reserved. [less ▲]

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