We contend that carbon fiber reinforced silicon carbide material (C/SiC), developed by IABG, represents the state-of-the-art for ultra-lightweight, high precision optomechanical structures that must operate in adverse environments and over wide ranges of temperature. C/SiC employs conventional NC machining/milling equipment to rapidly fabricate near-net shape parts, providing substantial schedule, cost, and risk savings for high precision components. Unlike powder based SiC ceramics, C/SiC does not experience significant shrinkage during processing, nor does it suffer from incomplete densification. By modifying certain process steps, the thermal and mechanical properties of C/SiC are tunable in certain ranges. This paper focuses on recent advances in C/SiC technology and application of this technology to high precision, lightweight applications such as meter-class optics and optical mounts. We also introduce a design for new, high precision mounts based upon standard optical grade C/SiC (formulation A-3) and a custom formulation of C/SiC (D-4) which was engineered for Schafer Corporation by IABG. The A-3 and D-4 formulations have a near-perfect CTh match with silicon, making them the ideal material to athermally support ultra-lightweight silicon optics that will operate in a cryogenic environment
A new material designated C/SiC is the basis for a current ultra-lightweight scan mirror (ULSM) ESA/ESTEC technology development contract for the METEOSAT Second Generation (MSG) Programme (Ref. {1 }). It consists of random-oriented carbon fibres as "greenbody which is shaped to the designed configuration, and is infiltrated in the liquid phase with Si resuiting in a SiC enriched surface layer, with a CVD grown SiC optical polishing layer. The reflective coating finally is silver under a dedicated protection layer.The requirements for this mirror are rather stringent: during 7 years in a geostationary orbit of life it will permantly be exposed to centrifugal forces induced by the satellite spinning at 100 rpm. Due to high image quality requirements for the imager -designated SEVIRI (Spinning Enhanced Visible IR Imager) -the MTF degradation caused by the scan mirror alone are defined to 3 %, resulting in rather high surface quality requirements. The main contribution is the spin induced mirror tip deflection which turned out to be the design driver.The technologically most challenging requirement is to develop a scan mirror with 800 x 500 mm2 effective aperture and a central cutout -the telescope is a Gregory concept -to withstand tight environmental requirements at a mass which was specified as < 6 kg.The ESA contract covers a baseline concept with the subsequently presented design of a monolithic C/SiC mirror, mated to a CFRP structure by isostatic mounts. At the end of this technology programme, a fully tested 1 :1 scale mirror with silver and protection coating will be rendered to ESA.Since this contract is a technology contract, applications beyond the MSG scan mirror are borne in mind, including higher optical surface qualities such as X130 or curved surfaces, also aspheric mirrors of possibly even larger diameters.The manufacturing and optical process implement subcontractors which are not listed among the authors, i.e. SGL Carbon/Meitingen, FRG, for the Si infiltration; Schunk Kohlenstofftechnik/GieBen, FRG, for the CVD SiC coating; REOSC Optique, Ballainvilliers, France for the optical polishing, and Jenoptik, Jena, FRG, for the silver and protection coating. O-8194-1514-6/94/$6.OO SPIE Vol. 2210 / 395 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/04/2015 Terms of Use: http://spiedl.org/terms
Die Entwicklung bzw. Weiterentwicklung von hochtemperaturbeständigen Werkstoffen zum Einsatz zwischen etwa 1000°C und 2000°C bedingt auch die Weiterentwicklung der Hochtemperaturprüf‐ und Meßtechnik zur Ermittlung der benötigten Werktoffkennwerte. Es werden ausgewählte, charakteristische prüftechnische Probleme bei der Ermittlung mechanischer Kennwerte bei Temperaturen über 1000°C angesprochen, prüftechnische Lösungen vorgestellt und Ergebnisbeispiele mitgeteilt.
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