EN-AVT-131-08 - Materials Selection, Modeling and...

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RTO-EN-AVT-131 8 - 1 Materials Selection, Modeling and Mechanical Design S. Mark Spearing School of Engineering Sciences University of Southampton Southampton, SO17 1BJ UK [email protected] ABSTRACT These lecture notes address materials and structures issues associated with the MIT Microfabricated gas turbine engine. An overview of the project and the performance goals is provided. These are translated into requirements for the materials and structural design. Particular emphasis is provided on the approaches taken to designing with brittle materials at low temperatures and designing with ductile creeping materials at high temperature. A novel approach to structural reinforcement using SiC in combination with Si is introduced. 1.0 INTRODUCTION This lecture will provide an overview of material selection, structural design and the requirements for material and structural models motivated by the MIT Microengine project. This project has been running since 1994, and is motivated by opportunities for small scale propulsion and portable power generation. The key guiding principles of the project are: 1) μfabrication of high strength and/or refractory materials enables the concept of high-power density μsystems (mm scale): μgas turbine engines, μrockets, μcompressors, μpumps, μhydraulic pumps/energy harvesters, μrefrigerators. 2) Power densities can approach those of full-sized prime movers and power generators (100 W/cc). 3) Cost could be very low given sufficient demand (10 8 units/year). 4) Power microsystems could be an enabling technology for new concepts: Portable power, propulsion, cooling, flow control. In addition to the microengine several other projects using microfabrication processes have been initiated at MIT, some of which are shown as images in figure 1. Spearing, S.M. (2005) Materials Selection, Modeling and Mechanical Design. In Micro Gas Turbines (pp. 8-1 – 8-16). Educational Notes RTO-EN-AVT-131, Paper 8. Neuilly-sur-Seine, France: RTO. Available from: http://www.rto.nato.int/abstracts.asp .
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Materials Selection, Modeling and Mechanical Design 8 - 2 RTO-EN-AVT-131 Figure 1: Images showing Microfabricated Devices and Components. In order to realize these devices there are certain physical requirements that must be met: 1) High peak cycle temperatures (1600-2500 K), which translates into a requirement for high temperature materials. 2) High peripheral speeds (400-600 m/s). Which implies highly stressed rotating parts (100’s of MPa). Note: rotor power density is proportional to (tip Mach No.) 2 which in turn is proportional to stress. 3) Low friction bearings (air bearings for μengine): Avoid sliding contacts at all costs. 4) Reasonable component efficiencies which implies a requirement for close tolerances (better than 1 μm). Requirements 1) and 2) have implications for the chosen materials and items 3) and 4) for the processes
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This note was uploaded on 11/10/2010 for the course AEROSPACE AE 1202 taught by Professor Dr.adib during the Spring '10 term at Sharif University of Technology.

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EN-AVT-131-08 - Materials Selection, Modeling and...

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