ENGR 240 - 11.28.07

ENGR 240 - 11.28.07 - s = Δε/t slope in secondary stage...

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ENGR 240 – November 28, 2007 Creep o Deformation at a constant stress over a long period of time o Often the limiting factor in the lifetime of a part o Most important for metals with T ≥ 0.4T M (in Kelvin) o Stages of Creep Primary decreasing creep rate due to strain hardening Secondary constant creep rate (linear plot), balance between competing strain hardening and recovery, this stage has longest duration Tertiary accelerated rate, formation of cracks and voids Steady state creep rate εdot
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Unformatted text preview: s = Δε/t slope in secondary stage • Important design parameter for long life applications Types of Metal Alloys and Applications o Magnesium Density – • Very light • Lightweight • Low elastic moldulus • High resistance to Cold work • Corrosive in marine environments • Stiffer • More recyclable • Cheaper than engineering plastics • Applications o Luggage o Aircraft and missile components o Portable devices o...
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