Topic 3a_Plastic Behavior_s

Topic 3a_Plastic Behavior_s - Topic 3a Plastic Behavior...

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1 1 Topic 3a: Plastic Behavior MATE 210 Introduction to Engineering Materials 2 Topic 3a Outline Topic 3a Outline Composition Structure Performance Processing Elastic Crystal Structure Fracture
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2 3 Application: Turbine Blades 4 Turbine Blades Blades inserted in a rotor A variety of blades Turbine blades are crucial components in steam turbine power generators and gas turbine engines. They convert the thermal energy of highly compressed exhaust gasses to rotary mechanical motion.
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3 5 Loading Conditions Turbine blades see high stresses, particularly at the blade root, as they rotate at speeds around 14,000 rpm. 6 Temperature Conditions Exhaust gasses can be extremely hot, causing the blade to experience high temperatures at the blade tip. The engine is most efficient at high temperatures.
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4 7 Tip Rub • If the turbine blade stretches as a result of high stresses and temperatures, the tip of the blade can contact the casing causing considerable damage. 8 Crystal Orientation • One solution to this problem is to use single crystal turbine blades. Poly-crystalline Blade Single Crystal Blade
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5 9 Plastic Properties Composition Structure Performance Processing 10 Stress – Strain Curve Temporary (elastic) deformation occurs the yield strength Permanent (plastic) deformation occurs the yield strength
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6 11 ICA - Ductile Tensile Test Observations: (as you watch the videos, make note of what you see). 1. 2. 12 Plastic Tensile Properties : The stress needed to cause measurable permanent deformation (usually in metals) : The maximum stress a material can withstand prior to fracture during a tensile test : The maximum strain a material can endure prior to fracture during a tensile test
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7 13 Yield Strength The yield strength is the stress needed to produce a small, but specified amount of plastic strain in a material. 0.2 % Offset Method: Stress Strain 0 0.001 0.002 0.003 0.004 14 Ultimate Tensile Strength The tensile strength is the maximum engineering stress a material can handle without failure. It is also the point at which necking occurs. Strain x
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8 15 Typical Strength Values 16 Ductility Extent of plastic deformation at fracture. Since ε plastic >> ε elastic at the point of fracture, we may approximate the ductility as the total strain just before failure, ε f .
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  • Winter '05
  • Niebuhr
  • Tensile strength, plastic deformation, Van der Waal, turbine blades, single crystal, single crystal turbine

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Topic 3a_Plastic Behavior_s - Topic 3a Plastic Behavior...

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