ENGR 240 - 10.5.07

ENGR 240 - 10.5.07 - ENGR 240 October 5 2007 Lyp lower...

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ENGR 240 – October 5, 2007 Well-defined yielding o Sudden drop in stress o Yield strength average of stress at σ Lyp region o Luders Bands Stress concentrates in ceratin regions and then yield (bands form) Creates dislocations Bands nucleate at σ Uyp Bands propagate at σ Lyp Reoccurring at σ Lyp Ductility o Amount of plastic deformation you can induce before fracture o Opposite of brittle o Measured in 2 ways Percent elongation (%EL) %EL = (ℓ f - ℓ 0 )/ℓ 0 x 100 Values Measured o %EL at fracture o %EL after fracture o %EL at fracture is larger than after fracture o ductility uses %EL after fracture (only want to account for plastic deformation) Strain recovery o Metals small o Polymers larger Percent Reduction in Area (%RA) %RA = (A 0 – A f )/A 0 x 100 Brittle metal fracture strain usually less than 5% ****Mechanical Properties vary with temperature**** Toughness o The ability of a material to absorb energy up to the fracture point o
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