10-16-Lecture

10-16-Lecture - 1 ENGR 213 F A I L U R E FAILURE matls...

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Unformatted text preview: 1 ENGR 213 F A I L U R E FAILURE matls selection & processing inadequate design misuse poor maintenance Failure issues fracture - separation into > 2 pieces ductile brittle fatigue creep DUCTILE FRACTURE metals, polymers stable crack propagation, warning Soft metals neck to point Harder metals neck some voids form & coalesce, shear rough, cup-and-cone fracture surface 4 Brittle Fracture Little defo before failure Break along lines/ridges Cleavage Failure along atomic planes planes thru grains FRACTURE MECHANICS flaws ALWAYS exist & concentrate stress voids, grain boundaries, etc Stress raisers simplest theory uses elliptical voids Explains stress distribution around flaws Wider theory fracture mechanics Quantify resistance to fractures - frac toughness ELLIPTICAL FRAX Max stress m at tips a = crack length = curvature radius of tip m / = K t = stress conc factor Best for brittle Ductile lower than predicted Ks Critical stress for crack propagation t m a 2 = energy surf spec : 2 : critical s s c a E = FRACTURE TOUGHNESS K Ic Kc = matl resistance to brittle frac Units MPa-m 1/2 Y = f (crack & specimen size & geometry) Dimensionless...
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This note was uploaded on 03/26/2008 for the course ENGR 213 taught by Professor Dr.stubbs during the Fall '04 term at Texas A&M.

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10-16-Lecture - 1 ENGR 213 F A I L U R E FAILURE matls...

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