ENGR 240 - 11.26.07

ENGR 240 - 11.26.07 - ENGR 240 November 26, 2007 Failure o...

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ENGR 240 – November 26, 2007 Failure o Fracture – separation of something into 2 or more pieces due to an applied static (not changing with time) stress Two types Ductile plastic deformation o Polymers, metals Brittle no plastic deformation o ceramics Ductile specimen fracture (Necking) as necking begins, you start to get microvoids microvoids grow and coalesce (form a crack) crack propagates crack rapidly propagates around perimeter of neck until fracture Brittle specimen failure Rapid crack propagation For metals very hard, fine grained, relatively smooth at the surface Brittle Crystalline materials crack propagation is repeated, breaking of atomic bonds along specific crystallographic planes (cleaving (transgranular)) o Intergranular crack propagation along grain boundaries o Fracture Mechanics Stress Concentration Fracture strength is a function of cohesive forces between atoms
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ENGR 240 - 11.26.07 - ENGR 240 November 26, 2007 Failure o...

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