Chapter 8

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Unformatted text preview: The fracture of a Al bicycle crank arm. • – Overload simple fracture • Material fails due to increasing stress – Fatigue Fracture • Material fails due to sustained cyclic loading – Creep Fracture • Material fails due to a sustained steady load at an elevated temperature • – Stress‐corrosion cracking – Corrosion fatigue – Creep fatigue • Material failure may be due to… – – – – … poor design … choosing the wrong material … materials failing to meet specifications … materials degradation Ship-cyclic loading from waves. 3 From Fig. 9.0, Callister (original Neil Boenzi, The New York Times.) • • Fracture: crack formation and propagation in response to an imposed stress 2 Fracture Modes classified based on the ability of the material to experience plastic deformation – Ductile stable • Exhibit substantial plastic deformation large % RA, ef, and % elongation often 20% • High energy absorption Ductile Material – Brittle unstable • Little or no plastic deformation low ef, and % elongation often 1% • Low energy absorption • Ductility is a function of: – Temperature – Strain rate – Stress rate Brittle Material • • Ductile fracture is induced by plastic deformation. It’s caused by damage accumulation. – nucleation, growth, coalescence of voids • • After tensile instability starts, the damage is concentrated in the neck. Note the importance of particles. Indicates plastic deformation fibrous 6 • Occurs by rapid crack propagation • Fracture surfaces will have their own distinctive patterns; for example: – Steel chevron markings – Lines or ridges originating from near the center of the cross section – Amorphous materials shiny, smooth surface • Cleavage: crack propagation corresponding to the successive and repeated breaking of atomic bonds along specific crystallographic planes...
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This note was uploaded on 10/14/2011 for the course ENGINEER CHEM ENG 3 taught by Professor Ghosh during the Spring '11 term at McMaster University.

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