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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.
- Spring '11