Fracture Aspects - Chapter 8 Fracture: Microscopic Aspects...

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Unformatted text preview: Chapter 8 Fracture: Microscopic Aspects Fracture in Metals Fracture in Metals Fracture in Metals Fracture in Metals Crack Nucleation Three types of crack nucleation mechanisms Brittle: Dislocations practically immobile near region of crack nucleation Semibrittle: Dislocations mobile, but only on a restricted number of slip planes Ductile: No restrictions on the movement of dislocations other those inherent in the crystalline structure of the material Fracture in Metals Ductile Fracture Role of plastic deformation is very important Single crystals : Slip on slip plane followed by necking Polycrystals : Microstructural features (ie. second phases or internal interfaces) dictate fracture Fracture in Metals Ductile Fracture (a) Failure by shear (glide) in a pure metal. (Reprinted with permission from D. Broek, Elementary Engineering Fracture Mechanics , 3rd ed. (The Hague, Netherlands: Martinus Nijhoff, 1982), p. 33.) (b) A point fracture in a soft single-crystal sample of copper. (Courtesy of J. D. Embury.) Fracture in Metals Slide adapted from M. Weaver UA. Ductile Fracture Zener-Stroh Crack Crack formed by lattice rotation caused by twinning Fracture in Metals Ductile Fracture: High Temperature W-Type Cavitation w-type cavitation at a grain-boundary triple point. r-Type Cavitation r-type cavitation at a grain boundary Fracture in Metals Ductile Fracture: Microcavities (nucleation, growth and coalescence) Slide adapted from M. Weaver UA.Slide adapted from M....
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Fracture Aspects - Chapter 8 Fracture: Microscopic Aspects...

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