Transcription of Ductile vs. brittle fracture
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Ductile vs. brittle fracture
1 MSE 2090: Introduction to Materials ScienceChapter 8, FailureHow do Materials Break?Chapter Outline: Failure Ductile vs. brittle fracture Principles of fracture mechanics9 Stress concentration Impact fracture testing Fatigue (cyclic stresses)9 Cyclic stresses, the S N curve9 Crack initiation and propagation9 Factors that affect fatigue behavior Creep(time dependent deformation)9 Stress and temperature effects9 Alloys for high-temperature useNot tested: in fracture Data extrapolation methods2 MSE 2090: Introduction to Materials ScienceChapter 8, FailureFracture: separation of a body into pieces due to stress, at temperatures below the melting point. Steps in fracture : crack formation crack propagation FractureDepending on the ability of material to undergo plastic deformation before the fracture two fracture modes can be defined - Ductile or brittle Ductile fracture - most metals (not too cold): Extensive plastic deformation ahead of crack Crack is stable : resists further extension unless applied stress is increased brittle fracture - ceramics, ice, cold metals: Relatively little plastic deformation Crack is unstable : propagates rapidly without increase in applied stressDuctile fracture is preferred in most applications3 MSE 2090: Introduction to Materials ScienceChapter 8, FailureBrittle vs.
Peening”- firing small shot into surface to be treated. High-tech solution - ion implantation, laser peening. ¾Case Hardening - create C- or N- rich outer layer in steels by atomic diffusion from the surface. Makes harder outer layer and also introduces compressive stresses ¾Optimizing geometry - avoid internal corners, notches etc. shot ...
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