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530.352 Materials Selection

530.352 Materials Selection. Lecture #19 Other deformation modes Wednesday October 26 th , 2005. Deformation modes: metals and ceramics :. Dislocations Grain Boundary sliding Twinning Diffusion. Grain boundary sliding:. . . Twinning :. . mirror plane. . whole region shears.

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530.352 Materials Selection

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  1. 530.352 Materials Selection Lecture #19 Other deformation modesWednesday October 26th, 2005

  2. Deformation modes: metals and ceramics : • Dislocations • Grain Boundary sliding • Twinning • Diffusion

  3. Grain boundary sliding:  

  4. Twinning :  mirror plane  whole region shears

  5. Twinning in nc-Al:

  6. atoms diffuse from side to top Diffusion of atoms : 

  7. Diffusion • Vacancies play an important role in atomic diffusion • See alsohttp://www.ifh.uni-karlsruhe.de/ifh/studneu/envflu_I/Animations/reflecting.gif

  8. Polymers:

  9. Noncrystalline Polymers:

  10. Non-crystalline polymers: • T < 0.8Tg • Brittle fracture • T~0.8Tg • Onset of plasticity • T~Tg • Extensive “cold-drawing” • Drawing, Shear banding, Crazing • T>1.05Tg • Uniform viscous flow

  11. Necking in polymers

  12. Chain alignment during necking

  13. Shear banding in polymers

  14. Crazing in polymers

  15. Crystalline polymers

  16. Stages of deformation

  17. General Strength of Polymers 5 4 3 2 1 Tensile Strength (103 psi) 2 4 6 8 10 12 Molecular weight (105)

  18. E  Deformation of Amorphous Solids: • Local rearrangement of atoms or molecules. • Occurs in response to applied stress. • Requires energy (bond breaking) - thermal activation. Stress - strain response of Newtonian glasses :   = o exp(Ev/RT) .

  19. E Elongation Force  o  time time  Deformation of Amorphous Solids: Constant elongation: Constant force:

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