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530.352 Materials Selection

530.352 Materials Selection. Lecture #16: Dislocations Tuesday October 18 th , 2005. U. ~ 2  Th. E. F.  Th. r o. 1.25r o. r. Theoretical strength :. 2  Th = E  = E  L/L o 2  Th = E 0.25r o /r o = E/4  Th = E/8. Atomic description of plasticity:.

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530.352 Materials Selection

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  1. 530.352 Materials Selection Lecture #16: DislocationsTuesday October 18th, 2005

  2. U ~ 2Th E F Th ro 1.25ro r Theoretical strength : . 2Th = E= E L/Lo 2Th = E 0.25ro/ro = E/4 Th = E/8

  3. Atomic description of plasticity:

  4. Slip easier with defects Hard to pull all at once x Much easier

  5. Defects in crystals • 0 - D • vacancies • 1-D • dislocation lines • 2-D • fault planes • grain boundaries

  6. Dislocation is the boundary between slipped and unslipped regions.

  7. Edge dislocations

  8. Burger’s Circuit • Start with atom “S”. • Count 4 to the right. • Count 4 down. • Count 4 to the left. • Count 4 up. • Finish with atom “F” • b connects S with F RHSF convention : Burger’s vector (b) S F

  9. t b Geometry of Edges Note: b is perpendicular to t t x b -> extra half plane

  10. Motion of Edges   t |b| b 

  11. Motion of Edges  t |b| b 

  12. Screw dislocations

  13. F S Burger’s Vector of Screws Note: b is parallel to t

  14. Motion of Screws

  15. Motion of Screws

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