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Hardness testing - localized deformation Brinell Vickers Knoop Rockwell

Last class. Hardness testing - localized deformation Brinell Vickers Knoop Rockwell Hardness/tensile strength correlation Impact testing - energy absorbed upon fracture Effect of temperature. Today. More mechanical testing Fracture toughness Fracture surfaces Creep Fatigue

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Hardness testing - localized deformation Brinell Vickers Knoop Rockwell

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  1. Last class Hardness testing - localized deformation Brinell Vickers Knoop Rockwell Hardness/tensile strength correlation Impact testing - energy absorbed upon fracture Effect of temperature

  2. Today More mechanical testing Fracture toughness Fracture surfaces Creep Fatigue Crystal structure

  3. Common specimen configurations pre-cracked here before testing - usually 1000 cycles, 0.03 in/in strain Fracture toughness- KIc = Yca resistance to brittle fracture in presence of a crack - resistance to crack propagation under load

  4. Fracture toughness Hypothetical example - surface crack in a semi-infinite sheet loaded in tension Find critical crack size

  5. ductile fracture intergranular fracture transgranular fracture Some fracture surfaces

  6. Crack origins

  7. Creep deformation under small loads at elevated temps.

  8. Fatigue deformation under small cyclic loads

  9. Fatigue S-N curves & endurance limit

  10. Fatigue failure fatigue crack w/ beachmarks

  11. Crystal structures of materials - • where are the atoms? • Polymers - mostly not crystalline • structure extremely complicated • Ceramic materials - complicated • many different types of atom arrangements Metals - really simple - most have one of three types

  12. Crystal structures of pure metals Most pure metals exhibit one of three types 1. cubic close packing (ccp or A1) 2. hexagonal close packing (hcp or A3) 3. A2 (almost universally referred to by the confusing notation 'bcc')

  13. Crystal structures of pure metals cubic close-packed (ccp) close-packed plane of atoms

  14. C B Crystal structures of pure metals cubic close-packed (ccp) ABCABC layer sequence close-packed plane of atoms A C A A B

  15. close-packed plane of atoms hexagon Crystal structures of pure metals hexagonal close-packed (hcp) Zn, Cd, Co, Ti, Zr……

  16. B Crystal structures of pure metals hexagonal close-packed (hcp) ABAB layer sequence close-packed plane of atoms B A B A A

  17. Fe, V, Cr, Mo, W, Ta…… some empty space Crystal structures of pure metals A2 structure - so-called "bcc" metal structure almost close-packed atom planes

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