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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
Crystal structure
Fracture toughness - KIc = Yc a
resistance to brittle fracture in presence of
a crack - resistance to crack propagation
under load
Common specimen
configurations
pre-cracked here
before testing usually 1000
cycles, 0.03 in/in
strain
Fracture toughness
Hypothetical example - surface crack in a semiinfinite sheet loaded in tension
Find critical crack size
Some fracture surfaces
ductile fracture
intergranular
fracture
transgranular
fracture
Crack origins
Creep
deformation under small loads at
elevated temps.
Fatigue
deformation under small cyclic loads
Fatigue
S-N curves & endurance limit
Fatigue failure
fatigue crack w/ beachmarks
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
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')
Crystal structures of pure metals
cubic close-packed (ccp)
close-packed plane of atoms
Crystal structures of pure metals
cubic close-packed (ccp)
ABCABC layer sequence
close-packed plane of atoms
A
C
C
B
B
A
A
Crystal structures of pure metals
hexagonal close-packed (hcp)
Zn, Cd, Co, Ti, Zr……
close-packed
plane of atoms
hexagon
Crystal structures of pure metals
hexagonal close-packed (hcp)
ABAB layer sequence
B
close-packed plane of atoms
A
B
A
B
A
Crystal structures of pure metals
A2 structure - so-called "bcc" metal structure
almost close-packed atom planes
Fe, V, Cr, Mo, W, Ta……
some empty space