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

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

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

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

Some fracture surfaces ductile fracture transgranular fracture transgranular fracture intergranular fracture intergranular fracture

Crack origins

Creep deformation under small loads at elevated temps. Creep deformation under small loads at elevated temps.

Fatigue deformation under small cyclic loads Fatigue deformation under small cyclic loads

Fatigue S-N curves & endurance limit Fatigue S-N curves & endurance limit

Fatigue failure fatigue crack w/ beachmarks 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 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') 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) close-packed plane of atoms

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

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

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