Chapter 6 : Mechanical Properties of Metals I

Question 1

What are wrought alloy products?

Answer 1

metals and alloys that are manufactured by hot and cold working

Question 2

Hot rolling is?

Answer 2

a metal is preheated and then rolled intill it is to diffuclt

Question 3

Annealing is what?

Answer 3

reheating treatment to remove any cold work

Question 4

What is % cold reduction?

Answer 4

(initial thickness - final thickness)/initial thickness *100

Question 5

What is Extrusion?

Answer 5

a plastic forming proccess occured by taking a metal under high pressures nad forcing it through an opening in a die

Question 6

What are the two types of extrusion?

Answer 6

Direct and Indirect

Question 7

What are the two differences between direct and indirect extrusion?

Answer 7

direct - billet forced by ram (billet is being moved)

indirect - hollow ram holds the die (ram moves)

Question 8

Forging a metal is what? What are the two types?

Answer 8

hammering or pressing the metal to form a shape

the two types of forging are hammered and pressed

Question 9

What are some other metal forming proccess?

Answer 9

Wire drawing and deep drawing

Question 10

What is the difference between elastic and plastic deformation?

Answer 10

elastic - when a metal or alloy will return to its original position/shape
plastic - when a metal or alloy will NOT return to its original position/shape

Question 11

What is engineering stress?

Answer 11

Average uni-axial tensile force per original cross sectional area
σ = F/Ao
N/m^2 = 1 Pa = lb/in^2 = psi

Question 12

What are the unit conversion factors for Pa>psi, Pa>Mpa, psi>ksi>Mpa

Answer 12

1 psi = 6.89E3 Pa
10^6 Pa = 1 MPa
100 psi = 1 ksi = 6.89 MPa

Question 13

What is engineering strain?

Answer 13

ε  = (L - Lo)/Lo 
L = final length
Lo = initial length
in./in or m/m
%ε = ε*100%

Question 14

Poisons ratio is?

Answer 14

ν = ε lateral/ ε longitudinal = εx/εz = -εy/εz

Question 15

What is the formula for shear stress?

Answer 15

τ = S (shear force) / A (area where shear force acts)
N/m^2 = Pa = psi = lb/in^2

Question 16

What is the formula for shear strain?

Answer 16

λ = a (amount of shear displacement) / h (distance over which the shear stress acts).
λ = a/h = tanθ

Question 17

What is pure elastic shear?

Answer 17

a relationship between shear stress and shear strain
τ = λ*G
where G = elastic modulus

Question 18

What is casting?

Answer 18

continuous/semi-continuous mold for more intricate designs

Question 19

What are the strengthening mechanisms?

Answer 19

1. Change the grain size - smaller grains are smaller
2. solid solution strengthening - add one or more elements
3. cold working or strain hardening - increases the deformities
4. second phase strengthening

Question 20

What is the difference between engineering stress and true stress?

Answer 20

Engineering - area is initial

true - area is instantaneous

Question 21

What is hot working?

Answer 21

Heating the metal to reduce cold working, called annealing

Question 22

What is annealing?

Answer 22

removal of dislocations

Question 23

What happens to the metal in hot working?

Answer 23

1. softens
2. more ductile,
3. gets rid of dislocations

Question 24

What happens to the metal in cold working?

Answer 24

1. becomes harder
2. stronger
3. more brittle (ductility decreases)
4. creates dislocations
5. increases tensile strength until fracture

Question 25

What is the temperature buffer for hot and cold working?

Answer 25

0.4 the melting temp, hot working above, cold working below.

Question 26

What are some of the hardness tests?

Answer 26

1. Rockwell
2. Knoop
3. Vickers
4. Brinswell

Question 27

What is hardness?

Answer 27

a measure of the resistance of any alloy to plastic deformation

Question 28

Flux is?

Answer 28

the net flow of atoms, the diffusion rate

Question 29

Explain slip

Answer 29

occurs more easily on certain crystallographic planes (slip plane)
FCC {111} ,
BCC {110},

Question 30

Dislocations move easier through what planes?

Answer 30

through closed packed planes (CPP)

Question 31

What is twinning?

Answer 31

part of the atomic lattice deforms to make a mirror image of undeformed region adjacent to twinned region
HCP - most likely to twine
BCC - will twine
FCC - least likely to twine

Question 32

What are the affects of cold working?

Answer 32

harder, stronger, more brittle (more dislocaitons)

Question 33

Diffusion is fastest in?

Answer 33

interstitial diffusivity along the grain boundary (faster because it has more room and space to move)

Question 34

What are the affects of carburizing a metal?

Answer 34

harder, stronger, more brittle

Question 35

What are the steps of annealing?

Answer 35

1. recovery
2. recrystallization
3. grain growth
   note that 1-3 the temperature is increasing

Question 36

What is hardness?

Answer 36

resistance to plastic deformation

Question 37

What is toughness?

Answer 37

measure of how much energy a material can absorb before breaking

Question 38

What is super-plasticity?

Answer 38

Superplasticity is the ability of a material to sustain plastic deformation levels exceeding 1000% without fracture