mse 200 exam 2

Question 1

Shear stress

Answer 1

σ = F / Ao

stress horizonally rather than vertically (tensile strength)

Question 1

Tensile strength

Answer 1

σ = F/Ao

tensile strength = force / cross sectional area

Question 2

Elastic deformation

Answer 2

Non permanent and reversable

Question 3

yield strength

Answer 3

stress at which noticable plasic deformation has occured

Question 4

plastic deformation

Answer 4

process in which the object due to applied force changes its size or shape in a way that is not reversible

Question 5

Slip

Answer 5

Movement of dislocations in materials under applied stress and causes deformation

Question 6

What affects slip

Answer 6

• crystal structure of material
• temperature of material
• presence of barriers (grain boudnaries, point defects, impurities

Question 7

what does introducing slip barriers do

Answer 7

strengthen material

Question 8

Comparison of discolations and crystal sturctures

Answer 8

FCC: many close-packed planes/directions
HCP: only 1 plane, 3 directions
BCC: None

Question 9

HCP has fewer slip planes and are more ____

Answer 9

brittle

Question 10

Ductility

Answer 10

amount of plastic deformation at failure

Question 11

ductility percent elongation

Answer 11

%EL = (lf-l0)/lo X 100

Question 12

ductility percent reduction in area

Answer 12

%RA = (Ao-Af)/Ao x 100

Question 13

resilience

Answer 13

ability of a material to absorb energy during elastic deformation

Question 14

linear stress-strain curve formula

Answer 14

Ur = 1/2(σy)(ey)

Question 15

Toughness

Answer 15

amount of energy absorbed before fracture

Question 16

how to measure toughness

Answer 16

approximate area under the stress-strain cruve at fracture point

Question 17

hardness

Answer 17

measure of resistnace to surface plastic deformation - dent or scratch

Question 18

safety factor

Answer 18

σw = σy/N
σw = working stress: F/A
σy = yield strength

Question 19

dislocation density

Answer 19

total dislocation length/unit volume

Question 20

edge dislocation motion

Answer 20

dislocation line moves in the same direction as force, perpendicular to t

Question 21

screw dislocation motion

Answer 21

perpendicular to force
if force is -> screw spins clockwise

Question 22

FCC slip system

Answer 22

slip plane: {111}
slip direction: (110)
number of slip systems: 12

Question 23

BCC slip system

Answer 23

slip plane: {110}
slip direction: (111)
number of slip systems: 12/24

Question 24

more active slip systems means

Answer 24

more ductile material

Question 25

required tensile strength to cause yielding

Answer 25

σy = Tcrss/Tr Tr = σcosλcosΦ

Question 26

resolved shear stress

Answer 26

Tr = σcosλcosΦ

Question 27

if resolved shear stress < critical resolved shear stress..

Answer 27

no yielding

Question 28

what are the 3 primary strengthening mechanics

Answer 28

grain size reduction, solid solution strengthening, cold working

Question 29

as %CW increases..

Answer 29

yield strength ( σy) increases tensile strength increases ductility decreaes

Question 30

heating(annealing)

Answer 30

removes effects of cold working

Question 31

3 annealing stages

Answer 31

Recovery, recrysallization, grain growth

Question 32

annealing causes tensile strength to ____ and ductility to _____

Answer 32

decrease. increase

Question 33

3 types of failure

Answer 33

fracture, fatigue, creep

Question 33

fracture: brittle vs ductile

Answer 33

brittle: little or no plastic deformation, rapid crack propagation, fails without warning ductile: significant plastic deformation, slow crack propagation, fails with warning

Question 34

stress at crack tip formula

Answer 34

σm = 2σo(a/Pt)^(1/2) σm = stress at crack tip σo = applied stress a = length of crack Pt = radius of curvature

Question 35

a value for internal crack and external crack

Answer 35

2a and a

Question 36

fracture toughness formula

Answer 36

Kc = Yσc*sqrt(pi*a) kc = fracture toughness Y = dimensionless parameter σc = critical stress a = crack length

Question 37

fatigue failure

Answer 37

failure under lengthy period of repeated stress or strain cycling

Question 38

3 general tecniques to improve fatigue life

Answer 38

1. reduce magnitude of mean stress 2. surface treatments 3. design changes

Question 39

creep

Answer 39

measure deformation vs time at constant stress

Question 40

3 stages of creep

Answer 40

1. primary creep 2. secondary creep 3. tertiary creep

Question 41

primary creep slope ____ with time

Answer 41

decreases

Question 42

secondary creep slope ____

Answer 42

constant with time

Question 43

tertiary creep slope ____ with time

Answer 43

increases

Question 44

time to rupture

Answer 44

T(C+logtr)=m T = temperature C = constant, normally 20 tr = time to failure (rupture( m = function of applied stress

Question 45

eutectic

Answer 45

liquid transforms into 2 solids

Question 46

eutectoid

Answer 46

one solid phase transforms into 2 other solid phases

Question 47

peritectic

Answer 47

liquid and one solid phase transform to a second solid phase

Question 48

austenite (y) to pearlite

Answer 48

slow cool

Question 49

austenite (y) to bainite

Answer 49

moderate cool

Question 50

austenite (y) to martensite

Answer 50

rapid quench

Question 51

martensite to tempered martensite

Answer 51

reheat