mse 200 exam 2 Flashcards
Shear stress
σ = F / Ao
stress horizonally rather than vertically (tensile strength)
Tensile strength
σ = F/Ao
tensile strength = force / cross sectional area
Elastic deformation
Non permanent and reversable
yield strength
stress at which noticable plasic deformation has occured
plastic deformation
process in which the object due to applied force changes its size or shape in a way that is not reversible
Slip
Movement of dislocations in materials under applied stress and causes deformation
What affects slip
- crystal structure of material
- temperature of material
- presence of barriers (grain boudnaries, point defects, impurities
what does introducing slip barriers do
strengthen material
Comparison of discolations and crystal sturctures
FCC: many close-packed planes/directions
HCP: only 1 plane, 3 directions
BCC: None
HCP has fewer slip planes and are more ____
brittle
Ductility
amount of plastic deformation at failure
ductility percent elongation
%EL = (lf-l0)/lo X 100
ductility percent reduction in area
%RA = (Ao-Af)/Ao x 100
resilience
ability of a material to absorb energy during elastic deformation
linear stress-strain curve formula
Ur = 1/2(σy)(ey)
Toughness
amount of energy absorbed before fracture
how to measure toughness
approximate area under the stress-strain cruve at fracture point
hardness
measure of resistnace to surface plastic deformation - dent or scratch
safety factor
σw = σy/N
σw = working stress: F/A
σy = yield strength
dislocation density
total dislocation length/unit volume
edge dislocation motion
dislocation line moves in the same direction as force, perpendicular to t
screw dislocation motion
perpendicular to force
if force is -> screw spins clockwise
FCC slip system
slip plane: {111}
slip direction: (110)
number of slip systems: 12
BCC slip system
slip plane: {110}
slip direction: (111)
number of slip systems: 12/24
more active slip systems means
more ductile material
required tensile strength to cause yielding
σy = Tcrss/Tr
Tr = σcosλcosΦ
resolved shear stress
Tr = σcosλcosΦ
if resolved shear stress < critical resolved shear stress..
no yielding
what are the 3 primary strengthening mechanics
grain size reduction, solid solution strengthening, cold working
as %CW increases..
yield strength ( σy) increases
tensile strength increases
ductility decreaes
heating(annealing)
removes effects of cold working
3 annealing stages
Recovery, recrysallization, grain growth
annealing causes tensile strength to ____ and ductility to _____
decrease. increase
3 types of failure
fracture, fatigue, creep
fracture: brittle vs ductile
brittle: little or no plastic deformation, rapid crack propagation, fails without warning
ductile: significant plastic deformation, slow crack propagation, fails with warning
stress at crack tip formula
σm = 2σo(a/Pt)^(1/2)
σm = stress at crack tip
σo = applied stress
a = length of crack
Pt = radius of curvature
a value for internal crack and external crack
2a and a
fracture toughness formula
Kc = Yσcsqrt(pia)
kc = fracture toughness
Y = dimensionless parameter
σc = critical stress
a = crack length
fatigue failure
failure under lengthy period of repeated stress or strain cycling
3 general tecniques to improve fatigue life
- reduce magnitude of mean stress
- surface treatments
- design changes
creep
measure deformation vs time at constant stress
3 stages of creep
- primary creep
- secondary creep
- tertiary creep
primary creep slope ____ with time
decreases
secondary creep slope ____
constant with time
tertiary creep slope ____ with time
increases
time to rupture
T(C+logtr)=m
T = temperature
C = constant, normally 20
tr = time to failure (rupture(
m = function of applied stress
eutectic
liquid transforms into 2 solids
eutectoid
one solid phase transforms into 2 other solid phases
peritectic
liquid and one solid phase transform to a second solid phase
austenite (y) to pearlite
slow cool
austenite (y) to bainite
moderate cool
austenite (y) to martensite
rapid quench
martensite to tempered martensite
reheat
