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Exp 9 : Creep & Impact Tests (Method (4) pull, swing the pendulum…
Exp 9 : Creep & Impact Tests
Creep test
theory
subjecting specimen to constant load/stress
maintain temp constant
measure deformation/strain
plot as elapsed time
Creep Curve
(3 stages)
Primary
occur at beginning
mostly transently
not steady state
continuosly decreasing creep rate(slope diminishes w/ time)
material - creep resistance increase/strain hardening
Secondary
creep rate become roughly steady (steady state)
creep rate constant (plot linear)
the stage w/ the longer duration
Tertiary
creep rate begin accelarate
cross sectional area of material decrease
necking/ internal voiding decreases the effective area of specimen
due to
ultimate failure ''rupture''
due to
grain boundary separation
formation of internal cracks,cavities,voids
Method
1)Sample loading
Remove the extensometer
Place the sample,tighten the extensometer
Pull furnace carefully(sample fully covered)
lock furnace,insert heat insulation refractory
2)Pre-loading
pre-loading load should 10% of total creep(based on stress-strain curve of specific sample
determine creep load,place master load
adjust load support until displacement ''0''
set load coloum,insert load pin
3)Parameter setup for steel sample
select
operation(O)
Test Start
machine 01
Test Type Creep(C)
Input temp : 650ºc(0.4T)
Dimension :10mm
stress : 28.02 MPa
Time : 168h
Loading increasing interval : 0
beyond limitation alarming : 15℃
Creep Deformation :4℃
Original Gauge Length : 100mm
Pre-loading: 200kN
Main Loading : 2000kN
Creep Quantity Alarming : 12.5 mm
4) set Displacement ''0''
5) -wait,temperature constant in furnace,
-start loading process(when massage oading appear
-press auto button to start experiment
6) Analyse result
Impact Test
(determines the amount of energy absorbed by a material during fracture)
Charpy Impact Test
''Charpy V-notch test''
high strain-rate test
to study temperature-dependent ductile–brittle transition
striking a standard notched specimen with a controlled weight pendulum swung from a set height
show metal brittle/ductile
horizontally,notch facing away the pendulum
IZOD Impact Test
ASTM standard method
determining the impact resistance of materials
Vertically,notch facing toward the pendulum
Method
1) Pull pendulum(height set), set indicator at max loading
2) let pendulum swing(record zero error)
3) Place Charpy specimen
4) pull, swing the pendulum
record energy used
5) soak 1 specimen in liquid nitrogen(2min)
6) take out fast(l<5 sec),place in specimen holder,pull & swing pendulum,
7) repeat using specimen other specimen(record hardness value)
8) plot charpy & hardness values w/ tempering temp on one graph
importance
high tempering temp
high impact value
low hardness value
soaked in nitrogen(ʆ) - highest hardnest value/lower impact (more brittle)
by: NIZ
