2 a) possible additional sources of error (creep test)
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2 a) possible additional sources of error (creep test) • temperature not constant over time • light (optical strain gages!) may be not constant • humidity (sample affected!) not constant • load or displacement may not be const. • machine/instrument creeping • creeping of strain gage • etc. ( d a y / n i g h t ! )
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2 a) possible additional sources of error (creep test). temperature not constant over time light ( optical strain gages !) may be not constant humidity (sample affected !) not constant load or displacement may not be const . machine / instrument creeping creeping of strain gage - PowerPoint PPT Presentation
Transcript of 2 a) possible additional sources of error (creep test)
2 a) possible additional sources of error (creep test)
• temperature not constant over time• light (optical strain gages!) may be not constant• humidity (sample affected!) not constant• load or displacement may not be const.• machine/instrument creeping• creeping of strain gage• etc.
(day / night!)
2 b) Analyzing a creep experiment
0 1 2 3 4 5 6 7 80
5
10
15
20
Dis
plac
emen
t [%
]
Time [min]
secondary
tertiary
primary
0 1 2 3 4 5 6 7 80,000
0,001
0,002
0,003
0,004
0,005
Com
plia
nce
D(t
) [1
/MP
a]
Time [min]
0 1 2 3 4 5 6 7 8
1E-3
0,002
0,003
0,004
0,005
Com
plia
nce
D(t
) [1
/MP
a]
Time [min]
𝐷(𝑡)=𝜀(𝑡)𝜎 0
creep compliance
note that the values of e are given in %, so you have to divide them by 100
to evaluate creep compliance is only useful in the secondary region (marked by )D is in the range of 1/MPa
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
2 c) i. time-temperature-shift for master curve at 120°C
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
2 c) i. result: master curve at 120°C
master curve at 120°C
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
master curve at 120°C
2 c) ii. predict compliance after 5 days
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
master curve at 120°C
5 d = 5*24*60 min = 7200 min
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
master curve at 120°C
5 d = 5*24*60 min = 7200 min
D(5 d) ≈ 1/psi
2 c) iii. possible prediction range at 120°C
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
master curve at 120°C
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
10-3 10-1 101 103 105
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
master curve at 120°C
40000 min == 0,9 months == 0,1 years
130°C 125°C 122°C 120°C 115°C 110°C 100°C 90°C
102 104 106 108 1010
10-6
10-5
10-4
10-3
10-2
Time (min)
Com
plia
nce
D(t
) (1
/psi
)
master curve at 90°C
3e+9 min == 70000 months == 5700 years
for comparison: possible prediction range at 90°C
3. Fatigue testing
a) three examples of applications cyclic stress loading
1. wings of airplanes2. turbine blades3. rotor blades
(nicht sehr schwer, wenn zwei davon schon in b) genannt sind)
b) Wöhler curve and estimation of life time
10-1 100 101 102 103 104 105 106 107 108
20
40
60
80
100
120 Stress
Str
ess
[MP
a]
Cycles N
b) Wöhler curve and estimation of life time
10-1 100 101 102 103 104 105 106 107 108
20
40
60
80
100
120 Stress
Str
ess
[MP
a]
Cycles N
i. N(40 MPa) ≈ 9000 ii. N(27 MPa) ≈ 300000
i. N(40 MPa) ≈ 9000 tlife = N/f = 9000 * 1 / 0,5 s = 18000 s = = 5 hours
ii. N(27 MPa) ≈ 300000 tlife = N/f = 300000 * 1 / 1000 s = 300 s = = 5 minutes
(aim: to show that cyclic loaded components must have huge safetyfactors, if fatigue testing is not performed)
