1. 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. 2 b) Analyzing a creep experiment
tertiary
secondary
primary

3. D is in the range of 8−9∙ 10 −4 1/MPa
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 8−9∙ 10 −4 1/MPa

4. 2 c) i. time-temperature-shift for master curve at 120°C

13. 2 c) i. result: master curve at 120°C

14. 2 c) ii. predict compliance after 5 days
master curve at 120°C

15. master curve at 120°C
5 d = 5*24*60 min = 7200 min

16. D(5 d) ≈ 4∙ 10 −4 1/psi
master curve at 120°C
5 d = 5*24*60 min = 7200 min

17. 2 c) iii. possible prediction range at 120°C
master curve at 120°C

18. master curve at 120°C
40000 min =
= 0,9 months =
= 0,1 years

19. for comparison: possible prediction range at 90°C
master curve at 90°C
3e+9 min =
= months =
= 5700 years

20. 3. Fatigue testing
a) three examples of applications cyclic stress loading
wings of airplanes
turbine blades
rotor blades
(nicht sehr schwer, wenn zwei davon schon in b) genannt sind)

21. b) Wöhler curve and estimation of life time

22. b) Wöhler curve and estimation of life time
(aim: to show that cyclic loaded components must have huge safety
factors, if fatigue testing is not performed)
i. N(40 MPa) ≈ 9000
ii. N(27 MPa) ≈
i. N(40 MPa) ≈ 9000
tlife = N/f = 9000 * 1 / 0,5 s = s = = 5 hours
ii. N(27 MPa) ≈
tlife = N/f = * 1 / 1000 s = 300 s = = 5 minutes