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Published byHunter Oldroyd Modified over 2 years ago

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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. (day / night!)

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**2 b) Analyzing a creep experiment**

tertiary secondary primary

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**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

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

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

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**2 c) ii. predict compliance after 5 days**

master curve at 120°C

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

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

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**2 c) iii. possible prediction range at 120°C**

master curve at 120°C

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

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**for comparison: possible prediction range at 90°C**

master curve at 90°C 3e+9 min = = months = = 5700 years

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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)

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**b) Wöhler curve and estimation of life time**

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**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

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