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Published byHunter Oldroyd Modified about 1 year 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 secondary tertiary primary

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creep compliance note that the values of are given in %, so you have to divide them by 100

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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 master curve at 120°C

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2 c) ii. predict compliance after 5 days

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

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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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40000 min = = 0,9 months = = 0,1 years

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

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3. Fatigue testing a) three examples of applications cyclic stress loading 1.wings of airplanes 2.turbine blades 3.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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i. N(40 MPa) ≈ 9000ii. N(27 MPa) ≈ i. N(40 MPa) ≈ 9000 t life = N/f = 9000 * 1 / 0,5 s = s = = 5 hours ii. N(27 MPa) ≈ t life = N/f = * 1 / 1000 s = 300 s = = 5 minutes (aim: to show that cyclic loaded components must have huge safety factors, if fatigue testing is not performed)

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