10. • Specimen materials ( ferrous – non ferrous)
Specimen Preparation For Creep Test
1. Round cross – section specimen.
2. Sheet or plate specimen.
• Specimen shape :
➢ Specimen Preparation For Creep Test
11. Specimen Preparation For Creep Test Cont…
1. Round cross – section specimen.
2. Sheet or plate specimen
threaded ends
shouldered ends
12. • The gage length of a specimen should be uniform.
• Specimens should be smooth and free from scratches or
other stress raisers and should be machined to minimize
cold working or surface distortion.
• the stress or the load required to provide a certain stress,
the smallest original cross-sectional area should be used.
Specimen Preparation For Creep Test Cont…
17. Procedure
1. Preparation of the creep specimen
2. Erection of the specimen in the machine
3. Heating to the test temperature (~ 4 hours)
➢ Carrying out the creep test
18. Procedure Cont…
4. Starting the test
5. Following up the test up to fracture
6. Ending the test
➢ Carrying out the creep test
** The test temperature should be constant and non-switch off of the electric current should be insured.
• starting data acquisition
• loading the specimen
25. Temperature
➢ Temperature Effect on Creep Test
The temperature at which a material starts to creep depends on
its melting point.
It is found that creep in metals starts when the temperature > 0.3 - 0.4 Tm
(the melting temperature in Kelvin)
Most metals have high melting points and hence they start to creep only at
temperatures much higher than room temperature.
28. Aluminum starts to creep above 100 C (Tm=933 K)
Creep of carbon steels is important at temperatures above 500 C
(Tm=1810 K)
Lead is a low melting metal (Tm = 600 K) it creeps even at
room temperature.
Temperature Cont…
➢ Temperature Effect on Creep Test
29. Effect of the stress Effect of the temperature
➢ Effect of the stress & temperature on the creep-curve
Temperature Cont…
31. ➢ Creep and Creep-Rupture Testing
Rupture strength
Creep tests:
measure the amount of creep
strain as a function of time.
Creep-rupture tests:
measure the time to fracture for a
given temperature and stress levels.
34. • The Larson–Miller parameter is a means of predicting the lifetime of
material vs. time and temperature.
• The value of the parameter is usually expressed as
LMP = T(C + log t)
• where C is a material specific constant, often approximated as 20, t is
the time in hours, and T is the temperature in kelvins.
Rupture strength Cont…
➢ Larson-Miller parameter
42. Creep applications in industry Cont…
➢Displacement-limited applications
Displacement-limited applications in which
precise dimensions or small clearances must be
maintained such as in:
*Turbine rotors in jet engines
*Steam turbines.
43. ➢Rupture-limited applications
Rupture-limited applications in which precise dimensions are
not essential but fracture must be
avoided such as in:
*High-pressure steam tubes and pipes
*Pressure vessel
Creep applications in industry Cont…
