This document outlines the process for creep testing. It discusses the mechanism of creep, specimen preparation, testing machines, procedures, results including creep curves, and the effect of temperature. It also covers rupture strength measurement using the Larson-Miller parameter and precautions for the testing process. Applications of creep testing in industry include displacement-limited components like turbine rotors, rupture-limited parts like steam pipes, and stress-relaxation-limited uses such as suspended cables.

1. Creep Testing

2. ➢ Intro (Muhammad Sa’eed)
➢ Mechanism (Hassan Tarek)
➢ Specimen (Muhammad Sayed)
➢ Machine (Muhammad Zaki)
➢ Procedures (Najeh Fayez)
Outlines
➢ Results (Amir Mos’ad)
➢ Effect of temperature (Islam M. Reda)
➢ Rupture strength (Muhammad Ali)
➢ Precautions (Mahmoud Mukhtar)
➢ Apps (Muhammad Mostafa)

3. introduction

4. MECHANISMS OF CREEP
Testing

5. MECHANISMS OF CREEP Testing
➢ MECHANISMS OF CREEP
a) Dislocation climb
b) Vacancy Diffusion
c) Grain boundary sliding

6. ➢ Dislocation movement
MECHANISMS OF CREEP Testing Cont…

7. ➢ Vacancy Diffusion
MECHANISMS OF CREEP Testing Cont…

8. ➢ Grain boundary sliding
MECHANISMS OF CREEP Testing Cont…

9. Specimen Preparation For
Creep Test

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…

13. Machine

14. Machine
1- creep testing machine

15. Machine Cont…
2- parts of machine

16. Procedure

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

19. Results

20. ➢ Stopping the tensile test in the elastic region!
Results

21. But Now! A Creep Curve
Results Cont…

22. ➢ Stages of creep curve
Results Cont…

23. ➢ Creep Rate Curve
Results Cont…

24. Temperature

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.

26. Temperature Cont…

27. Temperature Cont…

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…

30. Rupture strength

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.

32. Rupture strength Cont…

33. Rupture strength Cont…

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

35. Rupture strength Cont…
➢ Larson-Miller parameter

36. Precautions

37. 1. temperatures : {-.+2%}
higher than R.T
creep start (0.3 – 0.4)T.m
Thermostatic furnance
Precautions
➢ Technical
Examples
carbon steels: above 500 C (Tm=1810 K)
Aluminum : above 100 C (Tm=933 K)
Lead : low melting metal .. R.T(Tm = 600 K)

38. 2. Load :-
• constant
• uniaxial Load
• Applied smoothly and gently… (shock/failure) specimen
3. Free from vibration
4. Measuring devices must be very sensitive
5. Humidity : { -.+ 5%}
Precautions Cont…
➢ Technical

39. ➢ Safety
Precautions Cont…

40. Creep applications in industry

41.  Displacement-limited applications
 Rupture-limted applications
 Stress-relaxation limited applications
Creep applications in industry

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…

44. ➢Stress-relaxation-limited applications
Stress-relaxation-limited applications in which an initial
tension relaxes with time such as in:
*Suspended cables
*Tightened bolts
Creep applications in industry Cont…