Creep Testing
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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.
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
- 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.
- 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.
- 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
- 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…