FAKULTI KEJURUTERAAN MEKANIKAL

UNIVERSITI TEKNOLOGI MALAYSIA

SKUDAI, JOHOR

TUTORIAL 2

(METALS CREEP)

1. a) What is creep failure?

b) Explain why metal creep normally occurs at high temperature.

c) What is the difference between tensile test and creep test methods? Give the important

information that can be achieved from each method.

2. a) Discuss the normal creep behavior of a metal.

b) What is the meaning of “balance” that is occurred during second stage of creep and

explain why this stage is important in engineering design.

3. The following data was obtained from a creep test of an aluminium alloy at 200OC. Plot the

creep curves and determine the applied stress that can increase the minimum creep rate to 4.8

x 10-3

mm/m.hr

Time (hr) Strain at 60 MPa(mm/m) Strain at 35 MPa(mm/m)

0 0.320 0.108

20 0.532 0.215

60 0.815 0.332

90 1.000 0.400

120 1.200 0.477

140 1.320 0.532

170 1.477 0.610

220 1.800 0.723

4. Steady state creep data taken from an iron at a stress level of 140 MPa are given below:

dε/dt (hr-1

) T(K)

6.6 x 10-4

1090

8.8 x 10-2

1200

If the stress exponent, n, is 8.5, determine the steady state creep rate at 1300 K and a stress

level of 83 MPa.

5. Determine the stress required for failure of Astroloy in 100000 hours at temperatures of 650OC

and 870OC by using the Larsen-Miller parameter below.

6. Based on the figure below, determine:

i) initial elastic strain

ii) rupture time

iii) steady state creep rate

iv) creep rate at 59 MPa