This set of Mechanical Metallurgy online test focuses on “Fatigue of Metals – Cumulative Fatigue Damage & Sequence Effects – 2”.
1. The value of the notch sensitivity factor lies between __________
a) 0 to 1
b) 1 to 2
c) 0 to infinity
d) minus infinity to plus infinity
Explanation: The notch sensitivity factor indicates the severity of a notch upon the reduction of fatigue strength. So, q=0 mean no effect and q=1 mean maximum effect and all the values lie in between zero to one.
2. The size of the component does play a role in deciding the fatigue life of the element.
Explanation: The statement is true. It is generally observed the larger components have lower fatigue strength compared to their replica lab sample.
3. As the surface roughness of the material increases, fatigue property of the material ___________
c) remain the same
d) no relationship
Explanation: The surface roughness is symbolic of the troughs and valley on the surface. If the material has high surface roughness, it will have more cracks on the surface so it will act as stress raiser and it will result in a decrease of the fatigue property.
4. The “par bar” kind of sample used for ___________
a) tensile strength
b) creep strength
c) fatigue strength affected by the surface roughness
d) the effect of the notch on the fatigue strength
Explanation: The effect of the surface roughness is well known to us. To systematically calculate the effect of roughness on fatigue strength, the “par bar” are prepared in which sample of varying surface roughness are tested for fatigue strength.
5. The carburization of the surface has positive effect in improving the fatigue property of the material.
Explanation: The carburization increases the case hardness of the material, and anything which strengthens the surface, improves the fatigue property of the material.
6. The Almen Strip is used in __________
a) shot peening
Explanation: The Almen strip is thin steel strip used in shot peening to quantify the severity of process. It is generally made of SAE 1070 steel.
7. The cycle ratio is defined as _____________
a) the ratio of the cycles of overstressing at the prestress to the virgin fatigue life at this same stress
b) the ratio of virgin fatigue life to cycles of overstressing at this same stress
c) the ratio of nominal stress to maximum stress
d) the ratio of Kf to Kt
Explanation: Overstressing is the process of testing a virgin specimen for some number of cycles less than failure at stress above the fatigue limit, and subsequently running the specimen to failure at another test stress. The ratio of the cycles of overstressing at the pre-stress to the virgin fatigue life at this same stress is called the cycle ratio.
8. The under-stressed sample have ____________ fatigue life than a virgin sample.
d) cannot say
Explanation: The under-stressing is the process in which sample is tested below the fatigue limit for a number of cycles and then the fatigue test is run. This improves the fatigue life of the sample due to strain hardening at the tip of cracks.
9. If the sample is tested for a large number of cycles below its fatigue limit and the stress is gradually increased above the fatigue limit, the true fatigue limit of material will _______
c) no effect
d) cannot say
Explanation: It has been observed that if a sample has been under stress below the fatigue limit for long time and then stress is gradually increased, then the endurance limit of the material will improve. This procedure is called coaxing.
10. Which of the following material shows a strong coaxing effect?
c) Low-alloy steel
d) Mild steel
Explanation: The mild steel and iron ingot show a strong effect of coaxing while the brass, aluminum and heat treated low-alloys steel show little improvement in properties by coaxing.
Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.
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