This set of Mechanical Metallurgy written test Questions & Answers focuses on “Fatigue of Metals – Machine Design Approach – 2”.
1. The corrosion fatigue is defined as the _________
a) chemical attack
c) cycle stress
d) chemical attack and cycle stress
Explanation: The corrosion fatigue is the result of cycle stress and chemical attack on the component simultaneously. This type of fatigue is more detrimental than normal fatigue.
2. Which one of the following is only present in the corrosion fatigue?
a) Crack on surface
b) Pits on surface
c) Striation marks
Explanation: The chemical attack on the surface creates pits on the surface. These pits act as the potential site for stress concentration, and fatigue takes place on repetitive loading.
3. Is it possible that the material which shows the fatigue limit in normal environment does not show any endurance limit in a corrosive environment.
Explanation: The corrosion attack accelerates the crack growth rate, so the steady state of crack propagation becomes difficult to achieve, hence the fatigue limit is lost.
4. The number of pits generated on the surface of the material under fatigue corrosion are ________ than the number of pits on the surface of the same sample when it is tested only under corrosion environment.
d) no pattern
Explanation: The corrosion of material produces the oxide layer on the surface, but the stress breaks this layer repetitively, which causes more pit to form on the surface.
5. The stainless steel components are coated with _________ to control the fatigue corrosion.
Explanation: The zinc and cadmium are generally coated on the stainless steel and aluminum component to protect them from fatigue corrosion cracking.
6. The fretting is the process of ____________
a) corrosion due to water
b) relative motion between 2 metal causing the corrosion
c) corrosion due to air
d) fatigue due to excessive stress
Explanation: The fretting is defined by the relative motion between the two metals part which causes the rubbing and small metal oxide debris will form. This will cause fatigue of the component.
7. As the temperature decreases, there is a sudden change in the fatigue limit of the material, similar to what has been observed in the ductile to brittle transition.
Explanation: The statement is not correct, as there is a sudden change in the impact strength of the material below a specific temperature, but this does not cause the sudden drop in the fatigue strength value.
8. The fatigue strength of the metal ____________ with increasing temperature.
c) remains the same
d) no relation
Explanation: The general trend is the fatigue strength of material decrease with increase in the temperature with few exceptions. As the temperature becomes much greater, the creep becomes the chief phenomena of failure.
9. Which of the following statement is correct?
a) Fatigue and creep both are transcrystalline
b) Fatigue and creep both are intercrystalline
c) Fatigue is transcrystalline while the creep is intercrystalline
d) Fatigue is intercrystalline while the creep is transcrystalline
Explanation: As we know that the fatigue crack flows across the grain, so it termed as the transgranular or transcrystalline. While the creep is the phenomena which takes place along the grain boundary, so it is intergranular.
10. At any given temperature, the creep will __________ with increasing mean stress.
c) remain the same
d) no relation
Explanation: The creep rate increases with an increase in the mean stress of cycle loading or stress. It follows the same pattern as the fatigue.
11. The fatigue strength of the material ___________ as the grain decreases.
c) remains the same
d) no relation
Explanation: The fine grain material gives the best fatigue strength. It is because the transgranular crack propagation becomes difficult.
12. At higher temperature, if higher frequency of stress cycle is applied on the material, fracture will be ___________ and at lower frequency of stress, the fracture will be ___________
a) intergranular, intergranular
b) transgranular, transgranuler
c) intergranular, transgranular
d) transgranuler, intergranular
Explanation: At the higher frequency of stress, the fatigue crack growth is much fast, and it is less selective about the chosen path so that the fracture will be transgranular. But as the frequency reduces, the mode of fracture shifts towards the intergranular mode.
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