This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Metallurgical Aspects”.
1. In fatigue failure, the behaviour of material under cyclic load generally differs from that under monotonic load.
a) True
b) False
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Explanation: The study of behaviour of material in its fatigue failure is very important to understand for the design and manufacturing purpose. The behaviour of material under cyclic load generally differs from that under monotonic load. Fatigue in the form of initiation of a defect is followed by its growth till the operating load is reached to rupture condition.
2. In cyclic loading of material, the crack is generally initiated by a sudden or abrupt failure of the material.
a) True
b) False
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Explanation: In a work-piece subjected to cyclic loading, a fatigue crack is generally initiated on a microscopically small scale which further followed by the growth of crack to a macroscopic size. And in last cycle, the material or specimen fails due to fatigue and fracture occurs which defines complete failure of the work-piece.
3. The quality of the metal surface is a very important consideration, which greatly affects the fatigue life of the material.
a) True
b) False
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Explanation: The fatigue phenomenon is generally considered as a mechanism which occurs in metallic materials. The study of the fatigue phenomenon is very necessary for considering several technical conditions which affects the fatigue life and fatigue crack growth in the material, such as the material surface quality, residual stress etc.
4. Decarburization is a process which can increase the fatigue limit of the material in case of cyclic loading.
a) True
b) False
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Explanation: In case of cyclic loading, decarburization is a process which is defined as the depletion of carbon from the surface of steel alloy. It can significantly reduce the fatigue limit of the steel material. For testing the materials, a batch of similar specimens is selected and then the fatigue strength is determined by considering free surface of the material.
5. Fabrication methods of materials greatly affect the geometry of defects in the material.
a) True
b) False
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Explanation: The geometry of defects in the material is greatly influenced by the fabrication methods and also by the quality control procedures which involved the manufacturing of products. Fatigue is a general type of failure, and thus the defect geometry has a significant effect on the fatigue life of the material.
6. The fatigue limit or strength of the material can change with respect to time.
a) True
b) False
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Explanation: In many experiments, it has been concluded that the fatigue limit or strength of the material after a long period of time of a metallic material which does not heat up and which surface is not reacted with any other substance chemically during a test remains constant for almost all the practical conditions or purposes.
7. Environmental conditions can affect the fatigue life of material more severely than the sharp stress concentration conditions.
a) True
b) False
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Explanation: Environmental conditions can greatly affect the fatigue condition of materials which may be more severe than the sharp stress concentrations conditions. In general, corrosion and temperature are the two main environmental factors which greatly influence the fatigue behaviour of material structures.
8. Corrosion fatigue is very small problem and it has negligible effects on the material properties.
a) True
b) False
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Explanation: Fatigue under corrosion is called as corrosion fatigue which is a very complex problem. It mainly refers to the combination of corrosive environment and repeated stress, which can be more detrimental than the other conditions. Repeated stress accelerates the corrosion in material which further accelerates the fatigue conditions in the material.
9. At low temperature condition of the material, its fracture toughness decreases substantially.
a) True
b) False
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Explanation: The fracture toughness of the material substantially decreases at low temperature. But at high or elevated temperature, the mean or average stress conditions are extremely complex because of the interactions between fatigue and environmental conditions. At high temperature, the material is plastically deformed with less force.
10. Neutralization of preexisting defects in the material can lower the chances of fatigue failure.
a) True
b) False
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Explanation: The fatigue life of material can be improved by various treatments which generally includes grinding, shot peening, spot heating, hammer peening, heat treatment etc. And also by considering strategies like neutralization of preexisting defects and reducing local stress concentration, fatigue life of material can be improved.
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