This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Yield Point Phenomenon”.
1. The elongation that occurs at constant load is called ____
a) Homogeneous elongation
b) Elastic elongation
c) Yield point elongation
d) Constant elongation
Explanation: Yield point elongation is the elongation that occurs at constant load. It is about 15 to 20 times the elastic elongation. Elastic elongation is 0.1 percent for most of the metals.
2. The yield point is ____
Explanation: The stress at which transition occurs above the elastic limit is called yield point. It can be sharp or gradual.
3. Which material shows yield point phenomena?
c) Low carbon steel
Explanation: Aluminium and copper are ductile materials with gradual yield point. Glass is ceramic which rarely undergo yielding. Low carbon steel shows yield point phenomenon.
4. Yield point elongation is ____ times the elastic elongation.
Explanation: Elastic elongation is generally 0.1 percent. Yield point elongation is 15 to 20 times the elastic elongation. This point may vary from material to material.
5. What term is used for the load at which a sudden drop occurs in a conventional tensile curve?
a) Plastic instability
b) Upper yield point
c) Lower yield point
d) Static load
Explanation: Yield point is of two types. The upper yield point is the load at which a sudden drop occurs in a conventional tensile curve. Lower yield point is lower constant load at which appreciable yielding occurs.
6. Which term is different from others?
a) Yield point
b) Fracture point
c) Proportional limit
d) Elastic limit
Explanation: Fracture point is different from the other three terms. Other three terms define the stress above Hooke’s limit. At this point, stress is no longer proportional to strain produced.
7. Stretcher strains are because of ____
b) Strain hardening
c) Lüders bands
d) Cold rolling
Explanation: stretcher strains are because of lüders bands. These bands generate irregularities on the sheet surface. It destroys the surface finish.
8. What process is used to overcome stretcher strains?
a) Deep drawing
b) Skin rolling
Explanation: Skin rolling treatment is given to sheets. It removes the discontinuous yield point from tensile curve. Hence stretcher strains don’t ruin the sheet surface finish.
9. What percent of cold reduction is given in skin rolling?
a) < 0.5%
Explanation: In skin rolling small cold reduction is given to the sheet. It is in the range of 0.5-2%. It is given immediately before the forming operation so as to avoid the recurrence of yield point.
10. What is the main reason for discontinuous yielding?
a) Grain boundaries
b) Substitutional atoms
c) Interstitial atoms
Explanation: Discontinuous yielding is caused by the presence of interstitial atoms. These may be carbon and nitrogen atoms in steel. These atoms lock the dislocations.
11. Cottrell atmosphere is a yield point phenomenon related term.
Explanation: Solute atoms in material tend to restrict motion of dislocations. These atoms occupy positions below edge dislocations. This is called the Cottrell atmosphere.
12. Lower stress is required to initiate yielding.
Explanation: Once dislocations are made free, their motion needs the lower stress. A higher stress is required to initiate yielding. But a lower stress is required to continue it.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
To practice all areas of Mechanical Behaviour & Testing of Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.