Question 1
Cottrell atmosphere is a conceptual term of yield point phenomenon.
A. True
B. False
View Answer
Answer: Option A
Explanation:
Solute atoms in material tend to restrict motion of dislocations. These atoms occupy positions below edge dislocations. This is called the Cottrell atmosphere.
Question 2
Lower stress is required to initiate yielding.
A. True
B. False
View Answer
Answer: Option B
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.
Question 3
The elongation that occurs at constant load is called ____
A. Homogeneous elongation
B. Elastic elongation
C. Yield point elongation
D. Constant elongation
View Answer
Answer: Option C
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.
Question 4
What is the main reason for discontinuous yielding?
A. Grain boundaries
B. Substitutional atoms
C. Interstitial atoms
D. Vacancies
View Answer
Answer: Option C
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.
Question 5
What percent of cold reduction is given in skin rolling?
A. < 0.5%
B. 0.5-2%
C. 2-5%
D. 5-10%
View Answer
Answer: Option B
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.
Question 6
What process is used to overcome stretcher strains?
A. Deep drawing
B. Skin rolling
C. Bending
D. Finishing
View Answer
Answer: Option B
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.
Question 7
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
View Answer
Answer: Option B
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.
Question 8
Stretcher strains are because of ____
A. Necking
B. Strain hardening
C. Lüders bands
D. Cold rolling
View Answer
Answer: Option C
Explanation:
stretcher strains are because of lüders bands. These bands generate irregularities on the sheet surface. It destroys the surface finish.
Question 9
Which material shows yield point phenomena?
A. Aluminium
B. Copper
C. Low carbon steel
D. Glass
View Answer
Answer: Option C
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.
Question 10
Which of the following term will be seen in the plastic zone?
A. Yield point
B. Fracture point
C. Proportional limit
D. Elastic limit
View Answer
Answer: Option B
Explanation:
The fracture point is the point of stress at which the fracture of specimen takes place usually after plastic deformation. Whereas yield point, proportional limit and elastic limit can be seen in the elastic region of the stress strain.
Question 11
Yield point is the point of _________ at which transition from elastic to plastic happens.
A. Stress
B. Strain
C. Toughness
D. Resilience
View Answer
Answer: Option A
Explanation:
The stress at which transition occurs above the elastic limit is called yield point. It can be sharp or gradual.