# Mechanical Behaviour Questions and Answers – Yield Point Phenomenon

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. Yield point is the point of _________ at which transition from elastic to plastic happens.
a) Stress
b) Strain
c) Toughness
d) Resilience

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?
a) Aluminium
b) Copper
c) Low carbon steel
d) Glass

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.
a) 2
b) 20
c) 200
d) 2000

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

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 of the following term will be seen in the plastic zone?
a) Yield point
b) Fracture point
c) Proportional limit
d) Elastic limit

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.

7. Stretcher strains are because of ____
a) Necking
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
c) Bending
d) Finishing

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%
b) 0.5-2%
c) 2-5%
d) 5-10%

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
d) Vacancies

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 conceptual term of yield point phenomenon.
a) True
b) False

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.
a) True
b) False

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.

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