# Mechanical Behaviour Questions and Answers – Variables Affecting Impact Value

This set of Mechanical Behaviour Questions and Answers for Campus interviews focuses on “Variables Affecting Impact Value”.

1. Above critical speed, what happens to the energy required to rupture a material when striking velocity increases?
a) Increases slowly
b) Increases rapidly
c) Decreases slowly
d) Decreases rapidly

Explanation: Above critical speed, the energy required to rupture a material rapidly decreases with increasing striking velocity. This doesn’t happen below the critical speed.

2. Critical velocity is higher for annealed steels than hardened.
a) True
b) False

Explanation: The critical velocity is much less for annealed steels. It is higher for hardened steel. It is because of internal stresses.

3. The energy loss should be ____________ by the manufacturer by ________
a) Minimized, heavy foundation of machine
b) Minimized, addition of weight to specimen
c) Maximized, heavy foundation of machine
d) Maximized, addition of weight to specimen

Explanation: The energy loss should be minimized by the manufacturer through a heavy foundation of the machine. The fraction of energy is lost due to absorption in vice and structure.

4. A sharp notch ________ the yield stress and ________ the transition temperature?
a) Increase, Increase
b) Increase, decrease
c) Decrease, Increase
d) Decrease, decrease

Explanation: The presence of notch affects the impact value. The yield stress increases with a sharp notch. The transition temperature also increases.

5. A ________ notch is preferred in Charpy test.
a) Shallow V-shaped
b) U shaped
c) Shallow U-shaped
d) Keyhole shaped

Explanation: A shallow V-shaped notch is preferred in the Charpy test. It is because sharp notch raises yield stress and transition temperature.

6. The energy absorbed by a notched test bar of a ductile material under impact load is commonly called ________
a) Static toughness
b) Impact strength
c) Notch-bar toughness
d) Fracture energy

Explanation: The energy absorbed by a notched test bar of a ductile material under impact load is commonly called Notch-bar toughness. The energy absorbed by the material at fracture is a measure of impact strength. It is also called impact toughness.

7. The transition temperature is found to be ________ as the grain size decreases.
a) Increasing
b) Decreasing
c) Remaining constant
d) First increasing then decreasing

Explanation: The transition temperature is found to be decreasing as the grain size decreases. Yield strength is a function of grain size. It is related by the Hall-Petch relationship.

8. Value of ϒm will decrease if _________
a) Increase in number of unpinned dislocation sources
b) Increase test temperature
c) Increase crack velocity
d) Blunting of crack

Explanation: ϒm is plastic work done around the crack. It will decrease if crack velocity is increased. It will enhance with an increase in test temperature.

9. What does an increase in temperature causes?
a) Increase in PN stress
b) Decrease in dislocation velocity
c) Increase in fracture energy
d) Decrease in slip planes.

Explanation: With an increase in temperature, fracture energy increases. It is because of the decrease in P-N stress. It also increases dislocation velocity.

10. Which element decreases DBTT of steel?
a) Ni
b) Mn
c) Al
d) Mo

Explanation: Mn content when increased 0.10%, lowers DBTT by 5°C. P, Si and O raise the DBTT of steel. Carbon also raise the DBTT.

11. What is aluminum responsible for in steel?
a) Decrease notch toughness
b) Deteriorate strength
c) Lower oxygen content
d) Increase growth strength

Explanation: Aluminium combine with oxygen and nitrogen. It creates aluminum nitride. It enhances the rate of nucleation and strength.

12. Which element increases DBTT of steel?
a) Ni
b) Mn
c) Al
d) Mo

Explanation: Molybdenum raises DBTT of steel. Ni and Mn lowers DBTT. Al combines with Nitrogen and lower DBTT.

13. Strain ageing raises the DBTT.
a) True
b) False

Explanation: Strain ageing raises the DBTT of steel. It reduces tensile ductility and notch toughness of low carbon steel.

Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.

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