Mechanical Behaviour Questions and Answers – The Shear Strength of Ideal and Real Crystals

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This set of Mechanical Behaviour Questions and Answers for Freshers focuses on “The Shear Strength of Ideal and Real Crystals”.

1. The internal energy of crystal ___________ if atoms are displaced from their mean position.
a) Rises
b) Decreases
c) Remains constant
d) Varies independently
View Answer

Answer: a
Explanation: In a perfect crystal all atoms occupy equilibrium positions. This arrangement possesses minimum energy. This energy increases with the displacement of atoms from these positions.
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2. In a perfect crystal, shear stress is __________
a) Very high
b) Negative
c) Zero
d) Very low
View Answer

Answer: c
Explanation: Shear stress is the component of stress. In a perfect crystal, not displacement takes place. So shear stress is zero.

3. ____ stress increases from the force vector component which is parallel to the material cross section.
a) Normal
b) Shear
c) Tensile
d) Yield
View Answer

Answer: b
Explanation: Shear stress is denoted τ. It arises from the force vector component which is parallel to the cross section. Normal stress (σ) arises from the force vector component perpendicular to the cross section.

4. What is SI unit of shear stress?
a) Pa
b) N
c) psi
d) gm.cm-1s-2
View Answer

Answer: a
Explanation: Shear stress his ratio of the force applied to the cross sectional area. So the unit is N/m2 or Pa. psi is avoirdupois unit.

5. Which symbol is used to denote shear stress?
a) σ
b) τ
c) ε
d) e
View Answer

Answer: b
Explanation: Shear stress is denoted as τ. Normal stress is denoted by σ. True strain and engineering strain is denoted by ε and e.
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6. What is a theoretical shear strength of perfect crystal?
a) G
b) G/2π
c) G/4π
d) G/8π
View Answer

Answer: b
Explanation: The maximum shear stress required for plastic deformation in a perfect crystal is G/2π. It is known as theoretical shear strength of perfect crystal. Here G is shear modulus.

7. What is the range of theoretical shear strength of ductile metals?
a) 1 to 10 GPa
b) 2 to 20 GPa
c) 10 to 100 GPa
d) 20 to 200 GPa
View Answer

Answer: b
Explanation: Theoretical shear strength is given by G/2π. Shear modulus (G) of ductile metals is 10 to 100 GPa. It gives the theoretical strength of 2 to 20 GPa.

8. What is a theoretical shear strength of brass perfect crystal?
a) 5 GPa
b) 6 GPa
c) 8 GPa
d) 10 GPa
View Answer

Answer: b
Explanation: Shear modulus of brass is 40 GPa. By using G/2π, theoretical shear strength comes out to be 6 GPa.

9. Shear stress is a function of the displacement.
a) True
b) False
View Answer

Answer: a
Explanation: Shear stress changes with increasing displacement of atoms. This displacement is due to external energy. This energy may be in form of thermal energy or mechanical work.

10. Real crystals deform at theoretical shear strength.
a) True
b) False
View Answer

Answer: b
Explanation: Real crystals deform at much lower values than theoretical shear strength. It is due to the presence of defects. The important defect is dislocation here.
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Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.

To practice all areas of Mechanical Behaviour for Freshers, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn