# Mechanical Behaviour Questions and Answers – Elastic Deformation

This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Elastic Deformation”.

1. If the material recovers the original dimensions, when an external load is removed, this deformation is known as ______ deformation.
a) plastic
b) permanent
c) elastic
d) irreversible

Explanation: If the applied load is small, the material deforms temporarily. The material recovers its original dimensions on the removal of a load in such case. This type of deformation is known as elastic deformation.

2. The negative ratio between the lateral strain and the direct tensile strain is known as ______
a) True strain
b) Engineering strain
c) Poisson’s ratio
d) Elastic modulus

Explanation: The negative ratio between the lateral strain and the direct tensile strain is called Poisson’s ratio. Its range is in between 0.25 and 0.50.

3. What is the relation between shear modulus (G) and elastic modulus (E)?
a) G = E
b) G = 0.35 E
c) G = 0.50 E
d) G = 0.75 E

Explanation: G and E are related as G = E/2 (1 + v). Here v is Poisson’s ratio, which varies between 0.25 and 0.50. On approximation of this relation, we get G = 0.35 E.

4. What is the expression for bulk modulus?
a) E/2(1 + v)
b) E/3(1 – 2v)
c) E/ (1 – 2v)
d) E/3(1 + v)

Explanation: Bulk modulus is reciprocal of compressibility of material. It is expressed as K = E/3(1 – 2v). Here E is elastic modulus and v is Poisson’s ratio.

5. Compressibility is reciprocal of _____
a) Shear modulus
b) Elastic modulus
c) Bulk modulus
d) Poisson’s ratio

Explanation: Bulk modulus (K) is a reciprocal of compressibility. Compressibility is represented by β. Hence K = 1/ β.
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6. _____ is an anisotropic property of a crystal.
a) Elastic modulus
b) Density
c) Poisson’s ratio
d) Damping

Explanation: Elastic modulus is an anisotropic property of a crystal. Its value varies with crystal directions. While Poisson’s ratio, damping and density are isotropic properties.

7. What is the value of elastic modulus of graphite in the direction parallel to sheets?
a) 8 GPa
b) 400 GPa
c) 580 GPa
d) 950 GPa

Explanation: Elastic modulus of graphite is observed differently in different directions. It is 950 GPa in direction parallel to sheets. While the average value in all directions is 8 GPa.

8. The restoring force depends on _____
a) Interatomic bond strength
b) Melting point
c) Crystallization
d) Thermal conductivity

Explanation: To produce a given strain, a larger load is required for a higher strain. The restoring force depends on strength of interatomic bonds. As strength increases, restoring attractive forces also increase.

9. What is the reason for elastic deformation?
a) Dislocations intersection
b) Twinning
c) Slip
d) Displacement of atoms to a fraction interatomic distance

Explanation: On application of small amount of load, atoms may displace to a fraction of interatomic distance. It is known as elastic deformation. On removal of load, atoms come to their equilibrium positions.

10. Elastic modulus can’t be changed by ______
a) alloying
b) cold working
c) heat treatment
d) by increasing section thickness

Explanation: Heat treatments are unable to change the elastic modulus significantly. It is because it only changes the slightly atomic spacing. Drastic change in alloy composition can increase elastic modulus.

11. By altering composition or heat treatment, elastic modulus can be increased to very high orders.
a) True
b) False

Explanation: Alternation in a composition can only change elastic modulus to a small level. Heat treatment is unable to improve elastic modulus of material significantly. They both can increase the elastic modulus only less than 10%.

12. For higher intermolecular bond strength, value of elastic modulus is higher.
a) True
b) False

Explanation: Modulus of elasticity is a measure of the stiffness of a material. For higher intermolecular bond strength, stiffness increases. Value of elastic modulus is also observed higher.

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