# Mechanical Behaviour Questions and Answers – Structure-Mechanical Property Relation

This set of Mechanical Behaviour Interview Questions and Answers focuses on “Structure-Mechanical Property Relation”.

1. Mechanical properties of single phase alloys cannot be improved by ____________
a) Cold working
b) Thermomechanical treatment
c) Heat treatment
d) Grain refining

Explanation: Only one phase is present on the wide range of temperature in single phase alloys. So microstructure can’t be changed by heat treatment. Cold working, thermomechanical treatment and grain refining can change their properties.

2. Second phase present as a continuous network at grain boundaries, gives ___________
a) Ductility
b) Toughness
c) Brittleness
d) Corrosion resistance

Explanation: When the second phase forms a continuous network at grain boundaries, it makes material brittle. This microstructure reduces ductility, toughness and corrosion resistance of the alloy. This brittleness increases with amount of the second phase.

3. Which microstructure possesses the best combination of ductility and toughness?
a) Second phase along grain boundaries
b) Second phase at grain boundaries
c) Second phase within the matrix
d) Second phase uniformly distributed throughout matrix

Explanation: Best microstructure should consist uniform distribution of second phase throughout the matrix. Presence of second phase on or along grain boundaries introduces brittleness. This causes a reduction in ductility and toughness.

4. Which shape of second phase particles is preferred?
a) Flakes
b) Nodules
c) Spheroids
d) Plates

Explanation: Spherical shaped second phase particles give the best mechanical properties. Flakes, nodules and plates shaped, on the other hand, act as internal notches. These reduce the toughness of a material.

5. Single phase alloys have better _____ properties than their respective pure metals.
a) Electrical
b) Thermal
c) Mechanical
d) Formability

Explanation: Single phase alloys have better mechanical properties than pure metals. It is due to solid solution strengthening. Electrical, thermal and formability properties of pure metals are generally higher.
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6. Which property deteriorates with a decrease in grain size?
a) Ductility
b) Tensile strength
c) Fatigue
d) Creep

Explanation: With a decrease in grain size, creep strength of material deteriorates. It is because the grain boundary area becomes weaker on high temperatures. Ductility, tensile strength and fatigue strength improve with grain refinement.

7. Which property is measured to decide the density of point defects?
a) Electrical resistivity
b) Fatigue strength
c) Malleability
d) Toughness

Explanation: Point defects greatly affect electrical resistivity of the material. This is a basis of doping process in semiconductors. With an increase in temperature, vacancies increase and electrical conductivity of semiconductors increases.

8. Which one is structure sensitive property?
a) Melting point
b) Density
c) Specific heat
d) Ductility

Explanation: Ductility is a structure sensitive property. It depends on microstructure, grain size and second phase particles’ shape. Density, melting point and specific heat are structure insensitive properties.

9. Which one is structure insensitive property?
a) Fracture strength
b) Yield strength
c) Elastic modulus
d) Electrical conductivity

Explanation: Elastic modulus is a structure insensitive property. It only changes when a drastic change in composition is done. Fracture strength, yield strength and electrical conductivity are structure sensitive properties.

10. Finer the spheroid second phase particles, better are the mechanical properties.
a) True
b) False

Explanation: With the fineness, the distribution in matrix increases. Thus these particles provide more resistance to dislocation motion and retain good tensile strength. These particles also retain good ductility.

11. At elevated temperatures, single phase materials are preferred.
a) True
b) False

Explanation: At elevated temperatures, two or more phase microstructures are preferred. Dispersed second phase particles provide good thermal stability. These also improve creep properties.

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