# Mechanical Behaviour Questions and Answers – Composite Strengthening

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

1. Reinforcement of SiC fibers increases fracture toughness of glass ceramic to about ____________
a) 2 times
b) 3 times
c) 4 times
d) 5 times

Explanation: Glass ceramics have fracture toughness 8.2 MPa m-1/2. When reinforced with SiC fibers, it becomes 17.6 MPa m-1/2. It is almost twice.

2. Reinforcement of fibers of SiC improve flexural strength of glass ceramic to almost ____________
a) 2 times
b) 3 times
c) 4 times
d) 6 times

Explanation: Glass ceramics have a flexural strength of 206 MPa. While reinforcing, it becomes 826 MPa. It is 4 times improved.

3. What is an effect of an increase in diameter of fiber on strength?
a) Increases linearly
b) Decreases linearly
c) Remains constant
d) Increases non-linearly

Explanation: With the increase in the diameter of fiber the strength of the overall composite decreases linearly. It is due to the concentration of defects or flaws in the fibers.

4. What is the concentration of particles by volume in dispersion strengthened composites?
a) Less than 1%
b) 1 – 15%
c) 15-20%
d) 25-30%

Explanation: The concentration of dispersoids greatly affect the properties of composite. It is kept in between 1-15%. On further increase it can deteriorate mechanical properties.

5. What is the size range in dispersoids in dispersion strengthened composites?
a) Less than 1 nm
b) 1 – 10 nm
c) 0.01 – 0.1 µm
d) 0.1 – 1 µm

Explanation: Dispersoids in composites vary in size from 0.01 to 0.1 µm. Their size is an important factor for mechanical properties. Fine size dispersoids provide better properties.
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6. Which composite is used in electrical contact materials?
a) Ag-CdO
b) Pt-ThO2
c) Pb-PbO
d) Be-BeO

Explanation: Ag-CdO system is used in electrical contact materials. This is because of their anti-spark property. Be-BeO is used in aerospace and nuclear reactor.

7. Which composite system is used in making bulb filaments?
a) Be-Beo
b) Ag-CdO
c) W-ThO2
d) Co-ThO2

Explanation: W-ThO2 is important material for making bulb filaments. ThO2 is used as dispersoids. Tungsten is an electrical resistant matrix.

8. The composite of metal matrix and ceramic materials as reinforcement are known as ___
a) Dispersoids
b) Cermets
c) Metalloids
d) Vicalloy

Explanation: Composites comprising ceramic reinforcement in metal matrix are referred to as cermets. Most common ceramics used are SiC, B4C, Al2O3 and TiC. These have high temperature properties.

9. What is the size of particulates in particular composites?
a) 0.1 – 1 µm
b) 1 – 50 µm
c) 50 – 100 µm
d) Higher than 100 µm

Explanation: Size of particulates is 1 to 50 µm. It is higher than the size of dispersoids. Here load is taken by both matrix and particles.

10. Fibers for which l >> lc are known as ____
a) Continues
b) Discontinuous
c) Random
d) Alligned

Explanation: Fibres having l >> lc are known as continuous. While those with l < lc are discontinuous. Here l and lc are length and critical length for fibers.

11. The ability to carry the applied load is doesn’t depend on the length of fiber.
a) True
b) False

Explanation: The load which can be carried by fiber, depends on its length also. The length of fiber must exceed a critical value for effective performance. Critical length is shown as lc.

12. Strength of the composite depends on the strength of the fibers.
a) True
b) False

Explanation: For higher strength composite strength of fibers should be high. The volume content of the fiber phase should be high.

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