This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Metal Matrix Composites”.
1. Which is not a general classification of Metal Matrix Composites (MMC)?
a) Fiber-reinforced MMC
b) Particulate-reinforced MMC
c) SiC-reinforced MMC
d) In situ MMC
View Answer
Explanation: The Metal Matrix Composites can be generally divided into 4. They are Fiber-reinforced MMC, Particulate-reinforced MMC, Dispersion-strengthened MMC and In situ MMC. SiC-reinforced MMC is an MMC that is reinforced with Silicon carbide fibers specifically.
2. Which type of MMC contains either continuous or discontinuous fiber reinforcements?
a) Particulate-reinforced MMC
b) Fiber-reinforced MMC
c) In situ MMC
d) Dispersion-strengthened MMC
View Answer
Explanation: The fiber-reinforced MMC can be classified as continuous fiber MMC and discontinuous fiber MMC. In Continuous fiber MMC fibers are embedded in a certain direction in the matrix whereas fibers are aligned in different directions in the second category.
3. Which MMC contains platelet type reinforcements?
a) In situ MMC
b) Dispersion-strengthened MMC
c) Particulate-reinforced MMC
d) Fiber-reinforced MMC
View Answer
Explanation: Particulate-reinforced MMC contains either platelets or particles that vary in size from 0.5 to 100 mm. The particulates can be embedded into the metal matrix to higher volume fractions than the whiskers.
4. Dispersion-strengthened MMC contains particles that are greater than 0.1 μm diameter.
a) True
b) False
View Answer
Explanation: Dispersion-strengthened MMC contains particles that are less than 0.1 μm in diameter. A dispersion-strengthened composite is one in which tiny particles are uniformly dispersed in the matrix in order to enhance the strength and other properties.
5. What is the main reason for the limited use of boron fiber-reinforced MMC’s?
a) High-cost
b) Non-compatibility in most applications
c) Complex manufacturing process
d) Difficulty to control the chemical reaction
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Explanation: Boron fiber-reinforced MMCs have been developed for 20 years. However, their use is limited due to difficulty in controlling the chemical reaction between the molten metal and fibers. The mechanical properties of the composite get worsened due to the formation of a brittle phase resulting from the chemical reaction.
6. Which is not a characteristic of Silicon carbide(SiC)?
a) Less prone to oxidation reaction
b) Less expensive
c) Thermal conductivity
d) Low melting point
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Explanation: SiC is very cheap compared to carbon and boron fibers. They have a very high melting point of 2830°C and have good thermal conductivity. Furthermore, Silicon carbide is less prone to oxidation reaction even at higher processing temperatures.
7. The modulus of metals is an order of magnitude higher than that of polymers.
a) True
b) False
View Answer
Explanation: Metals are capable of undergoing strain hardening and large plastic deformation after yielding. In fact, metals exhibit higher fracture toughness and strain to failure than polymers matrices.
8. For brittle fiber MMCs, the composite strength is limited by fiber fracture.
a) True
b) False
View Answer
Explanation: Since the composite strength is limited by fiber fracture in brittle fiber MMCs, the MMCs will fail as soon as the composite strain reaches the fiber failure strain. SiC fiber-reinforced alloys are an example of brittle fiber MMCs.
9. Which is inversely proportional to the reinforcement volume fraction?
a) Tensile modulus
b) Strain to failure ratio
c) Yield strength
d) Tensile strength
View Answer
Explanation: The strain-to-failure decreases with increasing reinforcement volume fraction. Usually, at volume fractions below 15%, the MMC shows brittle character while at 30% to 40% it exhibits ductile behaviour.
10. Tungsten fiber-reinforced copper alloys are ductile fiber MMCs.
a) True
b) False
View Answer
Explanation: In ductile fiber MMCs, the fiber also plastically deforms and yields with the matrix. Moreover, unless the fiber fails by necking, the MMC strength is limited by the fiber failure strain which enables the ductile property. Beryllium fiber-reinforced aluminium alloys are also an example of ductile fiber MMCs.
Sanfoundry Global Education & Learning Series – Composite Materials.
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