This set of Composite Materials Multiple Choice Questions & Answers (MCQs) focuses on “Carbon Matrix Composites”.
1. Which type of composite consists of carbon fibers embedded in a carbonaceous matrix?
a) Metal matrix composites
b) Ceramic matrix composites
c) Carbon matrix composites
d) Polymer matrix composite
View Answer
Explanation: The carbon matrix composite is also referred to as carbon-carbon(C-C) composites since it consists of a carbon matrix embedded with carbon fibers. These composites are widely used in the aerospace industry such as brake pads for aircraft, nozzles for rocket engines and heat shields for spacecraft.
2. Carbon matrix(C-C) composites are thermally stable up to 3000°C in any conditions.
a) True
b) False
View Answer
Explanation: Carbon matrix (CMC) composites are thermally stable up to 3000°C only in a nonoxidative environment. In the presence of oxygen, the composite will oxidize and degrade even at 400-500°C unless it is protected by a surface coating.
3. External coating or internal modification can be done to protect C-C composites against oxidation.
a) True
b) False
View Answer
Explanation: The presence of oxygen will result in oxidation and degradation of the composite at higher temperatures. It can be prevented either by an external coating or an internal modification.
4. Which is an oxide coating?
a) SiC
b) SiO2
c) Si3N4
d) HFB2
View Answer
Explanation: Two types of external coatings are used in the carbon matrix composites. SiO2, Al2O3 are some of the oxide coatings. The oxide coatings are called so because of the presence of oxygen in it. While SiC, Si3N4, and HFB are examples of non-oxide coatings.
5. Low oxygen permeability is the only critical requirement for an external coating.
a) True
b) False
View Answer
Explanation: Thermal expansion matching and low oxygen permeability are the two most critical requirements for the external coating. The thermal expansion mismatch between carbon matrix composite and the external coating will result in breaking of the coating into small pieces from the composite surface due to cracking.
6. The shear strength and modulus of Carbon matrix composites are very low.
a) True
b) False
View Answer
Explanation: It is one of the limitations of the carbon matrix composites. Low oxidation resistance is also another limitation of C-C composites. While the tensile strength, compressive strength and thermal conductivity of these composites are very high.
7. What will result due to the strong bond between fibers and matrix in a carbon matrix composite?
a) Fiber pull-out
b) Energy absorption
c) High fracture toughness
d) Faster composite failure
View Answer
Explanation: In C-C composites, the failure strain of the matrix is lower than that of fibers. So, if a strong bond exists between the carbon matrix and fibers, the failure of the matrix will immediately lead to the failure of fibers and eventually result in the composite failure in a brittle manner.
8. Which is not a factor influencing energy absorption by the composite?
a) Debonding
b) Fiber bridging
c) Fiber fracture
d) Fiber failure
View Answer
Explanation: If the bond strength between the carbon matrix and fiber is weak, the matrix cracking due to low strain will not produce rapid fiber failure. Instead of that, there will be energy absorption due to fiber fracture, fiber pull-out, fiber bridging and debonding. As a result of this energy absorption, the composite will possess high fracture toughness.
9. What is the approximate fracture energy value of a unidirectional C-C(Carbon fiber in carbon matrix) composites?
a) 2×101 J/m2
b) 2×102 J/m2
c) 2×103 J/m2
d) 2×104 J/m2
View Answer
Explanation: The fracture energy value of a fully densified unidirectional C-C composite is about 2×104J/m2. This is a very good range for the fracture energy since that of the premium grade graphite is only less than 102 J/m2.
10. Which among these is a method used for manufacturing C-C composites?
a) Vacuum hot pressing process
b) Liquid infiltration
c) Chemical vapour infiltration
d) Polymer pyrolysis
View Answer
Explanation: The starting material of this process is a carbon fiber preform, which can be unidirectional, bidirectional or multidimensional fabrics. At least 50 wt% of carbon is yielded in this process, by heating the liquid infiltrated preform. In general, the liquid infiltration is used with thick sections of preforms.
Sanfoundry Global Education & Learning Series – Composite Materials.
To practice all areas of Composite Materials, here is complete set of 1000+ Multiple Choice Questions and Answers.
If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]
