This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Mechanical Properties of Graphene”.
1. Mechanical properties of graphene are not affected by the presence of defects.
a) True
b) False
View Answer
Explanation: Mechanical properties of graphene are highly influenced by the presence of defects in its lattice structure. The presence of grain boundaries in graphene can affect its intrinsic tensile strength. With the increase in the densities of point defects such as vacancies, stone wales etc., there is a huge reduction in the ultimate strength of graphene sheets.
2. Nanocomposites with graphene platelets (GPLs) showcase highly inflated values of fracture toughness. Which among the following is not a toughening mechanism for these materials?
a) Crack deflection
b) Crack decomposition
c) Crack branching
d) Crack bridging
View Answer
Explanation: Graphene is increasingly being used in nanocomposites due to its ultra high strength and fracture toughness. Nanocomposites comprising of graphene platelets exhibit highly enhanced fracture toughness. Infact, GPLs can provide greater toughness to nanocomposites than carbon nanofibres. The toughening mechanism behind this being crack deflection, crack branching and crack bridging.
3. How much is the intrinsic tensile strength of graphene?
a) 130 MPa
b) 130 GPa
c) 130 TPa
d) 130 Pa
View Answer
Explanation: Mechanical properties of graphene strongly depend on its crystal structure and defect configuration. Defect-free, monolayer graphene is observed to be strongest material ever tested. It shows an intrinsic strength of about 130 GPa (19,000,000 psi).
4. Which of the following in polycrystalline graphene is not responsible for the variation in Young’s modulus and fracture strength?
a) Temperature changes
b) Variations in strain rate
c) Decrease in grain size
d) Doping with nitrogen
View Answer
Explanation: The Young’s modulus and fracture strength in polycrystalline graphene are dependent on the temperature and strain rate. Moreover, there is a decrease in these mechanical properties when grain size is reduced from 10nm to 2.5nm.
5. Why are flat graphene sheets unstable with respect to scrolling?
a) Large surface energy and in-plane ductility
b) Small surface energy and out of plane ductility
c) Large surface energy and out of plane ductility
d) Small surface energy and in-plane ductility
View Answer
Explanation: Graphene scrolls are one dimensional nanomaterials that are similar to the multi-walled carbon nanotubes. These scrolls are cylindrical in shape. Flat graphene sheets are unstable with respect to scrolling because of its large surface energy and out of plane ductility.
6. What property in graphene is used for designing polycrystalline graphene with tuned folded structure?
a) Complicated arrangement
b) Compression parallel to grain boundaries
c) Enhanced bending of graphene sheets
d) Spatially inhomogeneous folded structures
View Answer
Explanation: In graphene, compression perpendicular to grain boundaries can actually enhance the bending of the sheets along grain boundary lines. This feature can be utilized in designing polycrystalline graphene samples having tuned folded structures.
7. Choose the incorrect statement from the following options.
a) In-plane σ bonds in graphene reduce tensile strength heavily
b) Elastic modulus of graphene decreases with increase in single vacancies
c) Defect-free graphene exhibits ultra-high elastic modulus
d) Wrinkles enhance adhesion between graphene and the underlying substrate
View Answer
Explanation: Monolayer graphene that is free from defects exhibit ultra-high modulus and elevated tensile strength. This can be attributed to the extremely strong in-plane σ bonds between neighbouring carbon atoms in graphene lattice.
8. Young’s modulus changes heavily when stone walls defects in graphene are in close neighbourhood of each other.
a) True
b) False
View Answer
Explanation: Point defects such as stone walls and vacancies greatly influence the Young’s modulus and strength of graphene. There is a dramatic change in these mechanical properties when the neighbouring defects are in proximity and are interacting with each other. This is more pronounced when the distance between the adjacent defects is smaller than 2nm.
9. What is the reason behind the enhancement of the mechanical properties of Ni-graphene composites?
a) Prevention of dislocation sliding in nickel
b) Poor interaction between nickel and graphene
c) Target substrate is smooth
d) Increase in dislocation sliding in nickel
View Answer
Explanation: Nickel-graphene composites have been prepared by the incorporation of graphene nanosheets into a nickel matrix through a plating process. The mechanical properties of these composites are increased because of the high interaction between nickel and graphene and also due to the prevention of dislocation sliding in nickel matrix by graphene.
10. Young’s modulus for graphene corresponds to which of the following options?
a) 5.0 ± 0.2 TPa
b) 1.0 ± 0.1 TPa
c) 100.0 ± 0.5 TPa
d) 150.0 ± 0.9 TPa
View Answer
Explanation: Young’s modulus of a solid material measures its stiffness. It is defined by the ratio of longitudinal stress and strain in a material. Young’s modulus value of graphene is observed at 1.0 ± 0.1 TPa (nearly 150,000,000psi), assuming an effective thickness of 0.335nm.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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