This set of Mechanical Behaviour Question Paper focuses on “Toughening in Ceramics”.
1. What is the reason for limited applications of ceramics in structural applications?
a) Brittle nature
b) Poor surface finish
c) Poor aesthetic
d) Less tensile strength.
View Answer
Explanation: Brittle nature is the main problem in ceramics. Structural applications require some ductility. Brittle ceramics undergo catastrophic failure.
2. What is the relation between critical fracture stress and flaw size?
a) σfr α a
b) σfr α a2
c) σfr α 1/a
d) σfr α 1/(a)1/2
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Explanation: σfr α Eϒ/ (a)1/2. Here, E is the elastic modulus. Fracture surface energy is ϒ and a is the flaw size.
3. What is an example of alloyed ceramic?
a) Pewter
b) Sialon
c) Monel
d) Amalgam
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Explanation: Pewter is an alloy of tin, copper and antimony. Monel is alloy of Nickel and Copper. Sialon is alloyed ceramic of Si3N4 and other ceramics.
4. What is on X and Y axis on R-curves?
a) Stress intensity factor versus crack length
b) Fracture surface energy versus crack length
c) Critical fracture stress versus elastic modulus.
d) Critical fracture stress versus fracture strength
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Explanation: The stress intensity factor (toughness) is showed as K. It is taken on the Y axis. Crack length is taken on X-axis of R-curves.
5. Which material shows a gradual rising R-curve with failure governed by R-curve behaviour?
a) High toughness and strength
b) High toughness / low strength
c) Low toughness / strength
d) Low toughness and strength
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Explanation: Materials are of 2 types. High toughness/low strength and low toughness/high strength. The former one shows gradual rising R-curve with failure governed by R-curve behaviour.
6. Which materials show steeply rising R-curve?
a) High toughness and strength
b) High toughness / low strength
c) Low toughness / strength
d) Low toughness and strength
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Explanation: Materials are of 2 types. High toughness/low strength and low toughness/high strength. The later ones show steeply rising R-curve and failure occurs in accordance with the Griffith theory.
7. In which technique ceramics are toughened by incorporation of second phase whiskers?
a) Crack deflection
b) Transformation
c) Crack bridging
d) Microcrack
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Explanation: Crack deflection occurs at grain boundaries. This is because the stress is no longer normal to the crack plane. Whiskers are also used for deflection.
8. In what temperature range zirconia is cubic?
a) Below 1100˚C
b) 1100-2360˚C
c) 2360-2680˚C
d) Above 2680˚C
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Explanation: Zirconia has a cubic structure from 2360 to 2680˚C. 2680˚C is the melting point of zirconia. This cubic structure is of CaF2 type.
9. What is the structure of zirconia in a temperature range of 1100 to 2360˚C?
a) Monoclinic
b) Cubic
c) Tetragonal
d) Hexagonal
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Explanation: Zirconia solidifies as cubic FCC structure at 2680˚C. At 2360˚C, it undergoes phase transformation. Its structure changes to distorted tetragonal.
10. What is the volume % change in a transformation from tetragonal to monoclinic?
a) 1
b) 2
c) 3
d) 4
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Explanation: The phase transformation causes 3% volume change. It is anisotropic. It causes the development of cracks.
11. R-curve behaviour is a material related property.
a) True
b) False
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Explanation: R-curve behaviour is not a material related property. It depends on geometry.
12. Microcracks can be used to toughen the ceramics.
a) True
b) False
View Answer
Explanation: In microcrack toughening, microcracks are introduced in the controlled amount. It is done by interval stresses during their processing. These cracks blunt the crack tip.
Sanfoundry Global Education & Learning Series – Mechanical Behaviour & Testing of Materials.
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