This set of Mechanical Behaviour Multiple Choice Questions & Answers (MCQs) focuses on “Strengthening of Ceramics”.
1. In general, ceramics fail under ___________ stress.
Explanation: Ceramics have good shear and compressive strength. While their tensile strength is poor. So these fail under tensile stress.
2. Low tensile strength of ceramics is related to ___________
b) Structural defects
c) Grain boundaries
Explanation: The low tensile strength of ceramics can be correlated to the presence of structural defects. These generate during fabrication. These are pores, voids, surface flaws, inclusions etc.
3. What is the common process of fabrication of ceramics?
Explanation: Ceramics are commonly fabricated by sintering. This may be a liquid or solid phase. Ceramics have very high melting points so melting and casting are difficult.
4. Presence of pores in ceramics ____________ the true cross-section over which the applied load is acting.
c) Doesn’t change
d) Can increase or decrease
Explanation: Pores in ceramic bodies reduces true cross-section over which the load is applied. It is because of empty sites. It reduces UTS of ceramics.
5. The strength ____________ with increasing the volume fraction of pores.
a) Linearly decreases
b) Linearly increases
c) Exponentially increases
d) Exponentially decreases
Explanation: Strength of ceramic is given by:
σp = σ0 exp(-BP)
Where P is volume fraction porosity. Hence strength exponentially reduces with increase in pores.
6. Surface compressive stresses enhance ______________ of ceramic.
a) Thermal shock resistance
d) Grain boundary area
Explanation: Surface compressive stress enhances thermal shock resistance. It causes strengthening. In this process, a surface layer with higher volume than the original matrix is generated.
7. Smaller the grain size ____________ will be the fracture stress.
d) Can’t say
Explanation: Smaller the grain size, finer will be surface flow. Hence, high stress will be required to crack the ceramic. So fracture stress will be higher.
8. __________ glass is thermally strengthened glass.
Explanation: Tempered glass is thermally strengthened glass. Thermal strengthening involves heating glass uniformly to softening temperature then chilling by blast of air or oil.
9. Tempered glass consists __________ stresses at center and _______ at the surface.
a) Tensile, tensile
b) Tensile, compressive
c) Compressive, tensile
d) Compressive, compressive
Explanation: Tempered glass is given quenching and temper treatment. It generates tensile stresses at centre while compressive at surface. It makes it very strong.
10. In following options, what is not a purpose of glazing?
a) Introduce residual surface compressive stress
b) Make ceramic impermeable to liquid
c) Make article attractive
d) Coarsening of grain size
Explanation: Glazing is used to strengthen glass-ceramics. It develops residual compressive stresses. It makes ceramic attractive and impermeable to liquid.
11. Glazes are alumina mixtures.
Explanation: Glazes are silicate mixtures. These are similar to silicate glasses. These are mixed with water to apply on a ceramic body in form of a slip.
12. Ion implantation causes improvement in fracture toughness and fatigue strength.
Explanation: Ion implantation introduces residual compressive surface stresses. These stresses tend to close surface cracks of ceramics and raise their toughness. This also improves fatigue strength.
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