Advanced structural ceramics (like alumina or silicon carbide) possess exceptional compressive strength, hardness and thermal resistance. However, their structural application is heavily limited by their inherent lack of which property?
- AChemical inertness
- BFracture toughnessCorrect
- CDielectric strength
- DModulus of elasticity
Solution
Concept
Fracture toughness of structural ceramics
Formula
KIc = Y × σ × \√(π × a)
Step-by-step solution
1. Advanced structural ceramics (such as alumina, silicon carbide, and silicon nitride) feature high hardness and compressive strength. 2. However, the lack of mobile dislocation systems prevents plastic energy dissipation at crack tips. 3. This low resistance to crack propagation is quantified by low fracture toughness (KIc), leading to catastrophic brittle failure. 4. Hence, their structural application is heavily limited by their inherent lack of fracture toughness. Answer: B
Explanation
Structural ceramics possess covalent and ionic atomic bonds that provide exceptional hardness, compressive strength, and high melting points. However, because their crystal lattices contain no active dislocation slip systems to absorb crack-tip stresses, their fracture toughness is inherently very low. This deficiency makes structural ceramics highly sensitive to microscopic surface defects and prone to catastrophic brittle failure.
Why the other options are wrong
A) Chemical inertness is an outstanding advantage of ceramics, not a limitation. C) Dielectric strength in electrical ceramics is high and desirable for insulation. D) Modulus of elasticity of ceramics is very high, often exceeding structural steel.
Shortcut
Ceramics = High hardness and compressive strength, but low fracture toughness (brittle).
Common mistake
Selecting chemical inertness or elastic modulus, which are actually exceptionally high in structural ceramics.
Correct answer: B) Fracture toughness