Composite Materials MCQ with answer and solution

Concept

Compressive strength of structural ceramics

Formula

NONE

Step-by-step solution

1. Ceramics feature strong ionic and covalent bonds that resist lattice deformation under compressive forces. 2. Under compression, internal micro-cracks and flaws are squeezed shut, allowing the full intrinsic lattice strength to be developed. 3. Under tension, however, stress concentrations at flaw tips induce rapid brittle crack propagation. 4. As a result, compressive strength is characteristically high in ceramics relative to metals. Answer: B

Explanation

Ceramics possess rigid ionic and covalent chemical bonds that provide exceptional resistance to compressive stress and indentation. Because compressive loading tends to close micro-cracks rather than open them, ceramics exhibit compressive strengths far exceeding those of common structural metals. Conversely, their tensile capacity remains poor due to flaw-induced brittle fracture.

Why the other options are wrong

A) Tensile strength of ceramics is typically only 10% of their compressive strength due to flaw sensitivity. C) Ceramics exhibit virtually zero ductility because dislocations cannot move easily through ionic lattices. D) Fracture toughness is inherently low in ceramics, rendering them brittle under impact.

Shortcut

Ceramics = Very high compressive strength, but weak and brittle in tension.

Common mistake

Assuming ceramics have high fracture toughness or tensile strength due to their hardness.