Chapter 7, Problem 7.1P

Interpretation Introduction

Interpretation:

The effect on toughness of alumina ceramic when SiC fiber having low toughness brittle ceramic is embedded within Alumina needs to be explained.

Concept introduction:

Alumina is brittle and has low toughness. Silicon carbide is a compound of carbon and silicon produced at very high temperature.

Answer to Problem 7.1P

When silicon carbide (sic) fibers are embedded within the alumina, its toughness improves due to the interface between fiber and alumina matrix.

Explanation of Solution

Ceramics materials are brittle in nature and have low tensile strength and toughness which makes them weaker.

There is a tendency of crack formation. When a tensile force is applied on ceramic material, cracks in the structure get elongated. When crack grows, energy gained by cracks increases and then gets absorbed by the material.

But when these ceramics are embedded with fibers like silicon carbide, the toughness of ceramic matrix increases.

Ceramic matrix composites are the materials in which ceramics are embedded with reinforcement these matrix having low toughness.

Also, if the bonding between matrix and fiber is sufficiently bad, the fibers are pulled out of matrix consuming energy.

The stress intensity factor, k is calculated as follows:

$k=f\sqrt{\pi a}$

From the formula, stress intensity factor k is directly proportional to tensile strength. This means, if tensile stress increases, the value of k also increases.

Silicon carbide has a higher tensile strength than alumina. Hence if we embed the SiC with alumina, it will result in higher tensile strength.

Thus, toughness will increase with an increase in tensile strength.

Conclusion

Thus, it can be stated that silicon carbide embedded with alumina so as to increases the toughness of the alumina ceramic matrix.