Composite Materials free study notes for Diploma / BTech

1. Introduction

Composite materials are engineered materials made by combining two or more distinct materials to achieve superior properties that individual materials cannot provide alone.

Key Idea

• One material acts as reinforcement (strength provider)
• Another acts as matrix (binder/support)

Examples

• Fiberglass
• Reinforced concrete
• Carbon fiber composites

2. Structure of Composite Materials

6

Main Components

1. Matrix Phase
   • Continuous phase
   • Holds reinforcement together
   • Transfers load
2. Reinforcement Phase
   • Discontinuous phase
   • Provides strength and stiffness

3. Classification of Composite Materials

(A) Based on Reinforcement Type

1. Fiber Reinforced Composites (FRC)

• Fibers embedded in matrix
• Types:
  • Glass fiber (GFRP)
  • Carbon fiber (CFRP)
  • Aramid fiber (Kevlar)

2. Particle Reinforced Composites

• Particles distributed in matrix
• Example: Concrete

3. Laminar (Layered) Composites

• Layers bonded together
• Example: Plywood

4. Classification Based on Matrix Material

(A) Polymer Matrix Composites (PMC)

• Lightweight
• Examples: Fiberglass

(B) Metal Matrix Composites (MMC)

• High strength and temperature resistance
• Example: Aluminum reinforced with SiC

(C) Ceramic Matrix Composites (CMC)

• High temperature resistance
• Used in aerospace

5. Properties of Composite Materials

Mechanical Properties

• High strength-to-weight ratio
• High stiffness
• Improved fatigue resistance

Thermal Properties

• Good heat resistance (especially CMCs)
• Low thermal expansion

Chemical Properties

• Corrosion resistant

6. Advantages of Composites

• Lightweight
• High strength
• Tailorable properties
• Corrosion resistance
• Better fatigue performance

7. Disadvantages of Composites

• High manufacturing cost
• Difficult to repair
• Complex fabrication
• Anisotropic properties (vary with direction)

8. Manufacturing Processes

6

Common Methods

1. Hand Lay-Up
   • Simple method
   • Used for large structures
2. Filament Winding
   • Fibers wound on mandrel
   • Used for pipes and tanks
3. Pultrusion
   • Continuous process
   • Produces uniform cross-section
4. Resin Transfer Molding (RTM)
   • Resin injected into mold

9. Applications of Composite Materials

Aerospace

• Aircraft wings
• Spacecraft structures

Automotive

• Car body parts
• Lightweight components

Construction

• Reinforced concrete
• Structural panels

Marine

• Boat hulls

Sports

• Bicycles, rackets

---

10. Comparison with Conventional Materials

Property	Composites	Metals	Ceramics
Weight	Very low	Medium	Medium
Strength	High	Moderate	High (brittle)
Corrosion	Excellent	Poor	Excellent
Cost	High	Moderate	Moderate

11. Key Concepts

(A) Specific Strength

$$\text{Specific Strength} = \frac{\text{Strength}}{\text{Density}}$$Specific Strength=DensityStrength​

(B) Anisotropy

• Properties depend on direction
• Important in fiber composites

12. Failure Mechanisms

• Fiber breakage
• Matrix cracking
• Delamination (layer separation)

---