Advanced Composite Materials: Structure and Reinforcement Types

Understanding Composite Materials

Composites are formed when two or more distinct materials combine to yield a combination of properties superior to those obtainable from the original constituent materials alone. These materials are selected to provide unusual combinations of characteristics, such as:

• Stiffness and strength
• Weight reduction
• Performance at high temperatures
• Corrosion resistance
• Hardness or conductivity

Classification of Composites

Composites can involve various material combinations, including metal-metal, metal-ceramic, metal-polymer, ceramic-ceramic, or polymer-polymer. They are typically classified into three primary categories:

1. Particulate composites
2. Fiber composites
3. Laminar composites

Particle-Reinforced Composites (PRCs)

In particle-reinforced composites, particles of a hard and brittle material are dispersed uniformly and surrounded by a softer, ductile matrix. PRCs are generally divided into two main categories:

1. Dispersion-hardened composites
2. True particulate composites

Dispersion-Hardened Composites (DHCs)

The particles in dispersion-hardened composites are extremely small, often cited with diameters in the range of 100–2500 microns (though context implies very fine particles). Because these fine particles impede the movement of dislocations, they produce a pronounced hardening effect, requiring only small amounts of the dispersed material.

At normal temperatures, dispersion-hardened composites are stronger than most metal alloys. However, the strength of the composite gradually decreases as the temperature increases. By contrast, their thermal creep resistance is significantly higher than that of pure metals and alloys.

True Particulate Composites

These composites contain large amounts of coarse particles that effectively hinder sliding and movement within the material structure. True particulate composites include many combinations of metals, ceramics, and polymers, and they are specifically designed to produce unusual combinations of properties and improved overall strength.

Fiber-Reinforced Composites (FRCs)

Fiber-reinforced composites are engineered to improve resistance to stress, fatigue, stiffness, and the strength-to-weight ratio. This is achieved through the introduction of strong, rigid, and often brittle fibers within a softer, ductile matrix.

The functional roles of the components are distinct:

• The matrix material transmits the applied force to the fibers and provides necessary ductility and toughness.
• The fibers carry the majority of the applied load.

Unlike dispersion-hardened composites, the resistance of fiber-reinforced composites increases significantly both at room temperature and at elevated temperatures. A wide variety of fiber-reinforced materials are employed across numerous industries.