Composites

A composite is a class of materials that combines different materials with the objective of getting more desirable combinations of properties.

Introduction:

Isotropic Material:

Isotropic material has properties that are the same in all directions. For example, the Young’s modulus of steel is the same in all directions.

Anisotropic Material:

At a point in an anisotropic material, material properties are different in all directions.

Composite Materials Main Structure:

A composite is a structural material that consists of two or more combined constituents that are combined at a macroscopic level and are not soluble in each other. One constituent is called the reinforcing phase and the one in which it is embedded is called the matrix. The reinforcing phase material may be in the form of fibers, particles, or flakes. The matrix phase materials are generally continuous. Examples of composite systems include concrete reinforced with steel and epoxy reinforced with graphite fibers, etc.

-Types of Matrices:

- Types of Reinforcements:

Composite related terminologies and general classification:

Matrix: The continuous phase.

Reinforcement: The dispersed phase.

Interface: Two dimensional plane between reinforcement and matrix

Interphase: Coated phase.

Polymer Matrix Composite:

In the way to reduce weight and improve the mechanical properties by use a weak polymer matrix with a stronger reinforcement, the polymer matrix composite is used. Polymer Matrices: It is divided into two types:

- Thermoplastics.

- Thermosets.

1- Thermoplastic: a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling.

Properties:

- High fracture toughness.

- Excellent damping characteristics.

- Processing techniques require further development.

Some of thermoplastic materials: Polyether ether ketone (PEEK), Polyphenylene Sulfide (PPS), Polysulfone.

2- Thermoset : is a plastic that is irreversibly cured from a soft solid or viscous liquid prepolymer or resin. Most widely used polymer matrix material.

Properties:

- High service temperatures.

- Better flame resistance.

- Relatively low strain to failure.

Some of thermoset materials: Epoxy, Polyester, Vinyl ester. Epoxy is the most widely thermoset polymer that used as a polymer matrix for polymer matrix composite products.

Reinforcements :

Fiber reinforced is the most widely used in polymer matrix composites industry. It divided into two types: Continuous and discontinuous fiber.