Composite materials

Composite materials, often shortened to composites, are engineered materials made of two or more constituent materials with different physical or chemical properties which remain separate on a macroscopic level within the finished structure. The physical properties of composite materials are generally not isotropic (independent of direction of applied force) in nature, but rather are typically orthotropic (different depending on the direction of the applied force or load).

In contrast, isotropic materials (for example, aluminum or steel) typically have the same stiffness regardless of the directional orientation of the applied forces and/or moments.

The most primitive man-made composite materials were straw and mud combined to form bricks for building construction. Composites are made up of individual materials known as constituent materials. There are two categories of constituent materials: matrix and reinforcement. At least one portion of each type is required. Wood is a natural composite of cellulose fibers in a matrix of lignin. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials allows the designer of the product or structure to choose an optimum combination.

Engineered composite materials must be formed to shape. The matrix material can be introduced to the reinforcement before or after the reinforcement material is placed into the mold cavity or onto the mold surface. The matrix material experiences a melding event, after which the part shape is essentially set. Depending upon the nature of the matrix material, this melding event can occur in various ways such as chemical polymerization or solidification from the melted state.

A variety of molding methods can be used according to the design requirements. The principal factor affecting the methodology is the nature of the chosen matrix and reinforcement materials. Another important factor is the gross quantity of material to be produced. Large quantities can be used to justify high capital expenditures for rapid and automated manufacturing technology.

Most commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyamide, polypropylene and others.

Composite materials have become popular (despite their high cost) in high-performance products that need to be lightweight, yet strong enough to take harsh loading conditions such as aerospace components (tails, wings, fuselages, propellers), boat hulls, bicycle frames and racing car bodies. Other uses include fishing rods, storage tanks, and baseball bats. The new Boeing 787 structure, including the wings and fuselage, is composed largely of composites. Composite materials are also becoming more common in the field of orthopedic surgery.

1. Find in the text English equivalents for the following words and word-combinations:

Відповідно з, недоступний, в основному, принаймні, оптимальне поєднання, форма деталі, на відміну від цього, розплавлений стан, витрати капіталу, умови навантаження, найбільш поширений, загальна кількість.

5. Answer the following questions:

1. What are composite materials?

2. Do constituent materials in composite materials have different properties?

3. Do these materials remain separate on a macroscopic level within the finished structure?

4. What properties are called isotropic?

5. What properties are called orthotropic?

6. What are constituent materials of a composite called?

7. What is the role of the reinforcement?

8. Are composite materials cheap?

9. Where are composite materials used?

1. Agree or disagree with the following statements. Prove your reason. Use the expression “As far as I know now…”

1. The constituent materials which make up composites have similar physical and chemical properties.

2. The physical properties of composite materials change depending on the direction of the applied load.

3. The stiffness of steel changes if the direction of the applied force remains the same.

4. Composite materials are popular because they are very cheap.

5. Composite materials are used in products which must be light and strong.

6. People have begun using composite materials only recently.

7. There are no natural composite materials.