Nonmetallic Aircraft Materials – Part Two (Advantages/Disadvantages and Safety of Composite Materials)

in Aircraft Materials Processes and Hardware

In the 1940s, the aircraft industry began to develop synthetic fibers to enhance aircraft design. Since that time, composite materials have been used more and more. When composites are mentioned, most people think of only fiberglass, or maybe graphite or aramids (Kevlar). Composites began in aviation, but now are being embraced by many other industries, including auto racing, sporting goods, and boating, as well as defense industry uses.

A “composite” material is defined as a mixture of different materials or things. This definition is so general that it could refer to metal alloys made from several different metals to enhance the strength, ductility, conductivity or whatever characteristics are desired. Likewise, the composition of composite materials is a combination of reinforcement, such as a fiber, whisker, or particle, surrounded and held in place by a resin, forming a structure. Separately, the reinforcement and the resin are very different from their combined state. Even in their combined state, they can still be individually identified and mechanically separated. One composite, concrete, is composed of cement (resin) and gravel or reinforcement rods for the reinforcement to create the concrete.

Advantages/Disadvantages of Composites

Some of the many advantages for using composite materials are:

• High strength to weight ratio

• Fiber-to-fiber transfer of stress allowed by chemical bonding

• Modulus (stiffness to density ratio) 3.5 to 5 times that of steel or aluminum

• Longer life than metals

• Higher corrosion resistance

• Tensile strength 4 to 6 times that of steel or aluminum

• Greater design flexibility

• Bonded construction eliminates joints and fasteners

• Easily repairable

The disadvantages of composites include:

• Inspection methods difficult to conduct, especially delamination detection (Advancements in technology will eventually correct this problem.)

• Lack of long term design database, relatively new technology methods

• Cost

• Very expensive processing equipment

• Lack of standardized system of methodology

• Great variety of materials, processes, and techniques

• General lack of repair knowledge and expertise

• Products often toxic and hazardous

• Lack of standardized methodology for construction and repairs

The increased strength and the ability to design for the performance needs of the product makes composites much superior to the traditional materials used in today’s aircraft. As more and more composites are used, the costs, design, inspection ease, and information about strength to weight advantages will help composites become the material of choice for aircraft construction.

Composite Safety

Composite products can be very harmful to the skin, eyes, and lungs. In the long or short term, people can become sensitized to the materials with serious irritation and health issues. Personal protection is often uncomfortable, hot, and difficult to wear; however, a little discomfort while working with the composite materials can prevent serious health issues or even death.

Respirator particle protection is very important to protecting the lungs from permanent damage from tiny glass bubbles and fiber pieces. At a minimum, a dust mask approved for fiberglass is a necessity. The best protection is a respirator with dust filters. The proper fit of a respirator or dust mask is very important because if the air around the seal is breathed, the mask cannot protect the wearer’s lungs. When working with resins, it is important to use vapor protection. Charcoal filters in a respirator will remove the vapors for a period of time. If you can smell the resin vapors after placing the mask back on after a break, replace the filters immediately. Sometimes, charcoal filters last less than 4 hours. Store the respirator in a sealed bag when not in use. If working with toxic materials for an extended period of time, a supplied air mask and hood are recommended.

Avoid skin contact with the fibers and other particles by wearing long pants and long sleeves along with gloves or barrier creams. The eyes must be protected using leak-proof goggles (no vent holes) when working with resins or solvents because chemical damage to the eyes is usually irreversible.