The disadvantages of composites include:

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 help composites become the material of choice for aircraft construction.

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 remove the vapors for a period of time. When removing the respirator for breaks, and upon placing the mask back on, if you can smell the resin vapors, 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, 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.

The purpose of reinforcement in reinforced plastics is to provide most of the strength. The three main forms of fiber reinforcements are particles, whiskers, and fibers.

A particle is a square piece of material. Glass bubbles (Q-cell) are hollow glass spheres, and since their dimensions are equal on all axes, they are called a particle.

A whisker is a piece of material that is longer than it is wide. Whiskers are usually single crystals. They are very strong and used to reinforce ceramics and metals.

Fibers are single filaments that are much longer than they are wide. Fibers can be made of almost any material and are not crystalline like whiskers. Fibers are the base for most composites. Fibers are smaller than the finest human hair and are normally woven into cloth-like materials.

Composites can be made with or without an inner core of material. Laminated structure with a core center is called a sandwich structure. Laminate construction is strong and stiff, but heavy. The sandwich laminate is equal in strength, and its weight is much less; less weight is very important to aerospace products.

The core of a laminate can be made from nearly anything. The decision is normally based on use, strength, and fabricating methods to be used.

Various types of cores for laminated structures include rigid foam, wood, metal, or the aerospace preference of honeycomb made from paper, Nomex®, carbon, fiberglass, or metal. Figure 7-14 shows a typical sandwich structure. It is very important to follow proper techniques to construct or repair laminated structures to ensure the strength is not compromised. Taking a high-density laminate or solid face and back plate and sandwiching a core in the middle make a sandwich assembly. The design engineer, depending on the intended application of the part, decides the selection of materials for the face and the back plate. It is important to follow manufacturers’ maintenance manual specific instructions regarding testing and repair procedures as they apply to a particular aircraft.

Reinforced plastic is a thermosetting material used in the manufacture of radomes, antenna covers, and wingtips, and as insulation for various pieces of electrical equipment and fuel cells. It has excellent dielectric characteristics that make it ideal for radomes; however, its high strength-to-weight ratio, resistance to mildew, rust, and rot, and ease of fabrication make it equally suited for other parts of the aircraft.