Fiberglass is the most common composite material, made of glass fibers embedded in a resin matrix. It was first used on boats and automobiles in the 1950s in a commercial passenger jet, the Boeing 707. In the early days of the retail airplane industry, composite materials were minimal; only two percent of the aircraft’s structure was fiberglass. However, as the company developed new airplanes and materials, the use of composites increased, with the 787 Dreamliner incorporating 50% of the structure.
The main advantage of composite materials is their light weight. Airplanes with composite aerostructures typically weigh less than their metal counterparts, and their lighter weight means reduced fuel costs. Boeing estimates that comparable composite aero-structures weigh as much as 20 percent less than similar aluminum structures. Furthermore, Boeing’s research shows that composite materials require much less maintenance than aluminum. For example, composite tail panels on the B777 require 35% less maintenance than their aluminum counterparts.
However, just like aerospace and defense many of these composite aerostructures use epoxy resin, which is known for its poor fire performance. Most epoxy resins readily ignite when fire exposes, releasing copious amounts of heat. In addition, most structural-grade epoxy resins fail to meet FAA cabin fire safety regulations. As a result, most passenger aircraft interiors are made with molded phenolic resin or fiberglass-phenolic composite materials.
Shape Memory Polymer Composites
The elasticity and deformation recovery time of shape memory polymer composites depends on the applied voltage. The faster the voltage, the smaller the deformation recovery time will be. For example, a 7.2 wt% Ag/CCF/H-EP composite can deform and recover its shape in 9 s at 160 V. Voltages higher than this may cause the material to burn.
While shape memory polymers have been known for decades, they have only recently gained importance within the scientific community and industrial circles. This is because they have superior properties for many applications. For example, shape memory polymers are not electrically conductive, and their stiffness is lower than their alloys. However, this does not mean they are not helpful for the aerospace industry. These materials can be incorporated into composite aerostructures for several reasons, and they are currently being used in many applications.
The electrical response shape memory of Ag/CCF/H-EP was tested using rectangular samples. To test the material’s shape memory, the samples were heated to a target temperature and then bent into a “U” shape at a rate of 30 deg s-1. The rectangular pieces were then immersed in a cold-water bath to stop the bending.
Shape Memory Alloys
SMAs exhibit various mechanical properties that vary according to their transformation’s temperature range. They have a strong deformation capacity at low temperatures and develop pseudoelasticity upon heating. In contrast, austenite is not deformable and therefore does not undergo shape memory after heating. In composite structures, shape memory alloys are typically used in components that require a high degree of elongation and stiffness.
Another application for shape memory alloys is in the development of prosthetic hands. These prosthetics can dynamically change their shape according to different flight conditions. They can be controlled by SMA actuators coupled to their face sheets to produce complex shape changes. This technology can reduce the noise of jet engine nozzles and decrease fuel burn during cruise flights. The researchers plan to test the effects of SMAs in composite aerostructures in a wind tunnel.
Fiber Reinforced Plastics
Composite materials consist of a polymer matrix and reinforcing fibers, typically carbon, glass, basalt, or aramid. They can also include other substances, such as wood or asbestos. These materials are commonly referred to as fiber composites. Fibers are generally more robust and stiffer than polymers and provide the composite material with a high strength-to-weight ratio.
FRP is a class of material composed of a matrix and a set of reinforcing filaments. The fibers are inserted into the matrix to enhance its strength and elasticity. The power and elasticity of a fiber-reinforced plastic depend on the type of fiber, its volume, and its orientation. Therefore, the reinforcement composite material has higher strength-to-weight ratios than non-reinforced polymer materials.
There are many challenges in manufacturing a composite material. First, the material must be structurally and economically feasible. Unfortunately, there is a shortage of long-term data on composite materials’ environmental and economic benefits. However, some studies are underway to determine how the material will impact the environment. By-products produced during the production of composite materials must be assessed, as well as the sustainability of constituent materials.