Advantages of Composite Materials in the Aerospace Industry

Overview

Not long after the beginnings of powered flight, metals became the materials of choice for the structures of aircraft. Aluminum became the predominant choice for it’s lightweight, alloying capabilities, fatigue performance, and lower cost of production as compared to other materials. Typically, an aircraft’s primary, secondary, and tertiary structure would have been made of aluminum; metal alloys being considered the state-of-the-art technology for decades. Fast forward to the present where current materials for structural aircraft design have evolved to favour the use of advanced composite materials. What factors have influenced the change in this material composition of aircraft?

Composites consist of two or more materials that, when combined, will provide structural properties and performance capabilities not obtainable from any one material component alone. Performance properties of a composite can be tailored to it’s specific application: high heat, extreme cold, extreme stiffness, fatigue-resistance flexibility, and much more. In the aviation industry however, properties are tailored to be beneficial to the aircraft type and its flight performance requirements. In this way, composite material selection in aircraft structures can be optimized for the specific flight performance required. These are some of the advantages that composite materials provide to the aerospace industry.

Why Composites Over Aluminum or Other Metals?

Weight Reduction

A common property of composite materials is their light weight-to-strength ratio or “specific strength”. Specific strength is a material’s tensile or compression force per unit area at the point of failure, divided by its density. It is also known as the strength/weight ratio. In composite fiber laminate applications, tenacity is the usual measure of specific strength. With less weight in the aircraft structure, significant operational cost savings are realized; payload yields increased, maintenance costs decreased, and greater flight range is obtained, among many other positive attributes.

Heat Resistance

One aspect of glass and carbon fiber-based composites is the ability to resist deterioration when operated at extreme high temperatures. A prime example was the ablative ‘heat shields’ used on the Mercury, Gemini, and Apollo space capsules and the protective tiles of the Space Shuttle. Heat resistance of carbon-based and ceramic coated structures, will enable the production of Hypersonic passenger aircraft traveling at speeds in excess of Mach 6, (six times the speed of sound!), which will produce outer surface temperatures exceeding 1,000 degrees Fahrenheit due to friction with the atmosphere.

High-Impact Resistance

Similar to heat resistance, certain composite materials such as Aramid fiber can yield high-impact resistance properties. Aircraft can sustain massive and catastrophic structural damage when making contact with another object at high speeds such as impact with a large bird or hail in a storm cloud. In the case of military aircraft, ceramic-aramid composites can resist damage from ballistic impact. Certain combinations of glass fiber and toughened epoxy resin can be in excess of seven times more effective than the equivalent thickness of steel in armor protection.

Corrosion Resistance

One exceptional property of composite materials is the near-zero issue of corrosion. Unlike metals, especially aluminum, composite materials have excellent resistance to galvanic corrosion. This eliminates the number one cause of structural repairs in aluminum aircraft. The use of composite materials can allow for the design of structures such as wings, fuselage, flight controls, turbofan engine blades, and even helicopter rotor blades that have unlimited operational fatigue life.

Thermal Stability

While in flight, aircraft structures are subjected to large and rapid changes in temperature. In hot climates an aircraft may start on the ground with surface temperatures exceeding 120 deg.F however, as it climbs through the atmosphere the ambient air temperature cools dramatically to -60 deg.F or lower. An important quality in aircraft design is structural thermal stability. The all-metal supersonic Concord would stretch considerably due to air friction heating; this will not be the case with the new all-composite BOOM Supersonic passenger airliner.

When comparing the advantages of composites vs. metals, it is easy to see why composite materials are now dominating in the design and construction of new aircraft. Although metals will always be in use and cannot be entirely replaced by composites in certain applications, composites provide a variety of design possibilities that are not achievable with metals technologies alone.