by Michael R. Favaloro, Ticona technical marketing manager — Fortron PPS Composites — Americas

The incorporation of light weight plastic and composite materials in commercial aerospace vehicles is becoming a common design practice for reducing vehicle weight and achieving fuel savings.

These materials are conquering traditional metal domains throughout the aircraft. They’ve reached such an advanced stage of development that some complex thermoplastic components would actually be impossible to produce in metal. Even if these parts could be made in metal, the costs would be prohibitive.

Today, 1,000 components on the Airbus A380, weighing more than 2.5 tons, are produced from composites with a Fortron^® polyphenylene sulfide (PPS) matrix. This high-performance composite material is used in exterior components such as wing leading edge noses, or ribs and stiffeners that strengthen the fuselage. Interior applications include the lumbar support made from carbon-fiber reinforced composite, which is integrated into the seat back. Compare its 150 grams to a comparable support in aluminum that weighs in at 280 grams — nearly twice as much.

And breakthroughs like these are coming at an accelerated pace. One such breakthrough involves a first-of-kind, welded thermoplastic composite rudder and elevator tail section on the new Gulfstream G650 business jet, which made a successful maiden flight in late 2009. This aerospace breakthrough received an Innovation Award at the JEC Composites show in Paris earlier this year.

This is a great example of collaboration:

·        Fokker Aerostructures designed and developed the tail section and, with KV Engineering, industrialized a new induction welding method for the composite rudder and the elevator tail that eliminates both cost and weight associated with drilling and riveting or bonding.  The high-performance composite parts are based on a PPS matrix from Ticona and developed by Royal Ten Cate in the form of prepregs. The parts remain hard, impact-resistant, stiff and dimensionally stable, and are 20 percent lighter than those made from traditional materials such as metal and light alloys. The net result are tough thermoplastic composite parts with lower cost and lighter weight than their comparable metallic designs.

In the near future, even more exciting developments are on the horizon, especially composite seat frames for passenger seat assemblies to help reduce weight and cost even more.

About 400,000 seat frames are manufactured each year for the aerospace industry, with the vast majority being made of aluminum. Composite seat frame assemblies, historically covered by strict guidelines established by both the Federal Aviation Administration (FAA) and aircraft manufacturers, offer weight savings opportunities vs. their metallic counterparts, but two obstacles have restricted their use:

·        Cost

·        Flammability, smoke generation, toxicity (FST) performance

Aluminum seat frames designed to meet commercial aircraft standards are relatively inexpensive to make. A simplistic description for an aircraft seat frame is a high end lawn chair, designed to meet high torsional load requirements. Any composite matrix and process selection must be based on the ability to meet FST performance criteria and high volume low cost production methods.

New seat frames under development are designed to achieve a substantial weight reduction and be manufactured in high volume at low cost. The frames are made from carbon fiber reinforced polyphenylene sulfide (PPS) thermoplastic resin. The high torsional load requirements of the application were achieved by selection of braided carbon reinforcement.

The resin was selected over a number of candidates for several reasons. PPS is commercially available in a unidirectional tape prepreg form. This form is suitable for high volume production processing methods. Unlike thermoset prepreg materials, thermoplastics are already polymerized and only heated so they can be softened and re-formed to final shape. Thermoset prepregs must be heated to polymerization temperatures, and held at temperature over a period of time as polymerization occurs. Consequently, the process cycle time for a thermoplastic prepreg is much shorter than that for a thermoset.

PPS also meets FST and heat generation standards for aircraft interior applications. Competitive thermoplastic materials that also meet FST, such as polyether imide (PEI), polyether ether ketone (PEEK), and polyether ketone ketone (PEKK), are much more expensive than PPS.

The new carbon/PPS composite seat frames weigh 30 percent less than their aluminum counterparts — a cost savings since aeronautical engineers indicate that for every pound taken out of an aircraft it saves $1,000 in annual fuel costs — while meeting high torsional load requirements. They also meet FST requirements, which thermoset composite seat frames can no longer meet.

The bottom line: When you take out weight, you significantly reduce your operating cost. It's no wonder the aeronautic industry and others are investigating the hard, impact-resistant, stiff and dimensionally stable high-performance composite materials that promise to the reduce weight and cost of tomorrow's applications.

Next month we’ll look at a family of high performance resins, liquid crystal polymers (LCPs), and why the electronic industry is choosing this material to make miniature and ultrathin parts down to 0.1 millimeter wall thickness.

For Ticona technical papers and more information about Fortron PPS for thermoplastic composites, visit http://www.ticona.com/composites.