AMT Advanced Composites: Fibers, Fabrics, Resins & Repair

What is a composite structure?

A structure made by combining two or more different materials to create a stronger or improved material.

What are three early examples of composite structures?

Mud mixed with straw, adobe bricks, and other natural fiber-reinforced building materials.

How much fiberglass is used on the Boeing 747?

Approximately 10,000 square feet.

How have advanced composites evolved, and what is FRP?

Advanced composites combine improved materials and bonding methods. FRP stands for Fiber Reinforced Plastics.

Why is it important to repair rather than scrap composite parts?

It is more economical and saves replacement costs.

What three fabric patch characteristics are important for distributing repair stresses?

Weave, fiber type, and positioning.

What are the advantages of using composites?

Lightweight, corrosion resistant, strong, flexible, fewer fasteners, and capable of forming large structures.

What three factors determine the strength of composites?

Type of fibers, bonding material (matrix), and how the part is designed to handle stress.

How does the Grumman X-29 provide adequate wing strength?

Carbon/graphite fibers are laminated in multiple layers, with fibers running in different directions.

What are the approximate percentages of composite materials on the C-17?

40% carbon fiber, 20% fiberglass, and 40% aramid.

Where are composites used on the Boeing 757?

Secondary structural components, flight controls, fairings, and doors.

What are Nomex panels and where are they used on the Boeing 767?

Honeycomb core panels used in flooring, under-seat areas, main aisles, and galleys.

What are the Boeing 777 vertical fin and engine cowls made of?

Composite materials including carbon fiber and fiberglass, with carbon-fiber/epoxy skins used in engine cowls.

What are the three common types of reinforcing fibers?

Fiberglass, aramid, and carbon/graphite.

What are the two uncommon reinforcing fibers?

Ceramic and boron.

What is fiberglass made from?

Small strands of molten silica glass.

What are the three common types of fiberglass used in aviation?

E-glass, S-glass, and C-glass.

What is a matrix?

The bonding material that completely surrounds and supports the reinforcing fibers, usually resin.

Describe aramid fiber.

A lightweight, yellow fiber with high tensile strength, flexibility, and excellent vibration resistance.

What is aramid used for in aircraft?

Lightweight, high-strength components, impact-resistant structures, and vibration-resistant applications.

What are the disadvantages of aramid?

It can fray when cut or drilled, absorbs moisture, and is difficult to machine.

What is the difference between carbon and graphite fiber terminology?

Americans commonly use graphite, while Europeans commonly use carbon.

What characteristics of carbon fiber are useful for aircraft?

High strength, stiffness, and rigidity with low weight.

How does carbon compare to Kevlar?

Carbon has greater compressive strength but is generally less flexible than Kevlar.

What is the disadvantage of carbon fiber?

It is brittle, can splinter or crack, and can cause galvanic corrosion when in contact with aluminum.

How is boron fiber made?

By depositing boron onto a thin tungsten filament.

What are the characteristics of boron fiber?

High strength, stiffness, compressive strength, and extreme hardness.

Where are ceramic fibers best utilized?

Applications requiring extremely high-temperature resistance.

How does resin affect the tensile strength of fabric?

Too much resin can make the structure more brittle and reduce the effective strength of the fiber reinforcement.

What is fiber science?

The selective placement and orientation of fibers to obtain the greatest strength for a particular application.

In what direction are fibers strongest?

Parallel to the direction the fibers run.

What is warp?

The threads that run lengthwise through the fabric, parallel to the selvage edge.

What is fill?

The threads that run perpendicular to the warp threads.

What is the selvage edge?

The tightly woven edge of fabric that prevents unraveling.

Why is bias important in composites?

Fabric can stretch along the bias, allowing it to conform to curved surfaces.

What does glass fiber yarn terminology describe?

How the individual glass filaments are grouped and formed into yarn.

What does 1575 denier mean with regard to aramid?

It identifies the yarn's weight. Denier measures grams per 9,000 meters of yarn.

What does 4.5K tow mean with regard to carbon fiber?

A bundle containing approximately 4,500 continuous carbon filaments.

What is unidirectional fiber?

Fiber reinforcement in which the major fibers run in one direction.

What is bidirectional or multidirectional fabric?

Fabric with fibers oriented in two or more directions.

What is mat fabric?

Chopped fibers compressed or bonded together to form a mat.

What is the difference between plain and satin weaves?

Plain weave alternates over and under each thread. Satin weave passes over several threads before going under one.

What characteristics determine fabric styles?

Yarn construction, weight, thickness, and weave.

How is fabric weight measured?

Ounces per square yard or grams per square meter.

What are hybrids and why are they used?

Combinations of different fiber types used to combine their strengths and advantages.

What are the different types of hybrids?

Intraply hybrids, interply hybrids, and selective fiber placement.

How is epoxy resin different from polyester resin?

Epoxy generally provides better bonding, greater strength, and lower shrinkage than polyester resin.

What is a limitation of using thermoplastics for structural components?

They can soften when heated and may lose strength at elevated temperatures.

How are thermoplastics and thermosetting plastics different?

Thermoplastics soften when heated and can be reshaped. Thermosetting plastics chemically cure and cannot be remelted.

Why are epoxy resins commonly used in composite fabrication and repair?

They provide excellent adhesion, strength, flexibility, and resistance to moisture and chemicals.

How are hardware-store epoxy systems different from aircraft-grade systems?

They are not manufactured or tested to the same aircraft specifications and may lack the required strength and flexibility.

What is the most important rule when working with epoxy resins?

Use exactly the resin and hardener specified by the manufacturer.

What is the trade-off when using flexibilizers in epoxy resin?

They can reduce tensile strength and resistance to chemicals and solvents.

What is crosslinking?

The formation of three-dimensional chemical bonds between molecules during curing.

Where are polybutadiene resins commonly found?

Coatings, adhesives, and potting compounds.

How do temperature cure ranges affect crosslinking of polybutadiene resin systems?

Higher curing temperatures generally produce more complete crosslinking and a harder, stronger material.

What are important recommendations when working with resins and catalysts?

Follow manufacturer instructions, measure accurately, mix thoroughly, bring materials to the proper temperature, avoid oversized batches, observe shelf life and pot life, prepare clean surfaces, use proper protective equipment, and follow curing requirements.

What is pot life?

The amount of time a mixed resin and hardener remain workable before they begin to harden.