an aerospace manufacturing perspective introduction to composites

An Aerospace An Aerospace Manufacturing Manufacturing

PerspectivePerspective

Introduction to CompositesIntroduction to Composites

Course Overview Course Overview

Composite Material Structure Composite Material Components Aluminum versus Composites Advantages and Disadvantages in Aerospace Composite Applications Composite Manufacturing Techniques Subsequent Composite Modules

copyright J. Anderson, 2008

Composites in AviationComposites in Aviation

– What are composites?Combinations of different materials which yield

a product with superior propertiesComposite armor used by the Greeks in

antiquitiy– (http://www.youtube.com/watch?v=Aznz9mj5grA)

Modern composites, or advanced composites are typically fiber reinforced plastics.


Fiber Reinforced Plastic (FRP) Fiber Reinforced Plastic (FRP) CompositesComposites

Consists of at least two materialsConsists of at least two materials– Plastic which binds the fibers together, also called Plastic which binds the fibers together, also called

the matrixthe matrix– Fibers, typically small in diameter and long in lengthFibers, typically small in diameter and long in length

Fibers may also be short in length to facilitate Fibers may also be short in length to facilitate processing – e.g., injection molded nylon with processing – e.g., injection molded nylon with glass fibersglass fibers

– In general the matrix imparts toughness, or crack In general the matrix imparts toughness, or crack resistance, and the fiber imparts ultimate strengthresistance, and the fiber imparts ultimate strength


Fiber Reinforced Plastic Composites, Fiber Reinforced Plastic Composites, contd.contd.

Fibers

Plastic Matrix


Function of the Fiber

Carry the load– 70 to 90% of load carried by fibers

Provide structural properties to the composite– Stiffness– Strength– Thermal stability

Provide electrical conductivity or insulation


Function of the Matrix

Binds the fibers together Provides rigidity and shape to the structure Isolates fibers to slow crack propagation Surface quality Corrosion and wear protection for fibers


Relative Strength of Fiber and Matrix

Str

ess

Strain

Carbon Fiber

Polyester Resin

Note that for the same level of stress, the fiber deforms much less than the resin.

This leads to the composite material being much stronger in the direction of the fiber. If the fibers are unidirectional (all in the same direction) the composite material is strong in the direction of the fibers, but weak in the directions perpendicular to the fibers.

We can alleviate this by adding multiple plies laid with the fiber direction different.copyright J. Anderson, 2008

Varying Fiber Direction in Plies

Varying fiber direction in plies builds a laminate structure with strength in more than one direction


Commercial Fiber

Fibers are available as Yarn – a bundle of fibers twisted together

– Tow - Large bundles (Carbon Fiber), several thousand fibers

– Roving - Large bundles (Fiber Glass)

Uni-directional tape Woven fabric or mat


Material Configurations

copyright J. Anderson, 2008courtesy Ten Cate Avdanced Composites

Composite Fiber Materials

Common Fibers Used in Composites– Glass, or fiberglass

Starts as a silica sand– Carbon

Starts as a polyacrylonitrile fiber


Types of Plastics used in Types of Plastics used in Composites Composites

Plastics are polymer materials, that is to say that they are made up of long chain molecules. There are two types of plastics based on how these molecules are bonded together.•Thermoplastics

•Thermoplastics can be melted and re-solidified when cooled.

• Thermosets• Start out as liquids or paste-like solids and become rigid when cured. Thermosets can’t be re-melted once cured.


Common Thermoset Plastics used in High Performance Composites

Thermosets– Epoxy– Polyester– Phenolics– Cyanate Esters– Bismaleimide (BMI) – Polyimide

Thermoplastics– Nylon– Polyetheretherketone (PEEK)


Aluminum vs. CompositesAluminum vs. Composites

Aluminum is an “isotropic material”, which means it has the same properties in all directions.

Composites are “anisotropic” which means they have different properties depending on the direction of the fibers vs. the direction of the applied loading.

•Composites are built in layers called ply’s that are stacked “laid-up” to form a laminate.•Each layer has fibers that run in defined directions.•Because of the layers the properties are different “in-plane” vs. “through the thickness”


Advantages of Composite Materials Advantages of Composite Materials over Metals for Aerospaceover Metals for Aerospace

• Light weight • Resistance to corrosion • High resistance to fatigue damage • Reduced machining • Tapered sections and compound contours easily accomplished• Can orientate fibers in direction of strength/stiffness needed• Possible reduced number of assemblies and reduced fastener count when co-cure or co- consolidation is used • Absorb radar microwaves (stealth capability)• Thermal expansion close to zero reduces thermal problems in outer space applications


Disadvantages of Composite Disadvantages of Composite Materials over Metals for AerospaceMaterials over Metals for Aerospace

• Corrosion problems can result from improper coupling with metals, especially when carbon or graphite is used (sealing is essential)• Degradation of structural properties under temperature extremes and wet conditions• Poor energy absorption and impact damage• May require lightning strike protection• Expensive and complicated inspection methods • Reliable detection of substandard bonds is difficult


Design Comparison Studies for Lockheed L-1011 Aircraft

Inboard Aileron

Aluminum Composite

Weight (lbs) 141 104

# of Ribs 18 10

# of Parts 398 205

# of Fasteners 5253 2574

Vertical Fin Box

Aluminum Composite

Weight (lbs) 858 623

# of Assemblies 21 15

# of Parts 714 229

# of Fasteners 40800 10150

From “Composite Airframe Structures”, Niucopyright J. Anderson, 2008

Composite Usage in Boeing 777Composite Usage in Boeing 777


Composite Component ContentComposite Component Content

copyright J. Anderson, 2008Chart courtesy of Composites Market Reports

Building Composite PartsBuilding Composite Parts

Composite parts are built by laying up multiple plies (layers) using molds (or tools) then cured under heat and pressure.


Combining the Fibers with Matrix

There are several methods for arranging the fibers and plastic in the desired shape. We can arrange the fibers, usually as a fabric, in the mold and then pour on the liquid matrix material. For one part we might hand cut the fabric and fit it into the mold .


Ply Cutting and Kitting

copyright J. Anderson, 2008Photo courtesy Accudyne Systems, Inc

For a production system we wish to make the same part many times, in the most efficient manner, and have the same process every time.

In this case we use a CNC cutting machine to cut the patterns out, then assemble a “kit” of raw materials to make a part.

Wet Lay Up

We can arrange the fibers, usually as a fabric, in the mold and then pour on the resin. Typically the resin is a two part formulation that, once mixed reacts in a fixed time. In order to make the lightest part with the necessary strength, we must control the amount of resin we use on the part. The process includes;•Laying the fabric in the mold•Saturating the fabric with mixed liquid resin•Working the resin into the fabric so that it conforms to the mold•Adding another ply of fabric•Repeat the application of resin and working as above•Continue until all the plys are in place, excess resin has been worked to the edges, and the composite conforms to the mold


Wet Lay Up, contd.


PrePreg Lay Up

In wet layup it is very hard to control the amount of resin.This problem may be addressed by impregnating fabric with a pre-mixed resin. This “prepreg” material is held at low temperatures to retard the curing process.The prepreg sheets or tape are laid into the mold, and heated to cure.


Debulking the Part


Oven Cure

Once the layup is accomplished and the part is debulked, we can put it into a furnace to cure the resin. Typically the parts are instrumented with a thermocouple to track the temperature of the part in the oven. The temperature of the oven is increased until the thermocouple registers the correct curing temperature and then the part is “soaked” at temperature until it is cured.


Autoclave Cure

copyright J. Anderson, 2008Photo courtesy WSF Ind & ASC Process Sys.

Typical Autoclave Cycle


Vacuum Resin Infusion

Vacuum resin infusion is similar to wet lay up except that the fabric is laid out in the mold, the part is vacuum bagged, and resin is pulled into the bag and through the fabric by a vacuum pump.

copyright J. Anderson, 2008Photos courtesy Airtech Adv. Materials

Automated Lay Up


Tow Placement

copyright J. Anderson, 2008Photo courtesy Accudyne Systems, Inc & Cincinnati Machine

High Dexterity Tape Placement


Variable Angle Ply Lamination


Large Parts

copyright J. Anderson, 2008courtesy ATK

Future Directions


• More Automation• Embedded sensors and actuators• “Out of Autoclave” high performance

materials

Subsequent Composites Modules


Composite Specifications in Drawings Manufacturing Techniques Process Control and Tooling

You Have Just Completed

The Introduction To Composites

an aerospace manufacturing perspective introduction to composites

Documents

fibers copyright

glass fibers fibers

matrix fibers

commercial fiber fibers

direction copyright

length fibers

bundle of fibers

composites plastics