Intro to Composites R2010

8/13/2019 Intro to Composites R2010

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An AerospaceManufacturing

Perspective

Introduction to Composites


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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


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Composites in Aviation

What are composites?

Combinations of different materials which yield

a product with superior properties

Composite armor used by the Greeks in

antiquitiy

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

Modern composites, or advanced composites

are typically fiber reinforced plastics.

http://www.youtube.com/watch?v=Aznz9mj5grAhttp://www.youtube.com/watch?v=Aznz9mj5grA


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Fiber Reinforced Plastic (FRP)

Composites

Consists of at least two materials

Plastic which binds the fibers together, also called

the matrix

Fibers, typically small in diameter and long in

length

Fibers may also be short in length to facilitate

processinge.g., injection molded nylon with

glass fibers

In general the matrix imparts toughness, or crack

resistance, and the fiber imparts ultimate strengthcopyright J. Anderson, 2008


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Fiber Reinforced Plastic Composites,

contd.

Fibers

Plastic Matrix



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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



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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



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Relative Strength of Fiber and Matrix

Stress

Strain

Carbon

Fiber

Polyester Resin

Note that for the same level ofstress, the fiber deforms much less

than the resin.This leads to the composite materialbeing much stronger in the directionof the fiber. If the fibers areunidirectional (all in the samedirection) the composite material is

strong in the direction of the fibers,but weak in the directionsperpendicular to the fibers.

We can alleviate this by addingmultiple plies laid with the fiber

direction different.copyright J. Anderson, 2008


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Commercial Fiber

Fibers are available as

Yarna 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



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Material Configurations

copyright J. Anderson, 2008courtesy Ten Cate Avdanced Composites


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Composite Fiber Materials

Common Fibers Used in Composites

Glass, or fiberglass

Starts as a silica sand

Carbon

Starts as a polyacrylonitrile fiber



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Common Thermoset Plastics used in

High Performance Composites

Thermosets Epoxy

Polyester Phenolics

Cyanate Esters

Bismaleimide (BMI)

Polyimide

Thermoplastics Nylon

Polyetheretherketone (PEEK)



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Advantages of Composite Materials

over Metals for Aerospace

Light weight

Resistance to corrosion

High resistance to fatigue damageReduced 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



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Disadvantages of Composite

Materials over Metals for Aerospace

Corrosion problems can result from improper couplingwith metals, especially when carbon or graphite is used

(sealing is essential)Degradation of structural properties under temperatureextremes and wet conditionsPoor energy absorption and impact damage

May require lightning strike protectionExpensive and complicated inspection methodsReliable detection of substandard bonds is difficult



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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, Niu copyright J. Anderson, 2008


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Composite Usage in Boeing 777



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Composite Component Content

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


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Building Composite Parts

Composite parts are built by

laying up multiple plies

(layers) using molds (or

tools) then cured under heatand pressure.



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Combining the Fibers with Matrix

There are several methods for arranging the fibers

and plastic in the desired shape. We can arrange thefibers, usually as a fabric, in the mold and then pour

on the liquid matrix material. For one part we mighthand cut the fabric and fit it into the mold .



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Ply Cutting and Kitting

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

For a production system we

wish to make the same partmany 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.


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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 resinWorking 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 beenworked to the edges, and the composite conforms to the mold



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Wet Lay Up, contd.



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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. Thisprepreg 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.



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Debulking the Part



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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 thenthe part is soaked at temperature

until it is cured.



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Autoclave Cure


Photo courtesy WSF Ind & ASC Process Sys.


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Typical Autoclave Cycle



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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 thebag and through the fabric by a

vacuum pump.


Photos courtesy Airtech Adv. Materials


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Automated Lay Up



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Tow Placement

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


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High Dexterity Tape Placement



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Variable Angle Ply Lamination



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Large Parts

copyright J. Anderson, 2008courtesy ATK


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Future Directions


More Automation

Embedded sensors and actuatorsOut of Autoclave high performance

materials


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Subsequent Composites Modules

i ht J A d 2008

Composite Specifications in Drawings

Manufacturing Techniques

Process Control and Tooling

You Have Jus t Completed

The Introduct ion To Composi tes

Intro to Composites R2010

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