chapter 19 manufacturing with composites. composite - definition structures made of two or more...

Chapter 19

Manufacturing with Composites

Composite - Definition

• Structures made of two or more distinct materials

• The materials maintain their identity during the process

• The materials maintain their identity after the final component is fully formed.

Key Points

• Fabric Types

• Resin Types

• Manufacturing Techniques

• Curing Techniques

• Sandwiches and Honeycombs

• Joining of Composites

• Pros and Cons of Composites

Where are Composites Used?

• Recreational boats

• Cars

• Airplanes and other aircrafts

• Aerospace

• High performance sporting goods

• Appliances, tools, and machinery

• Tanks and pipes

What is a Composite?

• First produced about 50 years ago

• A “Judicious” combination of two or more materials that produces a “Synergistic” effect

Judicious

• Implies that the components are carefully selected to provide the desired physical and chemical characteristics

Synergistic

• The whole product is better than the sum of its individual components

• Word coined by Buckminster Fuller

• Illustrated concept by using a rope as an example

Composites are made up of a fiber and a matrix

• Fiber can be short or long strands of material

• Matrix is a the material that holds the fibers together

• Natural composites – celery, corn stalks, and sugar cane

• Manmade composite – reinforced concrete

Composite Classification

• Matrix– Material that surrounds the other components

• Fillers– Randomly oriented equally dispersed particles

• Fiber Reinforcement– Usually the main component in differing forms

Simple and Advanced Composites

• Simple Composite (Reinforced plastic) – Fiber laid in random directions or very short

• Advance Composite – Long fibers are laid in a given direction, long, and continuous

Fiber orientation

• Unidirectional

• Biaxial (Cross-ply)– Random orientation

• Laminates– Cross layering of unidirectional composites

Composite System Categories

• Fiber – Resin• Fiber – Ceramic• Carbon – Metal• Metal – Concrete• Metal – Resin• Metal – Elastomer• Fiber – Elastomer• Wood – Resin

Typical Fabrics Used in Composites

Glass• Can be long and continuous or

short• Can use many different types ex:

Soda lime – easy and low cost• Fiberglass white color can be dyed

to any color

Kelvar• Can be long and continuous • Same family as nylon• Distinctive yellow color

Graphite (carbon)• Made by burning a material in the

absence of oxygen, other elements burn off leaving carbon

• Should be called carbon fiber• Always black

Strength to Weight

Why Chose Glass?

• Excellent thermal and impact resistance

• High tensile strength

• Good chemical resistance

• Outstanding insulating properties

• Lower cost

Glass Types

E-glass• Low cost - $1 per pound• Used in 90% of glass reinforcement• Good electrical resistance• Used in aircraft radomes and

antennae and computer circuit boards • Good resistance to sodium carbonate

(base)• Good high temperature performance

High strength glass• $6 per pound• S-glass or S2-glass(U.S.)• R-glass (Europe)• T-glass (Japan)• Contains more silica oxide, aluminum

oxide, and magnesium oxide• 40% to 70% stronger• Originally used for military applications

(S2 for commercial)• Good resistance to hydrochloric and

sulfuric acid• Good resistance to sodium carbonate

(base)

• Good high temperature performance

C-glass• Corrosion resistant • Good resistance to hydrochloric and

sulfuric acid• Poor high temperature performance

Why Chose Graphite?

• Higher tensile strength and stiffness than glass

• Used in high-tech applications where product needs exceptional fiber properties and customer is willing to pay premium

Why Chose Kevlar?

• Highest quality

• High breaking strength

• More impact resistant

• Lightest weight

• Highest tensile strength

Comparisons of Fibers & Steel

Tensile Strength

0

100,000

200,000

300,000

400,000

500,000

600,000

Steel-low

Steel-highGlass

Kevlar

Graphite-low

Graphite-high

Fiber Types

lb/in

2

Comparisons of Fibers & SteelDensity

0

1

2

3

4

5

6

7

8

9

10

SteelGlass

Kevlar

Graphite-low

Graphite-high

Fiber Types

gm

/cm

3

Hybrids

• Combination of different fibers within a single matrix

Intraply Interply

Hybrids

Selective PlacementInterply Knitting

Resins• Must be compatible with fibers• Two types

Thermosetting

Crosslinks during curing

Sets into final rigid form

Used widely

Lower price tag

Ease of handling

Good balance of mechanical, electrical, and chemical resistance properties

Thermoplastic

Needs higher temperature processing

Remains plastic and can be reheated and reshaped

Used less

High performance

Higher costs

Higher temperature performance

Better damage resistance

Higher compressive strength

High vibrational damping

Viscoelasticity

Resins – Two Types

• ABS• PMMS• Fluorocarbon (Teflon)• Nylon• Polycarbonate• Polyphenylene sulfide• Polypropylene• Styrene• Vinyl• Vinylidines

• Epoxy• Bakelite• Melamine• Polyesters• Urea-formaldehyde• Urethanes• Silicones

Thermoplastics Thermosetting

Manufacturing Techniques

• Hand layup or Hand-lay

• Pre-preg

• Filament winding

• Pultrusion

Open Mold Processes

• Hand Lay-up

• Spray-up

• Tape-laying

• Filament winding

Hand layup

• Oldest, Inexpensive, Little equipment required• Repair technicians and backyard boat builders

use this technique with fiberglass• Requires some skill to do• Wasteful use of resin• Product heavier compared to using other

techniques• Good for one of a kind products or prototypes

Hand layup Method

1. A form is coated with resin using a paintbrush, roller, swab, spatula or any other method

2. Fabric is pressed into the resin

3. Another coat of resin is applied on top

Pre-preg Method

1. Fabric saturated with resin2. Excess squeezed out by rollers3. Cured to B stage, material tacky4. Can be stored a week to 10 days if not used

right away. Refrigeration lengthens shelf life5. Can be wrapped around a mandrel, cut by

computer controlled machines or laid up on forms by robots

6. Must be put under pressure to finish curing

Filament Winding Method

• Good for convex shapes having no indentations

• Individual fibers are drawn through the resin and wrapped around a mandrel

• When complete pressure cured, mandrel removed

• Good method for aircraft nose cones, radar domes and missile nose cones and bodies

Pultrusion Method

• Good method for selective placement composites• A bundle of arranged fibers are drawn through a resin

bath• Then pulled through a selected shape heated die• Cured and cut to size• Good method to create channels, flange beams, T-

bars, and other shapes in very long lengths

Pultrusion

Curing Techniques

• Pressure forms

• Vacuum bagging

• Autoclaving

Pressure Form Method

• Uses a heated internal and external mold

• Can be used in mass production, but requires expensive equipment

Vacuum Bagging Method

• Simple and cheapest method• Used after hand layup or pre-preg of

material• Piece is placed in a polyethylene, rubber,

or airtight flexible bag• Vacuum pull in the bag exerts equal

pressure approximately 12 lb/in2

• Part or entire bag is heated to cure

Autoclaving Method

• Used when parts require more than one atmosphere of pressure

• An oven that can be sealed and pressure is then applied by air or other gasses

Other Composite Forms

Sandwiches• Styrofoam, syntactic foam, or polyurethane

foam wrapped in fiberglass, Kevlar, or graphite fibers and fused together

• Balsa wood could be used as a core to make sailboats

• Recent developments using ceramic cores for heat resistance

Other Composite Forms

Honeycombs• Honeycombed aluminum, Nomex,

fiberglass, graphite, or other material wrapped and bonded to composite materials

• Used in helicopter blades, truck and aircraft bodies, and some parts of aircraft wings and tail surfaces

Joining Composites

• Joined in conventional methods by threads, pins, rivets, and other mechanical methods

• Thermoplastic polymers joined by fusion welding

• Chemical joining

• Adhesives

Composites vs. Traditional Materials

• Lighter• Stronger• No fatigue failure• No corroding• Hard to break• Complicated shapes

• Delaminate• Blisters• Fabric cutting difficult• Material and curing

costs high

Pros Cons

Environmental Concerns

Reduction of styrene emissions• Exposure limited to 50 parts per

million (OSHA)• Hard to meet standards and

costly• Achieved by reducing styrene,

better transferring to molds, curing in closed systems

Development of biodegradable reinforced plastics

• Filling up landfills with computer and car parts, packaging, etc.

• Create matrices from soybean protein and use plant-based fibers such as ramie, pineapple leaves and banana stems

• Could be used in car and train interiors, computers and as packaging materials

• Low cost (when acceptance increases), biodegradable and renewable on a yearly basis

Websites

• www.composites-one.com

• www.msu.edu/~namaact/productinfo.htm