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