1. Aircraft Composite Structures Spokane Community College

2. Composite structures in Aircraft
Composite: combinations of two or move materials that differ in composition or form. In composites, the individual elements do not merge into each other as in plastics; each element brings something to the table and can be easily identified
Why use composites:
Excellent elastic properties
Ability to be customized in strength and stiffness
Damage tolerance characteristics
Sensitivity to environmental factors
High Strength to weight ratio
Excellent formability – complex contour and shapes
Elements of composite structures
Reinforcing material – structural strength
Matrix material – bonding substance
Core material – saves weight and designates shape
Slide

3. Fiberglass Strand of spun molten silica glass woven into cloth
Disadvantage – more weight/less strength
Two types
E-glass – electric glass – resistant to electricity
S-Glass – magnesia-aluminasilicate – high tensil strength
Originally used for fairings/etc. now improved

4. Aramid 1970’s – Dupont created aramid – KEVLAR Advantages
High tensile strength
Exceptional flexibility
High tensile stiffness
Low compressive properties
excellent toughness
Excellent vibration dampening characteristics
Disadvantage – stretches
Drilling and cutting is a problem – fizzy’s – can wick moisture, may also screw up holes

5. Carbon/Graphite
Produced in an inert atmosphere by the pyrolysis of organic fibers
Carbon and graphite are different –
Carbon lower temp for production and less carbon 93-95%
Graphite – Higher temp – 99% graphite
Advantages
High compression strength and stiffness
Disadvantages
Promotes galvanic corrosion when bonded with aluminum or steel – must have barrier and corrosion resistant treatment
BORON – Boron fibers deposited onto thin fibers of tungsten
Excellent compressive strength and stiffness, extremely hard
Hazardous to work with and expensive - no generally used in civilian aircraft
Ceramic Fibers – high temp applications – handle temps up to 2,200 degrees F.
Space shuttle and some firewalls

6. Fiber Science
Arrangement of the fibers in the fabric designates usage and properties
Tinsel strength – fabric only, lessens with matrix added
Lay up of fabric direction designates properties
Strength always runs parallel to the direction of the thread run
Fabric orientation (slide)
Warp – Threads that run the length of the fabric – 0 degrees
Interweaving colored thread often designates warp
Markings on pre-preg as well can designate warp
Weft or fill – Perpendicular to the warp
Create reinforcing of the cloth
Selvage edge = Tightly woven edge to keep from unraveling
Not for use – not same characteristics as the material
Bias – 45degree angle
Allows manipulation of the fabric – allows for movement unlike warp or Weft

7. Fabric Styles Fabric styles Unidirectional Multidirectional Mat
Unidirectional – Slide
Strength in a single direction
Occasional cross threads to hold the bundles in place
Bidirectional/multi directional
Warp usually outnumber the waft - more strength in the warp direction
Must be aligned in repair to give strength characteristics designated by the manufacturer
Intraply Hybird – different fibers woven together giving different strength and flexibility characteristics

8. Mats Chopped fibers compressed
Used in combination with woven and unidirectional fabrics – mats are not as strong, cheap filler

9. Fabric Weaves
Resistant to fiber breakout, damage and delamination vs. Unidirectional
Composites are available in many weaves based on characteristics
SLIDE
Physical stability decreases, lightness increases and pliability increases from plain weave to eight weave – Explain slide

10. Matrix Systems
Matrix – holds reinforcing fibers together – the ability of the matrix to transfer stress is the key to the strength of a composite structure.
RESIN – organic polymer – original Polyester resin – not sufficient strength and brittle – not for structural members
NOW – Resin matrix systems
Thermo plastic – not strong enough for structural applications by itself – must have other materials introduced
Heat formed – not structural due to lack of strength
If reheated will soften and perhaps change shape – Windshield on light aircraft
Thermosetting Resins – heat to form and assumes irreversible shape of the part
Types of Thermosetting resins –
Polyester resins – Used with fiberglass for non-structural parts
Give fiberglass cohesiveness and rigidly but not strength for structural members
Also –shrinks when cured – possible warpage
Epoxy Resins – Thermosetting plastic resins – two part – resin and catalyst - catalyst acts as the curing agent beginning the chemical action for hardening the epoxy.
Advantages – Excellent adhesion, useful for dissimilar material bonding – must be well designed and good preparation of the surfaces
Low shrinkage
High strength to weight ratio
Exceptional chemical resistance
Adheres to almost any material
Can be used in place of polyester in almost every application
Long shelf life
Short pot life
NOT EVERY type of resin is acceptable for every application – check the book
QUESTIONS - END