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Transcript of ASAS1 Composites
Increase in use of composites leads to development of new/improved manufacturing methods.
These methods allow developing of parts that are testing the limtatons of materials used.
Future applications will require developments in material properties itself.
Types of Composite Materials
High material strength-to-weight ratio
The Boeing 787 is 20% lighter than an equivalent aircraft made entirely of aluminium.
Lower cost of assembly due to lesser amount of parts
A mid-sized aluminium fuselage barrel requires around 50,000 fasteners whereas an equivalent composite barrel requires around 3000 fasteners.
Good corrosion and fatigue resistance against cyclic loading.
It is created using polyarcylonitrile(PAN), pitch or rayon fiber precursors.
Common types of composite materials used in aircraft
Slower manufacture compared to aluminium
A long time is spent on the lay-up of the fabric or pre-preg
Anisotropic properties requires careful designing of composite aircraft components
Boeing 787 Dreamliner
Composite Materials in Aircraft
F/A-18 - Ｇｒａｐｈｉｔｅ／Ｅｐｏｘｙ ｏｎ Ｗｉｎｇｓ， Ｈｏｒｉｚｏｎｔａｌ ａｎｄ Ｖｅｒｔｉｃａｌ Ｓｔａｂｉｌｉｚｅｒｓ ａｎｄ Ａｃｃｅｓｓ Doors. Usage: 45%
F-14 - Boron and Epoxy on Horizontal Stabilizer. Usage: 0.04%
AV-8B - Graphite/Epoxy on Wings, Horizontal Stabilizers, Overwing Fairing, Forward Fuselage and Control Surfaces. Usage: 40%
Fibres are drawn at high speeds, through small holes in electrically heated bushings, which forms the individual filaments.
The filaments are gathered into groups or bundles called "strands"
The filamens are attenuated from the bushings, water and air cooled.
A coating of a proprietary chemical binder or sizing is added to protect the filaments and enhance the composite laminate properties.
Good impact resistant.
Weighs more than carbon or aramid
Good electrical and thermal insulation
Transparent to radio frequency
PAN based fibers:
Good strength and modulus values up to 85-90Msi.
Excellent compresson strength for structural applications up to 1000ksi
Extremely high modulus values(up to 140Msi)
Favourable coefficient of thermal expansion
Can cause galvanic corrosion when used next to metals -> barrier material like glass and resin is required.
More brittle than glass or aramid.
Poly-metaphenylene isophthalamide is used to make meta- aramids.
P-phenylene terephthalamide is used to make para-aramids.
Aramids decompose before they melt -> produced by wet & dry spinning methods
Sulphuric acid as the solvent for spinning processes
Good impact resistance
Low radio frequency attenuation
Wet spinning methods:
A strong solution of polymer contains inorganic salts
Polymer is spun through a spinneret into weak acid or water to remove the salts
Dry spinning methods:
More difficulties in removing salt -> only used to produce weaker meta-aramid fibres
Post treatment by additional drawing is required to optimise fibre properties
Two forms: Woven and in continuous tows
Three grades of Kevlar:
Kevlar, Kevlar 29 and Kevlar 49
Kevlar 49 is usually applied in airplane
Prepreg and autoclave cure traditionally used to guarantee ultimate quality.
Not appropriate for large scale structures and preparation, cycle times are long
Rising build rate to satisfy demangs, Original Equipement Manufacturers (OEMs) needs to:
Increase production rate
This produced 2 trends:
Automated Fibre Placement (AFP) /Automated Tape Laying (ATL)
Provide rapid automated placement of strips of prepreg material onto mould
AFP can be used with complex geometries (steered over sharply curved surfaces) while wider tapes cannot without buckling some fibres and weakening the laminate
Cure done in or out of autoclave as long as appropriate material used
Examples: 787 nose and A350 fuselage panels
Out of autoclave processing
Out of autoclave processing
Laying up of dry fabric and introduction of resin either in wet or film form and using vacuum to pull it through fabric.
Variations of technique:
Resin film infusion (RFI)
Vacuum assisted resin transfer moulding (VARTM)
Allows use of technical textiles which provides more design freedom and enhanced through thickness properties.
Certain structural properties has to be compromised as resin usually has relatively low viscosity to allow flow through fabric.
Example: A380 rear bulkhead and A400M cargo door
Maintenance, Repair and Overhaul (MRO)
MRO requirements of composites very different from metals.
Shorter track record of use than metallic structures, many MRO companies do not have experience of maintaining composite structures.
Parts designed to cope with typical defects/ damage but non-destructive testing (NDT) required to pick up damage/growth beyond limits.
Specific challenges with maintenance:
Specific defects types due to inhomogeneous nature of composites
Defects are initiated during: manufacturing as well as in-service
Inspection regime usually involves use of several NDT techniques
New and developments in existing techniqques offer improves in current state of art, but need to be validated and certified.
Manufacturing Defect Types
Inappropriate fibre volume fraction
Overlap or gap between fibre bundles
Knots or missing roving
Inclusion and contamination
Uneven, insufficient or over curing
Non-uniform hardener content
Cure shrinkage (Delamination, broken and buckled fibres and matrix cracking)
Excessive porosity or voids
Poor wet-out and/or dry spots
In-Service Defect Types
UV damage & weathering
Erosion or abrasion
Coin and tap testing
Repair of damage involves cutting of fibres which cause strength and stiffness to be compromised
Repair uses 1 or 2 techniques:
Bolting a patch which increases weight
Scarf repair which requires clean conditions, are time consuming and expensive and difficult to store.
In field repair techniques based on dry fabric performs and infusion are being investigated. Possible problems centre around use of brittle resins for infusion and likelihood of poor fatigue life and shock resistance
Carbon Fibre Availability
Global usage of carbon fibre is growing in many industry sectors and growth rate is accelerating
Carbon fibre production globally in 2012 ~ 45000 tonnes.
Aerospace grade fibres are most expensive to produce and need to be certified before use, hence increase production limited.
Shortage in supply of suitable fibres drive prices up and make metal to be viable option in the future
3000 tonnes CFRP scrap produced annually, estimated 6000-8000 commercial planes to reach end-of-life dismantlemment by 2030
Neither landfill nor incineration disposal of CFRP scrap is optimal, and eventual ban on both due to environment regulations.
Must develop methods to recycle carbon fibres out of CFRP
Process recently been commercialised
BUT no real market for recycled product produced
Composites materials consist of more than one material, material formed at same time as the part. Hence, it is possible to incorporate other materials during processing to provide integrated functionality.
Self Healing Composites
'Lost wax' process
Sheffield Solid State Healing
To trigger self-healing, composites needs to be able to detect damage.
Examples from Bristol University:
Tow-steered composites with variable stiffness to form bi-stable structures
Morphing corrugated structures
Pestressed, bistable composites
Imperial College has produced a composite supercapacitor.
Prototypes are being developed for aircraft tertiary structures and automotive applications.
Fibre Optic/Bragg Gratings
Able to change shape to satisfy the need for motors and weight adding mechanisms.
Two types of effect caused by lightning strike:
Physical damage at attachment locations
Indirect effects from induced voltage and current
Prevention methods in composite structures
Copper foils and meshes in outer plies
Co-bonding copper strips to inside skins of panels
Insulation caps or collars, nuts and fasteners
Aluminium foil strips for shielding
Nickel-coated carbon fibres
MAST Consortium developed integral woven carbon fibre preform, improved damaged tolerance and lightning protection
Carbon nanotube coatings for lightning protection - Bristol.
Able to store energy could allow further reductions in weight with the removal of heavy batteries
History of Composites
There is no aircraft accident or incident directly caused by composite materials.
Composite Fire Incidents
In case of an incident involving an aircraft having composite materials, additional hazards may be created due the the presence of these materials.
Two members of recovery team complained of remarkably reduced exercise capacity
After initial crash, these men working on site well for 8 to 11 hours
Exposed to crash debris and small amount of smoldering aircraft parts.
They were texted using standard respiratory-related test.
Harrier GR5 crash in Denmark, 1990
Royal Air Force (RAF) Aircraft Recovery and Transportation Flight Team dispatched to site containing considerable amount of shattered and charred carbon composite fiber.
Team attempted to reduce hazard by containing dust with diluted carr underseal.
Wore facemasks and goggles.
F-117 Stealth Fighter Crash
Happened at Baltimore air show.
Released from burning of composite materials
Potential to be inhaled, causing respiratory irritation.
Exposed along the broken edges of composite wreakage
Sharp and needle-like, may puncture skin of investigation personnel if brushed against.
Skin punctured will experience irritation and sensitization.
Affected by exposure to pyrolized graphite and oher debris from F-18 wreckage site.
Experienced reduced exercise capacity for 5 months
• Structural material built to achieve specific structural properties
• Consists of two or more dissimilar constituents combined together
Results were inconclusive.
Experienced increasing discomfort, including sore eyes, throats and chests.
Site evacuated until improved safety measures could be identified and implemented.
Team returned using PVC overalls, service respirators, and ventilated helmets, previous symptoms disappear and never recur.
Cordoning off crash site and decontamination procedures aid in preventing these symptoms
Accident due to structural failure of the support assembly in left wing.
No consistent guidelines for dealing with mishaps involving composite materials
Wax-like material sprayed on fire debris to contain materials.
Firefighter and others near crash site fall ill from fumes emitted by fire.
Some of these fumes are believed to be the product of burning of resin in composite materials
Constituents are combined together at a
level and are not soluble in each other, but they act together as
Fibreglass, the first composite to be produced, was first produced by accident by blowing air into molten glass by researcher Dale Kleist in 1942.
Properties of the composite material is mostly superior to that of each individual material used to form the composite material
Widely adopted in the
due to their superior structural, electrical, thermal and tribological (
wearing due to friction; interacting surfaces in relative motion
) properties for their given weight
Boeing 787 has CFRP fuselage.
If Boeing wants to scale this down to produce new 737 with composites fuselage, hail stones could penetrate fuselage.
Use a tougher composite.
Where fibre reinforcement is concerned, reinforcement can be further classified into:
1. Anisotropic design
2. Quasi-isotropic design
Carbon Fibre was first produced in 1963 by the Royal Aircraft Establishment at Famborough, Hampshire UK. Rolls Royce used this in their aeroplane engines.
However, at the time of development, carbon fibre was too expensive and as a result made the engines too expensive. Thus, leading Rolls-Royce to be bankrupt.
Fun Fact: Thomas Edison was the first person to come up with CF by heating bamboo to use as a filament for his light bulb as it was fire resistant!
included in the initial design. However, boron composites had three significant problems which limited it
• The boron had to be deposited on a tungsten wire substrate.
• The processing was expensive.
• Boron filaments cannot be bent into tight radii.
Boron Composites were first produced in the year 1970.
The F-14 jet fighter was the first aircraft produced with boron composites
GLARE- Produced in 2005
“GLAss-REinforced” Fiber Metal Laminate
GLARE is a composite made up of alternating layers of thin Aluminium, layers of fiber glass and plastic matrix material.
Advantages over conventional aluminum construction are:
• Superior damage tolerance to impact and fatigue
• Better corrosion resistance
• Better fire resistance
• Lower specific weight
Construction of advanced composite materials in the 21st century
The definition of a composite material is that formed by a matrix constituent reinforced by a stronger, stiffer reinforcement.
There are two
composite structures used in the aviation industry
1. Solid laminate structure
2. Sandwich assembly structure
Bonded layers of reinforcement material supported by a matrix constituent.
Structural properties of such a structure (stiffness, dimensional stability and strength of laminate) depend on the stacking sequence of the plies.
Stacking sequence describes the distribution of ply orientations throughout laminate thickness.
Number of plies with chosen orientation increases, the more stacking sequences possible.
Formed by sandwiching a filler (core) material between two laminate surfaces.
Core supports the face sheets against buckling and resists out-of-plane shear loads. Must have high shear strength and compression stiffness.
Common filler type is the honeycomb core, usually made of aluminum, fiberglass or carbon.
: High strength to weight ratio, high bending stiffness.
Types of matrices
Organic Matrix Composites
Organic-matrix composites such as
, is the most commonly found type of composite as it is relatively low cost and requires very little manpower to assemble large, complex components as it is very easy to handle.
As such, it is immensely popular in the commercial aviation industry, and has also featured in many military aircraft.
Can be further divided into thermoset and thermoplastic types
Metal matrix composites
Ceramic matrix composites
Mainly used to provide wear and abrasion resistance in extremely high-temperature applications, but the dangers and risk associated with the manufacturing of such composites results in the small number of commercial products adopting this particular type.
Functions of the matrix constituent
Lee Jia Min
to composite material
reinforcement material [fibre] from
the reinforcement together [good adhesive properties]
Transfers any applied loads
to and between the reinforcement material
reinforcing fibres in
• Determines the
maximum service temperature
of composite material
1) Solid laminate structure
2) Sandwich assembly
1. Polymer-matrix composites
2. Carbon-matrix composites
Type of resin that once cured, is unable to return uncured, or soft state. [irreversible]
Type of resin that may be repeatedly softened with heat even after first curing
were developed to retain some advantages of metallic materials, [such as chemical inertness, high shear strength, and good property retention at high temperatures] while benefiting from the excellent strength-to-weight ratio of composites.
Instead, they are now used on high-mach airframes and critical rotating components of advanced gas turbine engines
, due to the higher costs of MMCs beside its Organic counterpart, this technology has yet to be widely adopted in the commercial aviation sector.
More commonly known as fibre
Serves to provide superior levels of strength and stiffness to composite material
Single group of filament or fibre ends
All filaments are in same direction and
Unidirectional (fibrous tape)
Produced directly from bundles of
tows running in one direction
by small threads
Have strength in fibre direction but virtually
no strength across fibres
Tows are twisted to form yarns, and
yarns are woven to form fabrics
Most widely used form of fibre reinforcement in aerospace industry due to
for layup of complex shapes as compared to unidirectional tapes
Anisotropic stress design
Quasi-isotropic stress design
Warp fibres are laid
in one direction
Strongest specific properties
primary loading direction
Lowest specific properties for loads
to fibre direction -> can be overcome by varying the laminate architecture (having various layers cross-plied to each other)
Mimics properties of isotropic materials
such as aluminum and titatium
Uniform properties in all directions
Capable of carrying loads in all similar directions as that of isotropic materials
Gavin Lee Ju-lian
Federal Aviation Administration. (2012). Chapter 7 : Advanced Composite Materials. Retrieved January 25, 2014, from http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_ch07.pdf
Gou, D. J. (n.d.). Chapter 1 Introduction to Composite Materials. Retrieved January 25, 2014, from Composite Materials Research Laboratory Department of Mechanical Engineering University of South Alabama: http://www.southalabama.edu/engineering/mechanical/faculty/gou/Teaching/ME582/ME%20582%20F06%20-%20Chapter%201%20Introduction.pdf
Miracle, D. B., & Donaldson, S. L. (n.d.). Introduction to Composites. Retrieved January 25, 2014, from http://www.compositecarbonfiberprop.com/carbon_fiber.pdf
Roylance, D. (2000, March 24). Introduction to Composite Materials. Retrieved January 25, 2014, from Masschusetts Institute of Technology, Department of Materials Science and Technology: http://ocw.mit.edu/courses/materials-science-and-engineering/3-11-mechanics-of-materials-fall-1999/modules/composites.pdf
ITE. (version 2.0 Jan 13). Composite Structural Repairs. ITE.
A. Mouritz. Introduction to Aerospace Materials.
Aircraft and Aerospace Fields. (n.d.). Retrieved January 11, 2014, from The Japan Carbon Fiver Manufacturers Association: http://www.carbonfiber.gr.jp/english/field/craft.html
CIRFS. (n.d.). Retrieved January 11, 2014, from European Man-made Fibres Association: http://www.cirfs.org/manmadefibres/fibrerange/Aramid.aspx
Dr Faye Smith, C. F. (2013). Avalon Consultancy Services Ltd. Retrieved January 18, 2014, from http://avaloncsl.files.wordpress.com/2013/01/avalon-the-use-of-composites-in-aerospace-s.pdf
Wright, M. T., Ariam, C., Robert, L., Joseph, L., Howard, L., Ross, A., et al. (200). Composite Materials in Aircraft Mishaps Involving Fire: A Literature Review. Naval Air Warfare Center Weapons Division.
Although it may appear as a groundbreaking piece of modern technology in commercial aviation, our research has shown us that the introduction of composites dates back to the post-WW2 period [late 1940s] where militaries worldwide successfully constructed prototype aircraft using a good portion of composite materials such as glass-fibre reinforced plastics. [Fiberglass] Up to this day, fiberglass is still widely used as it has properties such as thermal and electrical insulation, and noteworthy impact resistant capabilities which makes it a viable material for various primary structures on both commercial and military jets.
However, it has not always been smooth-sailing in the implementation of composites. Due to the vast difference in the structure of both metals and composites – metals being homogeneous and composites heterogeneous – maintenance and repairing of composite components have always been a concern as both materials react very differently when loaded beyond their designed limits. Furthermore, with the lack of any major incidents involving composite materials, it is extremely difficult to justify any research or development to improve or change existing composites on the market.
Probably the most important thing for us as the potential workforce in the aviation industry, is to take a mental note of the rate at which composites have stormed the industry, which really points to us the importance and benefits of composites and thus the increasing need for us to familiarize ourselves with at least the basic fundamental knowledge of such materials. In fact, with the launch of the Boeing 787 DreamLiner which airframe’s construction constitutes 50% worth of composite materials, further highlights the importance of composites’ knowledge. This project thus serves as a good opportunity for us to gain a better understanding of composites as a whole – whether it is the manufacturing processes, or the types of composites being experimented for future developments. Ultimately, the project has achieved its objective in enabling us to establish a grasp of the composite concept, and why it serves to be a good substitute for metals in many areas of aviation.
Notice how the tail of a Prince Rupert's glass drop becomes increasingly small.
Fibreglass was discovered the same way.
The idea was to somehow extract the glass into very fine 'tails'. Thus, resulting in fibres.
The initial use of composites in commercial industry was not viable because of it's high cost impacting the profit of the company.
However, the Energy Crisis in 1970 provided a significant incentive to use composites. Moreover, with the aid of successful experience in the military, it was easier to implement the use of it.
By: Vaibhav Kumar