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THE ART OF MATERIAL SELECTION FOR THE DESIGN AND MANUFACTURE OF AEROSPACE VEHICLES

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Title: THE ART OF MATERIAL SELECTION FOR THE DESIGN AND MANUFACTURE OF AEROSPACE VEHICLES


1
THE ART OF MATERIAL SELECTION FOR THE DESIGN AND
MANUFACTURE OF AEROSPACE VEHICLES
  • PERSONAL VIEW OF A SMALL AIRFRAMERS EMPLOYEE
  • INTERNAL REFERENCE MP-00-MI-10-061, ISSUE 1

2
ABOUT THE AUTHOR
  • Dr. Urs I. Thomann
  • MSc. in materials science
  • Graduate studies in corrosion resistant high
    strength steels
  • Ph.D. in composites science
  • with Pilatus since 2003
  • Materials and processes specialist
  • Project Manager, landing gear redesign
  • Since 2006, Director Production
    Management Trainer Aircraft

3
Contents
  • Driving forces for material selection
  • Yesterdays, todays and tomorrows material mix
    in aeroplanes
  • Some examples of material selections (or
    refusals)
  • A spotlight on composites benefits and
    challenges

4
MATERIAL SELECTION DRIVING FORCES
  • Cost reduction
  • Cost reduction
  • Cost reduction
  • Weight reduction, linked with cost through
    operating cost reduction (increased
    payload/range)
  • Maintenance cost (life cycle cost reduction)
  • Advanced technologies are only the means to
    achieve all but only financial goals in all
    phases of the products life!
  • Safety is always a built-in feature granted
    through compliance with ever more stringent
    regulations as issued by (multi)national
    authorities (EASA, FAA,...)

5
COST REDUCTION THROUGH COMPOSITES
  • Design integration ? fewer parts ? reduction of
    structural assembly labour ? cost reduction
  • Low density/high strength ? reduction of empty
    weight ? increased payload/range ? increased
    operating profit
  • Improved corrosion resistance ? lower life cycle
    cost
  • Potential estimated at 30 weight reduction, 40
    cost reduction compared with standard metal
    leight weight design (1990s)
  • BUT...

6
... THE ALUMINIUM FACTION DID NOT LAZE!
  • Advanced joining technologies ? design
    integration ? fewer parts ? reduction of
    structural assembly labour ? cost reduction
  • New alloys ? lower density/higher strength ?
    reduction of empty weight ? increased
    payload/range ? increased operating profit
  • Potential estimated at 20 weight reduction, 20
    cost reduction compared with standard metal
    light weight design (1990s)

7
A380 ALUMINIUM STRUCTURE BENCHMARK
8
AIRFRAME MATERIALS PAST, PRESENT, FUTURE
Composite weight percentage
  • Tendency
  • More composite materials
  • Tailored matieral mix to improve over all systems
    performance

9
EXAMPLES OF MATERIAL SELECTIONS (OR REFUSALS)
  • INTERNAL REFERENCE MP-00-MI-10-061, ISSUE 1

10
EFFICIENCY IMPROVEMENT THROUGH ADVANCED MATERIAL
TECHNOLOGIES
  • Higher combustion temperatures yield higher
    thermodynamic efficiency and thus lower fuel
    consumption
  • Todays technology with single crystal nickel
    alloys and oxide dispersioned strengthened (ODS)
    super alloys with bleed air cooling cannot
    provide the required step change in fuel
    consumption
  • New high temperature/high strength materials
    along with new design concepts required ? Ceramic
    matrix composites

11
WEIGHT REDUCTION THROUGH HIGH STRENGTH MATERIALS
  • Typical steel applications Heavily stressed
    bolts, bushings and special fittings in the
    landing gear and engine pylon, moderately
    temperature stressed portions of engine
    shrouds,...
  • Despite the tendency of decreasing steel weight
    fraction of the airframe there is still some
    weight saving potential by employing novel high
    strength, corrosion resistant steels
  • However, such novel alloys like e.g. nitrogen
    alloyed pressure electro slag remelted
    austhenitic stainless steels are still not
    offered (nor demanded) in aerospace certificated
    grades
  • Weight saving potential is probably not big
    enough to off-set certification cost

12
LESS OBVIOUS MATERIAL SELECTION CRITERIA PC-21
FIREWALL
  • Frame to separate cockpit from engine is
    manufactured from titanium
  • Firewall has to withstand an engine fire for a
    defined duration without allowing the heat to
    penetrate into the front cockpit
  • Titanium has much lower heat conductivity than
    steel or aluminium and retains reasonable
    strength at higher temperatures

13
ELASTOMERS
  • Still the best material to cope with excessive
    wear experienced by the tires is natural rubber!
  • O-ring seals and flexible hoses make sure to
    select the right material depending on media to
    be sealed against or flowing through
  • Chloroprene withstands fuel but not ozone and UV
    light
  • Isoprene is easy with ozone und UV light but not
    with fuel or hydraulic fluids
  • Nitrile butadiene rubber (NBR) happily swims in
    hydraulic fluids but should not be exposed to
    ambient air with ozone and UV light
  • Fluoropolymer rubbers are expensive but cope with
    almost every environment, even at somewhat
    elevated temperatures

14
POLYSULFIDE SEALANTS
  • Sealants are the true cost savers throughout an
    aeroplanes life
  • Making the pressurised fuselage air tight and the
    integral wing tank fuel tight is only the most
    obvious primary function of a true but modest
    champion
  • Seals crevices to prevent corrosion due to
    moisture entrapment
  • Releases chromates to prevent microbial attack in
    the integral tank
  • Chromates also actively inhibit corrosion in
    general

15
COMPOSITES FOR PROTOTYPING
  • Some composites manufacturing processes allow for
    quick prototyping at modest tooling and
    production cost
  • Ideal for validation of concept studies
    specifically for full scale aerodynamic tests
  • Risk mitigation, development cost reduction

PC-21 UWT H-tail fin 5 days from design to
prototype
16
A SPOTLIGHT ON COMPOSITES BENEFITS AND CHALLENGES
  • INTERNAL REFERENCE MP-00-MI-10-061, ISSUE 1

17
ALUMINIUM VS. COMPOSITE TRUCTURE
Aluminum
Composite
  • Long-term experience
  • High automation level
  • Advanced joining technologies
  • Standardized material
  • Standard Certification procedure
  • Low density (weight reduction)
  • High strength and stiffness
  • Improved fatigue behavior
  • Less corrosion
  • Design freedom
  • Reduced manufacturing costs
  • Reduced Direct Operating Costs

Advantages
  • Fatigue
  • Corrosion
  • Subprocesses
  • Design
  • Impact sensitivity
  • Environmental influences
  • Material manufacturing diversity
  • Certification (not standardized mat.)
  • High material cost

Challenges
18
IMPROVED CORROSION RESISTANCE ONLY HALF OF THE
TRUTH!
  • Yes, by and large carbon fibre composites are
    pretty much unaffected by corrosive environments,
    but...
  • ... aluminium alloys are even more affected when
    in direct contact with carbon fibres due to
    extreme electrochemical potential difference
    between carbon and aluminium
  • Cadmium plated stainless steel/nickel fasteners
    needed
  • More expensive
  • heavier than aluminium fasteners
  • More titanium in direct contact with carbon fibre
    composites employed
  • More expensive raw material and more complex
    production processes than aluminium
  • Similar specific strength/stiffness as aluminium

19
RAW MATERIAL DIVERSITY
Composite
Reinforcement (Fibers)
Matrix (Polymer)
Polymer
UD fabric
Woven fabric
Mat
Filament
Fiber
Thermosets
Thermoplastics
Carbon
Glass
Aramid
Epoxy
Natural
PEEK

Bismaleimide
PPS

HTA




Cyanesther
PEI

HTS

Phenolic


AS4



IMS

T700

T800



20
MANUFACTURING PROCESS DIVERSITY
21
COMPOSITE DESIGN, MANUFACTURING, MATERIAL
  • Design, e.g.
  • Integral or differential
  • Monolithic and/or sandwich
  • Frame-Stringer or Spar-Rips, etc.
  • Design philosophy
  • Safe life
  • Fail safe
  • damage tolerance
  • Strength and stiffness requirements
  • Static and dynamic analysis
  • Further considerations
  • Inspection
  • Repair procedure
  • Lightning protection
  • Electrical grounding
  • Process limitations
  • Laminate quality
  • Fiber volume fraction
  • Internal and external defects
  • Dimensions
  • Surface condition
  • Quantity
  • Quality control
  • Process qualification
  • Costs

Design
Interaction
Manufacturing
Material
  • Material properties
  • Semi-finished products
  • Environmental influences
  • Temperature
  • Humidity
  • Quality control
  • Availability
  • Price

22
CERTIFICATION
Composite
Metal
  • Proof Tests
  • Aircraft-specific specimens
  • Demonstrate ultimate load or fatigue capability
  • Include defects, damage, environmental effects
  • Validate Design

Same as composite
Very little tests in case of special design
features
  • Material Tests
  • Generic specimens
  • Determine material data
  • Understand deformations and failure modes
  • Establish Design

No tests due to standardized material and
long-term experience
23
CERTIFICATION
  • E.g. coupons tests
  • Mechanical properties, e.g.
  • Laminate Strength and stiffness etc. in tension,
    compression and shear.
  • Engineering data Strength in tension and
    compression with and without holes bearing
    strength Compression After Impact strength
  • Physical properties, e.g.
  • Density, glass transition temperature Tg, volume
    fraction, cured ply thickness
  • Environmental influences, e.g.
  • From -55C to 55C OAT in dry and wet conditions
  • Contaminations (hydraulic fluid, jet fuel,
    solvents, paint stripper)
  • Requirements for storage, handling, processing,
    machining etc.
  • Data must be established by means of a
    qualification programme for each specific
    composite material.

24
QUALITY CONTROL
  • Raw material testing
  • Physical and chemical tests
  • Mechanical coupons tests
  • Manufacturing control
  • Process control
  • Component testing
  • Visual inspection
  • Dimension and weight control
  • Ultrasonic inspection
  • Mechanical test of coupons which accompanied the
    curing process

25
SOME CRITICAL COMMENTS
  • Use of composites in aerospace is about to
    degenerate to a marketing crusade
  • Composites should not be used for the sake of
    composites usage but for their beneficial
    properties in some (but not all) applications
  • There is still a lot of black metal design even
    in the most recently developed products, which by
    and large defeats most of the composites
    advantages over standard materials
  • The holy grail lies in design integration and
    eventually certification of advanced joining
    techniques

26
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27
SUMMARY
  • Deep knowledge of the present state of the art in
    each class of materials is essential
  • There is no right or wrong material selection it
    is rather a complex decision making process
    depending on
  • OEMs design and manufacturing skill and
    experience level
  • Requirements
  • Balance of value and cost
  • Mastering the art of selecting the best
    performing material for any given purpose of
    application is really at the core of the
    successful design of an aerospace vehicle

28
THANKS FOR YOUR ATTENTION
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