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
  ManagementTrainer 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 THROUGHHIGH 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 CRITERIAPC-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 COMPOSITESBENEFITS 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
(No Transcript)
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