Transcript THE ART OF MATERIAL SELECTION FOR THE DESIGN
THE ART OF MATERIAL SELECTION FOR THE DESIGN AND MANUFACTURE OF AEROSPACE VEHICLES
PERSONAL VIEW OF A SMALL AIRFRAMER‘S EMPLOYEE INTERNAL REFERENCE: MP-00-MI-10-061, ISSUE 1
MP-00-MI-10-061 Materials for Aerospace Vehicles
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 21:37 15 U. Thomann 2
MP-00-MI-10-061
Contents
Materials for Aerospace Vehicles • Driving forces for material selection • Yesterday’s, today’s and tomorrow’s material mix in aeroplanes • Some examples of material selections (or refusals) • A spotlight on composites: benefits and challenges 21:37 15 U. Thomann 3
MP-00-MI-10-061 Materials for Aerospace Vehicles
MATERIAL SELECTION: DRIVING FORCES
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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 product‘s life!
Safety is always a built-in feature granted through compliance with ever more stringent regulations as issued by (multi)national authorities (EASA, FAA,...) 21:37 15 U. Thomann 4
MP-00-MI-10-061 Materials for Aerospace Vehicles
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 (1990‘s) 21:37 15 U. Thomann
BUT...
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MP-00-MI-10-061 Materials for Aerospace Vehicles
... THE ALUMINIUM FACTION DID NOT LAZE!
Friction Stir Welding • • Advanced joining technologies design integration fewer parts reduction of structural assembly labour cost reduction New alloys strength lower density/higher 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 (1990‘s) Laser Beam Welding or extrusion 21:37 15 U. Thomann 6
MP-00-MI-10-061 Materials for Aerospace Vehicles
A380 – ALUMINIUM STRUCTURE BENCHMARK
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MP-00-MI-10-061 Materials for Aerospace Vehicles
AIRFRAME MATERIALS: PAST, PRESENT, FUTURE
Tendency: • More composite materials • Tailored matieral mix to improve over all systems performance 21:37 15 U. Thomann 8
EXAMPLES OF MATERIAL SELECTIONS (OR REFUSALS)
INTERNAL REFERENCE: MP-00-MI-10-061, ISSUE 1
MP-00-MI-10-061 Materials for Aerospace Vehicles
EFFICIENCY IMPROVEMENT THROUGH ADVANCED MATERIAL TECHNOLOGIES
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max ambient • • Higher combustion temperatures yield higher thermodynamic efficiency and thus lower fuel consumption Today‘s 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 21:37 15 U. Thomann 10
MP-00-MI-10-061 Materials for Aerospace Vehicles
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 21:37 15 U. Thomann 11
MP-00-MI-10-061 Materials for Aerospace Vehicles
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 21:37 15 U. Thomann 12
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ELASTOMERS
Materials for Aerospace Vehicles • • 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 21:37 15 U. Thomann 13
MP-00-MI-10-061 Materials for Aerospace Vehicles
POLYSULFIDE SEALANTS
• Sealants are the true cost savers throughout an aeroplane‘s 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 21:37 15 U. Thomann 14
MP-00-MI-10-061 Materials for Aerospace Vehicles
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 21:37 15 U. Thomann 15
A SPOTLIGHT ON COMPOSITES: BENEFITS AND CHALLENGES
INTERNAL REFERENCE: MP-00-MI-10-061, ISSUE 1
MP-00-MI-10-061 Materials for Aerospace Vehicles
ALUMINIUM VS. COMPOSITE TRUCTURE
21:37 15 Aluminum • Long-term experience • High automation level • Advanced joining technologies • Standardized material • Standard Certification procedure • Fatigue • Corrosion • Subprocesses U. Thomann Composite • Low density (weight reduction) • High strength and stiffness • Improved fatigue behavior • Less corrosion • Design freedom • Reduced manufacturing costs • Reduced Direct Operating Costs • Design • Impact sensitivity • Environmental influences • Material + manufacturing diversity • Certification (not standardized mat.) • High material cost 17
MP-00-MI-10-061 Materials for Aerospace Vehicles
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 21:37 15 U. Thomann 18
MP-00-MI-10-061 Materials for Aerospace Vehicles
RAW MATERIAL DIVERSITY
Composite Reinforcement (Fibers) Filament UD fabric Woven fabric Fiber Mat Thermosets Matrix (Polymer) Polymer Thermoplastics Carbon HTA HTS AS4 IMS T700 T800 … … … … … … … … Glass … 21:37 15 Aramid … Natural … Epoxy Bismaleimide Cyanesther Phenolic … … … … … … PEEK PPS PEI … Diversity due to user-defined raw material combination Objective: Material combination = Design and manufacturing requirements U. Thomann 19
MP-00-MI-10-061 Materials for Aerospace Vehicles
MANUFACTURING PROCESS DIVERSITY
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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 Material Design • Process limitations • Laminate quality: - Fiber volume fraction - Internal and external defects - Dimensions • Surface condition • Quantity • Quality control • Process qualification • Costs Interaction Manufacturing • Material properties • Semi-finished products • Environmental influences: - Temperature - Humidity • Quality control • Availability 21:37 15 • Price U. Thomann 21
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CERTIFICATION
Composite Proof Tests
• Aircraft-specific specimens • Demonstrate ultimate load or fatigue capability • Include defects, damage, environmental effects Validate Design
Material Tests
• Generic specimens • Determine material data • Understand deformations and failure modes Establish Design 21:37 15 U. Thomann
Metal
Same as composite Very little tests in case of special design features No tests due to standardized material and long-term experience 22
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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 -55°C to +55°C 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.
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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 21:37 15 U. Thomann 24
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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 composite‘s advantages over standard materials • The holy grail lies in design integration and eventually certification of advanced joining techniques 21:37 15 U. Thomann 25
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SUMMARY
Materials for Aerospace Vehicles • 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 – OEM’s 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 21:37 15 U. Thomann 27
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THANKS FOR YOUR ATTENTION
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