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Composite Materials Fundamental considerations. How do composite materials differ from other engineering materials? What are the constituent materials, and how do their properties compare? How do the properties of the composite depend on the type, amount and arrangement of the constituents?
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Composite MaterialsFundamental considerations • How do composite materials differ from other engineering materials? • What are the constituent materials, and how do their properties compare? • How do the properties of the composite depend on the type, amount and arrangement of the constituents? • How are composite products made, and why does manufacture affect quality?
Fibres have better stiffness and strength compared to bulk materials • Atomic or molecular alignment(carbon, aramid) • Removal of flaws and cracks (glass) • Strain hardening (metals)
As fibre diameter is reduced, so is maximum possible crack size in glass. Theoretical strength is achieved in defect-free material (zero diameter!). D Hull: Introduction to Composite Materials J Gordon: The New Science of Strong Materials Carbon fibre – alignment of graphite sheets. Strong, in-plane covalent bonds; weak secondary bonds between sheets (cf polymer structures).
Carbon fibres seen under the electron microscope. Note the irregular surface. Fibre diameters are around 5 – 7 microns (thousandths of a mm).
Glass fibres being drawn from the furnace. Molten glass emerges through a bushing – the rate of pulling determines the fibre diameter. Because the fibres are so small, they lose heat very quickly.
The surface of a fractured composite, containing both carbon and glass fibres. Note the larger, smoother glass, and regions where fibres have been pulled out of the plastic matrix.
steel aluminium heat-treated aluminium alloy heat-treated alloy steel
Compare stiffness and strength per unit weight: Tensile strength / density Tensile modulus / density
Nominal properties – ‘high strength’ carbon fibres tensile strength (GPa) tensile modulus (GPa)
Nominal properties – ‘intermediate-high modulus’ carbon fibres
~ 0.02 mm • Young's Modulus (SWNT) ~ 1 TPa (1000 GPa) • Young's Modulus (MWNT) 1.28 TPa • Maximum Tensile Strength ~ 30 GPa (30,000 MPa)
Most reinforcing fibres (and thermosetting resins) are brittle (elastic to failure) Hollaway (ed), Handbook of Polymer Composites for Engineers
Types of Natural Fibre • Bast fibres (flax, hemp, jute, kenaf…)- wood core surrounded by stem containing cellulose filaments • Leaf fibres (sisal, banana, palm) • Seed fibres (cotton, coconut (coir), kapok) modulus / density
Structures cannot be made from fibres alone - the high properties of fibres are not realisable in practice A matrix is required to: • hold reinforcement in correct orientation • protect fibres from damage • transfer loads into and between fibres http://www.carlosantulli.net/aim2001.pdf
COMPOSITES - A FORMAL DEFINITION(Hull, 1981) 1. Consist of two or more physically distinct and mechanically separable parts. reinforcement(discontinuous phase) matrix (continuous phase) + fibres or particles short, ‘long’ or continuous
Concrete - hard particles (gravel) + cement (ceramic/ceramic composite). Properties determined by particle size distribution, quantity and matrix formulation Additives and fillers in polymers: carbon black (conductivity, wear/heat resistance) aluminium trihydride (fire retardancy) glass or polymer microspheres (density reduction) chalk (cost reduction) Cutting tool materials and abrasives (alumina, SiC, BN bonded by glass or polymer matrix; diamond/metal matrix) Electrical contacts (silver/tungsten for conductivity and wear resistance) Cast aluminium with SiC particles Examples of particulate composites
Alternative matrix materials Ceramic(CMCs) Metal (MMCs) Polymer(PMCs) Fibre: SiC; alumina; SiN Matrix: SiC;alumina;glass-ceramic;SiN Fibres improve toughness Fibre: boron; Borsic; carbon (graphite); SiC; alumina (Al2O3) Matrix: aluminium; magnesium; titanium; copper Fibres improve high temp creep; thermal expansion. thermoplastic thermoset Tough; high melt viscosity; ‘recyclable’ Brittle; low viscosity before cure; not recyclable The matrix material largely determines the processing method…
COMPOSITES - A FORMAL DEFINITION(Hull, 1981) 1. Consist of two or more physically distinct and mechanically separable parts. 2. Constituents can be combined in a controlled way to achieve optimum properties.
COMPOSITES - A FORMAL DEFINITION(Hull, 1981) 1. Consist of two or more physically distinct and mechanically separable parts. 2. Constituents can be combined in a controlled way to achieve optimum properties. 3. Properties are superior, and possibly unique, compared those of the individual components
Addition of properties: GLASS + POLYESTER = GRP (strength) (chemical resistance) (strength and chemical resistance) Unique properties: GLASS + POLYESTER = GRP (brittle) (brittle) (tough!)
Aerospace, defence, F1… Highly stressed Glass, carbon, aramid fibres Honeycomb cores Epoxy, bismaleimide… Prepregs Vacuum bag/oven/autoclave Highly tested and qualified materials Marine, building… Lightly stressed Glass (random and woven) Foam cores Polyester, vinylester… Wet resins Hand lay up, room temperature cure Limited range of lower performance materials ADVANCED COMPOSITES vs REINFORCED PLASTICS
Why are composites used in engineering? • Weight saving (high specific properties) • Corrosion resistance • Fatigue properties • Manufacturing advantages:- reduced parts count- novel geometries- low cost tooling • Design freedoms- continuous property spectrum- anisotropic properties
Anisotropic properties - fibres can be aligned in load directions to make the most efficient use of the material
Why aren’t composites used more in engineering? • High cost of raw materials • Lack of design standards • Few ‘mass production’ processes available • Properties of laminated composites:- low through-thickness strength- low interlaminar shear strength • No ‘off the shelf’ properties - performance depends on quality of manufacture
There are no ‘off the shelf’ properties with composites. Both the structure and the material are made at the same time. Material quality depends on quality of manufacture.
Metal (steel, aluminium, titanium, magnesium…)Composite (carbon fibre / epoxy)?
Aluminium or composite? 2005: Airbus engineers are claiming Boeing has rushed the development of the 7E7 Dreamliner. In particular, they say composite technology is not mature enough to build an all-composite fuselage. But the claims may be no more than a marketing ploy, in response to Boeing's criticism of weight overruns on the Airbus A380.
SEATTLE, Jan. 11, 2005 – Boeing recently completed the first full-scale composite one-piece fuselage section for its new 7E7 Dreamliner program, demonstrating concepts for 7E7 production that begins next year. The structure, 7 m long and nearly 6 m wide, is the 7E7's first major development piece. "This is a piece of aviation history," said Walt Gillette, Boeing vice president of Engineering, Manufacturing and Partner Alignment. "Nothing like this is already in production. Hundreds of aerospace experts from Boeing and our partners developed everything, including the design, tools that served as the mold, programming for the composite lay-down, and tools that moved the structure into the autoclave." He added that using composites "allowed us to create optimized structural designs and develop an efficient production process. We now see how all advanced airplanes will be built from this time forward."
Composite – wood, glass, carbon? Manufacture - prepreg, infusion…?
ADVANTAGES OF COMPOSITES(for construction applications) Aesthetic appeal Ability to mould complex shapes Various surface finishes available Lightweight Durability / Corrosion resistance Parts integration Cost effectiveness Electrical properties
POSSIBLE APPLICATIONS(in construction) Roofs / canopies Complete buildings Cladding panels Masts & towers Domes Unusual architectural features / structures Radomes Permanent or temporary formwork Strengthening / repair of conventional structures Tanks, covers, pipes, ducts etc
HARARE INTERNATIONAL AIRPORTARCHITECTURAL GRP STRUCTURE ON THE TOP OF THE AIR TRAFFIC CONTROL TOWER
FRPMOSQUEDOMES PHOTOS COURTESY OF NORTHSHORE COMPOSITES
FRP OBSERVATION CABIN & CARBON FIBREMAST GLASGOW SCIENCE CENTRE Photo - Carrillion