COMPOSITE MATERIALS Office Hours: Tuesday, 16:30-17:30 akalemtas@mu.edu.tr, akalemtas@gmail.com Phone: +90 252 211 19 17 Metallurgical and Materials Engineering Department
ISSUES TO ADDRESS Reinforcement Materials Properties Applications
Functions of the Reinforcements Function is to reinforce the primary phase Imbedded phase is most commonly one of the following shapes: Fibers Particles Flakes In addition, the secondary phase can take the form of an infiltrated phase in a skeletal or porous matrix Example: a powder metallurgy part infiltrated with polymer Possible physical shapes of imbedded phases in composite materials: (a) fiber, (b) particle, and (c) flake 2002 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 2/e
FIBERS Filaments of reinforcing material, usually circular in cross-section Diameters range from less than 0.0025 mm to about 0.13 mm, depending on material Filaments provide greatest opportunity for strength enhancement of composites The filament form of most materials is significantly stronger than the bulk form As diameter is reduced, the material becomes oriented in the fiber axis direction and probability of defects in the structure decreases significantly
Continuous versus Discontinuous Fibers Continuous fibers - very long; in theory, they offer a continuous path by which a load can be carried by the composite part Discontinuous fibers (chopped sections of continuous fibers) - short lengths (L/D = roughly 100) Important type of discontinuous fiber are whiskers - hairlike single crystals with diameters down to about 0.001 mm (0.00004 in.) with very high strength
Fiber Orientation The fibers may be oriented randomly within the material, but it is possible to arrange for them to be oriented preferentially in the direction expected to have the highest stresses. Such a material is said to be anisotropic (different properties in different directions), and control of anisotropy is an important means of optimising the material for specific applications. At a microscopic level, the properties of these composite are determined by the orientation and distribution of the fibers, as well as by the properties of the fiber and matrix materials. These topic known as composite micromechanics is concerned with developing estimates of the overall material properties from these parameters.
Fiber Orientation Three Cases One-dimensional reinforcement, in which maximum strength and stiffness are obtained in the direction of the fiber Planar reinforcement, in some cases in the form of a two-dimensional woven fabric Random or three-dimensional in which the composite material tends to possess isotropic properties Fiber orientation in composite materials: (a) one-dimensional, continuous fibers; (b) planar, continuous fibers in the form of a woven fabric; and (c) random, discontinuous fibers
Fibers
FIBER ORIENTATION A three dimensional weave is also possible This could be found when fabrics are knitted or weaved together
FIBER ORIENTATION The properties of fiber composites can be tailored to meet different loading requirements By using combinations of different fiber orientation quasi-isotropic materials may be produced Figure. (a) shows a unidirectional arrangement (b) shows a quasi-isotropic arrangement
FIBER ORIENTATION Strongest, but anisotropic Weaker, but isotropic
FIBER ORIENTATION Maximum strength is obtained when long fibers are oriented parallel to the applied load The effect of fiber orientation and strength can be seen in the plot
FIBERS COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Filament: a single thread like fiber Roving: a bundle of filaments wound to form a large strand Chopped strand mat: assembled from chopped filaments bound with a binder Continuous filament random mat: assembled from continuous filaments bound with a binder Many varieties of woven fabrics: woven from rovings
FIBERS COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Roving Filaments Close up of a roving
FIBERS COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Random mat and woven fabric (glass fibers)
FIBERS COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Carbon fiber woven fabric
FIBERS NEXTEL FIBERS
Fiber Materials Materials for Fibers Metals Steel Polymers Kevlar Ceramics SiC and Al 2 O 3 Carbon High elastic modulus Boron Very high elastic modulus Glass Most widely used filament The most important commercial use of fibers is in polymer composites
Particles and Flakes A second common shape of imbedded phase is particulate, ranging in size from microscopic to macroscopic Flakes are basically two-dimensional particles - small flat platelets The distribution of particles in the composite matrix is random, and therefore strength and other properties of the composite material are usually isotropic Strengthening mechanism depends on particle size
Interface INTERFACE: Zone across which matrix and reinforcing phases interact (chemical, physical, mechanical) To transfer the stress from matrix to reinforcement Sometimes surface treatment is carried out to achieve the required bonding to the matrix There is always an interface between constituent phases in a composite material. For the composite to operate effectively, the phases must bond where they join at the interface. Interfaces between phases in a composite material: Direct bonding between primary and secondary phases
Interphase In some cases, a third ingredient must be added to achieve bonding of primary and secondary phases. Called an interphase, this third ingredient can be thought of as an adhesive. Interfaces between phases in a composite material: Direct bonding between primary and secondary phases
Interphase Interphase consisting of a solution of primary and secondary phases Interfaces and interphases between phases in a composite material: Formation of an interphase by solution of the primary and secondary phases at their boundary
FIBER PROPERTIES Specific strength versus specific modulus for different types of fibers
FIBER PROPERTIES COMPARATIVE COST OF FIBER REINFORCEMENT
Fibers - Glass Fiberglass properties vary somewhat according to the type of glass used. However, glass in general has several well known properties that contribute to its great usefulness as a reinforcing agent: Tensile strength Chemical resistance Moisture resistance Thermal properties Electrical properties There are four main types of glass used in fiberglass: A glass C glass E glass S glass
GLASS FIBERS Due to the relatively inexpensive cost glass fibers are the most commonly used reinforcement There are a variety of types of glass, they are all compounds of silica with a variety of metallic oxides Designation Property or Characteristic E, electrical low electrical conductivity S, strength high strength C, chemical high chemical durability M, modulus high stiffness A, alkali high alkali or soda lime glass D, dielectric low dielectric constant - The most commonly used glass is E-glass, this is the most popular because of it s cost
Fibers - Glass Most widely used fiber Uses: piping, tanks, boats, sporting goods Advantages Low cost Corrosion resistance Low cost relative to other composites: Disadvantages Relatively low strength High elongation Moderate strength and weight Types: E-Glass - electrical, cheaper S-Glass - high strength
Fibers - Glass Glass fibers produced by spinning liquid glass directly to fine fibers. Just as in the Griffith experiments, the strength is based on small diameter. Modulus ranges from 70-90 GPa. Strength ranges from 1.7-5 GPa Breaking strain from 2 to 5% Density ~ 2.5 gm/cm 3. E glass (electrical, borosilicate glass) is the cheapest and most common. R glass and S glass is more expensive but more corrosion resistant, for example and higher strength.
Fibers Carbon Carbon fibers have gained a lot of popularity in the last two decades due to the price reduction Carbon fiber composites are five times stronger than 1020 steel yet five times lighter. In comparison to 6061 aluminum, carbon fiber composites are seven times stronger and two times stiffer yet still 1.5 times lighter Initially used exclusively by the aerospace industry they are becoming more and more common in fields such as automotive, civil infrastructure, and paper production
Fibers Carbon 2 nd most widely used fiber Examples aerospace, sporting goods Advantages high stiffness and strength low density intermediate cost Properties: Standard modulus: 207-240 GPa Intermediate modulus: 240-340 GPa High modulus: 340-960 GPa Diameter: 5-8 microns, smaller than human hair Fibers grouped into tows or yarns of 2-12k fibers
Fibers Carbon Modulus ranges from 200-750 GPa (cf. Steel-210) Strength ranges from 2-6 GPa Breaking strain ranges from 0.2-2 % Density ranges from 1.76-2.15 g/cm 3 Highest cost compared to glass or aramid, but greatest range of properties. Internal structure consists of radially-aligned graphite platelets, which leads to some anisotropy in properties in the fibers. Both thermal and electrical conductivity are generally good (but then insulation required where metals might be in contact for carbon-fiber composite).
Fibers Carbon Types of carbon fiber vary in strength with processing Trade-off between strength and modulus Intermediate modulus PAN (Polyacrylonitrile) fiber precursor heated and stretched to align structure and remove non-carbon material High modulus made from petroleum pitch precursor at lower cost much lower strength
Fibers Others Boron High stiffness, very high cost Large diameter - 200 microns Good compressive strength Polyethylene - trade name: Spectra fiber Textile industry High strength Extremely light weight Low range of temperature usage
Fibers Others Ceramic Fibers (and matrices) Very high temperature applications (e.g. engine components) Silicon carbide fiber - in whisker form. Ceramic matrix so temperature resistance is not compromised Infrequent use
Fiber Material Properties Steel: density (Fe) = 7.87 cm 3 ; TS=0.380 GPa; Modulus=207 GPa Al: density=2.71 g/cm 3 ; TS=0.035 GPa; Modulus=69 GPa
Fibers-Aramid -Aramid fibers are also becoming more and more common -They have the highest level of specific strength of all the common fibers -They are commonly used when a degree of impact resistance is required such as in ballistic armour -The most common type of aramid is Kevlar http://armorus.en.made-in- china.com/product/weenpacbauyc/china-covert- Aramid-Bulletproof-Vest-Body-Armor-TAT-FJ-2-.html
Fibers-Aramid http://www.texasarmoring.com/armored_vehicle_bulletproofing_materials.html Kevlar and Aramid Fibers (Opaque Armor) Only the highest grade, waterproof Kevlar and aramid fibers are used. These fibers offer superior blast, fragmentation, explosive and small arms ballistic protection. All materials are tested in an independent laboratory and are custom fabricated according to TAC specifications.
Fiber Strength
Fiber Reinforced Composites CHARACTERISTICS OF FIBER REINFORCED COMPOSITES As can be seen from this plot, the strength of the composite increases as the fiber length increases (this is a chopped E-glassepoxy composite)
Fiber Reinforced Composites Some commonly used fibers for polymer matrix composites: Glass fibers Carbon fibers Aramid fibers Some commonly used fibers for metal matrix composites: Boron fibers Carbon fibers Oxide ceramic and non-oxide ceramic fibers
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