1. UNIT 8 COMPOSITE MATERIALS

2. Composites Hari Prasad 2

3. Composites Composite materials are combination of two or more materials with more desirable combination of properties – Ex: get flexibility & weight of a polymer plus the strength of a ceramic Principle of combined action – Mixture gives “averaged” properties Hari Prasad 3

4. Advantages of Composites High strength to weight ratio Energy efficient Corrosion and weather resistant Properties for specific design conditions Directional properties Complex shapes can be made easily Hari Prasad 4

5. 5 Constituents Discontinuous phase – Reinforcement (dispersed phase) Continuous phase - Matrix PolymerComposite

6. COMPOSITES Composites can be classified by their matrix material which include: -Metal matrix composites (MMC’s) -Ceramic matrix composites (CMC’s) -Polymer matrix composites (PMC’s) or sometimes referred to as organic matrix composites (OMC’s)

7. 7 Terminology/Classification Composites: -- Multiphase material w/significant proportions of each phase. Dispersed phase: -- Purpose: enhance matrix properties. MMC: increase  y, TS, creep resistance CMC: increase Kc PMC: increase E,  y, TS, creep resistance -- Classification: Particle, fiber, structural Matrix: -- The continuous phase -- Purpose is to: - transfer stress to other phases - protect phases from environment -- Classification: MMC, CMC, PMC metalceramicpolymer

8. COMPOSITES MMC - Metal Matrix Composites -The matrix is relatively soft and flexible. -The reinforcement must have high strength and stiffness -Since the load must be transferred from the matrix to the reinforcement, the reinforcement-matrix bond must be strong. MMC use: -Two types of particulates ( dispersion strengthened alloys and regular particulate composites) -Or long fiber reinforcements

9. COMPOSITES PMC - Polymer Matrix Composites -The matrix is relatively soft and flexible -The reinforcement must have high strength and stiffness -Since the load must be transferred from matrix to reinforcement, the reinforcement-matrix bond must be strong CMC – Ceramic Matrix Composites -The matrix is relatively hard and brittle -The reinforcement must have high tensile strength to arrest crack growth -The reinforcement must be free to pull out as a crack extends, so the reinforcement-matrix bond must be relatively weak

10. Composite Survey

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12. CHARACTERISTICS OF FIBER REINFORCED COMPOSITES -Many factors must be considered when designing a fiber-reinforced composite including the length, diameter, orientation, amount and properties of the constituents, and the bonding between them. -The method used to produce the final product is also very important as it Indicates the type of properties just mentioned as well as the quality of the product.

13. CHARACTERISTICS OF FIBER REINFORCED COMPOSITES 1.Fiber length and diameter: Fiber dimensions are characterized by their aspect ratio l/d where l is the fiber length and d is the diameter. 2.The strength improves when the aspect ratio is large. 3.Typical fiber diameters are from 10  m to 150  m. Fibers often fracture because of surface imperfections. Making the diameter small reduces its surface area, which has fewer flaws. 4.Long fibers are preferred because the ends of the fiber carry less of the load. Thus the longer the fiber, the fewer the ends and the higher the load carrying capacity of the fibers.

14. 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-glass- epoxy composite)

15. 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

16. 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 Figure (b) shows a quasi-isotropic arrangement

17. FIBER ORIENTATION -A three dimensional weave is also possible -This could be found when fabrics are knitted or weaved together

18. FIBER PROPERTIES In most fiber-reinforced composites, the fibers are strong, stiff and lightweight. If the composite is to used at elevated temperatures, the fiber should also have a high melting temperature. The specific strength and specific modulus of fibers are important characteristics given by: Where TS is the tensile strength, E is the elastic modulus and  is the density.

19. FIBER PROPERTIES -On the left is a graph showing specific strength vs. specific modulus for different types of fibers

20. TYPES OF FIBERS 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

21. 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, electricallow electrical conductivity S, strengthhigh strength C, chemicalhigh chemical durability M, modulushigh stiffness A, alkalihigh alkali or soda lime glass D, dielectriclow dielectric constant -The most commonly used glass is E-glass, this is the most popular because of it’s cost

22. CARBON FIBERS -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

23. ARAMID FIBERS -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

24. COMPARATIVE COST OF FIBER REINFORCEMENT

25. 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

26. COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Above Left: Roving Above Right: Filaments Right: Close up of a roving

27. COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Random mat and woven fabric (glass fibers)

28. COMMERCIALLY AVAILABLE FORMS OF REINFORCEMENT Carbon fiber woven fabric

29. Fiber Alignment aligned continuous aligned random discontinuous Adapted from Fig. 16.8, Callister 7e.

30. MATRIX MATERIALS

31. POLYMER MATRIX MATERIAL -There are two basic categories of polymer matrices: -Thermoplastics -Thermoset plastics -Roughly 95% of the composite market uses thermosetting plastics -Thermoseting plastics are polymerized in two ways: -By adding a catalyst to the resin causing the resin to ‘cure’, basically one must measure and mix two parts of the resin and apply it before the resin cures -By heating the resin to it’s cure temperature

32. POLYMER MATRIX MATERIAL Common thermosetting plastics: -Phenolics: good electrical properties, often used in circuit board applications -Epoxies: low solvent emission (fumes) upon curing, low shrink rate upon polymerization which produces a relatively residual stress-free bond with the reinforcement, it is the matrix material that produces the highest strength and stiffness, often used in aerospace applications -Polyester: most commonly used resin, slightly weaker than epoxy but about half the price, produces emission when curing, used in everything from boats to RVs to piping to Corvette bodies

33. METAL MATRIX MATERIAL Common Metal Matrices: -Metal martices include aluminum, magnesium, copper, nickel, and intermetallic compound alloys - MMCs are better at higher temperatures than PMCs although production is much more difficult and expensive -MMCs can have applications such as fan blades in engines, clutch and brake linings, engine cylinder liners, etc.

34. The polymers that are used in PMCs are two types Thermoplastics Polyethyle ne polystyrenePolyamidesNylons polypropyl ene

35. Thermosets Epoxy Phenolic polyamide resins Polyester

36. MANUFACTURING WITH POLYMER MATRIX MATERIALS

37. MANUFACTURING OF POLYMER-MATRIX COMPOSITES -The method of manufacturing composites is very important to the design and outcome of the product -With traditional materials one starts out with a blank piece of material ie: rod, ingot, sheet, etc and works it to produce the desired part. -However, this is not the case with polymer-matrix composites. -With these composites the material and the component are being produced at the same time, therefore we aim for the product to be a net or near net shape with little to no post processing

38. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Hand Lay-Up/Spray-Up -Oldest and most commonly used manufacturing method -Usually used to produce polyester or epoxy resin parts such as boat hulls, tanks and vessels, pick-up truck canopies -The method is quite simple, the resin and reinforcement is placed against the surface of an open (one sided) mold and allowed to cure or in the case of spray-up the resin/reinforcement is sprayed onto the mold with a spray gun -Often a gel coat is applied to the mold prior to produce a better surface quality and protect the composite from the elements -A gel coat is a resin usually 0.4 to 0.7 mm thick, commonly seen on the outer surface of smaller boats

41. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Hand Lay-Up/Spray-Up -this process include: low initial start up cost, easy to change mold/design, on- site production possible (ie portable process) -The cons include: labor intensive, the quality of parts depends on operator’s skill and therefore inconsistent, only one good side to the part

48. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Filament Winding -A continuous reinforcement, either previously impregnated or impregnated during winding is wound around a rotating mandrel to form a composite part -Pros: fast lay-up speed, very accurate and repeatable product, possibility to use continuous fiber -Cons: expensive equipment, high cost for mandrel, poor surface finish, some shapes not possible -Examples: oxygen bottles for firemen, rocket motors, tennis rackets, shafts

50. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Filament Winding

51. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Filament Winding

52. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Resin Transfer Molding - Resin transfer molding is a manufacturing method that is quite similar to injection molding where plastic is injected into a closed mold -In the RTM process the preform (precut piece(s) of reinforcement) is placed in the mold, the mold is closed and the thermoset plastic matrix is injected into the mold, once the matrix is cured the part is ejected

53. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Prepreg -A pregreg (short for preimpregnated) is a composite that comes with the resin already added to the reinforcement -This means that the only concern when working with prepreg is shaping the part -Since the resin is already mixed (resin and catalyst) there is a limited shelf life -For the same reason prepreg must be cured in an oven or autoclave

54. Prepreg -Prepreg can be used in a few different ways -It can be placed against a mold similar to the hand lay-up method -Once placed in the mold the material must be compressed and cured according to a specific pressure/temperature cycle -This is often done by means of a vacuum bag where a thin plastic cover is secured overtop of the composite and the air is vacuumed out -This process can reduce manufacturing time and produce a stronger part (if a knitted preform is used) -Another process used is ‘automated tape lay-up’ -This process uses a large automated roller similar to a packing tape roller -The roller applies the tape with pressure which eliminates the need for a vacuum bag - Automated tape lay-up is used to produce large parts, generally in aerospace applications and is also capable of 3-d parts

56. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Pultrusion -Similar to extrusion of metal parts -Pultrusion involves pulling resin-impregnated glass strands through a die -Standard extruded shapes can easily be produced such as pipes, channels, I- beams, etc.

57. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Pultrusion

61. SHEET MOULDING COMPOUND (SMC)

63. MANUFACTURING OF POLYMER-MATRIX COMPOSITES Resin Transfer Molding

64. Pros: -Complex components can be produced -Components have two good surfaces -Component can be created within a fairly tight tolerance -High level of repeatability -Process can be automated and repeated -Process can be numerically modeled and analyzed Cons: -Molds often need to be designed using trial and error methods -‘race tracking’ may occur -‘wash out’ may occur -Air voids are easily formed with poor process parameters

65. Resin Transfer Molding Researcher from Aerospace Manufacturing Technology Center in Montreal molding members for a helicopter

66. POWDER METALLURGY TECHNIQUE 1.POWDER MANUFACTURING 2. POWDER MIXING/BLENDING 3. COMPACTING (POWDER PRESSING) 4.SINETRING 5. FINISHING OPERATION

69. THE END