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  • 1. Introduction To Composite Materials Mr. S. G. Kulkarni SVNIT SURAT
  • 2. Tutorial What is metal ? What is non metal ? What is alloy ? What are drawbacks of metals ? What is engineering ? Why we are studying practical ?
  • 3. Introduction to Composites1. What is the matrix in a composite and what materials are commonly used as a matrix?2. What is reinforcement in composites ?3. Be able to decide different factors responsible for properties of composite.4. Know the equation for the critical length (Lc) of a fiber.. Reading:
  • 4. Composites in Action
  • 5. Composite Material Two inherently different materialsthat when combined together producea material with properties that exceed the constituent materials.
  • 6. What is a composite Material?A broad definition of composite is: Two or more chemically distinctmaterials which when combined have improved properties over theindividual materials. Composites could be natural or synthetic.Wood is a good example of a natural composite, combination ofcellulose fiber and lignin. The cellulose fiber provides strengthand the lignin is the "glue" that bonds and stabilizes the fiber.Bamboo is a very efficient wood composite structure. The components arecellulose and lignin, as in all other wood, however bamboo is hollow. Thisresults in a very light yet stiff structure. Composite fishing poles and golfclub shafts copy this natural design.The ancient Egyptians manufactured composites! Adobe bricks are a goodexample. The combination of mud and straw forms a composite that isstronger than either the mud or the straw by itself. 6
  • 7. TutorialRevise the concept ofHardnessToughnessStiffnessYield strenthUltimate tensile strengthCompressive strenthTensile StrenthShear strengthDuctilenessBrittleness
  • 8. StrengthFor metals the most common measure of strength is the yield strength. Formost polymers it is more convenient to measure the failure strength, thestress at the point where the stress strain curve becomes obviously non-linear. Strength, for ceramics however, is more difficult to define. Failure inceramics is highly dependent on the mode of loading. The typical failurestrength in compression is fifteen times the failure strength in tension. Themore common reported value is the compressive failure strength.Yield StrengthThe yield strength is the minimum stress which produces permanentplastic deformation. This is perhaps the most common material propertyreported for structural materials because of the ease and relative accuracyof its measurement. The yield strength is usually defined at a specificamount of plastic strain, or offset, which may vary by material and orspecification. The offset is the amount that the stress-strain curve deviatesfrom the linear elastic line. The most common offset for structural metalsis 0.2%.
  • 9. Ultimate Tensile StrengthThe ultimate tensile strength is an engineering value calculated by dividing the maximum load on a materialexperienced during a tensile test by the initial cross section of the test sample. When viewed in light of the other tensiletest data the ultimate tensile strength helps to provide a good indication of a materials toughness but is not by itself auseful design limit. Conversely this can be construed as the minimum stress that is necessary to ensure the failure of amaterial.DuctilityDuctility is a measure of how much deformation or strain a material can withstand before breaking. The most commonmeasure of ductility is the percentage of change in length of a tensile sample after breaking. This is generally reportedas % El or percent elongation. The R.A. or reduction of area of the sample also gives some indication of ductility.ToughnessToughness describes a materials resistance to fracture. It is often expressed in terms of the amount of energy a materialcan absorb before fracture. Tough materials can absorb a considerable amount of energy before fracture while brittlematerials absorb very little. Neither strong materials such as glass or very ductile materials such as taffy can absorblarge amounts of energy before failure. Toughness is not a single property but rather a combination of strength andductility.The toughness of a material can be related to the total area under its stress-strain curve. A comparison of the relativemagnitudes of the yield strength, ultimate tensile strength and percent elongation of different material will give a goodindication of their relative toughness. Materials with high yield strength and high ductility have high toughness.Integrated stress-strain data is not readily available for most materials so other test methods have been devised to helpquantify toughness. The most common test for toughness is the Charpy impact test.In crystalline materials the toughness is strongly dependent on crystal structure. Face centered cubic materials aretypically ductile while hexagonal close packed materials tend to be brittle. Body centered cubic materials often displaydramatic variation in the mode of failure with temperature. In many materials the toughness is temperature dependent.Generally materials are more brittle at lower temperatures and more ductile at higher temperatures. The temperature atwhich the transition takes place is known as the DBTT, or ductile to brittle transition temperature. The DBTT ismeasured by performing a series of Charpy impact tests at various temperatures to determine the ranges of brittle andductile behavior. Use of alloys below their transition temperature is avoided due to the risk of catastrophic failure.
  • 10. Composites OfferHigh StrengthLight WeightDesign FlexibilityStrenthen of PartsNet Shape Manufacturing
  • 11. Composites Composites are combinations of two materials in which one of the material is called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other material called the matrix phase. Typically, reinforcing materials are strong with low densities while the matrix is usually a ductile or tough material. If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material.Components of composite materials Reinforcement: fibers Matrix materials Interface Glass Polymers Bonding Carbon Metals surface Organic Ceramics Boron Ceramic 11 Metallic
  • 12. Why Composites are Important Composites can be very strong and stiff, yet very light in weight, so ratios of strength-to-weight and stiffness-to-weight are several times greater than steel or aluminum Fatigue properties are generally better than for common engineering metals Toughness is often greater too Composites can be designed that do not corrode like steel Possible to achieve combinations of properties not attainable with metals, ceramics, or polymers alone
  • 13. Fiber Reinforced Polymer Matrix Matrix •Transfer Load to Reinforcement •Temperature Resistance •Chemical Resistance Reinforcement •Tensile Properties •Stiffness •Impact Resistance
  • 14. Matrix ConsiderationsEnd Use TemperatureToughnessCosmetic IssuesFlame RetardantProcessing MethodAdhesion Requirements
  • 15. Matrix Materials Functions of the matrix – Transmit force between fibers – arrest cracks from spreading between fibers  do not carry most of the load – hold fibers in proper orientation – protect fibers from environment  mechanical forces can cause cracks that allow environment to affect fibers Demands on matrix – Interlaminar shear strength – Toughness – Moisture/environmental resistance – Temperature properties – Cost
  • 16. Types of Composite MaterialsThere are five basic types of composite materials:Fiber, particle, flake, laminar or layered and filledcomposites.
  • 17. A. Fiber CompositesIn fiber composites, the fibers reinforce along the line of theirlength. Reinforcement may be mainly 1-D, 2-D or 3-D. Figureshows the three basic types of fiber orientation. 1-D gives maximum strength in one direction. 2-D gives strength in two directions. Isotropic gives strength equally in all directions.
  • 18. B. Particle Composites  Particles usually reinforce a composite equally in all directions (called isotropic). Plastics, cermets and metals are examples of particles.  Particles used to strengthen a matrix do not do so in the same way as fibers. For one thing, particles are not directional like fibers. Spread at random through out a matrix, particles tend to reinforce in all directions equally. Cermets (1) Oxide–Based cermets(e.g. Combination of Al2O3 with Cr) (2) Carbide–Based Cermets(e.g. Tungsten–carbide, titanium–carbide) Metal–plastic particle composites(e.g. Aluminum, iron & steel, copper particles) Metal–in–metal Particle Composites and Dispersion Hardened Alloys(e.g. Ceramic–oxide particles)
  • 19. C. Flake Composites - 1 Flakes, because of their shape, usually reinforce in 2-D. Two common flake materials are glass and mica. (Also aluminum is used as metal flakes)
  • 20. D. Laminar Composites - 1Laminar composites involve two or more layers ofthe same or different materials. The layers can bearranged in different directions to give strengthwhere needed. Speedboat hulls are among the verymany products of this kind.
  • 21. D. Laminar Composites - 4 A lamina (laminae) is any arrangement of unidirectional or woven fibers in a matrix. Usually this arrangement is flat, although it may be curved, as in a shell. A laminate is a stack of lamina arranged with their main reinforcement in at least two different directions.
  • 22. F. Combined Composites It is possible to combine several different materials into a single composite. It is also possible to combine several different composites into a single product. A good example is a modern ski. (combination of wood as natural fiber, and layers as laminar composites)
  • 23. E. Filled Composites There are two types of filled composites. In one, filler materials are added to a normal composite result in strengthening the composite and reducing weight. The second type of filled composite consists of a skeletal 3-D matrix holding a second material. The most widely used composites of this kind are sandwich structures and honeycombs.
  • 24. Figure (a) Model of a fiber-reinforced composite material showing direction in which elastic modulus is being estimated by the rule of mixtures (b) Stress-strain relationships for the composite material and its constituents. The fiber is stiff but brittle, while the matrix (commonly a polymer) is soft but ductile.
  • 25. Types of CompositesMatrix Metal Ceramic Polymerphase/Reinforcement Phase Powder metallurgy Cermets (ceramic- Brake padsMetal parts – combining metal composite) immiscible metalsCeramic Cermets, TiC, TiCN SiC reinforced Fiberglass Cemented carbides – used in tools Al2O3 Fiber-reinforced Tool materials metalsPolymer Kevlar fibers in an epoxy matrixElemental Fiber reinforced Rubber with metals carbon (tires)(Carbon, Bor Boron, Carbonon, etc.) Auto parts reinforced plastics aerospace MMC’s CMC’s PMC’s Metal Matrix Composites Ceramic Matrix Comp’s. Polymer Matrix Comp’s
  • 26. Composites – Metal Matrix The metal matrix composites offer higher modulus of elasticity, ductility, and resistance to elevated temperature than polymer matrix composites. But, they are heavier and more difficult to process.Ken Youssefi Mechanical Engineering Dept. 26
  • 27. Introduction to Composites1. What is the matrix in a composite and what materials are commonly used as a matrix?2. What is reinforcement in composites ?3. Be able to decide different factors responsible for properties of composite.4. Know the equation for the critical length (Lc) of a fiber.. Reading:
  • 28. Design ObjectivePerformance: Strength, Temperature, StiffnessManufacturing TechniquesLife Cycle ConsiderationsCost
  • 29. Matrix Types EpoxyEpoxies have improved strength and stiffness properties over polyesters. Epoxies offer excellent corrosion resistance and resistance to solvents and alkalis. Cure cycles are usually longer than polyesters, however no by-products are produced.Flexibility and improved performance is also achieved by the utilization of additives and fillers.
  • 30. Reinforcement Fiber Type Fiberglass Carbon Aramid Textile Structure Unidirectional Woven Braid
  • 31. Fiberglass E-glass: Alumina-calcium-borosilicate glass (electrical applications) S-2 glass: Magnesuim aluminosilicate glass (reinforcements)Glass offers good mechanical, electrical, and thermalproperties at a relatively low cost. E-glass S-2 glass Density 2.56 g/cc 2.46 g/cc Tensile Strength 390 ksi 620 ksi Tensile Modulus 10.5 msi 13 msi Elongation 4.8% 5.3%
  • 32. Aramid Kevlar™ & Twaron™Para aramid fiber characterized by high tensile strength and modulus Excellent Impact Resistance Good Temperature Resistance Density 1.44 g/cc Tensile Strength 400 ksi Tensile Modulus 18 Msi Elongation 2.5%
  • 33. Carbon Fiber PAN: Fiber made from Polyacrylonitrile precursor fiber High strength and stiffness Large variety of fiber types available Standard Modulus Intermediate ModulusDensity 1.79 g/cc 1.79 g/ccTensile Strength 600 ksi 800 ksiTensile Modulus 33 Msi 42 MsiElongation 1.8 % 1.8 %
  • 34. Woven FabricsBasic woven fabrics consists of two systems of yarnsinterlaced at right angles to create a single layer with isotropic or biaxial properties.
  • 35. Components of a Woven Fabric
  • 36. Basic Weave Types Plain Weave
  • 37. Basic Weave Types Satin 5HS
  • 38. Basic Weave Types 2 x 2 Twill
  • 39. Basic Weave Types Non-Crimp
  • 40. Braid Structure
  • 41. Types of Braids
  • 42. Triaxial YarnsA system of longitudinal yarns can be introduced which are held inplace by the braiding yarnsThese yarns will add dimensional stability, improve tensileproperties, stiffness and compressive strength.Yarns can also be added to the core of the braid to form a solid braid.
  • 43. MANUFACTURING PROCESSES OF COMPOSITES Composite materials have succeeded remarkably in their relatively short history. But for continued growth, especially in structural uses, certain obstacles must be overcome. A major one is the tendency of designers to rely on traditional materials such as steel and aluminum unless composites can be produced at lower cost. Cost concerns have led to several changes in the composites industry. There is a general movement toward the use of less expensive fibers. For example, graphite and aramid fibers have largely supplanted the more costly boron in advanced–fiber composites. As important as savings on materials may be, the real key to cutting composite costs lies in the area of processing.
  • 44. B. Molding OperationsMolding operations are used in making a large number ofcommon composite products. There are two types of processes:A. Open–mold (1) Hand lay–up (2) Spray–up (3) Vacuum–bag molding (4) Pressure–bag molding (5) Thermal expansion molding (6) Autoclave molding (7) Centrifugal casting (8) Continuous pultrusion and pulforming.
  • 45. 1. Hand Lay-upHand lay–up, or contact molding, is the oldest and simplestway of making fiberglass–resin composites. Applications arestandard wind turbine blades, boats, etc.)
  • 46. 2. Spray-upIn Spray–up process, chopped fibers and resins are sprayedsimultaneously into or onto the mold. Applications are lightlyloaded structural panels, e.g. caravan bodies, truckfairings, bathtubes, small boats, etc.
  • 47. 7. Centrifugal CastingCentrifugal Casting is used to form round objects such as pipes.8. Continuous Pultrusion and Pulforming Continuous pultrusion is the composite counterpart of metal extrusion. Complex parts can be made.
  • 48. Weight Considerations Aramid fibers are the lightest 1.3-1.4 g/cc Carbon 1.79 g/c Fiberglass is the heaviest 2.4 g/cc
  • 49. Strength Considerations Carbon is the strongest 600-800 ksi Fiberglass 400-600 ksi Aramids 400 ksi
  • 50. Stiffness Considerations Carbon is the stiffest 30-40 msi Aramids 14 msi Fiberglass 10-13 msi
  • 51. Cost Considerations Fiberglass is cost effective $5.00-8.00/lb. Aramids $20.00/lb Carbon $30.00-$50.00/lb
  • 52. Fabric StructuresWoven: Series of Interlaced yarns at 90 to each otherKnit: Series of Interlooped YarnsBraided: Series of Intertwined, Spiral YarnsNonwoven: Oriented fibers either mechanically, chemically, or thermally bonded
  • 53. Applications of Reinforced PlasticsPhenolic as a matrix with asbestos fibers was the first reinforced plasticdeveloped. It was used to build an acid-resistant tank. In 1920s it wasFormica, commonly used as counter top., in 1940s boats were made offiberglass. More advanced developments started in 1970s.Consumer CompositesTypically, although not always, consumer composites involve products thatrequire a cosmetic finish, such as boats, recreationalvehicles, bathwear, and sporting goods. In many cases, the cosmetic finishis an in-mold coating known as gel coat.Industrial CompositesA wide variety of composites products are used in industrialapplications, where corrosion resistance and performance in adverseenvironments is critical. Generally, premium resins such as isophthalic andvinyl ester formulations are required to meet corrosion resistancespecifications, and fiberglass is almost always used as the reinforcing fiber.Industrial composite products include underground storagetanks, scrubbers, piping, fume hoods, water treatment components, pressure Mechanical Engineering Dept. 53vessels, and a host of other products.
  • 54. Applications of Reinforced PlasticsAdvanced CompositesThis sector of the composites industry is characterized by the use ofexpensive, high-performance resin systems and high strength, high stiffnessfiber reinforcement. The aerospace industry, including military andcommercial aircraft of all types, is the major customer for advancedcomposites.These materials have also been adopted for use in sporting goods, wherehigh-performance equipment such as golf clubs, tennis rackets, fishingpoles, and archery equipment, benefits from the light weight – high strengthoffered by advanced materials. There are a number of exotic resins and fibersused in advanced composites, however, epoxy resin and reinforcement fiberof aramid, carbon, or graphite dominates this segment of the market. Mechanical Engineering Dept. 54
  • 55. Composites – Ceramic MatrixCeramic matrix composites (CMC) are used in applications whereresistance to high temperature and corrosive environment is desired.CMCs are strong and stiff but they lack toughness (ductility)Matrix materials are usually silicon carbide, silicon nitride andaluminum oxide, and mullite (compound of aluminum, silicon andoxygen). They retain their strength up to 3000 oF.Fiber materials used commonly are carbon and aluminum oxide.Applications are in jet and automobile engines, deep-seemining, cutting tools, dies and pressure vessels. Mechanical Engineering Dept. 55
  • 56. Ken Youssefi Mechanical Engineering Dept. 56
  • 57. Application of Composites Lance Armstrong’s 2-lb. Trek bike, 2004 Tour de FrancePedestrian bridge inDenmark, 130 feet long (1997) Swedish Navy, Stealth (2005)Ken Youssefi Mechanical Engineering Dept. 57
  • 58. Application of Composites in Aircraft Industry 20% more fuel efficiency andKen Youssefi Mechanical Engineering Dept.lbs. lighter 35,000 58
  • 59. Advantages of Composites Higher Specific Strength (strength-to-weight ratio) Composites have a higher specific strength than many other materials. A distinct advantage of composites over other materials is the ability to use many combinations of resins and reinforcements, and therefore custom tailor the mechanical and physical properties of a structure.The lowest properties for each material are associated with simple manufacturing processesand material forms (e.g. spray lay-up glass fibre), and the higher properties are associatedwith higher technology manufacture (e.g. autoclave moulding of unidirectional glassfibre), the aerospace industry. 59
  • 60. Advantages of CompositesDesign flexibilityComposites have an advantage over other materials because they can bemolded into complex shapes at relatively low cost. This gives designers thefreedom to create any shape or configuration. Boats are a good example ofthe success of composites.Corrosion ResistanceComposites products provide long-term resistance to severe chemical andtemperature environments. Composites are the material of choice foroutdoor exposure, chemical handling applications, and severe environmentservice. Mechanical Engineering Dept. 60
  • 61. Advantages of CompositesLow Relative InvestmentOne reason the composites industry has been successful is because ofthe low relative investment in setting-up a composites manufacturingfacility. This has resulted in many creative and innovative companies inthe field.DurabilityComposite products and structures have an exceedingly long life span.Coupled with low maintenance requirements, the longevity of composites is abenefit in critical applications. In a half-century of compositesdevelopment, well-designed composite structures have yet to wear out.In 1947 the U.S. Coast Guard built a series of forty-foot patrolboats, using polyester resin and glass fiber. These boats were used untilthe early 1970s when they were taken out of service because the designwas outdated. Extensive testing was done on the laminates afterdecommissioning, and it was found that only 2-3% of the originalstrength was lost after twenty-five years of hard service. Mechanical Engineering Dept. 61
  • 62. Disadvantages of Composites Composites are heterogeneous properties in composites vary from point to point in the material. Most engineering structural materials are homogeneous. Composites are highly anisotropic The strength in composites vary as the direction along which we measure changes (most engineering structural materials are isotropic). As a result, all other properties such as, stiffness, thermal expansion, thermal and electrical conductivity and creep resistance are also anisotropic. The relationship between stress and strain (force and deformation) is much more complicated than in isotropic materials.The experience and intuition gained over the years about the behavior ofmetallic materials does not apply to composite materials. Mechanical Engineering Dept. 62
  • 63. Disadvantages of Composites Composites materials are difficult to inspect with conventional ultrasonic, eddy current and visual NDI methods such as radiography.American Airlines Flight 587, broke apart overNew York on Nov. 12, 2001 (265 people died).Airbus A300’s 27-foot-high tail fin tore off.Much of the tail fin, including the so-calledtongues that fit in grooves on the fuselage andconnect the tail to the jet, were made of agraphite composite. The plane crashed becauseof damage at the base of the tail that had goneundetected despite routine nondestructivetesting and visual inspections. Mechanical Engineering Dept. 63
  • 64. Disadvantages of CompositesIn November 1999, America’s Cup boat “Young America”broke in two due to debonding face/core in the sandwichstructure. Mechanical Engineering Dept. 64
  • 65. SUMMARY What is the matrix in a composite and what materials are commonly used as a matrix? What are the possible strengthening mechanisms for particle reinforced composites (there are 2)? Be able to calculate upper and lower bounds for the Young’s modulus of a large particle composite. Know the equation for the critical length (Lc) of a fiber. Know the stress distribution on fibers of various lengths w/r Lc in a composite. Reading for next class
  • 66. ConclusionsComposite materials offer endless designoptions.Matrix, Fiber and Preform selections arecritical in the design process.Structures can be produced with specificproperties to meet end use requirements.