Composite Materials Raw Materials. Week

Transcription

1 Composite Materials Raw Materials Week

2 Content Reinforcements Matrix Materials Fabrics Prepregs Preforms Molding compound Honeycomb and core materials

3 Introduction Each manufacturing method utilizes a specific type of material system for part fabrication. One material system may be suitable for one manufacturing method, whereas the same material system may not be suitable for another fabrication method roll wrapping prepreg systems Injection molding Pellet form

4 Composite processing

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6 Reinforcements Inorganic fibers: Glass fibers: S-glass and E-glass Carbon or graphite fibers: from PAN and Pitch Ceramic fibers: Boron, SiC, Al2O3 Metal fibers and particles: steel, alloys of W, Ti, Ni, Mo etc. (high melting temperature metal fibers) Organic Fibres Aramid fibres Polymeric fibres Natural fibres

7 Introduction Reinforcements give all the necessary stiffness and strength to the composite. These are thin rod like structures. The most common ones: glass, carbon, aramid and boron fibers. Typical fiber diameters range from 5 µm to 20 µm Glass fiber is 5 to 25 µm; carbon fiber is 5 to 8 µm; aramid fiber is 12.5 µm; boron fiber is 100 µm Fibers are made into strands for weaving or winding operations Fibers are wound around a bobbin and collectively called rowing An untwisted bundle of carbon fibers is called tow.

8 Fibres and Bulk Materials

9 Fibres and Bulk Materials Absence of defects of a critical size Orientation of molecules along the fibre direction Favorable residual stresses introduced during the fibre manufacturing process The strength of glass fibres depends on the number of the defects of critical sizes which are less frequent in them compared to bulk glass In carbon and ail polymeric fibres, the higher strength is due to the alignment of graphitic planes or polymer molecules along the fibre direction. By an orientation process ( as in carbon and polymeric fibres ), there is also an increase in the Young's modulus of the fibres but isotropic fibres like glass fibres, the Young's modulus is essentially the same, both in fibres and in bulk forms

10 Carbon Fibres stiffest and strongest reinforcing fibres for polymer composites most used after glass fibres low density and a negative coefficient of longitudinal thermal expansion very expensive and can give galvanic corrosion in contact with metals generally used together with epoxy, where high strength and stiffness are required, i.e. race cars, automotive and space applications, sport equipment Carbon fibres are produced by the PAN or the pitch methods

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12 Carbon Fibre Processing types

13 Carbon fibres (pitch based) pitch - high molecular weight byproduct of distillation of petroleum heated >350 C, condensation reaction, formation of mesophase (LC) melt spinning into pitch fibers conversion into graphite fibers at ~2000 C

14 Carbon fibres (Pan based) PAN (polyarylonitrile) based carbon fibers PAN fibers (CH2-CH(CN)) Stabilization at C in O 2, depolymerization & aromatization, converting thermoplastic PAN to a nonplastic cyclic or ladder compound (CN groups combined and CH2 groups oxidized) Carbonization at C in an inert atmosphere to get rid of noncarbon elements (O and N) but the molecular orientation is still poor. Stretch and graphitization at >1800 C, formation of turbostratic structure

15 Carbon fibre texture model

16 Micro-structure

17 Carbon fibre mechanical properties

18 Carbon fibre mechanical properties

19 Carbon/graphite fabrication

20 Conversion of carbon to graphite

21 Grades of carbon fiber High-strength carbon fiber (without graphization) heat treatment below 1700C less crystalline and lower modulus (<365 GPa) High-modulus carbon fiber (with graphitization)=graphite fibre heat treatment above 1700 C More crystalline (~80%) and higher modulus (>365GPa) Carbon (IM) Intermediate Modulus Carbon (HM) High Modulus Carbon (UHM) Ultra-high Modulus

22 Properties of carbon compared to graphite Less conductive Lower in modulus Higher in strength Lower in oxidation resistance Cannot be intercalated

23 Carbon Fibres Advantages High strength Higher modulus Nonreactive Resistance to corrosion High heat resistance high tensile strength at elevated temperature Low density Disadvantages High cost Brittle

24 Glass fibres fine fibers with almost uniform, mainly round cross section, obtained from molten glass A. Textile glass fibers 1. Glass filament textile glass fiber of practically unlimited length with defined fiber diameter drawn from molten glass 2. Staple glass fiber textile glass fiber of finite length (spun fiber) and defined fiber diameter obtained from molten glass by mechanical means or by the use of gaseous media

25 Glass Fibre Manufacturing

26 Glass Fibres

27 Glass fibre types and raw materials B. 90% of glass fibers is E-glass (Aluminum Boron Silicate Glass). Other specialty glasses are available for specific applications 1. R and S glass fibers for increased strength 50% higher (used in Defence and aeronautical applications) 2. ECR glass for high acid resistance 3. AR- and Z-glass fibres (Zirconium oxide) for high alkaline environment 4. D-glass for improved dielectric properties 5. C-glass to build up anticorrosion layer against aggressive media. E-Glass is a low alkali glass with a typical nominal composition of SiO2 54wt%, Al2O3 14wt%, CaO+MgO 22wt%, B2O3 10wt% and Na2O+K2O less then 2wt%. Some other materials may also be present at impurity levels

28 Fibers Glass C. Surface Treatment usually applied to the glass during the drawing process 1. Lubricants, coupling agents, and other additives 2. Affect the processing properties and reinforcing effects in plastics. D. Safety Nontoxic and ecologically safe. Only issues are skin irritation on contact and inhalation. main purposes: 1) protecting the filaments from each other during processing and handling, 2) ensuring good adhesion of the glass fibre to the resin.

29 Glass Fibre Advantages high strength same strength and modulus in transverse direction as in longitudinal direction low cost Dsadvantages relatively low modulus high specific density (2.62 g/cc) moisture sensitive Reduced impact strength Directional warping Increased abrasion Reduces surface appearance quality

30 Transportation Electrical/Electronics Building Construction Infrastructure Aerospace/Defense Consumer/Recreation Medical Products

31 Organic (Polymeric) Fibres Aramid fibres Cellulosic Fibres Other Polymeric Fibres 1. Nylon 2. PP 3. PET 4. PE

32 Aramid (Kevlar) Fibres

33 The chains are highly oriented with strong interchain bonding which result in a unique combination of properties

34 Liquid Crystalline Behavior Anisotropic polymer solutions will exhibit liquid crystalline behavior. Liquid crystalline structures of PPD-T/H2SO4 solution

35 A dry-jet wet spinning process for spinning anisotropic solutions of aramid polymer to produce fibers.

36 Aramid thermal properties High melt temp >530 C High Tg* > 375 C Relatively high thermal stability Zero strength temperature** ~ 640 C Negative coefficient of thermal expansion with increasing temperature

37 Aramid Fibres Aramid fibres are synthetic organic fibres prepared from aromatic polyamides. These are high strength and high modulus fibres Aramid fibres are prepared by spinning the polymer poly p.phenylene-terephthalamide) (PPTA). The Polymer PPTA is synthesised through low temperature polycondensation of p-phenylene diamine and terephthaloyl chloride operties suitable for use in composite materials. PPTA molecules have very rigid backbones due to the presence of aromatic groups in the main chain and due to the absence of flexible linkages between these rigid moities. Because of this, when PPT A is dissolved in suitable solvents, the solutions become liquid crystals in certain concentration and temperature regimes. The liquid crystalline solution transforms to an isotropic state above 120 C. The important factors which determine the properties of aramid fibres are the molecular weight of the polymer, and the degree of molecular orientation in the fibres. The average molecular weight should be at least about 45,000 fibres and fibre axis is less than about 10degree

38 Aramid fibres Advantages high strength & modulus low specific density (1.47g/cc) relatively high temperature resistance Low creep Good dielectric properties Reduced coefficient of thermal expansion Greatly increased impact strength at elevates stress rates antiballistic Lubricational effect when surfaces containing Aramid fibers rub together Disadvantages Easy to fibrillate Low shear performance Moisture and UV sensitve poor transverse properties (compressive) susceptible to abrasion

39 Aramid Types Kevlar 29, E = 50 GPa Kevlar 49, E = 125 GPa Kevlar 149, E = 185 GPa

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41 Natural fibres

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43 Fibers Miscellaneous Miscellaneous Fibers A. Ceramic fibers high temperature, very abrasive 1. Aluminum Silica 2. Aluminum Oxide 3. Silicone Carbide 4. Zirconia Silica B. Metal Fibers high strength, abrasive 1. Aluminum 2. Nickel 3. Stainless Steel C. Polymer Fibers

44 Fibre forms one-dimensional, continuous fibers; (b) planar, continuous fibers in the form of a woven fabric; and (c) random, discontinuous fibers

45 Fibre preforms These are available are as continues (a), woven fabrics (b)and chopped strand mat(c). The major forms in which the fibres are used are the chopped strand mat and woven fabrics. These forms are structurally inefficient forms. Unidirectional tapes, though structurally more efficient, are difficult to handle and are also beset with shelf life and storage problems as they are generally pre-impregnated with a resin. In recent years some novel forms of reinforcements have been developed in developed countries. These new forms are structurally efficient, easy to handle and do not have storage problems associated with impregnated tapes. These forms include non-woven bidirectional fabrics, unidirectional knitted fabrics, veiled tapes, etc. The use of these structurally efficient forms of reinforcement can give about 20 per cent increase in strength and about 60 per cent increase in stiffness over comparable woven reinforcements. Thus it is necessary to develop structurally efficient forms of reinforcements like knitted unidirectional and bidirectional fabrics to increase the cost competitiveness of composite materials.

46 Fibre preforms

47 Fibre preforms Preforms with random orientation

48 Fibre preforms Preforms with controlled fibre orientation

49 Fibre preforms Woven fibre preforms

50 Type of weaving

51 Fibre preforms

52 Fibre preforms Stitched fibre preforms (Non-crimp fabrics)

53 Fibre preforms Cross section of composite with stitched fibre form

54 Fibre preforms Mechanical performance of glass fibre composites with different fibre preforms

55 Fibre preforms Carbon fibre types-price Carbon Fibre chopped 3 mm (250 TL/kg) Carbon Fibre continious 3K- (285 TL/kg) Carbon Fibre Braided 5-25mm (15TL/m) Carbon Fibre Fabric 200 gr/m2 3k plain-(145tl/m2)

56 Fibre preforms Prepregs Termoset prepregs Termoplastic prepregs

57 Fibre preforms Core materials to increase the laminate's stiffness by effectively 'thickening' it with a low-density core material the core must be capable of taking a compressive loading without premature failure. the core materials act as the beam's shear web

58 Homework questions 1. Define and distinguish the prepreg and other molding compounds (SMC, BMC) 2. Compare density yougs modulus and specific modulus of Carbon, Aramid, Steel,Titanium, Aluminium, Glass Fibres 3. Which fibres usually are used for balistic applications? Why? 4. What is the type of glass fibres based on their cmposition and basic features? 5. Define particle, fibre, whiskers, filament, tow and yarn 6. What is the type of carbon fibres? Give 2 basic differences each other. 7. Write 4 example for organic fibres. 8. What is the name of Kevlar and write 3 disadvantages? 9. What is the purpose of sizing in fibres and coupling agent for composites? 10. What is the difference in failure of glass fibres and aramid fibres (show with a sketch) 11. If an application needs high elongation and excellent strength wich type of fibre would be your first choice? 12. What are the fabric types used in composites? 13. Describe the difference expected in tensile strength and youngs modulus of glass fibres that short (2.5 cm) and that are long (25 cm) why would you expect this difference? 14. What is the role of long fibres in composites? 15. Are Carbon andgraphyde fibres same? If It is what s the difference? 16. What happens to moelculer structure of an organic fibre during drawing? What sequences does this have on its mechanical properties? 17. What are the basic differences in bulk and fibre forms of the same material? 18. What is the tex value of a bundle of 1000 carbon fibre which are 7 micron in diameter and have a denisty 1.8 g/cm3