MMF42007 Komposit (PIL)

1. MMF42007 Komposit (PIL) Dr. Ir. Anne Zulfia MSc

2. Pengenalan Material Komposit

3. Steels Cast irons Al-alloys Metals Cu-alloys Ni-alloys Ti-alloys GFRP CFRP Composites KFRP Plywood PE, PP, PC PA (Nylon) Polymers, elastomers Butyl rubber Neoprene Alumina Si-Carbide Ceramics, glasses Soda-glass Pyrex Woods Natural materials Natural fibres: Hemp, Flax, Cotton Polymer foams Metal foams Foams Ceramic foams Glass foams The world of materials

5. Pengertian Komposit • Komposit merupakan kombinasi dari dua material atau lebih yang memiliki fasa yang berbeda menjadi suatu material baru yang memiliki properti lebih baik dari keduanya. • Jika kombinasi ini terjadi dalam skala makroskopis maka disebut sebagai komposit. • Jika kombinasi ini terjadi secara mikoroskopis (molekular level) maka disebut sebagai alloy atau paduan.

6. Composites Composites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composites. Composites are used because overall properties of the composites are superior to those of the individual components. For example: polymer/ceramic composites have a greater modulus than the polymer component, but aren't as brittle as ceramics.

7. Composite materials – Introduction • Definition: a material composed of 2 or more constituents • Reinforcement phase (e.g., Fibers) • Binder phase (e.g., compliant matrix) • Advantages • High strength and stiffness • Low weight ratio • Material can be designed in addition to the structure

8. Two types of composites are:

9. Particle reinforced composites support higher tensile, compressive and shear stresses. Figure 1. Examples for particle-reinforced composites. (Spheroidized steel and automobile

10. The following are some of the reasons why composites are selected for certain applications: • High strength to weight ratio (low density high tensile strength) • High creep resistance • High tensile strength at elevated temperatures • High toughness

11. Examples of Composites • Natural • Wood • flexible cellulose fibers held together with stiff lignin • Bone • strong protein collagen and hard, brittle apatite • Artificial (man-made) • constituent phases are chemically distinct

12. Definitions • Composites often have only two phases • Matrix phase • continuous - surrounds other phase • Dispersed phase • discontinuous phase Matrix (light) Dispersed phase (dark)

13. Objectives • Definitions in composite materials • dispersed phase, matrix • Structure of composites • particle-reinforced • fiber reinforced • structural composites

14. Introduction • Engineering applications often require unusual combinations of properties • esp. aerospace, underwater, and transportation • can’t be achieved with a single material • e.g. - aerospace requires strong, stiff, light, and abrasion resistant material • most strong, stiff materials are dense and heavy • most light materials are not abrasion resistant • Solution is in composite materials

15. Examples of Composites • Natural • Wood • flexible cellulose fibers held together with stiff lignin • Bone • strong protein collagen and hard, brittle apatite • Artificial (man-made) • constituent phases are chemically distinct

16. Classification of Artificial Composites Composites Particulate Fiber Structural Large Dispersion Laminates Sandwich Particle Strengthened Panels Continuous Discontinuous Aligned Random

17. Properties of Composites Dependent on: • constituent phases • relative amounts • geometry of dispersed phase • shape of particles • particle size • particle distribution • particle orientation

18. Composite Parameters For a given matrix/dispersed phase system: • Concentration • Size • Shape • Distribution • Orientation

19. Parameters Distribution Concentration Orientation Size Shape

20. Classification of Artificial Composites Composites Particulate Fiber Structural Large Dispersion Laminates Sandwich Particle Strengthened Panels Continuous Discontinuous Aligned Random

21. Partikel sebagai penguat (Particulate composites) Large particle • Interaksi antara partikel dan matrik terjadi tidak dalam skala atomik atau molekular • Partikel seharusnya berukuran kecil dan terdistribusi merata • Contoh dari large particle composit: cement dengan sand atau gravel, cement sebagai matriks dan sand sebagai partikel Light Phase –Matrix (Cobalt) Dark Phase-Particulate (WC

22. Particle-Reinforced Composites • Divided into two classes • (based on strengthening mechanism) • Large particle • interaction between particles and matrix are not on the atomic or molecular level • particle/matrix interface strength is critical • Dispersion strengthened • 0.01-0.1 mm particles • inhibit dislocation motion

23. Large Particle Composites Examples: • Some polymers with added fillers are really large particle composites • Concrete (cement with sand or gravel) • cement is matrix, sand is particulate

24. CERMET Cutting Tool Light phase - Matrix (Cobalt) Dark phase- Particulate (WC)

25. Large Particle Composites Desired Characteristics • Particles should be approximately equiaxed • Particles should be small and evenly distributed • Volume fraction dependent on desired properties

26. Volume Fraction in Large Particle Composites • Elastic modulus is dependent on the volume fraction • “Rule of mixtures” equation • E- elastic modulus, V- volume fraction, m- matrix, p- particulate • upper bound • lower bound

27. Rule of Mixtures Actual Values Upper bound * * E - particulate * * * E- matrix * * Lower bound conc. of particulates

28. Large-Particle Composite Materials • All three material types • metals, ceramics, and polymers • CERMET (ceramic-metal composite) • cemented carbide (WC, TiC embedded in Cu or Ni) • cutting tools (ceramic hard particles to cut, but a ductile metal matrix to withstand stresses) • large volume fractions are used (up to 90%!)

29. Large Particle CompositesConcrete • Concrete is not cement) • Concrete is the composite of cement and an aggregate (fine sand or coarse gravel) • Reinforced concrete • a composite (large particle composite) - with a matrix which is a composite • steel rods, wires, bars (rebar, sometimes stretched elastically while concrete dries to put system in compression)

30. Dispersion Strengthened Composites • Metals and metal alloys • hardened by uniform dispersion of fine particles of a very hard material (usually ceramic) • Strengthening occurs through the interactions of dislocations and the particulates • Examples • Thoria in Ni • Al/Al2O3 sintered aluminum powder SAP • GP zones in Al

31. Classification of Artificial Composites Composites Particulate Fiber Structural Large Dispersion Laminates Sandwich Particle Strengthened Panels Continuous Discontinuous Aligned Random

32. Fiber sebagai reinforced Fiber yang digunakan harus: • Mempunyai diameter yang lebih kecil dari diameter bulknya (matriksnya) namun harus lebih kuat dari bulknya • Harus mempunyai tensile strength yang tinggi

33. Matriks yang dipadukan dengan fiber berfungsi sebagai : • Penjepit fiber • Melindungi fiber dari kerusakan permukaan • Pemisah antara fiber dan juga mencegah timbulnya perambatan crack dari suatu fiber ke fiber lain • Berfungsi sebagai medium dimana eksternal stress yang diaplikasikan ke komposit, ditransmisikan dan didistribusikan ke fiber.

34. Matriks yang digunakan harus : • Ductility tinggi • Memiliki modulus elastisitans lebih rendah daripada fiber • Mempunyai ikatan yang bagus antara matriks dan fiber • Biasanya secara umum yang digunakan adalah polimer dan logam

35. a. Short(discontinuous) fiber reinforced composites Aligned Random b. Continuous fiber (long fiber) reinforced composites

36. Fiber yang biasa digunakan antara lain : Fibers – Glass • Sangat umun digunakan, fiber yang murah adalah glass fiber yang sering digunakan untuk reinforcement dalam matrik polimer • Komposisi umum adalah 50 – 60 % SiO2 dan paduan lain yaitu Al, Ca, Mg, Na, dll. • Moisture dapat mengurangi kekuatan dari glass fiber • Glass fiber sangat rentan mengalami static fatik • Biasanya digunakan untuk: piping, tanks, boats, alat-alat olah raga

37. Sifat-Sifatnya • Densitynya cukup rendah ( sekitar 2.55 g/cc) • Tensile strengthnya cukup tinggi (sekitar 1.8 GPa) • Biasanya stiffnessnya rendah (70GPa) • Stabilitas dimensinya baik • Resisten terhadap panas • Resisten terhadap dingin • Tahan korosi

38. Keuntungan : • Biaya murah • Tahan korosi • Biayanya relative lebih rendah dari komposit lainnya Kerugian • Kekuatannya relative rendah • Elongasi tinggi • Keuatan dan beratnya sedang (moderate) Jenis-jenisnya antara lain : • E-Glass - electrical, cheaper • S-Glass - high strength

39. Fibers - Aramid (kevlar, Twaron) • Biasanya digunakan untuk : Armor, protective clothing, industrial, sporting goods • Keuntungan :kekutannya cukup tinggi, dan lebih ductile dari carbon

40. Carbon Fibers • Densitaskarbon cukup ringan yaitu sekitar 2.3 g/cc • Struktur grafit yang digunakan untuk membuat fiber berbentuk seperti kristal intan. • Karakteristik komposit dengan serat karbon : • ringan; • kekuatan yang sangat tinggi; • kekakuan (modulus elastisitas) tinggi. • Diproduksi dari poliakrilonitril (PAN), melalui tiga tahap proses : • Stabilisasi = peregangan dan oksidasi; • Karbonisasi= pemanasan untuk mengurangi O, H, N; • Grafitisasi = meningkatkan modulus elastisitas.

41. Flat flakes sebagai penguat (Flake composites) Fillers sebagai penguat (Filler composites)

42. Structurtal Composite

43. Fiber-Reinforced Composites • Technologically, the most important type of composite • Characterized in terms of specific strength or specific modulus = strength (or E) per weight • usually want to maximize specific strength and modulus • Subclasses: • Short fiber and continuous fiber lengths

44. Fiber Phase Requirements for the fiber • The small diameter fiber must be much stronger than the bulk material • High tensile strength Different classifications • whiskers (single crystal - large aspect ratio) • fibers (polycrystalline or amorphous) • wires (large diameters - usually metal)

45. Matrix Phase Function • Binds fibers together • Acts as a medium through which externally applied stress is transmitted and distributed to the fibers • Protects fiber from surface damage • Separates fibers and prevents a crack from one fiber from propagating through another

46. Matrix Phase Requirements • Ductile • Lower E than for fiber • Bonding forces between fiber and matrix must be high • otherwise fiber will just “pull-out” of matrix • Generally, only polymers and metals are used as matrix material (they are ductile)

47. Influence of Fiber Length • Mechanical properties depend on: • mechanical properties of the fiber • how much load the matrix can transmit to the fiber • depends on the interfacial bond between the fiber and the matrix • Critical fiber length - depends on • fiber diameter, fiber tensile strength • fiber/matrix bond strength

48. Influence of Fiber Length • Critical fiber length - lc • “Continuous” fibers l >> 15 lc • “Short” fibers are anything shorter 15 lc lc = sfd/2tc where d = fiber diameter tc = fiber-matrix bond strength sf = fiber yield strength No Reinforcement

49. Influence of Fiber Orientation • Fiber parameters • arrangement with respect to each other • distribution • concentration • Fiber orientation • parallel to each other • totally random • some combination

50. Influence of Fiber Orientation • Stage I - elastic deformation with intermediate • Stage II - matrix yields • Failure - Non-catastrophic. When fibers fracture, you now have new fiber length and matrix is still present