1. + Introduction to composites - fibers CME/MSE 404G. Polymeric Materials Fall 2012 Figures taken from: P.K. Mallick. Fiber-Reinforced Composites, Materials, manufacturing, and design. 3 rd Ed., CRC Press. 2008 fibers

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9. + Properties of commercial fibers average values from manufacturers fiber D,  m g/cm t E t, GPa Y t, GPa % strain COTE Poisson ’s ratio E-glass102.5472.43.454.950.2 S-glass102.4986.94.352.90.22 PAN, T300 71.762313.651.4-0.60.2 Pitch, P55 102.03801.90.5-1.3NA Kevlar 49 11.91.451313.622.8-2NA Spectra 900 380.971172.593.5NA fibers 9

10. + Fibers: 2012 references; new research on fibers for composites fibers 10

11. + In-class exercise fibers 11

12. + Each team is to find composites applications for their fibers assignments fibers 12

13. + Team responses fibers 13

14. + Fiber bundles Typical fibers have very small diameters, so that fiber bundles are used for ease of handling. Untwisted = strand, end (glass & Kevlar fibers); =tow (carbon fibers) Twisted = yarn fibers 14

15. + Single fiber test ASTM D3379 - ASTM D3379-75(1989)e1 Standard Test Method for Tensile Strength and Young's Modulus for High-Modulus Single-Filament Materials (Withdrawn 1998) A single filament is mounted along the centerline of a slotted tab using adhesive at each end The tab ends are gripped in the tensile machine and the midsection is cut Constant loading rate until failure fibers 15

16. + Single fiber mounting for tensile test fibers 16

17. + Tensile property determinations Definitions F u – force at failure A f = average filament cross-sectional area (planimeter measurement via photos of filament ends L f = gage length C = true compliance (via loading rate) Tensile strength Tensile modulus fibers 17

18. + Typical tensile strengths of fibers Typical fibers have high strength, high orientation Stress-strain curves are nearly linear up to failure Most fail brittlely Most fibers are prone to damage with handling and with contact to other surfaces fibers 18

19. + Model for fiber tensile strengths fibers 19

20. + Model application fibers 20

21. + Typical applications: Weibull distribution Time to failure: failure rate is proportional to time raised to the nth power, k=n+1 Cases 0 < k < 1: failure rate decreases with time. Example = infant mortality or early failure of electrical circuits k = 1: failure rate is constant over time. Example = random external events k > 1: failure rate increases with time. Example = aging process fibers 21

22. + Weibull: probability density In-class question: Interpret each curve with respect to a time-to-failure data set. Hint: the integral of each curve = 1. fibers 22

23. + Weibull: cumulative distribution In-class question: Interpret each curve with respect to a time-to-failure data set. Hint: the upper limit of each curve = 1. fibers 23

24. + Failure rates fibers 24

25. + Quantile plots fibers 25

26. + Figure 2.4 fibers 26

27. + Example data: failure strength at a given fiber length fibers 27

28. + Weibull distribution fibers 28

29. + fibers 29

30. + Quantile plots fibers 30

31. + Problem 2.5. Mallick MSE 599 P2_5.xlsx fibers 31

32. + Analysis of flaws in high- strength carbon fibres from mesophase pitch Janice Breedon Jones, John Barr, Robert Smith, J. Materials Sci., 14, (1980), 2455-2465 fibers 32

33. + Data taken at two guage lengths, 20 mm and 3.2 mm fibers 33

34. + Effect of gauge length on strength why should there be an effect? fibers 34

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39. + Single mode of failure should show similar Weibull plot slopes Similar slope suggests the same failure modes for each gauge length fibers 39

40. + Extrapolate to 0.3 mm length expected load transfer length for multifilament fibres of this diameter (3.8 Gpa) If the failure mechanisms are similar, we can extrapolate the tensile strength to shorter gauge lengths, estimating the tensile strength for lengths that are difficult to measure experimentally. fibers 40

41. + Flaw strength distributions and statistical parameters for ceramic fibers: the normal distribution M. R’Mili, N. Godin, J. Lamon, Phys. Rev. E, 85, 051106 (2012) Large sets of ceramic fibre failure strengths from tows of 500 – 1000 filaments Flaws generated by ultrasonic Flaw strengths are distributed normally fibers 41

42. + SiC-based Nicalon filaments fibers 42

43. + Quasi-linear regression failure of fiber tows For probabilities less than 4%, there is an under- estimate of the number of first failures. This is likely due to the detection of low energy events near the filtering threshold. This is probably not a bimodal distribution of flaws. fibers 43

44. + Comparison of model and fiber failure data Very good indeed. fibers 44

45. + General effect of aspect ratio on tensile strength fibers 45

46. + Dry glass bundle. 3000 filaments Single filament shows a linear stress-strain curve. Bundle shows a nonlinear stress-strain curve prior to maximum stress, and progressive failure after maximum stress. Both effects are due to statistical distribution of the filament strengths. Some fail as the load increase. After the maximum stress, highly loaded fibers continue to fail, but not all at once fibers 46

47. + Fiber production Glass fibers fibers 47

48. + fibers 48

49. + Types of glass fibers tensile strength = 3.45 GPa; surface flaws reduce this to 1.72 GPa Continuous strand roving [strand = parallel filaments, n > 204] Woven roving [roving = group of untwisted strans/ends wound on a cylindrical forming package] Chopped strands – continuous strands cut to specific lengths; 3.2 – 12.7 for injection molding Chopped strand mats - 50.8 mm for chopped strand mats Woven roving mat Milled glass fibers, 0.79 to 3.2 mm; plastic fillers fibers 49

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58. + Glass fiber compositions fibers 58

59. + Glass fiber properties fibers 59

60. + Sizing chemistries fibers 60

61. + fibers 61

62. + fibers 62

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65. + fibers 65

66. + Boron fibers fibers 66

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69. + fibers 69

70. + http://www.angelfire.com fibers 70 Boron Fibers Boron is an inherently-brittle material. It is commercially made by chemical vapor deposition of boron on a substrate, that is, boron fiber as produced is itself a composite fiber. In view of the fact that rather high temperatures are required for this deposition process, the choice of substrate material that goes to form the core of the finished boron fiber is limited. Generally, a fine tungsten wire is used for this purpose. A carbon substrate can also been used. The first boron fibers were obtained by Weintraub by means of reduction of a boron halide with hydrogen on a hot wire substrate. The real impulse in boron fiber fabrication, however, came only in 1959 when Talley used the process of halide reduction to obtain amorphous boron fibers of high strength. Since then, the interest in the use of strong but light boron fibers as a possible structural component in aerospace and other structures has been continuous, although it must be admitted that this interest has periodically waxed and waned in the face of rather stiff competition from other so-called advanced fibers, in particular, carbon fibers.

71. + synthesis fibers 71 Reduction of boron Halide : Hydrogen gas is used to reduce boron trihalide: 2BX 3 + 3 H 2 = 2 B + 6 HX where X denotes a halogen: Cl, Br, or 1. In this process of halide reduction, the temperatures involved are very high, and, thus, one needs a refractory material, for example, a high melting point metal such as tungsten, as a substrate. It turns out that such metals are also very heavy. This process, however, has won over the thermal reduction process despite the disadvantage of a rather high-density substrate (the density of tungsten is 19.3 g cm -3) mainly because this process gives boron fibers of a very high and uniform quality. There are many firms producing boron fibers commercially using this process. In the process of BCI3, reduction, a very fine tungsten wire (10-12 micron diameter) is pulled into a reaction chamber at one end through a mercury seal and out at the other end through another mercury seal. The mercury seats act as electrical contacts for resistance heating of the substrate wire when gases (BCl3, + H2,) pass through the reaction chamber where they react on the incandescent wire substrate. The reactor can be a one- or multistage, vertical or horizontal, reactor. BCl3, is an expensive chemical and only about 10% of it is converted into boron in this reaction. Thus, an efficient recovery of the unused BCl3, can result in a considerable lowering of the boron filament cost.

72. + Kevlar fibers 72

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83. + Carbon fibers fibers 83 Graphitic orientation a.Circumferentially orthotropic b.Radially orthotropic c.Transversely isotropic d.Circumferential + radial e.Circumferential + random

84. + Carbon fibers fibers 84 Graphitic orientation a.Circumferentially orthotropic b.Radially orthotropic c.Transversely isotropic d.Circumferential + radial e.Circumferential + random In-class question: the most common orientation for pitch fibers

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86. + Filament failure under compression fibers 86

87. + Compression failure cannot be determined directly by simple compression tests on filaments Indirect methods are used, such as the loop test, in which a filament is bent into a loop until it fails. The compressive strength is determined from the compressive strain at the fiber surface. fibers 87

88. + Fiber compressive strength fiberTensile strength, GPa Compressive strength, GPa E-glass3.44.2 PAN T-3003.22.7-3.2 AS4 carbon3.62.7 GY-70 carbon1.861.06 P100 carbon2.20.5 Kevlar 493.50.35-0.45 Boron3.55 fibers 88

89. + fibers 89 Effect of fiber diameter on strength Explain this phenomena

90. + fibers 90 Effect of fiber diameter on strength Fiber that are formed by spinning processes usually have increased strength at smaller diameters due to the high orientation that occurs during processing.