A numerical study on the thermal expansion coefficients of fiber
A numerical study on the thermal expansion coefficients of fiber A numerical study on the thermal expansion coefficients of fiber
25 a Figure 2.10 Chemical structure of aramid fiber (a), knotted Kevlar aramid fiber (b) (Chawla, 1998). b They have been in use for a long time to improve wear resistance of plastic parts. Aramid fiber is superior to other wear resistant additives due to its easier dispersion and minimal effect on mechanical properties of filled materials. Incorporation of fibers increases the impact strength of composites. Further improvements in mechanical properties can be obtained by modification of the surface with OH and COOH groups. The presence of these groups was found to increase adhesion to many polymers. The degree of modification should be carefully controlled because the mechanical strength of the fiber and the performance of its composite may be adversely affected (Wypych, 2000). The high moisture absorption of aramid fibers is their biggest disadvantage. It was reported in the literature that moisture absorption by epoxy laminates degrades their mechanical properties. Hygroscopic fibers provide an easy route for moisture ingress. The addition of aramid fibers to epoxy and phenolic composites slightly improves their flame resistance and decreases smoke formation. This fiber also has a high resistance to shock loading and a low density, these two factors combined promote its use in bulletproof clothing. 2.2.2.6 Whiskers
26 Whiskers are monocrystalline short fibers with extremely high strength. This high strength is because of the absence of crystalline imperfections such as dislocations and having no grain boundaries. Typically whiskers have a diameter of a few µm and a length of a few mm (Figure 2.11). thus their aspect ratio (length/diameter) can vary from 50 to 10000. Whiskers do not have uniform dimensions or properties. This is perhaps their greatest disadvantage. Handling and alignment of whiskers in a matrix to produce a composite is another problem. Figure 2.11 Scanning electron micrograph of SiC whiskers (Chawla, 1998).
- Page 1 and 2: DOKUZ EYLÜL UNIVERSITY GRADUATE SC
- Page 3 and 4: M.Sc THESIS EXAMINATION RESULT FORM
- Page 5 and 6: A NUMERICAL STUDY ON THE THERMAL EX
- Page 7 and 8: CONTENTS Page THESIS EXAMINATION RE
- Page 9 and 10: 4.2.1 Geometry Creation............
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- Page 19 and 20: 10 polymers. Thermosetting polymers
- Page 21 and 22: 12 Metals are strong and tough. The
- Page 23 and 24: 14 Table 2.1 Properties of reinforc
- Page 25 and 26: 16 2.2.2.2 Carbon Fibers Carbon is
- Page 27 and 28: 18 use is in aircraft industry foll
- Page 29 and 30: 20 strength and a reasonable Young
- Page 31 and 32: 22 1. Processing the conventional f
- Page 33: 24 (orthorhombic) of polyethylene h
- Page 37 and 38: 28 3.2 Factors Affecting the Coeffi
- Page 39 and 40: 30 3.2.4 Thermal Cycling The primar
- Page 41 and 42: 32 3.3.1 Mechanical Dilatometry Thi
- Page 43 and 44: 34 absolute accuracy of about ± 0.
- Page 45 and 46: 36 3.3.3 Strain Gauges This relativ
- Page 47 and 48: 38 • The composite is macroscopic
- Page 49 and 50: 40 3.4.1.3 Equation of Van Fo Fy In
- Page 51 and 52: 42 and the thermal expansion coeffi
- Page 53 and 54: 44 P P 11 33 2 A 22 − A = Det A A
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- Page 57 and 58: CHAPTER FOUR FINITE ELEMENT METHOD
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- Page 65 and 66: 56 5.2 Mesh Creation 10-node tetrah
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- Page 73 and 74: 64 Table 6.1 Comparison of the expe
- Page 75 and 76: 66 Longitudinal CTE (1/°C) 2.25E-0
- Page 77 and 78: 68 Longitudinal CTE (1/°C) 2.00E-0
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- Page 81 and 82: 72 Longitudinal CTE (1/°C) 1.00E-0
- Page 83 and 84: 74 Ishikava, T., Koyama, K., & Koba
26<br />
Whiskers are m<strong>on</strong>ocrystalline short <strong>fiber</strong>s with extremely high strength. This high<br />
strength is because <strong>of</strong> <strong>the</strong> absence <strong>of</strong> crystalline imperfecti<strong>on</strong>s such as dislocati<strong>on</strong>s<br />
and having no grain boundaries. Typically whiskers have a diameter <strong>of</strong> a few µm and<br />
a length <strong>of</strong> a few mm (Figure 2.11). thus <strong>the</strong>ir aspect ratio (length/diameter) can vary<br />
from 50 to 10000. Whiskers do not have uniform dimensi<strong>on</strong>s or properties. This is<br />
perhaps <strong>the</strong>ir greatest disadvantage. Handling and alignment <strong>of</strong> whiskers in a matrix<br />
to produce a composite is ano<strong>the</strong>r problem.<br />
Figure 2.11 Scanning electr<strong>on</strong> micrograph <strong>of</strong> SiC whiskers (Chawla, 1998).
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