1. Reinforcement And Matrix
Reinforcement or fibre type and property
Matrix
Interface
Adhesive and reinforcing mechanism
BDA40703 HT2012

2. BDA40703 HT2012

3. Resulted formation of interfacial phases and interfaces (boundaries)
Synthetic composites consist of mixtures of the different classes of materials:
Metal
Ceramic
Polymer
During composite processing, interfacial reactions can occur between the matrix and reinforcement materials.
Resulted formation of interfacial phases and interfaces (boundaries)
BDA40703 HT2012

4. The adhesion between matrix and reinforcement COMPOSITES PROPERTIES
WHY???
The matrix
The reinforcement
The adhesion between matrix and reinforcement
DETERMINES
COMPOSITES PROPERTIES
BDA40703 HT2012

5. The reinforcement The matrix or binder
bears the stresses.
When these reinforcements are not randomly distributed, which is often the case, the properties are anisotropic, being enhanced in the reinforcement direction.
The matrix or binder
ensures the cohesion of the composite
distributes and damps the impacts or stresses
protect the composite from the environment.
The cohesion of the matrix and reinforcements can be damaged, even in the bulk, by moisture or chemical surface attack.
BDA40703 HT2012

6. Figure 1: Strength of composites with variety of reinforcements
BDA40703 HT2012

7. CLASSIFICATION OF COMPOSITES
Composites classifications by
Matrix
Reinforcement
BDA40703 HT2012

8. CLASSIFICATION OF COMPOSITES (by reinforcements)
Particle- reinforced
Large particle
Dispersion strengthened
Fiber- reinforced
Continuous (aligned)
Discontinuous (short)
Aligned
Randomly
oriented
Structural
Laminates
Sandwich panels
BDA40703 HT2012

9. Types of Reinforcements
Fibres
Filled
Particle filled
Microspheres
Whiskers
Flake
Particulates
BDA40703 HT2012

10. Whiskers Flakes Usually ceramics
High moduli strengths and low densities
Resist temperature, mechanical damage and oxidation
Strength varies inversely with effective diameter
Flakes
Can be densely packed
Not expensive and cost < than fibres
Disadvantages – lack of size & shapes control and product defects
Advantages over fibres in structural applications – uniform mechanical props in flakes planes, high theoretical modulus of elasticity
BDA40703 HT2012

11. Filled
Structure infiltration with second phase filler material
Structure /skeleton – honeycomb structure (network of open pores
May be irregular structures or precise geometrical shapes like polyhedrons, short fibres or spheres.
Advantages – Increased stiffness, thermal resistance, stability, strength and abrasion resistance, porosity
Disadvantages – limited method of fabrication
Microspheres
Advantages – high specific gravity, stable particle size, strength and controlled density, good flow properties, distribute stress uniformly
Solid microspheres – glass material and low in density
Hollow microspheres – silicate based. Larger than solid microspheres. Less sensitive to moisture (reduce attraction between particles
BDA40703 HT2012

12. Figure 2: SEM images of porous microspheres/nanofibers composite film and water contact angle of such film
BDA40703 HT2012

13. Isotropy Anisotropy Orthotropic
Figure 3:
Isotropy =
A material whose properties are not dependent on the direction along which they are measured (same props)
Anisotropy
A material whose properties are dependent on the direction along which they are measured (vary props)
Orthotropic
Properties vary along the directions of each of the axes
BDA40703 HT2012

14. Requirement of reinforcements:
Stronger than matrix
Stiffer than matrix
Capable to change failure mechanism to advantage of composite
Function of reinforcements:
Provide strength
Provide heat resistance
Provide corrosion resistance
Provide rigidity
BDA40703 HT2012

15. Fibres Operational Definition:
An elongated material having a more or less uniform diameter or thickness less than 250 µm and an aspect ratio > than 100 µm aspect ratio = ratio of length to diameter (or thickness)
Upper limit of 70 vol% fibre usage in composite body is set to avoid fibre-fibre contact
BDA40703 HT2012

16. Fiber characteristic for high performance applications (Drescher, 1969)
A small diameter with respect to its grain size or its microstructural unit .
Allows higher fraction of theoretical strength to be obtained in bulk form.
Result of size effect – smaller size, lower probability of imperfections
A high aspect ratio (l/d)
Allows transfer of high fraction of applied load through the matrix to the stiff and strong fibre
High degree of flexibility
Characteristic of material with high modulus and small diameter
BDA40703 HT2012

17. Fibre Surface Area Consider fibre with length, l and diameter, d
Fiber surface area, SA = πdl
Fiber volume, vf = ( π/4) d2l
Thus;
Fiber surface are for a given volume inversely varies with the fibre diameter
Fibre diameter (-), fiber surface area (+), interfacial area (+)
BDA40703 HT2012

18. Fibre Length Distribution
Direct methods:
Use an optical micrograph – analyse with image analysis
Data plotted as histogram (allocate to size bins)
Meaningful average fibre length:
Number average
Ni = number of fibres of length Li
BDA40703 HT2012

19. Weight (or volume) average fibre length
Wi = weight of fibres of length Li
LN < LW
LENGTH DISTRIBUTION BASED ON WEIGHT ARE MORE MEANINGFUL, SINCE IT REFLECTS PROPOTION OF TOTAL FIBER AT ANY LENGTH
BDA40703 HT2012

20. Figure 4: Fibre length distribution data
BDA40703 HT2012

21. GROUPS OF FIBRES FIBRES Natural Vegetable Animal Mineral Regenerated
Synthetic
BDA40703 HT2012

22. Natural Fibres Vegetable Fibre eg. flax , cotton , hemp, jute etc.
Based on cellulose
Short/Discontinuous fibre
Mineral Fibre
eg. asbestos, wollastonite
Short fibres
Provide thermal insulation, thus applied in boilers, roof panels
Animal Fibre
Based on animal proteins
eg. silk, wool
Discontinuous and continuous fibres
BDA40703 HT2012

23. Vegetable Fibres
JUTE
HEMP
FLAX
BDA40703 HT2012

24. Figure 5: Examples of vegetable fibres
COCONUT FIBRE
KENAF
PINEAPPLE
Figure 5: Examples of vegetable fibres
BDA40703 HT2012

25. Mineral Fibres Asbestos Wollastonite
Figure 6: Examples of vegetable fibres
BDA40703 HT2012

26. Animal Fibres Cashmere Alpaca Figure 7: Examples of animal fibres
BDA40703 HT2012

27. MOLECULAR STRUCTURE ARRANGED
COMMON TRAITS AMONG NATURAL FIBRES:
MOLECULAR STRUCTURE ARRANGED
IN FIBRILLAR MANNER
Figure 8: Example of cotton Fibre
BDA40703 HT2012

28. Regenerated Fibre
From basic fibre which is obtained naturally (natural fibre)
Example is rayon which is regenerated from cellulose (from wood)
Figure 9: Example of Rayon fibre
BDA40703 HT2012

29. Synthetic Fibre Manufactured fibres
Manufactures of fibres are complex and involved number of processing steps
Variability in between fibres is large thus affecting properties
BDA40703 HT2012

30. Quiz What are the classifications of these fibres? Silk Collagen
BDA40703 HT2012

31. Classifications of fibres (based on diameter & character)
Whiskers
Thin single crystals
Large length to diameter ratio
High degree crystalline perfection
EXPENSIVE
Fibers
Polycrystalline/amorphous
Eg. Ceramics & polymers
Wires
Large diameter
Usually metals
FIBRES
BDA40703 HT2012

32. Aligned Continuous Fibres
• Examples:
--Metal: g'(Ni3Al)-a(Mo)
by eutectic solidification.
--Glass w/SiC fibers
formed by glass slurry
Eglass = 76GPa; ESiC = 400GPa.
(a)
From F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.22, p. 145 (photo by P. Davies); (b) Fig , p. 349 (micrograph by H.S. Kim, P.S. Rodgers, and R.D. Rawlings). Used with permission of CRC
Press, Boca Raton, FL.
(b)
From W. Funk and E. Blank, “Creep deformation of Ni3Al-Mo in-situ composites", Metall. Trans. A Vol. 19(4), pp , Used with permission.
BDA40703 HT2012

33. Discontinuous, random 2D fibres
• Example: Carbon-Carbon
--process: fiber/pitch, then
burn out at up to 2500C.
--uses: disk brakes, gas
turbine exhaust flaps, nose
cones.
(b)
(a)
• Other variations:
--Discontinuous, random 3D
--Discontinuous, 1D
Adapted from F.L. Matthews and R.L. Rawlings, Composite Materials; Engineering and Science, Reprint ed., CRC Press, Boca Raton, FL, (a) Fig. 4.24(a), p. 151; (b) Fig. 4.2(b) p Reproduced with permission of CRC Press, Boca Raton, FL.
BDA40703 HT2012

34. • Critical fiber length for effective stiffening & strengthening:
fiber strength in tension
fiber diameter
shear strength of
fiber-matrix interface
• Ex: For fiberglass, fiber length > 15mm needed
• Why? Longer fibers carry stress more efficiently!
Shorter, thicker fiber:
Longer, thinner fiber:
Adapted from Fig. 16.7, Callister 6e.
Poorer fiber efficiency
Better fiber efficiency
BDA40703 HT2012

35. Figure 10: Dependency of composite performance to fibre length
BDA40703 HT2012

36. Fibers and Properties Fibers and Properties Glass Fibre
Over 95% used in reinforced polymers
Inexpensive, easy to manufacture, possess high strength and stiffness, low density, resistant to chemicals, good insulator
Disadvantages – break when subjected to high tensile stress for long period
Available in mats, tapes, cloth, continuous and chopped filaments
BDA40703 HT2012

37. Two types of glass used for making glass fibres: E glass & S glass
Lime-aliminium- borosillicate glass
Continuous fibre
S glass:
Silicate-Alumina- Magnesia
Higher strength to weight ratio
Figure 11: Examples of glass fibres
BDA40703 HT2012

38. Soda lime glass is known as A-glass.
Table 1: Compositions (% wt) of various glasses used in fiber production.
Soda lime glass is known as A-glass.
The type E is the most widely used glass fiber
Types S and R are glasses with enhanced mechanical properties
Type C resists corrosion in an acid environment
Type Z in an alkaline environment
Type D is used for its dielectric properties
BDA40703 HT2012

39. Table 1:
Mechanical properties of a number on different properties of types of glass.
BDA40703 HT2012

40. Quartz and Silica Fibres
Quartz fibers are made from natural quartz (99.9% SiO)
Silica and quartz are similar
Highly elastic
Can be stretched to 1% of their length before break point
Resistant to acids and moisture
Withstand temperature up to 1600oC
Figure 15: Quartz and Silica fibres
BDA40703 HT2012

41. Alumina fibres
Basically developed for usage in metal matrices (Mg and Al)
Contains ~ 50 wt% of alumina and silica
Usually are glassy fibres but crystalline if contains less silica
Resistant to high temperature and higher stiffness
Better compressive strength than tensile strength
High service temperature (~1000oC) – high meting temperature (~2000oC)
Example of short fibres are from clay or related clay material by spinning or casting process
BDA40703 HT2012

42. Silicon Carbide Fibres
Boron Fibres
Boron-tungsten fibers (boron deposited on tungsten and carbon)
Properties change with diameter
Changing ratio of boron to tungsten - surface defects change according to size
Remarkable stiffness and strength (~ 5 X higher in tensile modulus)
Silicon Carbide Fibres
Similar to boron fibres – deposited over metals (tungsten and carbon)
Process: CVD
Difference: more dense, prone to surface damage, only 35% strength loss at elevated temperature up to 1350oC
BDA40703 HT2012

43. Figure 13: Silicon carbide fibres
Figure 12: Boron fibres
Figure 13: Silicon carbide fibres
BDA40703 HT2012

44. Aramid Fibres Generic name for aromatic polyamide fibres
Trade name: Kevlar (first produced by Du Pont)
Chemical repeating unit is aromatic polyamide
High tensile strength, high modulus and low weight
Prone to photo- degradation on exposure to sunlight
Figure 14: Examples of vegetable fibres
Fire resistant
Poor acid and alkaline resistance
BDA40703 HT2012

45. Graphite fibres Carbon fibre: from element poly-acrylo-nitrile (PAN)
Consist 91 – 94% carbon
Produced at 1320oC
Without air/oxidising environment, can withstand temperature up to 2600oC
Not used extensively in metal matrices since the fibre can react chemically during fabrication
Figure 16: Graphite fibres
BDA40703 HT2012

46. Fibres are graphitised at 1950 – 3000oC
Graphite fibres:
Over 99% carbon
Fibres are graphitised at 1950 – 3000oC
Properties remain unchanged at very high temperature
Stiffness is as high as the graphite content
Disadvantage: stiffness and strength are inversely proportional to each other
BDA40703 HT2012