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

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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

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

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

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

CLASSIFICATION OF COMPOSITES Composites classifications by Matrix Reinforcement BDA40703 HT2012

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

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

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

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

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

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

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

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

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

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

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

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

Figure 4: Fibre length distribution data BDA40703 HT2012

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

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

Vegetable Fibres JUTE HEMP FLAX BDA40703 HT2012

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

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

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

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

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

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

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

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

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, 2000. (a) Fig. 4.22, p. 145 (photo by P. Davies); (b) Fig. 11.20, 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. 987-998, 1988. Used with permission. BDA40703 HT2012

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, 2000. (a) Fig. 4.24(a), p. 151; (b) Fig. 4.2(b) p. 351. Reproduced with permission of CRC Press, Boca Raton, FL. BDA40703 HT2012

• 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

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

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

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

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

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

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

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

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

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

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

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

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