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EBB 220/3 POLYMER COMPOSITE. What is Composites?. Combination of 2 or more materials Each of the materials must exist more than 5% Presence of interphase The properties shown by the composite materials are differed from the initial materials Can be produced by various processing techniques.

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what is composites
What is Composites?
  • Combination of 2 or more materials
  • Each of the materials must exist more than 5%
  • Presence of interphase
  • The properties shown by the composite materials are differed from the initial materials
  • Can be produced by various processing techniques
constituents of composite materials
Constituents of composite materials
  • Matrix phase
  • Continuous phase, the primary phase.
  • It holds the dispersed phase and shares a load with it.
  • 2. Dispersed (reinforcing) phase
  • The second phase (or phases) is imbedded in the matrix in a
  • continuous/discontinuous form.
  • Dispersed phase is usually stronger than the matrix, therefore it is sometimes
  • called reinforcing phase.
  • 3. Interface
  • Zone across which matrix and reinforcing phases interact (chemical, physical,
  • mechanical)
matrix function
Matrix: Function

however the distribution of loads depends on the interfacial bondings

reinforcement can be in the form of
Reinforcement can be in the form of:
  • Continuous fiber
    • Organic fiber- i.e. Kevlar, polyethylene
    • Inorganic fiber- i.e. glass, alumina, carbon
    • Natural fiber- i.e. asbestos, jute, silk
  • Short fiber
  • whiskers
  • Particle
  • Wire
interface function
Interface: Function
  • To transfer the stress from matrix to reinforcement

Sometimes surface treatment is carried out to achieve the required bonding to the matrix

slide8

Characteristics of dispersed phase that might influence the properties of composites

a) Concentration (b) size (c) shape (d) distribution (e) orientation

examples of composites
Examples of composites
  • Particulate & random
  • Discontinuous fibers & unidirectional
  • Discontinuous fibers & random
  • Continuous fibers & unidirectional
classification based on matrices
Classification based on Matrices

Composite materials

Matrices

Polymer Matrix Composites (PMC)

Metal Matrix Composites MMC)

Ceramic Matrix Composites (CMC)

Thermoset

Thermoplastic

Rubber

properties of composites depend on
Properties of composites depend on
  • Amount of phase

- Amount/proportion (can be expressed in weight fraction (Wf) or volume fraction (Vf))of phases strongly influence the properties of composite materials.

Xc = Xf Vf + Xm (1 - Vf ) - Rule of Mixture

Xc = Properties of composites

Xf = Properties of fiber

Xm= Properties of matrix

voids
Voids
  • Free volume
  • Gas emission leads to voids in the final product
  • In composites- Voids exist in the matrix, interface and in between fiber & fiber
  • Voids create stress concentration points- influence the properties of the composites
geometry of dispersed phase particle size distribution orientation
Geometry of dispersed phase (particle size, distribution, orientation)
  • Shape of dispersed phase (particle- spherical or irregular, flaky, whiskers, etc)
  • Particle/fiber size ( fiber- short, long, continuous); particle (nano or micron size)
  • Orientation of fiber/particle (unidirection, bi-directions, many directions)- influence isotropic dan an-isotropic properties
  • Dictribution of dispersed phase (homogenus/uniform, inhomogenus)
processing technique and parameters
Processing technique and parameters
  • Influence final product, selection of correct raw materials, void content, etc
glass fiber
Glass Fiber

The types of glass used are as follows:

  • E-Glass – the most popular and inexpensive glass fibers. The designation letter “E” means “electrical” (E-Glass is excellent insulator). The composition of E-glass ranges from 52-56% SiO2, 12-16% A1203, 16-25% CaO, and 8-13% B203
  • S-Glass – stronger than E-Glass fibers (the letter “S” means strength). High-strength glass is generally known as S-type glass in the United States, R-glass in Europe and T-glass in Japan. S-Glass is used in military applications and in aerospace. S-Glass consists of silica (SiO2), magnesia (MgO), alumina (Al2O3).
  • C-Glass – corrosion and chemical resistant glass fibers. To protect against water erosion, a moisture-resistant coating such as a silane compound is coated onto the fibers during manufacturing. Adding resin during composite formation provides additional protection. C-Glass fibers are used for manufacturing storage tanks, pipes and other chemical resistant equipment.
glass fiber1
Glass Fiber
  • Fiberglasses (Glass fibers reinforced polymer matrix composites) are characterized by the following properties:
  • High strength-to-weight ratio;
  • High modulus of elasticity-to-weight ratio;
  • Good corrosion resistance;
  • Good insulating properties;
  • Low thermal resistance (as compared to metals and ceramics).
  • Fiberglass materials are used for manufacturing: boat hulls and marine structures, automobile and truck body panels, pressure vessels, aircraft wings and fuselage sections, housings for radar systems, swimming pools, welding helmets, roofs, pipes.
carbon fiber
Carbon Fiber
  • The types of carbon fibers are as follows:
  • UHM (ultra high modulus). Modulus of elasticity > 65400 ksi (450GPa).
  • HM (high modulus). Modulus of elasticity is in the range 51000-65400 ksi (350-450GPa).
  • IM (intermediate modulus). Modulus of elasticity is in the range 29000-51000 ksi (200-350GPa).
  • HT (high tensile, low modulus). Tensile strength > 436 ksi (3 GPa), modulus of elasticity < 14500 ksi (100 GPa).
  • SHT (super high tensile). Tensile strength > 650 ksi (4.5GPa).
carbon fiber1
Carbon Fiber
  • Carbon Fiber Reinforced Polymers (CFRP) are characterized by the following properties:
  • Light weight;
  • High strength-to-weight ratio;
  • Very High modulus elasticity-to-weight ratio;
  • High Fatigue strength;
  • Good corrosion resistance;
  • Very low coefficient of thermal expansion;
  • Low impact resistance;
  • High electric conductivity;
  • High cost.
  • Carbon Fiber Reinforced Polymers (CFRP) are used for manufacturing: automotive marine and aerospace parts, sport goods (golf clubs, skis, tennis racquets, fishing rods), bicycle frames.
kevlar fiber
Kevlar Fiber
  • Kevlar is the trade name (registered by DuPont Co.) of aramid (poly-para-phenylene terephthalamide) fibers.
  • Kevlar fibers were originally developed as a replacement of steel in automotive tires.
  • Kevlar filaments are produced by extrusion of the precursor through a spinnert. Extrusion imparts anisotropy (increased strength in the lengthwise direction) to the filaments.
  • Kevlar may protect carbon fibers and improve their properties: hybrid fabric (Kevlar + Carbon fibers) combines very high tensile strength with high impact and abrasion resistance.
kevlar fiber1
Kevlar Fiber
  • Kevlar fibers possess the following properties:
  • High tensile strength (five times stronger per weight unite than steel);
  • High modulus of elasticity;
  • Very low elongation up to breaking point;
  • Low weight;
  • High chemical inertness;
  • Very low coefficient of thermal expansion;
  • High Fracture Toughness (impact resistance);
  • High cut resistance;
  • Textile processibility;
  • Flame resistance.
  • The disadvantages of Kevlar are: ability to absorb moisture, difficulties in cutting, low compressive strength.
kevlar fiber2
Kevlar Fiber
  • There are several modifications of Kevlar, developed for various applications:
  • Kevlar 29 – high strength (520000 psi/3600 MPa), low density (90 lb/ft³/1440 kg/m³) fibers used for manufacturing bullet-proof vests, composite armor reinforcement, helmets, ropes, cables, asbestos replacing parts.
  • Kevlar 49 – high modulus (19000 ksi/131 GPa), high strength (550000 psi/3800 MPa), low density (90 lb/ft³/1440 kg/m³) fibers used in aerospace, automotive and marine applications.
  • Kevlar 149 – ultra high modulus (27000 ksi/186 GPa), high strength (490000 psi/3400 MPa), low density (92 lb/ft³/1470 kg/m³) highly crystalline fibers used as reinforcing dispersed phase for composite aircraft components.
reasons for the use of polymeric materials as matrices in composites
Reasons for the use of polymeric materials as matrices in composites
  • i. The mechanical properties of polymers are inadequate for structural purposes, hence benefits are gained by reinforcing the polymers
  • Processing of PMCs need not involve high pressure and high temperature
  • The equipment required for PMCs are much simpler
disadvantages of pmc
Disadvantages of PMC
  • Low maximum working temperature
  • High coefficient of thermal expansion- dimensional instability
  • Sensitivity to radiation and moisture
classification of polymer matrices
Classification of Polymer Matrices
  • 1. Thermoset
  • 2. Thermoplastic- crystalline & amorphous
  • 3. Rubber
thermoset
Thermoset
  • Thermoset materials are usually liquid or malleable prior to curing, and designed to be molded into their final form
  • has the property of undergoing a chemical reaction by the action of heat, catalyst, ultraviolet light, etc., to become a relatively insoluble and infusible substance.
  • They develop a well-bonded three-dimensional structure upon curing. Once hardened or cross-linked, they will decompose rather than melt.
  • A thermoset material cannot be melted and re-shaped after it is cured.
  • Thermoset materials are generally stronger than thermoplastic materials due to this 3-D network of bonds, and are also better suited to high-temperature applications up to the decomposition temperature of the material.
thermoplastic
Thermoplastic
  • is a plastic that melts to a liquid when heated and freezes to a brittle, very glassy state when cooled sufficiently.
  • Most thermoplastics are high molecular weightpolymers whose chains associate through weak van der Waalsforces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene).
  • The bondings are easily broken by the cobined action of thermal activation and applied stress, that’s why thermoplastics flow at elevated temperature
  • unlike thermosetting polymers, thermoplastic can be remelted and remolded.
slide36
Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name
  • Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the Tg. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS and PC.
  • Generally, amorphous thermoplastics are less chemically resistant
slide37
Depends on the structure of the thermoplastics, some of the polymeric structure can be folded to form crystalline regions, will crystallize to a certain extent and are called "semi-crystalline" for this reason.
  • Typical semi-crystalline thermoplastics are PE, PP, PBT and PET.
  • Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque.
  • Why HDPE exhibits higher cystallinity than LDPE?
comparison of typical ranges of property values for thermoset and thermoplastics
Comparison of typical ranges of property values for thermoset and thermoplastics
  • Properties t/set t/plastic
  • Young’s Modulus (GPa)1.3-6.0 1.0-4.8
  • Tensile strength(MPa) 20-180 40-190
  • Max service temp.(ºC) 50-450 25-230
  • Fracture toughness,KIc 0.5-1.0 1.5-6.0

(MPa1/2)

thermoplastics are expected to receive attention compared to thermoset due to
Thermoplastics are expected to receive attention compared to thermoset due to:
  • Ease of processing
  • Can be recycled
  • No specific storage
  • Good fracture modulus
rubber
Rubber
  • Common characteristics;
    • Large elastic elongation (i.e. 200%)
    • Can be stretched and then immediately return to their original length when the load was released
  • Elastomers are sometimes called rubber or rubbery materials
  • The term elastomer is often used interchangeably with the term rubber
  • Natural rubber is obtained from latex from Hevea Brasiliensis tree which consists of 98% poliisoprena
  • Synthetic rubber is commonly produced from butadiene, spt styrene-butadiene (SBR) dan nitrile-butadiene (NBR)
slide41
To achieve properties suitable for structural purposed, most rubbers have to be vulcanized; the long chain rubber have to be crosslinked
  • The crosslinking agent in vulcanization is commonly sulphur, and the stiffness and strength increases with the number of crosslinks