EBB 220/3POLYMER 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

Constituents of composite materials

1. Matrix phaseContinuous phase, the primary phase. It holds the dispersed phase and shares a load with it.

2. Dispersed (reinforcing) phaseThe 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. InterfaceZone across which matrix and reinforcing phases interact (chemical, physical,mechanical)

Matrix: Function

however the distribution of loads depends on the interfacial bondingshowever the distribution of loads depends on the interfacial bondings

Reinforcement: Function

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

To transfer the stress from matrix to reinforcement

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

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

Characteristics of dispersed phase that might influence the properties of composites

Characteristics of dispersed phase that might influence the properties of composites

Classification of compositesClassification of composites

Examples of composites

a) Particulate & randomb) Discontinuous fibers & unidirectionalc) Discontinuous fibers & randomd) Continuous fibers & unidirectional

Classification based on MatricesComposite materials

Matrices

Polymer Matrix Composites

(PMC)

Metal Matrix Composites

MMC)

Ceramic Matrix Composites

(CMC)

Thermoset Thermoplastic

Rubber

What is Hybrid composites?What are the advantages of hybrid composites?

Widely used- ease of processing & lightweight

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

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)

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

Influence final product, selection of correct raw materials, void content, etc

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.

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.

Glass 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 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.

Carbon 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 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 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.

Kevlar Fiber

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 Low maximum working

temperature High coefficient of thermal

expansion- dimensional instability

Sensitivity to radiation and moisture

Classification of Polymer Matrices1. Thermoset2. Thermoplastic- crystalline &

amorphous3. Rubber

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 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 weight polymers whose chains associate through weak van der Waals forces (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.

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

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

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:

Ease of processing Can be recycled No specific storage Good fracture modulus

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)

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