COMPOSITE MATERIALSsablon.mu.edu.tr/Icerik/metalurji.mu.edu.tr/Sayfa/... · Composite Materials Asst.Prof. Dr. Ayşe KALEMTAŞ Functions of the Reinforcements Function is to reinforce

Composite Materials Asst. Prof. Dr. Ayşe KALEMTAŞ Composite Materials Asst. Prof. Dr. Ayşe KALEMTAŞ

COMPOSITE

MATERIALS

Asst. Prof. Dr. Ayşe KALEMTAŞ

Office Hours: Tuesday, 16:30-17:30

[email protected], [email protected]

Phone: +90 – 252 211 19 17

Metallurgical and Materials Engineering Department

mailto:[email protected]







ISSUES TO ADDRESS

Reinforcement Materials

Properties

Applications


Functions of the Reinforcements

Function is to reinforce the primary phase

Imbedded phase is most commonly one of the following shapes:

Fibers

Particles

Flakes

In addition, the secondary phase can take the form of an infiltrated

phase in a skeletal or porous matrix

Example: a powder metallurgy part infiltrated with polymer

©2002 John Wiley & Sons, Inc. M P Groover, “Fundamentals of Modern Manufacturing 2/e”

Possible physical shapes of imbedded phases in composite materials:

(a) fiber, (b) particle, and (c) flake


FIBERS

Filaments of reinforcing material, usually circular in

cross-section

Diameters range from less than 0.0025 mm to about 0.13 mm,

depending on material

Filaments provide greatest opportunity for strength

enhancement of composites

The filament form of most materials is significantly stronger

than the bulk form

As diameter is reduced, the material becomes oriented in the

fiber axis direction and probability of defects in the structure

decreases significantly


Continuous versus Discontinuous Fibers

Continuous fibers - very long; in theory, they offer a

continuous path by which a load can be carried by the

composite part

Discontinuous fibers (chopped sections of continuous

fibers) - short lengths (L/D = roughly 100)

Important type of discontinuous fiber are whiskers - hair-

like single crystals with diameters down to about 0.001 mm

(0.00004 in.) with very high strength


Fiber Orientation

The fibers may be oriented randomly within the material, but it is

possible to arrange for them to be oriented preferentially in the

direction expected to have the highest stresses. Such a material

is said to be anisotropic (different properties in different

directions), and control of anisotropy is an important means of

optimising the material for specific applications.

At a microscopic level, the properties of these composite are

determined by the orientation and distribution of the fibers, as

well as by the properties of the fiber and matrix materials. These

topic known as composite micromechanics is concerned with

developing estimates of the overall material properties from

these parameters.


Fiber Orientation – Three Cases

One-dimensional reinforcement, in which maximum strength and stiffness are obtained

in the direction of the fiber

Planar reinforcement, in some cases in the form of a two-dimensional woven fabric

Random or three-dimensional in which the composite material tends to possess

isotropic properties

Fiber orientation in composite materials: (a) one-dimensional, continuous fibers;

(b) planar, continuous fibers in the form of a woven fabric; and (c) random, discontinuous fibers


Fibers


FIBER ORIENTATION

A three dimensional weave is also possible

This could be found when fabrics are knitted or weaved together


FIBER ORIENTATION

The properties of fiber composites can be tailored to meet different loading requirements

By using combinations of different fiber orientation quasi-isotropic materials may be produced

Figure. (a) shows a unidirectional arrangement

(b) shows a quasi-isotropic arrangement


FIBER ORIENTATION

Strongest, but

anisotropic Weaker, but

isotropic


FIBER ORIENTATION

Maximum strength is

obtained when long fibers

are oriented parallel to

the applied load

The effect of fiber

orientation and strength

can be seen in the plot


FIBERS

COMMERCIALLY AVAILABLE FORMS OF

REINFORCEMENT

Filament: a single thread like fiber

Roving: a bundle of filaments wound to form a large

strand

Chopped strand mat: assembled from chopped

filaments bound with a binder

Continuous filament random mat: assembled from

continuous filaments bound with a binder

Many varieties of woven fabrics: woven from rovings


FIBERS


REINFORCEMENT

Close up of a roving Roving Filaments


FIBERS


REINFORCEMENT

Random mat and woven fabric (glass fibers)


FIBERS


REINFORCEMENT

Carbon fiber woven fabric


FIBERS

NEXTEL FIBERS


Fiber Materials

Materials for Fibers

Metals – Steel

Polymers – Kevlar

Ceramics – SiC and Al2O3

Carbon – High elastic modulus

Boron – Very high elastic modulus

Glass – Most widely used filament

The most important commercial use of fibers is in polymer composites


Particles and Flakes

A second common shape of imbedded phase is

particulate, ranging in size from microscopic to

macroscopic

Flakes are basically two-dimensional particles - small flat

platelets

The distribution of particles in the composite matrix is

random, and therefore strength and other properties of the

composite material are usually isotropic

Strengthening mechanism depends on particle size


INTERFACE: Zone across which matrix and reinforcing phases interact (chemical, physical,

mechanical)

To transfer the stress from matrix to reinforcement

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

There is always an interface between constituent phases in a composite material. For the composite to operate effectively, the phases must bond where they join at the interface.

Interface

Interfaces between phases in a composite material: Direct bonding between

primary and secondary phases


In some cases, a third ingredient must be added to

achieve bonding of primary and secondary phases.

Called an interphase, this third ingredient can be thought

of as an adhesive.

Interphase

Interfaces between phases in a composite material: Direct bonding between

primary and secondary phases


Interphase

Interphase consisting of a solution of primary and

secondary phases

Interfaces and interphases between phases in a composite material: Formation

of an interphase by solution of the primary and secondary phases at their

boundary


Specific strength versus

specific modulus for

different types of fibers

FIBER PROPERTIES


FIBER PROPERTIES

COMPARATIVE COST OF FIBER REINFORCEMENT


Fibers - Glass

– Tensile strength

– Chemical resistance

– Moisture resistance

– Thermal properties

– Electrical properties

There are four main types of glass used in fiberglass:

– A–glass

– C–glass

– E–glass

– S–glass

Fiberglass properties vary somewhat according to the type of glass used.

However, glass in general has several well–known properties that contribute to

its great usefulness as a reinforcing agent:


GLASS FIBERS

Due to the relatively inexpensive cost glass fibers are the most commonly used reinforcement

There are a variety of types of glass, they are all compounds of silica with a variety of metallic oxides

Designation Property or Characteristic

E, electrical low electrical conductivity

S, strength high strength

C, chemical high chemical durability

M, modulus high stiffness

A, alkali high alkali or soda lime glass

D, dielectric low dielectric constant

- The most commonly used glass is E-glass, this is the most popular

because of it’s cost


Fibers - Glass

Most widely used fiber

Uses: piping, tanks, boats, sporting goods

Advantages

Low cost

Corrosion resistance

Low cost relative to other composites:

Disadvantages

Relatively low strength

High elongation

Moderate strength and weight

Types:

E-Glass - electrical, cheaper

S-Glass - high strength


Fibers - Glass

Glass fibers produced by spinning liquid glass directly to

fine fibers. Just as in the Griffith experiments, the strength

is based on small diameter.

Modulus ranges from 70- 90 GPa.

Strength ranges from 1.7-5 GPa

Breaking strain from 2 to 5%

Density ~ 2.5 gm/cm3.

“E glass” (electrical, borosilicate glass) is the cheapest

and most common. “R glass” and “S glass” is more

expensive but more corrosion resistant, for example and

higher strength.


Fibers – Carbon

Carbon fibers have gained a lot of popularity in the last

two decades due to the price reduction

“Carbon fiber composites are five times stronger than

1020 steel yet five times lighter. In comparison to 6061

aluminum, carbon fiber composites are seven times

stronger and two times stiffer yet still 1.5 times lighter”

Initially used exclusively by the aerospace industry they

are becoming more and more common in fields such as

automotive, civil infrastructure, and paper production


Fibers – Carbon

2nd most widely used fiber

Examples

aerospace, sporting goods

Advantages

high stiffness and strength

low density

intermediate cost

Properties:

Standard modulus: 207-240 GPa

Intermediate modulus: 240-340 GPa

High modulus: 340-960 GPa

Diameter: 5-8 microns, smaller than human hair

Fibers grouped into tows or yarns of 2-12k fibers


Fibers – Carbon

Modulus ranges from 200-750 GPa (cf. Steel-210)

Strength ranges from 2-6 GPa

Breaking strain ranges from 0.2 - 2 %

Density ranges from 1.76- 2.15 g/cm3

Highest cost compared to glass or aramid, but greatest

range of properties.

Internal structure consists of radially-aligned graphite

platelets, which leads to some anisotropy in properties in

the fibers. Both thermal and electrical conductivity are

generally good (but then insulation required where metals

might be in contact for carbon-fiber composite).


Fibers – Carbon

Types of carbon fiber

vary in strength with processing

Trade-off between strength and modulus

Intermediate modulus

PAN (Polyacrylonitrile)

fiber precursor heated and stretched to align

structure and remove non-carbon material

High modulus

made from petroleum pitch precursor at lower cost

much lower strength


Fibers – Others

Boron

High stiffness, very high cost

Large diameter - 200 microns

Good compressive strength

Polyethylene - trade name: Spectra fiber

Textile industry

High strength

Extremely light weight

Low range of temperature usage


Fibers – Others

Ceramic Fibers (and matrices)

Very high temperature applications (e.g.

engine components)

Silicon carbide fiber - in whisker form.

Ceramic matrix so temperature resistance is

not compromised

Infrequent use


Fiber Material Properties

Steel: density (Fe) = 7.87 cm3; TS=0.380 GPa; Modulus=207 GPa

Al: density=2.71 g/cm3; TS=0.035 GPa; Modulus=69 GPa


Fibers-Aramid

-Aramid fibers are also becoming

more and more common

-They have the highest level of

specific strength of all the

common fibers

-They are commonly used when

a degree of impact resistance is

required such as in ballistic

armour

-The most common type of

aramid is Kevlar http://armorus.en.made-in-

china.com/product/weEnpAcbaUYC/China-Covert-

Aramid-Bulletproof-Vest-Body-Armor-TAT-FJ-2-.html


Fibers-Aramid

Kevlar and Aramid Fibers (Opaque Armor)

Only the highest grade, waterproof Kevlar and aramid fibers are used.

These fibers offer superior blast, fragmentation, explosive and small arms

ballistic protection. All materials are tested in an independent laboratory

and are custom fabricated according to TAC specifications.

http://www.texasarmoring.com/armored_vehicle_bulletproofing_materials.html


Fiber Strength


Fiber Reinforced Composites

CHARACTERISTICS OF FIBER REINFORCED

COMPOSITES

As can be seen

from this plot, the

strength of the

composite

increases as the

fiber length

increases (this is a

chopped E-glass-

epoxy composite)


Fiber Reinforced Composites

Some commonly used fibers for polymer matrix

composites:

Glass fibers

Carbon fibers

Aramid fibers

Some commonly used fibers for metal matrix

composites:

Boron fibers

Carbon fibers

Oxide ceramic and non-oxide ceramic fibers


Thanks for your kind

attention

THE END


Any

Questions

Documents

COMPOSITE MATERIALSsablon.mu.edu.tr/Icerik/metalurji.mu.edu.tr/Sayfa/... · Composite Materials Asst.Prof. Dr. Ayşe KALEMTAŞ Functions of the Reinforcements Function is to reinforce