Svnit composite materials

Introduction To Composite Materials

Mr. S. G. KulkarniSVNIT SURAT

Tutorial

What is metal ?What is non metal ?What is alloy ?What are drawbacks of metals ?What is engineering ?Why we are studying practical ?

Introduction to Composites1. What is the matrix in a composite and what materials are commonly

used as a matrix?

2. What is reinforcement in composites ?

3. Be able to decide different factors responsible for properties of composite.

4. Know the equation for the critical length (Lc) of a fiber..

Reading:

Composites in Action

http://www.sr-71.org/photogallery/blackbird/

Composite Material

Two inherently different materials that when combined together produce a material with properties that exceed

the constituent materials.

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What is a composite Material?

A broad definition of composite is: Two or more chemically distinct materials which when combined have improved properties over the individual materials. Composites could be natural or synthetic.

Wood is a good example of a natural composite, combination of cellulose fiber and lignin. The cellulose fiber provides strength and the lignin is the "glue" that bonds and stabilizes the fiber.

The ancient Egyptians manufactured composites! Adobe bricks are a good example. The combination of mud and straw forms a composite that is stronger than either the mud or the straw by itself.

Bamboo is a very efficient wood composite structure. The components are cellulose and lignin, as in all other wood, however bamboo is hollow. This results in a very light yet stiff structure. Composite fishing poles and golf club shafts copy this natural design.

TutorialRevise the concept of

HardnessToughnessStiffnessYield strenthUltimate tensile strengthCompressive strenthTensile StrenthShear strengthDuctilenessBrittleness

Strength For metals the most common measure of strength is the yield strength. For most polymers it is more convenient to measure the failure strength, the stress at the point where the stress strain curve becomes obviously non-linear. Strength, for ceramics however, is more difficult to define. Failure in ceramics is highly dependent on the mode of loading. The typical failure strength in compression is fifteen times the failure strength in tension. The more common reported value is the compressive failure strength.

Yield Strength The yield strength is the minimum stress which produces permanent plastic deformation. This is perhaps the most common material property reported for structural materials because of the ease and relative accuracy of its measurement. The yield strength is usually defined at a specific amount of plastic strain, or offset, which may vary by material and or specification. The offset is the amount that the stress-strain curve deviates from the linear elastic line. The most common offset for structural metals is 0.2%.

Ultimate Tensile Strength The ultimate tensile strength is an engineering value calculated by dividing the maximum load on a material experienced during a tensile test by the initial cross section of the test sample. When viewed in light of the other tensile test data the ultimate tensile strength helps to provide a good indication of a material's toughness but is not by itself a useful design limit. Conversely this can be construed as the minimum stress that is necessary to ensure the failure of a material. Ductility Ductility is a measure of how much deformation or strain a material can withstand before breaking. The most common measure of ductility is the percentage of change in length of a tensile sample after breaking. This is generally reported as % El or percent elongation. The R.A. or reduction of area of the sample also gives some indication of ductility. Toughness Toughness describes a material's resistance to fracture. It is often expressed in terms of the amount of energy a material can absorb before fracture. Tough materials can absorb a considerable amount of energy before fracture while brittle materials absorb very little. Neither strong materials such as glass or very ductile materials such as taffy can absorb large amounts of energy before failure. Toughness is not a single property but rather a combination of strength and ductility. The toughness of a material can be related to the total area under its stress-strain curve. A comparison of the relative magnitudes of the yield strength, ultimate tensile strength and percent elongation of different material will give a good indication of their relative toughness. Materials with high yield strength and high ductility have high toughness. Integrated stress-strain data is not readily available for most materials so other test methods have been devised to help quantify toughness. The most common test for toughness is the Charpy impact test. In crystalline materials the toughness is strongly dependent on crystal structure. Face centered cubic materials are typically ductile while hexagonal close packed materials tend to be brittle. Body centered cubic materials often display dramatic variation in the mode of failure with temperature. In many materials the toughness is temperature dependent. Generally materials are more brittle at lower temperatures and more ductile at higher temperatures. The temperature at which the transition takes place is known as the DBTT, or ductile to brittle transition temperature. The DBTT is measured by performing a series of Charpy impact tests at various temperatures to determine the ranges of brittle and ductile behavior. Use of alloys below their transition temperature is avoided due to the risk of catastrophic failure.

Composites Offer High StrengthLight WeightDesign FlexibilityStrenthen of PartsNet Shape Manufacturing

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Composites

Composites are combinations of two materials in which one of the material is called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other material called the matrix phase.

Typically, reinforcing materials are strong with low densities while the matrix is usually a ductile or tough material. If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material.

Reinforcement: fibers

GlassCarbonOrganicBoronCeramicMetallic

Matrix materials

PolymersMetalsCeramics

Interface

Bonding surface

Components of composite materials

Why Composites are Important

Composites can be very strong and stiff, yet very light in weight, so ratios of strength‑to‑weight and stiffness‑to‑weight are several times greater than steel or aluminum

Fatigue properties are generally better than for common engineering metals

Toughness is often greater too Composites can be designed that do not corrode like steel Possible to achieve combinations of properties not

attainable with metals, ceramics, or polymers alone

Fiber Reinforced Polymer Matrix

Matrix • Transfer Load to

Reinforcement• Temperature Resistance• Chemical Resistance

Reinforcement

• Tensile Properties• Stiffness• Impact Resistance

Matrix Considerations

End Use TemperatureToughnessCosmetic IssuesFlame RetardantProcessing MethodAdhesion Requirements

Matrix Materials Functions of the matrix

– Transmit force between fibers– arrest cracks from spreading between fibers

do not carry most of the load– hold fibers in proper orientation– protect fibers from environment

mechanical forces can cause cracks that allow environment to affect fibers

Demands on matrix – Interlaminar shear strength– Toughness– Moisture/environmental resistance– Temperature properties– Cost

Types of Composite Materials

There are five basic types of composite materials: Fiber, particle, flake, laminar or layered and filled composites.

A. Fiber CompositesIn fiber composites, the fibers reinforce along the line of their length. Reinforcement may be mainly 1-D, 2-D or 3-D. Figure shows the three basic types of fiber orientation.

1-D gives maximum strength in one direction.

2-D gives strength in two directions.

Isotropic gives strength equally in all directions.

B. Particle Composites Particles usually reinforce a composite equally in all directions (called

isotropic). Plastics, cermets and metals are examples of particles. Particles used to strengthen a matrix do not do so in the same way as

fibers. For one thing, particles are not directional like fibers. Spread at random through out a matrix, particles tend to reinforce in all directions equally.

Cermets (1) Oxide–Based cermets(e.g. Combination of Al2O3 with Cr) (2) Carbide–Based Cermets(e.g. Tungsten–carbide, titanium–carbide) Metal–plastic particle composites(e.g. Aluminum, iron & steel, copper particles) Metal–in–metal Particle Composites and Dispersion

Hardened Alloys(e.g. Ceramic–oxide particles)

C. Flake Composites - 1

Flakes, because of their shape, usually reinforce in 2-D. Two common flake materials are glass and mica. (Also aluminum is used as metal flakes)

D. Laminar Composites - 1 Laminar composites involve two or more layers of

the same or different materials. The layers can be arranged in different directions to give strength where needed. Speedboat hulls are among the very

many products of this kind.

D. Laminar Composites - 4 A lamina (laminae) is any

arrangement of unidirectional or woven fibers in a matrix. Usually this arrangement is flat, although it may be curved, as in a shell.

A laminate is a stack of lamina arranged with their main reinforcement in at least two different directions.

F. Combined Composites It is possible to combine several

different materials into a single composite. It is also possible to combine several different composites into a single product. A good example is a modern ski. (combination of wood as natural fiber, and layers as laminar composites)

E. Filled Composites There are two types of filled composites. In one,

filler materials are added to a normal composite result in strengthening the composite and reducing weight. The second type of filled composite consists of a skeletal 3-D matrix holding a second material. The most widely used composites of this kind are sandwich structures and honeycombs.

Figure (a) Model of a fiber‑reinforced composite material showing direction in which elastic modulus is being estimated by the rule of mixtures (b) Stress‑strain relationships for the composite material and its constituents. The fiber is stiff but brittle, while the matrix (commonly a polymer) is soft but ductile.

Types of CompositesMatrix phase/Reinforcement Phase

Metal Ceramic Polymer

Metal Powder metallurgy parts – combining immiscible metals

Cermets (ceramic-metal composite)

Brake pads

Ceramic Cermets, TiC, TiCNCemented carbides – used in toolsFiber-reinforced metals

SiC reinforced Al2O3 Tool materials

Fiberglass

Polymer Kevlar fibers in an epoxy matrix

Elemental (Carbon, Boron, etc.)

Fiber reinforced metalsAuto partsaerospace

Rubber with carbon (tires)Boron, Carbon reinforced plastics

MMC’s CMC’s PMC’sMetal Matrix Composites Ceramic Matrix Comp’s. Polymer Matrix Comp’s

Mechanical Engineering Dept. 26Ken Youssefi

Composites – Metal MatrixThe metal matrix composites offer higher modulus of elasticity, ductility, and resistance to elevated temperature than polymer matrix composites. But, they are heavier and more difficult to process.

Introduction to Composites1. What is the matrix in a composite and what materials are commonly

used as a matrix?

2. What is reinforcement in composites ?

3. Be able to decide different factors responsible for properties of composite.

4. Know the equation for the critical length (Lc) of a fiber..

Reading:

Design Objective

Performance: Strength, Temperature, StiffnessManufacturing TechniquesLife Cycle ConsiderationsCost

Matrix Types

Epoxy

Epoxies have improved strength and stiffness properties over polyesters. Epoxies offer excellent corrosion

resistance and resistance to solvents and alkalis. Cure cycles are usually longer than polyesters, however no

by-products are produced.

Flexibility and improved performance is also achieved by the utilization of additives and fillers.

Reinforcement

Fiber TypeFiberglassCarbonAramid

Textile StructureUnidirectionalWovenBraid

Fiberglass E-glass: Alumina-calcium-borosilicate glass

(electrical applications)

S-2 glass: Magnesuim aluminosilicate glass(reinforcements)

Glass offers good mechanical, electrical, and thermal properties at a relatively low cost.

E-glass S-2 glass

Density 2.56 g/cc 2.46 g/ccTensile Strength 390 ksi 620 ksiTensile Modulus 10.5 msi 13 msiElongation 4.8% 5.3%

Aramid

Kevlar™ & Twaron™

Para aramid fiber characterized by high tensile strength and modulus

Excellent Impact Resistance

Good Temperature Resistance

Density 1.44 g/ccTensile Strength 400 ksiTensile Modulus 18 MsiElongation 2.5%

Carbon Fiber

PAN: Fiber made from Polyacrylonitrile precursor fiber

High strength and stiffness

Large variety of fiber types available

Standard Modulus Intermediate Modulus Density 1.79 g/cc 1.79 g/ccTensile Strength 600 ksi 800 ksiTensile Modulus 33 Msi 42 MsiElongation 1.8 % 1.8 %

Woven Fabrics

Basic woven fabrics consists of two systems of yarns interlaced at right angles to create a single layer with

isotropic or biaxial properties.

Components of a Woven Fabric

Basic Weave Types

Plain Weave

Basic Weave Types

Satin 5HS

Basic Weave Types2 x 2 Twill

Basic Weave TypesNon-Crimp

Braid Structure

Types of Braids

Triaxial YarnsA system of longitudinal yarns can be introduced which are held in place by the braiding yarns

These yarns will add dimensional stability, improve tensile properties, stiffness and compressive strength.

Yarns can also be added to the core of the braid to form a solid braid.

MANUFACTURING PROCESSES OF COMPOSITES

Composite materials have succeeded remarkably in their relatively short history. But for continued growth, especially in structural uses, certain obstacles must be overcome. A major one is the tendency of designers to rely on traditional materials such as steel and aluminum unless composites can be produced at lower cost.

Cost concerns have led to several changes in the composites industry. There is a general movement toward the use of less expensive fibers. For example, graphite and aramid fibers have largely supplanted the more costly boron in advanced–fiber composites. As important as savings on materials may be, the real key to cutting composite costs lies in the area of processing.

B. Molding OperationsMolding operations are used in making a large number of common composite products. There are two types of processes:

A. Open–mold (1) Hand lay–up (2) Spray–up (3) Vacuum–bag molding (4) Pressure–bag molding (5) Thermal expansion molding (6) Autoclave molding (7) Centrifugal casting (8) Continuous pultrusion and pulforming.

1. Hand Lay-upHand lay–up, or contact molding, is the oldest and simplest way of making fiberglass–resin composites. Applications are standard wind turbine blades, boats, etc.)

2. Spray-upIn Spray–up process, chopped fibers and resins are sprayed simultaneously into or onto the mold. Applications are lightly loaded structural panels, e.g. caravan bodies, truck fairings, bathtubes, small boats, etc.

Continuous pultrusion is the composite counterpart of metal extrusion. Complex parts can be made.

7. Centrifugal Casting

Centrifugal Casting is used to form round objects such as pipes.

8. Continuous Pultrusion and Pulforming

Weight Considerations

Aramid fibers are the lightest

1.3-1.4 g/cc

Carbon

1.79 g/c

Fiberglass is the heaviest

2.4 g/cc

Strength Considerations

Carbon is the strongest

600-800 ksi

Fiberglass

400-600 ksi

Aramids

400 ksi

Stiffness Considerations

Carbon is the stiffest

30-40 msi

Aramids

14 msi

Fiberglass

10-13 msi

Cost Considerations

Fiberglass is cost effective

$5.00-8.00/lb.

Aramids

$20.00/lb

Carbon

$30.00-$50.00/lb

Fabric Structures

Woven: Series of Interlaced yarns at 90° to each other

Knit: Series of Interlooped Yarns

Braided: Series of Intertwined, Spiral Yarns

Nonwoven: Oriented fibers either mechanically, chemically, or thermally bonded

Mechanical Engineering Dept. 53

Applications of Reinforced Plastics

Phenolic as a matrix with asbestos fibers was the first reinforced plastic developed. It was used to build an acid-resistant tank. In 1920s it was Formica, commonly used as counter top., in 1940s boats were made of fiberglass. More advanced developments started in 1970s.

Typically, although not always, consumer composites involve products that require a cosmetic finish, such as boats, recreational vehicles, bathwear, and sporting goods. In many cases, the cosmetic finish is an in-mold coating known as gel coat.

Consumer Composites

A wide variety of composites products are used in industrial applications, where corrosion resistance and performance in adverse environments is critical. Generally, premium resins such as isophthalic and vinyl ester formulations are required to meet corrosion resistance specifications, and fiberglass is almost always used as the reinforcing fiber. Industrial composite products include underground storage tanks, scrubbers, piping, fume hoods, water treatment components, pressure vessels, and a host of other products.

Industrial Composites


Applications of Reinforced Plastics

This sector of the composites industry is characterized by the use of expensive, high-performance resin systems and high strength, high stiffness fiber reinforcement. The aerospace industry, including military and commercial aircraft of all types, is the major customer for advanced composites. These materials have also been adopted for use in sporting goods, where high-performance equipment such as golf clubs, tennis rackets, fishing poles, and archery equipment, benefits from the light weight – high strength offered by advanced materials. There are a number of exotic resins and fibers used in advanced composites, however, epoxy resin and reinforcement fiber of aramid, carbon, or graphite dominates this segment of the market.

Advanced Composites


Composites – Ceramic Matrix

Ceramic matrix composites (CMC) are used in applications where resistance to high temperature and corrosive environment is desired. CMCs are strong and stiff but they lack toughness (ductility)

Matrix materials are usually silicon carbide, silicon nitride and aluminum oxide, and mullite (compound of aluminum, silicon and oxygen). They retain their strength up to 3000 oF.

Fiber materials used commonly are carbon and aluminum oxide.

Applications are in jet and automobile engines, deep-see mining, cutting tools, dies and pressure vessels.



Application of Composites

Pedestrian bridge in Denmark, 130 feet

long (1997)

Swedish Navy, Stealth (2005)

Lance Armstrong’s 2-lb. Trek bike, 2004 Tour de France


Application of Composites in Aircraft Industry

20% more fuel efficiency and 35,000 lbs. lighter

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Advantages of Composites

Composites have a higher specific strength than many other materials. A distinct advantage of composites over other materials is the ability to use many combinations of resins and reinforcements, and therefore custom tailor the mechanical and physical properties of a structure.

Higher Specific Strength (strength-to-weight ratio)

The lowest properties for each material are associated with simple manufacturing processes and material forms (e.g. spray lay-up glass fibre), and the higher properties are associated with higher technology manufacture (e.g. autoclave moulding of unidirectional glass fibre), the aerospace industry.



Composites have an advantage over other materials because they can be molded into complex shapes at relatively low cost. This gives designers the freedom to create any shape or configuration. Boats are a good example of the success of composites.

Design flexibility

Composites products provide long-term resistance to severe chemical and temperature environments. Composites are the material of choice for outdoor exposure, chemical handling applications, and severe environment service.

Corrosion Resistance



One reason the composites industry has been successful is because of the low relative investment in setting-up a composites manufacturing facility. This has resulted in many creative and innovative companies in the field.

Low Relative Investment

Composite products and structures have an exceedingly long life span. Coupled with low maintenance requirements, the longevity of composites is a benefit in critical applications. In a half-century of composites development, well-designed composite structures have yet to wear out.

Durability

In 1947 the U.S. Coast Guard built a series of forty-foot patrol boats, using polyester resin and glass fiber. These boats were used until the early 1970s when they were taken out of service because the design was outdated. Extensive testing was done on the laminates after decommissioning, and it was found that only 2-3% of the original strength was lost after twenty-five years of hard service.


Disadvantages of Composites

The experience and intuition gained over the years about the behavior of metallic materials does not apply to composite materials.

properties in composites vary from point to point in the material. Most engineering structural materials are homogeneous.

Composites are heterogeneous

Composites are highly anisotropic

The strength in composites vary as the direction along which we measure changes (most engineering structural materials are isotropic). As a result, all other properties such as, stiffness, thermal expansion, thermal and electrical conductivity and creep resistance are also anisotropic. The relationship between stress and strain (force and deformation) is much more complicated than in isotropic materials.


Disadvantages of Composites

Composites materials are difficult to inspect with conventional ultrasonic, eddy current and visual NDI methods such as radiography.

American Airlines Flight 587, broke apart over New York on Nov. 12, 2001 (265 people died). Airbus A300’s 27-foot-high tail fin tore off. Much of the tail fin, including the so-called tongues that fit in grooves on the fuselage and connect the tail to the jet, were made of a graphite composite. The plane crashed because of damage at the base of the tail that had gone undetected despite routine nondestructive testing and visual inspections.


Disadvantages of CompositesIn November 1999, America’s Cup boat “Young America” broke in two due to debonding face/core in the sandwich structure.

SUMMARY

Reading for next class

What is the matrix in a composite and what materials are commonly used as a matrix?

What are the possible strengthening mechanisms for particle reinforced composites (there are 2)?

Be able to calculate upper and lower bounds for the Young’s modulus of a large particle composite.

Know the equation for the critical length (Lc) of a fiber. Know the stress distribution on fibers of various lengths w/r

Lc in a composite.

Conclusions

Composite materials offer endless design options.

Matrix, Fiber and Preform selections are critical in the design process.

Structures can be produced with specific properties to meet end use requirements.

Education

Svnit composite materials