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UNIT 1INTRODUCTION1. What is a composite?

A composite is structural materials that consist of two or more combined constituents that arecombined at a macroscopic level and are not soluble in each other. One constituent is called the

reinforcing phase and the one in which it is embedded is called the matrix. The reinforcingphase material may be in the form of fibres, particles, or flakes. The matrix phase materials aregenerally continuous. Examples of composite systems include concrete reinforced with steeland epoxy reinforced with graphite fibres, etc.2. What are advanced composites?

Advanced composite materials are manmade composite materials. They include as resin, metalor ceramic matrix composite systems reinforced with high strength, high modulus continuous ordiscontinuous forms (such as continuous fibres, chopped fibres, whiskers or particles). Theresultant material exhibits entirely distinct, but superior properties which are not exhibited by theconstituting elements. Advanced composites are composite materials that are traditionally usedin the aerospace industries. Theses composites have high performance reinforcements of a thin

diameter in a matrix material such as epoxy and aluminum.3. What are natural composites? Give examples.

The composite material that exists in nature is regarded as natural composites. Examples ofsuch composites include, wood (composed of cellulose and lignin), human or animal body(composed of bones and tissues) or even rocks and materials. Bones themselves arecomposites made of two components, the organic and inorganic. The organic componentconsists largely of carbohydrates, fats and proteins imparting pliability to the bones. The organiccomponent is calcium phosphate which provides rigidity and strength to the bones. Sea shellsand elephant tusk are also natural layered composites.4. What are the common types of composites?

The most typical types of composites consist of an addictive or reinforcement such as fibres orparticles embedded in a supporting material called matrix. Usually these are structural materialsbut they can also be special materials such as electrical conductors. Some composites have nomatrix and are composed of one or more constituent forms consisting of two or more differentmaterials. Laminates, for example, are composed entirely of layers which taken together, givethe composite its form. Plywood with multiple plies with different orientation of fibres is a typicallaminate composite. Sandwiches which are composed of a thick and light core material bondedon either side by a thin strong facing are also regards as composites. Many felts and fabricshave no body matrix but consist entirely of fibres of several compositions with or withoutbonding force.5. What is a reinforced composite?

A reinforced composite is one in which the primary purpose of the insert is to improve themechanical properties of the composite. The insert is called reinforcement. The composite isformed is called reinforced composite.

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6. What is Filled composite? Give some examples of fillers commonly used incomposites.

A filled composite consists of an insert whose main function is to alter the physical propertyother than the mechanical properties. Such an insert is called filler. Addition of filler also reduces

the cost of composite. Commonly used fillers include carbon black, calcium carbonate, mica,talc, barium carbonate, calcium sulphate, china clay and glass beads (also called spheres ofglass).7. What are the general requirements of all composite materials?

All the composite materials must meet the following requirementThe reinforcing phase must be distributed uniformly throughout the matrix and the reinforcedparticles and fibres must not be in direct contact with one another.

The reinforcing phase must not react with the matrix at the service temperature as this will affectthe interfacial bond with the matrix.

The reinforcing phase must not lose its strength and should be well bonded to the matrix.

Matrix must have lower modulus of elasticity as compared to the reinforcing phase.

8. List the various functions that a matrix phase performs in a composite material.

A matrix phase performs the following main functions:It binds the reinforcement in place in the structure and protects it from mechanical and chemicaldamage that might occur by abrasion of their surface or by chemical attack or some extraneoussource.

It separates the individual fibres and particles and deflects brittle crack that otherwise can passacross the entire cross section of the composite.

The matrix takes the load and transfers it to the reinforcement in case of fibre reinforced orparticle reinforced composites.

The matrix also gives shape to the composite.

In some instances the matrix controls the electrical and chemical properties of the composite.

9. What is the role of a coupling agent present in the interface between reinforcementand matrix?

A matrix-reinforcement interface plays an important role in a composite as the load istransferred from matrix to the fibres through this interface. The eventual properties of acomposite are greatly dependent on the nature of the interface. The desired characteristics ofthe interface are controlled by a third material called the coupling agent or compatilizer. Thecoupling agent can overcome the weak interaction between the matrix and the reinforcement.The matrix and the reinforcement differ in their chemical nature and surface characteristics butthe addition of coupling agent results in their association, leading to improve strength of theresultant composite.

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10. Differentiate between dispersion strengthened and particle strengthened composites.

Dispersion strengthened composites contain particles upto about 15% by volume having size inthe range 0.01m to 0.1m whereas the matrix of particle reinforced composites containsparticles in amounts from 15% to 40% by volume with size greater than 1.0m. in special cases,

particle content may be as high as 94%. In particulate composites both the matrix and particlesshare the load equally whereas the matrix carries the major load in dispersion strengthenedcomposites.11. What is the basic principle used in the fibre reinforced composites?

The basic principle used in fibre reinforced composites is that the materials are generallystronger in fibre form than in bulk form. This is due to the alignment of molecules along the fibreaxis. This preferred alignment makes the strength and modulus of both natural and syntheticfibres superior to those of the same material in the randomly oriented bulk form. That is whymajor part of the load is carried by the fibres and not by the bulk matrix. As fibres are to carrythe major portion of the applied load they should be much stronger and stiffer than the matrix.This property is also desirable for preventing the fibres from buckling under compressive

stresses.12. What are whiskers? Name some whiskers that are currently available.

Whiskers are very fine single crystal materials with diameters of the order of submicron. Theirlength may range from a fraction of a millimeter to several centimeters. The aspect ratio (i.e. thelength to diameter ratio) of whiskers generally ranges from 50 to 10000. Due to verifyingdiameter they contain very few or no dislocations and their strength approaches that of an idealor perfect crystal (i.e. the theoretically achievable limit). Their resistance against temperatureand strain to failure are very much higher than high performance fibres. The elastic strain tofracture may be as high as 5%. However, they suffer from the problem of brittleness and aredifficult process. Metals, oxides, carbides, halides and organic compounds have been grown inwhisker form. SiC, Si3N4, carbon, -alumina and K2O.6TiO2 whiskers are currently available.

Among these, SiC whiskers seem to be the best suited for metal-matrix compositereinforcement.13. Define Flake Composites.

Flakes are often used in place of fibers as can be densely packed. Metal flakes that are in closecontact with each other in polymer matrices can conduct electricity or heat, while mica flakesand glass can resist both. Flakes are not expensive to produce and usually cost less than fibers.Flake composites have a higher theoretical modulus of elasticity than fiber reinforcedcomposites. They are relatively cheaper to produce and be handled in small quantities.14. Name the various grades of glass fibres used as reinforcement in glass fibrereinforcement plastic (GRP).

There are three grades of glass fibres available for reinforcement in glass fibres reinforcedplastics. They are,E-glass (or electrical glass),

C-glass and

S-glass.

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15. List the types of fibres used as reinforcements in composites.

Organic fibres such as nylon and aramid; inorganic fibres of glass, graphite and ceramics; andstainless steel fibres and wires of tungsten are some typical fibre materials used asreinforcement in composites.

16. Give some of the characteristics of C-fibers.

C-glass (or chemical glass), is similar to E-glass in composition and provides excellentresistance to chemical, especially acids. When combined with E-glass reinforcement, this glassis very useful for surfacing mats for many applications that require corrosion resistance.17. What are the disadvantages of glass fibres?

The disadvantages of glass fibres are low modulus self abrasiveness which frequentlydecreases the potential strength, relatively low fatigue resistance and poor adhesion to matrixresins. This means that they do not impregnate the matrix well and uniformly. Therefore, thesefibres are never used for high performance composites. Through this adhesively can beimproved by sizing on the surface, this may provide a path for absorption of moisture and create

undesirable internal stresses.18. Define Solid Microspheres.

Solid Microspheres have relatively low density, and therefore, influence the commercial valueand weight of the finished product. Studies have indicated that their inherent strength is carriedover to the finished molded part of which they form a constituent. Solid glass Microspheres,manufactured from glass are most suitable for plastics. Solid glass Microspheres are coatedwith a binding agent which bonds itself as well as the spheres surface to the resin. Thisincreases the bonding strength and basically removes absorption of liquids into the separationsaround the spheres.19. What are the disadvantages of carbon fibres?

In spite of highly desirable characteristics, carbon fibres have certain disadvantages. They havelow impact toughness and high electrical conductivity. The later property may causeshortening in unprotected electrical machinery. Another disadvantage of carbon fibres is theirhigh cost. Due to high cost they are sometimes used in hybrid composites, along with relativelycheaper fibres such as glass.20. Define Microspheres.

Microspheres are considered to be some of the most useful fillers. Their specific gravity, stableparticle size, strength and controlled density to modify products without compromising onprofitability or physical properties are its their most-sought after assets. They are of two typesof microspheres they are solid microspheres and hollow microspheres.21. What are Kevlar fibres? What are the applications for which these fibres were

developed originally?

Kevlar is the trade name of aramid fibres developed at Du Pont Company. The two varieties ofKevlar that are most common include Kevlar 49 and Kevlar 29. These fibres were originallydeveloped to replace steel wire used in radial tyres. Kevlar is about five times stronger thansteel on weight to weight basis.

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22. Define Filled Composites.

Filled composites result from addition of filler materials to plastic matrices to replace a portion ofthe matrix, enhance or change the properties of the composites. The fillers also enhancestrength and reduce weight. Fillers may be the main ingredient or an additional one in a

composite. The filler particles may be irregular structures, or have precise geometrical shapeslike polyhedrons, short fibers or spheres.23. What is a carbon-carbon composites produced?

A carbon-carbon composite material consists of a carbonaceous matrix reinforced with carbonfibres in the form of continuous filament yarns, cloth, chopped fibres or three dimensional wovenreinforcement.24. What are aramid fibres?

Aramid is the generic term for fibres produced from aromatic polyamides. Polyamides are longchain polymers containing aromatic rings or so called as benzene rings. These rings recurrepeatedly in the structure of aramid fibres.

25. How is carbon fibres produced?

Carbon fibres are produced by pyrolysis of suitable carbonaceous products such aspolyacrylonitrile (PAN), pitch and staple rayon fibres called precursors. The process involvedthree stages, namely, stabilization, carbonization and graphitization.26. List some typical ceramic matrix composite systems.

Typical ceramic matrix composite systems include carbon-carbon composite, molybdenumdisulphide, Sic matrix/ carbon fibre composite, lithium alumino silicate matrix/ Nicalon (SiC)fibre, and ceramic matrix/ glass fibre composite.27. What are the advantages of thermo plastic matrices?

Superior toughness.

Short moulding cycle.

Capability of fusion bonding.

Infinite Prepreg shelf life.

Easy repairability.

Reusability of scrap.

28. List the disadvantages of thermoplastic matrices.

Higher temperature of processing.

Relatively low heat resistance.

Sensitivity to solvents.

29. What are the most common advanced composites?

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The most common advanced composites are polymer matrix composites (PMCs) consisting of apolymer (e.g., epoxy, polyester, urethane) reinforced by thin diameter fibres (e.g., graphite,aramid, boron). The reasons why they are the most common composites include their low cost,high strength, and simple manufacturing principles.

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30. What are hollow microspheres?

Hollow microspheres are essentially silicate based, made at controlled specific gravity. They arelarger than solid glass spheres used in polymers and commercially supplied in a wider range ofparticle sizes. Commercially, silicate-based hollow microspheres with different compositions

using organic compounds are also available.31. What are the drawbacks of polymer matrix composites?

The main drawbacks of PMCs include low operating temperatures, high coefficient of thermaland moisture expansion, and low elastic properties in certain directions.32. What are the principal fibers used in commercial applications?

The principal fibers in commercial use are various types of glass and carbons as well as Kevlar49.Other fibers, such as boron, silicon carbide, and aluminium oxide, are used in limitedquantities.33. What are the influences of fiber in a composite laminates?

Density.

Tensile strength and modulus.

Compressive strength and modulus.

Fatigue strength as well as fatigue failure mechanisms.

Electrical and thermal conductivities.

34. What are the principal advantages of glass fibers?

Low cost.

High tensile strength.

High chemical resistance.

Excellent insulating properties.

35. Define the term wettability.

The adhesion between the reinforcing fiber and the matrix in composite materials plays animportant role in the final mechanical properties of the material. It is called as wettability.36. Define Cermets/Ceramal.

The Cermets is an abbreviation for the "'ceramic" and "metal." A Cermets is a compositematerial composed of ceramic (Cer) and metallic (Met) materials. Cermets are ideally designedto have the optimal properties of both a ceramic, such as high temperature resistance andhardness, and those of a metal, such as the ability to undergo plastic deformation. The metal isused as a binder for an oxide, boride, carbide, or alumina. Generally, the metallic elements usedare nickel, molybdenum, and cobalt. Depending on the physical structure of the material,cermets can also be metal matrix composites, but cermets are usually less than 20% metal byvolume. It is used in the manufacture of resistors (especially potentiometers), capacitors, andother electronic components which may experience high temperatures.

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37. What are fiber metal laminates?

Fiber-reinforced polymer laminas can also be combined with thin aluminium or other metallicsheets to form metal-composite hybrids, commonly known as fiber metal laminates (FML).38. What are coupling and coating agents?

Coupling agents and coatings are applied on the fibers to improve their wetting with the matrixas well as to promote bonding across the fiber matrix interface. Both in turn promote a betterload transfer between the fibers and the matrix.39. What are the roles of matrix in FRP?

To keep the fibers in place.

To transfer stress between the fibers.

To provide a barrier against an adverse environment, such as chemicals and moisture.

To protect the surface of the fibers from mechanical degradation.

40. What are the classifications of polymers?

Thermoplastics

Thermosets.

41. What will happen when load applied to FRP at glass transition temperature?

When an external load is applied, it exhibits an instantaneous elastic deformation followed by aslow viscous deformation followed by a slow viscous deformation. With increasing temperature,the polymer changes into a rubber like solid capable of undergoing large, elastic deformationsunder external loads.

42. What is Interface?

The bonding between the fiber and the resin is called interface. It is a region where coating andmatrix diffused into each others domain and form a flexible, three - dimensional polymernetwork.43. Define the terms filament, strand, yarn.

Filament is defined as any fibre whose aspect ratio (length to diameter ratio) is for all practicalpurposes, infinity. Filament is thus a continuous fibre. The untwisted form of glass fibers iscalled as strand. A group of 200 or more fibers are called as strand. Strand is a primary bundleof continuous filaments combined in a single compact unit without twist. Yarn is a generic termused for strands of fiber or filaments in a form suitable for weaving.

44. What is roving?

A roving is a group of untwisted parallel strands wound on a cylindrical forming package.Rovings are used in continuous moulding operations, such as filament winding and pultrusion.

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UNIT 2REINFORCEMENT AND MATRICES1. Define the term fibres.

Polymers which can be drawn into long filament like materials having length to dimension ratio(i.e. aspect ratio) of at least 100 are called fibres. Some of the examples of fibres are nylon,

Terylene, cellulose, Kevlar, etc.2. Define the term resin.

The polymeric molecules in the form of flakes, granules pallets or viscous liquid are termed asresins. Resins can be subsequently shaped into usable and product.3. What are liquid resins?

If polymers are used as adhesives, potting compounds, sealants, etc. In liquid form, they arepreferred to as liquid resin, e.g. polyester resins, epoxy resins, phenolic resins, etc.4. List various factors affecting polymer materials properties.

Additives.

Branching.

Copolymerization.

Cross-linking.

Degree of crystallinity.

Glass transition temperature.

Molecular weight and molecular weight distribution.

Plasticizers.

Polymer structure and shape.

5. List the kind of structures commonly formed in polymers.

Three types of structures are commonly formed in polymers. They are,Linear.

Branched.

Network.

6. What do you mean by branching?

Branching is the process of bifurcation of long polymer chain into two branches at some pointalong its length. The formation and extent of side chains depends on the operating conditions ofpolymerization such as temperature, pressure and catalyst type.7. Give examples of various filler materials used in plastics.

Wood flour, chopped fabrics, asbestos, carbon black, talc, mica, gypsum, and milled glass areexamples of fillers.

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8. What is cross-linking?

Cross-linking is the process of introducing a primary covalent type link between polymer chainsor their segments using a chemical reagent (such as sulphur or oxygen in vulcanizationprocess). Physical means such as irradiation can also be used to introduce cross-links.

9. What are plasticizers? What is the purpose of adding them in a polymer? Name somecommon plasticizers.

Plasticizers are low molecular weight monomeric liquids that possess low volatility. They areadded to a polymer to impart plasticity and flexibility and thus improve processibility. Vegetableoils, low molecular weight polyesters and various phthalates are commonly used as plasticizers.10. What are fillers and what function do they impart?

Fillers are materials used to provide bulk and modify certain properties such as strength, impactresistance, heat resistance and other similar properties. They are generally chemically inert anddo not react with resin during processing.11. What are additives?

Additives are substance added to a polymer to modify or control its properties and reduce thecost. Various additives includes stabilizers, colorants, catalysts, lubricants, flame retardants, etc.Sometimes fillers and plasticizers are also included in the category of additives.12. Define the term polymer.

Polymers are high molecular weight organic materials made up of long chain moleculescontaining principally hydrogen and carbon and may also contain atoms of N, Cl, O and S.These are complex and giant molecules with molecular weight in the range of 104-107 andformed by many chemically bonded parts or units. Due to their high molecular weight, thesepolymers are also called high polymers.13. What for catalysts added to a polymer?

Catalysts are added to control the rate and extent of polymerization process in the resin.Catalysts are not used up in the reaction of polymerization. A catalyst may serve the followingreactions:Promote the polymerization.

Permit specific orientation reaction to occur.

Give the added benefits of initiating the reactions.

Catalysts also affect the shelf life of the polymer. Metallic as well as organic compounds areused as catalysts. A well known catalyst system is Ziegler-Natta catalyst.14. Why are lubricants added to polymer?

Many plastics when heated during processing they become sticky. To overcome this problemlubricants are added to the plastics.

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15. Define the term thermoplastics. Give some examples

Thermoplastics are the materials which can be reshaped or reformed into a new form even aftermoulding. In words, thermoplastics can be subjected to temperature and pressure again forforming a new design product. Some common examples are:

Nylon.

Polyethylene (PE).

Polystyrene (PS).

Polypropylene (PP).

Polyvinyl chloride (PVC).

Polymethyl methacrylate (PMMA).

Polyetherketone (PEK), etc.

16. What are thermosetting plastics? Give some examples.

The plastics which are once moulded cannot be reformed or shaped into new form are called

thermosetting plastics or simply thermosets. Once moulded cannot be reshaped even bysubjected to heat and pressure due to the non-softening characteristic of plastic. An exampleincludes phenolic resin (Bakelite), epoxy resins, etc.17. Which polymers are called naturally occurring polymers?

Polymers which are derived from plants and animals are called naturally occurring polymers.18. Name some of the naturally occurring and some synthetic polymers.

Cellulose.

Casein.

Silk.

Natural rubber.

Cotton.

Leather.

Resins.

Wood.

Tar.

Shellac are some naturally occurring polymers.

While plastics and elastomers (except natural rubber) are examples of synthetic or man-madepolymers.19. Define the term plastics.

There is no standard definition for the term plastics since there is no general agreement to anydefinition. In the simplest form plastics may be defined as a polymer which can be shaped into

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hard and tough usable articles through the application of heat and pressure. Examples ofplastics are PVC, PE, PS, etc.

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20. List the various advantages of plastics.

Articles of intricate shape can be fabricated with ease and can be produced in large quantity atlow cost.

They are lighter (low density) than metals.

They have good electric and thermal insulating properties.

Due to poor thermal conductivity they are very suitable for making handles of cooking utensils,electric iron box, steering wheel, etc.

They are resistant to corrosion and for rust.

They can be obtained in variety of colours and shades.

They show good dampering properties.

21. List the disadvantages of plastics.

They are dimensionally unstable and tend to warp or creep.

They are also thermally unstable

Some plastics give unpleasant odour.

Most of the plastics deteriorate when exposed to air and sunlight.

Most of the plastics can be easily scratched.

Good plastic parts are expensive, particularly in small lots.

Non-biodegradable.

22. Name various categories of thermoplastics.

Commodity thermoplastics

Transition thermoplastics

Engineering thermoplastics

High performance thermoplastics

Thermoplastic elastomers.

23. What is polypropylene and what is its repeated structural unit.

If on every second carbon atom on the main chain of polyethylene (PP) a hydrogen atom isreplaced by a methyl group then the resulting polymer is called polypropylene. The repeatstructural unit is:

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24. What is PEEK?

Polyether ether ketone (PEEK). It is a semi crystalline polymer with a maximum achievablecrystallinity of 48% when it is cooled slowly from its melt.25. What is the advantage of cynate ester resin?

Cynate ester resin has a high glass transition temperature (Tg 265 C), lower moistureabsorption than epoxies, good chemical resistance, and good dimensional stability. Itsmechanical properties are similar to those of epoxies.26. What is APC?

Continuous carbon fiber-reinforced PEEK composites are known in the industry as aromaticpolymer composite or APC.27. What is the function of fiber surface treatment?

The primary function of a fiber surface treatment is to improve the fiber surface wettability withthe matrix and to create a strong bond at the fiber-matrix interface.

28. Why the coupling agents are used with glass fiber?

Chemical coupling agents are used with glass fibers to (1) improve the fiber-matrix interfacialstrength through physical and chemical bonds and (2) protect the fiber surface from moistureand reactive fluids.29. Why silane is preferred as coupling agent with glass fibers?

The interfacial bond created by silanes allows a better load stress transfer between fibers andmatrix, which in turn improves the tensile strength as well as the interlaminar shear strength ofthe composite.30. Why the fillers are added to the polymeric materials?

Fillers are added to a polymer matrix for one or more of the following reasons:Reduce cost.

Increase modulus.

Stiffness.

Reduce mold shrinkage.

Control viscosity.

Produce smoother surface.

31. Write down some filler materials?

The most filler for polyester and vinyl ester resins is calcium carbonate (CaCo3), which is usedto reduce cost as well as mold shrinkage. Examples of other fillers are clay, mica, and glassmicro spheres.32. What is fiber architecture?

Fiber architecture is defined as the arrangement of fibers in a composite, which not onlyinfluences the properties of the composite, but also its processing.

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33. List various ceramic matrices.

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Aluminium oxide (Al2O3).

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Carbon, silicon carbide (SiC).

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Silicon nitride (Si3N4).

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34. Why coupling agents are added with composites?

Coupling agents are added to improve the wetting of fiber and promote bonding.35. What are acrylics?

Most acrylics are based on polymers of methyl methacrylate, that is, they are Polymethyl

methacrylate (PMMA) which may be modified by copolymerization or blending with othermonomers. Acrylics monomers MMA is a clear liquid made from acetone and sodium cyanide.On polymerization, they normally become clear. They can also be obtained by opaque varietiesincluding fluorescent shades.36. What are nylons and where does the name comes from?

The popular groups of Polyamides (PA) resins are known as nylons. They are produced by thecondensation reaction of diamine with dibasic acids or their derivatives. Depending on thenumber of carbon atoms on the amines or the acid components, various nylon designations areavailable. Examples are nylon 6, nylon 6/6, nylon6/10, etc.37. Write the applications of nylons.

Nylons are used great variety of household and industrial goods. Unbreakable cups andsaucers, bowls and tumblers are made in ivory luster nylons. Combs will not become toothlessage, zip fasteners that is unaffected by dry cleaning and doctors syringe are made of nylons.The typical industrial applications include unlubricated gears, cams, sleeve bearing, drivingbelts, valves, automobile speedometer, textile machinery, etc.38. What are polyesters? In what way they can be compared and contrasted withPolyamides?

Polyesters are the products obtained by the condensation of adipic acid and bifunctionalalcohols with removal of water. It is similar to polyamides in both condensation products andhas the common monomers acid molecules. However the other monomer is alcohol ins tead ofamines. Like nylon, polyester can be made in the form of unbranched thread like molecules

(thermoplastics).39. In what form is PET thermoplastic available?

PET thermoplastic is available as film, fibre and blow moulded products. The processing tothese forms leads to orientation or crystallization of molecular chain resulting in high strengthproperties.40. Give some uses of PET thermoplastics.

PET thermoplastic is widely used to make the popular polyester thread also known as Teryleneor Dacron used for sewing. Biaxially oriented film, also known as myler is used as photo film,magnetic tapes, capacitors, cooking bags, food container packing and coatings.

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41. Write some applications of PEEK.

PEEK is used as a coating and insulating material for high performance wiring, particularlyrequired for aviation and computer industries. PEEK filaments may be used for making clothsfor hot filtration purposes.

42. What are ladder polymers?

Ladder polymers are double stranded polymer in which aromatic rings are fused together orinterconnected by links around which rotation cannot occurs except by bond breaking. If thestructure of ladder polymers is perfect, the chain could be broken only if at least two bond on thesame rings were broken. Thus, ladder polymers exhibits great thermal stability.43. List the three classes of commercial polyesters.

Saturated or thermoplastic polyesters

Unsaturated or thermosetting polyester resins

The liquid polyester resins called simply polyesters.

44. What are unsaturated polyesters?

Unsaturated polyesters are thermosets composed of linear polyester polymer cross-linked withother monomers such as styrene. These are usually produced as solid moulding compoundsand are called alkyds.45. What are liquid polyester resins?

Liquid polyester resins are converted into solid plastics by simply adding an organic peroxidecatalyst for polymerization or curing takes place. During the curing and before hardening, fillersand reinforcements are added.46. In what way epoxy are similar to unsaturated polyesters?

Epoxy resins are similar unsaturated polyesters in that they are mixed with a cross linking agentwhich makes them set by forming a molecular network structure.47. In what forms epoxy are available?

Epoxies are available in both liquid and solid forms. To produce solid forms, the epoxy resinscured by using cross linking agents and catalyst or with hardeners containing active hydrogen todevelop the desired properties.48. What properties make epoxies suitable for coatings?

Toughness.

Flexibility.

Adhesion.

Chemical resistance.

49. What are coatings?

The coatings are provided to the fiber surface to protect the fibers from mechanical damage andenvironmental damage and also to enhance bonding of fiber to matrix.

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50. Give some applications of epoxies as coatings.

Process equipments,

tank and drum linings,

can coatings,

pipe linings,

protective coatings for the food industry

wire coatings

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UNIT 3MANUFACTURING OF ADVANCED COMPOSITES1. Draw the flowchart for composite laminate part fabrication?

2. Define release film?

These films are used to prevent the composite parts from adhering to tool surface. It is alsoplaced between the bleeder and breather plies as a separator film. It is used to prevent the resinflow into the breather piles, to which the vacuum system vents.3. What is Bleeder plies?

Bleeder plies (used for bleed bagging system) often fiberglass cloth fabric, are normally requiredto absorb excess resin and permit the escape of volatiles. Various solvents and other volatilechemicals in the Prepreg that take part in chemical reactions during layups must be vented, oran unacceptably porous structure will result.4. What is RTM process?

RTM: Resin Transfer Molding Process. In RTM, several layers of dry continuous strand mat,

woven roving, or cloth are placed in the bottom half of a two-part mold, the mold is closed, and acatalyzed liquid resin is injected into the mo ld via a centrally located sprue. The resin injectionpoint is usually at the lowest point of the mold cavity. The injection pressure is in the range of 69690 kPa (10100 psi).5. Define Breather plies.

Breather plies are usually fiberglass or synthetic fabric which is placed on top of the release filmto allow dispersion of vacuum pressure over the layup and removal of entrapped air or volatilesduring cure/consolidation. Coarse, open weave fabrics are used, otherwise bridging and bagfailure may occur.6. Define Shrinkage.

Shrinkage is the reduction in volume or linear dimension s caused by curing as well as thermalcontraction. Curing shrinkage occurs because of the rearrangement of polymer molecules into amore comp act mass as the cu ring reaction proceeds. The thermal shrinkage occurs during thecooling period that follows the curing react ion and may take place both inside and outside themold.

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7. What is resin flow?

The flow of resin through the fiber network is called resin flow. Proper flow of resin through a dryfiber network (in liquid composite molding [LCM]) or a Prepreg layup (in bag molding) is criticalin producing void-free parts and good fiber wet-out.

8. Define Voids.

The most common cause for void formation is the inability of the resin to displace air from thefiber surface during the time fibers are coated with the liquid resin. Void s may also be causedby air bubbles and volatiles en trapped in the liquid resin.9. What is the purpose of vacuum bag?

The vacuum bag provides the means of removing vapors, and encouraging the required resinflow, so its design and implementation are important.The vacuum is used to assist removal of trapped air or other volatiles.

The vacuum and pressure-temperature cycles are adjusted to permit maximum removal of air

with maximum resin flow.

10. What are the factors influencing the cure cycle?

It should be noted that the cure cycle depends on a number of factors, including resin chemistry,catalyst reactivity, cure temperature, and the presence of inhibitors or accelerators.11. What is called Gel time?

The viscosity increases with increasing cure time and temperature. The rate of viscosityincreases is low at the early stage of curing. After a threshold degree of curve is achieved, theresin viscosity increases at a very rapid rate. The time at which this occurs is called the gel time.12. What is the significance of finding Gel time?

The gel time is an important molding parameter, since the flow of resin in the mold becomesincreasingly difficult at the end of this time period.13. What are the types of open mould process?

Spray lay up

Hand lay up

Filament winding

Sheet moulding compound

14. What are the types of closed mould process?

Vacuum bag moulding

Pressure bag moulding

Compression moulding

Autoclave

Injection moulding.

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15. List out the preparation of moulding compound ingredients.

Resins

Plasticizers

Fillers

Lubricants

Catalysts

Stabilizers

Coloring materials.

16. Define Viscosity of Fluid.

Viscosity of a fluid is a measure of its resistance to flow under shear stresses. Low-molecular-

weight fluids, such as water and motor oil, have low viscosities and flow readily. High-molecular- weight fluid s, such as polymer melts, has high viscosities and flow only under highstresses. The two most important fact ors determining the viscosity of a fluid are thetemperature and shear rate.17. Write short notes on filament winding?

In a filament-winding process, a band of continuous resin-impregnated rovings ormonofilaments is wrapped around a rotating mandrel and cured to produce axisymmetric hollowparts.18. What is compression moulding?

Compression molding is used for transforming sheet-molding compounds (SMC) into finished

products in matched molds. The principal advantage of compression molding is its ability toproduce parts of complex geometry in short periods of time. Non uniform thickness, ribs,bosses, flanges, holes, and shoulders, for example, can be incorporated during thecompression-molding process.19. Give names of various polymers used in advanced polymer composites.

Epoxy

Phenolics

Acrylic

Amino acids

Urethane

Polyamide.

20. What are the types of filament winding patterns?

There are three types of patterns, they areHoop or circumferential winding

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Helical winding

Polar winding

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21. Define epoxy.

Epoxy resins are the most commonly used resins. They are low molecular weight organic liquidscontaining epoxide groups. Epoxide has three members in its ring: one oxygen and two carbonatoms.

22. What are prepregs?

Prepregs are a ready-made tape composed of fibers in a polymer matrix. They are available instandard widths from 3 to 50 in. (76 to 1270 mm). Depending on whether the polymer matrix isthermosets or thermoplastic, the tape is stored in a refrigerator or at room temperature,respectively. One can lay these tapes manually or mechanically at various orientations to makea composite structure.23. Name the materials used in hand layup process.

Materials: - Resins: Epoxy, Polyester, Vinyl ester, Phenolic etc.Fibers: Glass, Carbon, Aramid or natural fibers.24. What is the application of Bag molding process?

The Bag- molding process is used predominantly in the aerospace industry where highproduction rate is not an important consideration.25. How is the maximum temperature inside the layup determined?

The maximum temperature inside the layup depends on (a) the maximum cure temperature, (b)the heating rate, and(c) the initial layup thickness.26. Define blisters.

Blisters are interlaminar cracks formed at the end of molding due to excessive gas pressure inthe interior region of the molded part.27. What are the advantages of compression molding process?

The principal advantage of compression molding process is its ability to produce parts ofcomplex geometry in short periods of time.28. What are the various defects present in the compression molded SMC part?

The various defects present in the compression moulded SMC parts are,Blister

Surface pin holes

Voids

knit line

Fiber buckling

Insert

Sink mark etc.,

29. What is warpage?

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Warpage is critical in thin- section moldings and is caused by variations in cooling rate betweensections of different thickness or different fiber orientations.

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30. Give some examples for pultruded parts?

The common pultruded products are solid rods, hollow tubes, flat sheets, and beams of avariety of cross sections, including angles, channels, hat sections, and wide- flanged sections.31. What are the factors affecting the quality of composites?

The factors affecting the quality of composites are theCure time

Temperature

32. What is meant by pressure vessel forming?

Pressure-vessel forming is a method in which a pressure vessel is combined with integrally-heated tooling. Pressure vessel forming has the following advantages:Since a pressure vessel is a less expensive piece of equipment, its size is not limited by costand the production of large parts is easily feasible.

Dry or Prepreg material forms.

Matched die metal tools can be used (to control both part surfaces).

33. What is meant by match die forming?

Matched-die forming is a most widely used forming system for thermoplastics because it isavailable and vary from small simply operated hand processes to large computer controlledpresses. (The dies used are generally made of metal which can be internally heated and/orcooled. The dies are designed to fixed gap of close tolerance.34. What are the factors considered in match die forming?

High forming pressure required for good solidation.

High fabrication costs.

Friction at die interface.

Long heating and cooling times.

Non-uniform deformation/pressure, if thickness mismatch exists.

35. What are the types of graphite crystals arrangement in carbon fibers?

Arrangement of graphite crystals in a direction to the fiber axis:Circumferential.

Radial.

Random.

Radial-circumferential.

Random-circumferential.

36. What are the two types from which the carbon fibers are manufactured?

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Carbon fibers are manufactured from two types of precursors (starting materials), namely, textileprecursors and pitch precursors.

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37. Write short notes on autoclave molding.

Autoclave composite molding is a similar to pressure- bag and vacuum- bag molding but uses ahigh- pressure chamber instead. The advanced composite process produces denser, void freemoldings because higher heat and pressure are used during curing.

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UNIT 4MECHANICS OF LAMINATED COMPOSITES1. What are two basic approaches to the micromechanics of composite materials?

The two basic approaches to the micromechanics of composite materials areMechanics of materials

Elasticity.2. What are the approaches performed in elasticity?

The elasticity approach actually is at least three approachesBounding principles.

Exact solutions.

Approximate solutions.

3. Define lamina.

Initially stress free.

Linearly elastic.

Macroscopically homogeneous.

Macroscopically orthotropic.

4. Define stress.

Stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is ameasure of the average force per unit area of a surface within the body on which internal forcesact5. What are the basic assumptions made in lamination theory?

Fibers are uniformly distributed throughout the matrix.Perfect bonding exists between the fibers and the matrix.

The matrix is free of voids.

Both fibers and matrix behave as linearly elastic materials.6. Describe the maximum principal stress theory?

Maximum Principal Stress Theory - Yield occurs when the largest principal stress exceeds theuniaxial tensile yield strength. Although this criterion allows for a quick and easy comparisonwith experimental data it is rarely suitable for design purposes.

According to the maximum stress in the principal material directions is equal to or greater than

the corresponding ultimate strength.7. What are the uses of lamination theory?

Use of lamination theory: lamination theory is useful in calculating stresses and strains in eachlamina of a thin laminated structure.

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8. Describe the maximum principal strain theory?

Maximum Principal Strain Theory - Yield occurs when the maximum principal strain reaches thestrain corresponding to the yield point during a simple tensile test. In terms of the principalstresses this is determined by the equation:

9. What are isotropic materials?

An isotropic material is one which looks the same in every direction. We cannot define anyspecial direction using the material properties. In other words, none of the properties depend theorientation; it is perfectly rotationally symmetric. Note that in order to be isotropic the materialmust be homogenous on the length scale of interest, (i.e.,) the same at every point in thematerial. For instance, rubber is a very isotropic material. Take a rubber ball, and it will feel thesame and bounce the same however you rotate it. On the other hand, wood is an anisotropicmaterial: hit it with an axe and it will take more force to break of you are cutting across the grainthan along it.10. What are anisotropic materials?

An anisotropic material is a material which does not behave the same way in all directions. Takewood for example. Wood is very strong along the grain. Against the grain, however, it will easilybreak. An anisotropic material, properties are different in all directions so that the materialproperty symmetry.11. What are orthotropic materials?

By definition, an orthotropic material has at least 2 orthogonal planes of symmetry, wherematerial properties are independent of direction within each plane. Such materials require 9independent variables (i.e. elastic constants) in their constitutive matrices. In contrast, a materialwithout any planes of symmetry is fully anisotropic and requires 21 elastic constants, whereas amaterial with an infinite number of symmetry planes (i.e. every plane is a plane of symmetry) isisotropic, and requires only 2 elastic constants.

12. What are principal material directions?

For material directions 1, 2, and 3, you observe or specify any of these values, depending onthe model type and material orientation:The axes of the referenced coordinate system

One of the solid directions

For 3D material orientations, you select one of the following six combinations of the currentcoordinate system directions for the three principal material directions:

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13. What is called fiber pullout?

Fiber pull-out is one of the failure mechanisms in fiber-reinforced composite materials. Otherforms of failure include delamination, interlaminar matrix cracking, longitudinal matrix splitting,fiber/matrix debonding, and fiber fracture. The cause of fiber pull-out and delamination is weak

bonding. Fiber pullout is the opening of the matrix crack may cause broken fibers to pull outfrom the surrounding matrix. This is resisted by the friction at the fiber-matrix interface.14. Name any two FEA softwares used in composite?

FEA software: MSC-NASTRAN, ANSYS, ABAQUS, LS-DYNA.15. What are the failure modes observed during longitudinal tensile loading?

Failure modes:a) Fiber breakage.

b) Fiber pullout.

c) Matrix bridging.

16. What is important function of matrix in FRP?

An important function of the matrix in a fiber-reinforced composite material is to provide lateralsupport and stability for fibers under longitudinal compressive loading.17. What are the two failure modes present in compression?

Two different localized bucking modes areElastic micro buckling

Fibre kinking.

18. What are the assumptions made for macro mechanics of laminated composites?

The matrix is homogeneous, isotropic, and linear elastic.

The fiber is homogeneous, isotropic, linear elastic, continuous, regularly spaced, and perfectlyaligned.

The lamina (single layer) is macroscopically homogeneous, macroscopically orthotropic, linearelastic, initially stress-free, void-free, and perfectly bonded.

The laminate is composed of two or more perfectly bonded laminae to act as an integratedstructural element.

19. List few special types of laminates?

Unidirectional laminate

Angle-ply laminate

Cross-ply laminate

Symmetric laminate.

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20. What is the failure modes observed during longitudinal compressive loading?

Extensional mode

Shear mode.

21. What are quasi-isotropic laminate?

Quasi-isotropic laminate: these laminates are made of three or more laminas of identicalthickness and material with equal angles between each adjacent lamina.22. Why the mechanics of FRP is more complicated?

Fiber-reinforced composites are microscopically in homogeneous and non-isotropic. As a result,the mechanical of fiber-reinforced composites are far more complex than that of conventionalmaterials.23. What are assumptions made in FRP during analysis?Both fibers and matrix are linearly elastic isotropic materials.

Fibers are uniformly distributed in the matrix.

Fibers are perfectly aligned in the direction.

There is perfect bonding between fiber and matrix.

The composite lamina is free of voids.24. What is the difference between homogeneous and isotropic material?

For a homogeneous material, properties do not depend on the location, and for an isotropicmaterial the properties depends on location.25. What are the types of problems associated in interlaminar stresses?

Three types of interlaminar stress problems associated with three types of laminates:1. (q) Angle-ply laminates2. 0/90 Cross-ply laminates3. Combination of angle and cross ply laminates.26. Where the interlaminar stresses will be high?

Interlaminar stresses can be significantly high over a region equal to the laminate thicknessnear the free edges of a laminate. The free edges may be at the boundaries of a laminatedplate, around a cutout or hole, or at the ends of a laminated tube.27. Define rule of mixture.

The Rule-of-Mixtures model is used to describe three-dimensional solids having an arbitrary

number of material phases with arbitrary orientations and volume fractions. Orientations aredefined for each phase using a triad of space-fixed rotation angles in a 3-2-1 sequence. Theseangles rotate the composite material frame to the phase frame. The orientation of each phase isdefined by starting with the phase frame aligned with the composite frame and rotating thephase material frame degrees about the 3-axis of the composite material frame, then rotatingthe phase frame degrees about the 2-axis of the composite frame, and finally rotating the phaseframe degrees about the 1-axis of the composite frame. Rule-of-Mixtures composites are, ingeneral, fully anisotropic.

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28. What are hygroscopic strains?

The strain caused due to the swelling and contraction of moisture is called hygroscopic strains29. How a laminate is constructed?

A laminate is constructed by stacking a number of laminas in the thickness (z) direction.30. How the tensile load applied to the discontinuous fibers transferred to them?

Tensile load applied to a discontinuous fiber lamina is transferred to the fibers by a shearingmechanism between fiber and matrix.31. Define iso-stress and iso-strain.

Iso-strain and Iso-stress of a composite material, in an isostrain each component has a uniformdeformation, while in isostress each material has a uniform stress. The stress and strain, forisostrain and isostress, respectively, are in general additives but depend on the moduli andvolume fraction of each component.32. Define Micromechanics.

The study of composite material behaviour wherein the interaction of the constituent material isexamined in detail as part of the definition of the behaviour of the heterogeneous compositematerials.33. What are the advantages of Tsai-Hill failure criterion?

The advantages of Tsai-Hill failure criterion are:The variation of strength with angle of lamina orientation is smooth rather than having cuspsthat are not seen in experimental results.

The strength continuously decreases grows from 00 rather than the rise in uniaxial strengththat is characteristic of both the maximum stress and the maximum strain criteria.

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The maximum stress and strain criteria are incorrect by 100% at 300.

Considerable interaction exists between the failure strengths X, Y, S in the Tsai-Hill criterion, butnone exists in the previous criteria where axial, transverse, and shear failures are presumed tooccur independently.

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UNIT 5COMPOSITE STRUCTURES1. What are fatigue properties of composite material?

The fatigue properties of a material represent its response to cyclic loading, which is a commonoccurrence in many applications.

2. What are the variables influencing the cycle to failure?

The cycle to failure depends on a number of variables, such as Stress level, stress state, modeof cycling, process history, material Composition and environmental conditions.3. What is S-N diagram?

Fatigue behavior of a material is usually characterized by an S-N diagram, which shows therelationship between the stress amplitude or maximum stress and number of cycles to failure ona semi logarithmic scale.4. When will the number of cycles to failure increase?

The number of cycles to failure increases continually as the stress level is reduced.

5. What is the common practice of specifying the fatigue strength of the material?

It is common practice to specify the fatigue strength of the material at very high cycles, say, 10 0or 107 cycles.6. Write the ASTM code for tension-tension fatigue cycling test.

The tension-tension fatigue cycling test procedure is described in ASTM D3479.7. Name the two types of fatigue test on composites.

Stress-controlled and strain-controlled tests.8. Write the formula for finding the maximum fatigue stress.

The maximum fatigue stress can be estimated using the following relation,S= mlog (N) + bWhere S = Maximum fatigue stressN = Number of cycles to faila,b = constants.

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9. What will be the effect of lower fatigue strength in flexure?

The lower fatigue strength in flexure is attributed to the weakness of composites on thecompression side.10. What is the effect of notches on fatigue strength?

The fatigue strength of a fiber-reinforced polymer decreases with increasing notch depth as wellas increasing notch tip sharpness. Stacking sequence also plays an important role in the notcheffect in fiber-reinforced polymers.11. What is the damage mechanism during fatigue failure?

(a) Fiber breakage at high stress levels and (b) Matrix micro cracks followed by debonding atlow stress levels.12. Why strain-controlled test is expected produce a higher fatigue life than stress controlledtest?

Because of less damage development in a continuously reducing stress field, a strain-controlled

test is expected to produce a higher fatigue life than a stress-controlled test.13. What are the factors influencing strength of bonded joints?

Factors (bonded joints): the ratio of lap length to substrate thickness, modulus of adhesives.14. Write any two advantages of bonded composites.

1. Distribute the load over a larger area than mechanical joints.2. Require no holes.3. Add very little weight to the structure.15. Why failure theories are not applicable to composite materials?

Fiber-reinforced polymers are not isotropic, nor do they exhibit gross yielding. Thus, failure

theories developed for metals or other isotropic materials are not applicable to compositematerials.16. Write down the maximum strain theory.

According to the maximum strain theory, failure occurs when any strain in the principal materialdirections is equal to or greater than the corresponding ultimate strain.

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17. What are the basic joints of composites?

For composite laminates, the basic joints are either mechanical or bonded.18. Write any two advantages of mechanical joints.

1. Permit quick and repeated disassembly for repairs or replacements without destroying thesubstrates.2. Require little or no surface preparation.3. Are easy to inspect for joint quality.19. Write any two disadvantages of mechanical joints.

1. Require machining of holes that interrupt the fiber continuity.2. May reduce the strength of the substrate laminates.20. Write any two advantages of bonded joints.

1. Require no holes.2. Add very little weight to the structure.

21. Write any two disadvantages of bonded joints.

1. Are difficult to disassemble without either destroying or damaging substrates.2. Are difficult to inspect for joint quality.3. Need surface preparation (cleaning, pretreatment, etc...22. What are the basic failure modes in bolted joints?Basic failure modes in bolted laminates: (a) shear-out, (b) net tension failure, (c) cleavage, (d)bearing failure. Compositions of these failure modes are possible.22. Name the most widely used bonded joint.

The simplest and most widely used bonded joint is a single-lap joint.23. What are the basic bonded joints used in composite laminates?

Basic bonded joint configurations: (a) single-lap joint, (b) double-lap joint, (c) single and double-strap joints, (d) stepped lap joint, and (e) scarf joint.24. Write two important design considerations of bonded joints.

1. Increasing the ratio of lap length to substrate thickness h improves the joint strengthsignificantly at small L/h ratios, the improvement is marginal.2. Tapering the substrate ends at the ends of the overlap reduces the high normal stresses atthese locations.

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PREPARED AND PUBLISHED BY:Prof. T. Varun Kumar M.E., (Phd).

Assistant Professor,Department of Mechanical Engineering,P.A.College of Engineering and Technology,

Pollachi, Coimbatore - 642 002.