Important Questions with Answers

ANNA UNIVERSITY Part A '2' Marks Q & A

 

1. What are composite materials?

Composite materials, are a combination of two or more materials that are different in chemical composition.

Composite materials can be a combination of various materials, such as plastics, metals, fibers or ceramics.

 

2. How are composite materials classified?

Based on the reinforcement techniques, composites are classified as:

(a) Fiber-reinforced

(b) Structural

(c) Particle-reinforced

 

3. What is the function of matrix materials?

In composites, the matrix phase serves important functions. First it binds the reinforcement (fibers) together. It acts as a medium and transmits and distributes the external load to the fibers.

 

4. What are the type of composites based on the matrix materials?

Based on the matrix material

• Polymer matrix composites: In this the matrix Isnoita material is a polymer, reinforced by ceramic.

• Metal matrix composites: In this composite, the matrix alsite is a pure metal or an alloy and the reinforcement is a ceramic phase.

 

5. What are fibre reinforced plastics and its types?

Fibre reinforced plastics consist of fibres in a polymer resi  matrix.

The commonly used fibres are

(a) Glass Fibre Reinforced Plastics (GFRP)

 (b) Aramid Fibre Reinforced Plastics (AFRP)

 (c) Carbon Fibre Reinforced Plastics (CFRP)

 

6. What is fibre reinforced metals?

Metal Matrix Composites (MMC) provide high temperature resistance, non-flammability and greater resistance degradation by organic fluids when composed to polymer matrix composites.

Fibre reinforced MMCs contain continuous / discontinuous fibres or whiskers in a ductile metal matrix. oillatem

The ductile matrix materials are aluminium, magnesium, copper, titanium and super alloys. The continuous fibres are graphite, boron, alumina or silicon carbide. The whiskers of silicon carbide and silicon nitride are also used as reinforcement.

 

7. What are the advantages of composites?

1. Composite materials exhibit superior mechanical properties such as high strength, toughness, elastic modulus, fairly good fatigue and impact properties.

2. As FRP's are light weight materials, the specific strength and modulus is much higher than conventional materials.

3. In aeroplanes power to weight ratio is about 16 with composites compared to 5 with conventional materials. This helps in weight reduction and more pay load carrying capacity.

4. Fabrication of composites to any desired shape and size can be achieved with case.

5. They exhibit good corrosion resistance.

 

8. What are the limitation of composites?

1. Polymeric composites cannot be used for high temperature application.

2. Cost of composites is somewhat higher than many conventional materials.

 

9. Mention the application of composites?

1. Commercial aircraft

2. Military aircraft

3. Missiles

4. Space hardwares

5. Automobile and trucks

 

10. What are metallic glasses?

Generally, glass is an amorphous, brittle and transparent solid. We know that the metals are malleable, ductile and exhibit crystalline properties. The metallic glasses have the properties of both metals and glasses.

It is found that the metallic glasses are strong, ductile, malleable, opaque and brittle. They have good magnetic properties and high corrosion resistance.

 

11. What are the types of metallic glasses?

Metallic glasses are classified into two types:

(i) Metal - Metal metallic glasses

They are combination of metals

Example:

Metals        Metals

 

Nickel (Ni)  Niobium (Nb)

 Magnesium (Mg) - Zinc (Zn)

Copper (Cu) - Zirconium (Zr)

(ii) Metal - Metalloid metallic glasses

These are combinations of metals and m metalloids.

Example:

Metals : Metalloids

Fe, Co, Ni   B, Si, C, P

 

 

12. What are the properties of metallic glasses?

• Metallic glasses have extremely high strength, due to the absence of point defects and dislocation.

• They have high elasticity.

• They are highly ductile.

• Metallic glasses are not work-harden but they are work-soften. (work hardening is a process of hardening a material by compressing it)

• Electrical resistivity of metallic glasses is high and it does not vary much with temperature.

• Due to high resistivity, the eddy current loss is very small.

• The temperature coefficient is zero or negative.

• Metallic glasses have both soft and hard magnetic properties.

• They are magnetically soft due to their maximum permeabilities. Thus, they can be magnetised and demagnetised very easily.

 

13. What are the application of metallic glasses?

1.  They possess high physical and tensile strength. They are superior to common steels and thus they are very useful as reinforcing elements in concrete, plastic and rubber.

2. Strong ribbons of metallic glasses are used for simple filament winding to reinforce pressure vessels and to construct large fly wheels for energy storage.

3. Due to their good strength, high ductility, rollability and good corrosion resistance, they are used to make razor blades and different kinds of springs.

4. Since metallic glasses have soft magnetic properties, they are used in tape recorder heads, cores of high - power transformers and magnetic shields.

5. The use of metallic glasses in motors can reduce core loss very much when compared with conventional crystalline magnets.

 

14. What are shape memory alloys?

A group of metallic alloys which shows the ability to return to their original shape or size (i.e., alloy appears to have memory) when they are subjected to heating or cooling are called shape memory alloys.

 

15. What are the types of shape memory alloys?

There are two types of shape memory alloys

(i) One - way shape memory alloy

(ii) Two way shape memory alloy

A material which exhibits shape memory effect only upon heating is known as one-way shape memory. A material which shows a shape memory effect during both heating and cooling is called two-way shape memory.

 

16. Give example for shape memory alloys.

Generally, Ushape memory alloys are i intermetallic compounds having super lattice structures and metallic ionic - covalent characteristics. Thus, they have the properties of both metals and ceramics.

• Ni Ti alloy (Nitinol)

• Cu - Al-Ni alloy

 

17. Define shape memory effect.

The change in shape of a material at low temperature by loading and regaining of original shape by heating it, is known as shape memory effect.

The shape memory effect occurs in alloys due to the change in their crystalline structure with the change in temperature and stress.

• While loading, twinned  martensite  becomes deformef martensite at low temperature.

• On heating, deformed martensite becomes austenite (shape recovery) and upon cooling it gets transformed to twinned martensite.

 

18. What is pseudo elasticity?

Pseudo- elasticity occurs in shape memory alloys when it is completely in austenite phase (temperature is greater than A_f austenite finish temperature).0 - oid boog

Unlike the shape memory effect Pseudo – elasticity shape effect, Pseudo-elasticity occurs due to stress induced phase transformation without a change in temperature. The load on the shape memory alloy changes austenite phase into martensite.

As soon as the loading decreases the martensite begins to transform to austenite results in shape recovery.

This phenomenon of deformation of a SMA on application of large stress and regaining of original shape on removal of the load is known as psuedo elasticity.

This pseudo elasticity is also known as super elasticity.

 

19. Mention the application of shape memory alloys.

Shape memory alloys have a wide range of applications.

1. Microvalve (Actuators)

2. Toys and novelties

3. Medical field

Blood clot filters

Orthodontic applications

4. Antenna wires

5. Thermostats

6. Cryofit hydraulic couplings

7. Springs, shock absorbers and valves

8. Stepping motors

9. Titanium-aluminium shape memory alloys

 

20. What are the advantages of shape memory alloys?

• They are simple, compact and highly safe.

• They have good bio - compatibility.

• They have diverse applications and offer clean, silent and spark-free working condition.

• They have good mechanical properties and strong corrosion-resistance.

 

21. State the disadvantages of shape memory alloys.

• They have poor fatigue properties.

• They are expensive.

• They have low energy efficiency.

 

22. What are ceramic materials?

Most of the ceramics are compounds of metallic and non-metallic elements. The crystal structure of ceramics is more complex because at least two elements are involved in making a ceramic compound. Ceramics can be used at low as well as high temperatures.

Ceramic materials are obtained by firing them at high temperatures. Traditional ceramics are clay products like bricks, tiles and porcelain. China ceramics are obtained by firing clay products.

 

23. What are natural ceramic materials?

Ceramics can be natural or manufactured

Natural Ceramics

The most frequently used, naturally occuring ceramics are: Silica (SiO₂), Silicates and Clay minerals.

24. What are traditional ceramic materials?

Traditional components: clay, silica, and feldspar. Example of tradiational ceramics are glasses, tiles, bricks and porcelain.

 

25. What are engineering ceramic materials? eredam

Engineering ceramics are mainly pure compounds or oxides, carbides or nitrides of pure compounds. Some of the important engineering ceramics alumina (Al₂O₂) silicon nitride  (Si₃,N₄), silicon carbide (SiC) and zirconia (ZrO₂).

 

26. Give classification of ceramics based on crystal structure.

(i) Crystalline ceramics

(ii) Non-crystalline (Amorphous) ceramics

 (iii) Bonded ceramic

 

27. What is crystalline ceramics?

These have simple crystal structure, such as aluminium oxide (corundum), magnesium oxide, silicon carbide. Most of the oxides can be considered packing of oxygen ions with the cations occupying the tetrahedral and / or octahedral sites in the structure.

 

28. What are non-crystalline ceramics?

These are usually regarded super, cooled liquids. Their molecules are not arranged in regular geometric shapes. e.g. amorphous or fused SiO2 has each Si bonded to four O and each O is bonded to two Si.

This type of ceramics is used for mirrors, optical lenses, reinforcement fibres for GRP and optical fibres for data transmission.

 

29. What are bonded ceramics?

These ceramics contain both crystalline and non-crystalline materials which are bound together by a glassy matrix after firing. This group includes the lining and clay products.

Bonded ceramics are used as electrical insulators, refractory for furnace, spark plugs etc.

 

30. Mention the steps for the processing of ceramic materials.

(i) raw material processing,

(ii) fabrication

(iii) densification

 

31. What are the thermal properties of ceramics?

(i) Thermal capacity

• The specific heats of fine clay bricks are 0.25 at dod 1000°C and 0.297 at 1400°C.

(ii) Thermal conductivity

• The ceramic materials possess a very low thermal conductivity since they do not have enough free electrons.

 (iii) Thermal Shock

"Thermal shock resistance" is the ability of a material to resist cracking or disintegration of the material under sudden changes in temperature.

• Lithium compounds are in many ceramic compounds to reduce thermal expansion and provide excellent thermal shock resistance.

 

32. What are the mechanical properties of ceramics?

 • Compressive strength. Compressive strength in ceramics in general is many times greater than tensile strength.

• Shear strength. High shear strengths and low fracture auon strengths are generally characteristics of ceramics.

• Tensile strength. Tensile strength in ceramics are theoretically high.

• Torsional strength. Torsional strength is seldom nooilia considered as a critical property of ceramics since tensile and cantilever requirements will show the torsional strength of material.

• Toughness of Ceramic Materials Due to presence of covalent-ionic bonding, ceramics have low toughness.

 

33. State the electrical properties of ceramics.

• Ceramics are generally poor conductors of electricity because the electrons associated with the atoms ceramics are shared covalent or ionic bonds.

• Ceramic materials are are used in an electrical circuit both as the electrical insulators and as its functional parts.

• Ceramic materials have good dielectric capacity.

 

34. Mention the chemical properties of ceramics.

• The great majority of ceramic products, are highly resistant to all chemicals except hydrofluoric acid and to some extent, hot caustic solutions.

• Organic solvents do not affect the ceramics.

• Oxidic ceramics are completely resistant to oxidation, of abnueven even at very high temperatures.

• Magnesia, zirconia, porcelain, graphite, alumina, etc., are resistant to certain molten metals. They are used for making crucibles and furnace linings.

 

35. What are ceramic fibers?

They are known as refractory ceramic fibers.

Ceramic fibers comprise a wide range of amorphous or crystalline synthetic mineral fibers characterized by their refractory properties (i.e., stability at high temperatures).

They typically are made of alumina, silica, and other metal oxides or, less commonly, of nonoxide materials such as silicon carbide.

Most ceramic fibers are compounds of alumina and silica in an approximate 50/50 mixture.

 

36. What are the uses and application of ceramic fibers?

• Ceramic fibers are used as insulation materials, due to their ability to withstand high temperatures. They are used primarily for lining furnaces and kilns.

• The products are in the form of blankets, boards, felts, bulk fibers, vacuum-formed or cast shapes, paper and textiles.

• High-temperature resistant ceramic blankets and boards are used in ship building as insulation to prevent the spread of fires.

 

37. What are ferro electric ceramics?

Examples for the ferroelectric ceramics are Rochelle salt, BaTiO₃, SITO₃, PbTiO₃, LiNbO₃, NaNbO₃, KNbO₃, PbTa₂O₃, etc.

 

38. What are ferromagnetic ceramics?

The soft magnetic ceramics, exhibits similar properties as that of soft magnetic materials (metal counter parts).

The magnetic ceramic materials are classified into three types namely,

• spinel,

• garnets and

• hexagonal ferrites.

 

39. What is high alumina ceramics?

High alumina ceramics contains 85% or more by weight of Al₂O₃

• Alumina is nothing but an aluminium oxide (Al2O3), beorot which is the oldest engineering ceramic.

• Alumina is produced from bauxite (Al₂O₃ 2H₂O).

 

40. What are the characteristics of high alumina?

1. Alumina have excellent hardness, wear resistance and STS ved chemical inertness properties.

2. They are more stiffer than steels.

3. They are more stronger in compression than many hardened tool steels.

4. They retain 50% of their room temperature strength at elevated temperature (about 1093°C).

5. They possess very good environmental resistance.

6. These are mechanically strong, dense materials, unlike Jisa elle refractories which are usually porous.

7. They have ability to resist high temperature because they are poor thermal conductors.

 

41. What are the applications and uses of high alumina?

(i) Alumina is used as a refractory material for high 99rld of temperature applications.

(ii) Alumina makes an excellent high voltage insulator. Classical applications are for insulators in spark plugs and in insulating substrates to support integrated circuits.

(iii) Alumina based ceramic tools have very high abrasion resistance, high hardness and are chemically stable than high speed steels. So they are used in cutting cast irons, and steels to obtain good surface finish.

 

ANNA UNIVERSITY Part B (16 Marks) Questions

1. Discuss the classification of composites. Give detailed study of Fiber Reinforced Plastics (FRP) and Fiber reinforced metal (FRM)

2. Explain the preparation, types, properties and applications of metallic glasses.

3. Describe the type, properties and applications of shape memory alloys.

4. Discuss the classification of ceramics.

5. Explain the following manufacturing methods of ceramics

1. Slip casting

2. Isostatic pressing

3. Gas pressure bonding

6. Explain thermal, mechanical, electrical and chemical properties of ceramic materials.

7. Write notes on

(i) ceramic fibers

(ii) Ferroelectric ceramics,

(iii) Ferromagnetic ceramics,

(iv) High aluminium ceramics