Learning Objectives:

• Understand the importance of studying material properties while studying material behaviour.
• Define mechanical properties of a material such as strength, hardness, ductility, elasticity, etc.
• To relate mechanical properties with the behaviour of materials under load.

• Yield point In stress-strain curve, if the stress is too large, the strain deviates from being proportional to the stress. The point at which this happens is the yield point because there the material yields, deforming permanently (plastically).

• Yield stress Hooke’s law is not valid beyond the yield point. The stress at the yield point is called yield stress, and is an important measure of the mechanical properties of materials. In practice, the yield stress is chosen as that causing a permanent strain of 0.002.

• Strength is the measure of the ability of the material to with stand or to resist external forces. Higher the strength of the material, higher will be the resistance offered by the material to the applied external force. For example a wooden bar will break easily and iron bar will not break easily because the resistance offered by the iron bar is very high. Depending upon the type of loading the strength may be tensile, compressive, shear, torsional and bending.

• Tensile strength When stress continues in the plastic regime, the stress-strain passes through a maximum, called the tensile strength (\(s_{TS}\)).

• Malleability is the ability of a metal to be hammered into thin sheets. It is the ability of a solid to bend or be hammered into other shapes without breaking. Examples of malleable metals are gold, iron, aluminum, copper (to a degree) and lead. When a piece of hot iron is hammered it takes the shape of a sheet.

• Ductility The ability to deform before braking. It is the opposite of brittleness. Ductility can be given either as percent maximum elongation \(e_{max}\) or maximum area reduction.

• Brittleness is the property of the material because of which the material fails or breaks or fractures or ruptures without any appreciable amount of deformation, before failure.In other words, lack of ductility is brittleness. An elongation of less than 5% is often taken to indicate a brittle material. Example of brittle material: Chalk, glass, cast iron etc., it will not stretch and bend before breaking.

• Toughness is a measure of the amount of energy a material can absorb before failure or fracture takes place. The toughness of a material is expressed as energy absorbed (Nm) per unit volume of material (m\(^3\)) or Nm/m\(^3\).Toughness is related to impact strength i.e. resistance to shock loading and it is desirable in the components subjected to shock and impacts such as gears, hammer, anvil. The area under the stress and strain curve of brittle and ductile material represents the toughness of materials.

• Resilience is the capacity to absorb energy elastically. The energy per unit volume is the area under the strain-stress curve in the elastic region.

• Elasticity is the ability of a material to restore back to its original shape and size, after it has been subjected to tensile, compressive, torsional or shear stresses.

  • Modulus of Elasticity E is defined as the ratio of tensile stress to strain. It is determined by a tensile test.

  • Modulus of rigidity G is defined as the ratio of shear stress and strain and it is determined by a torsion test.

  • Bulk modulus K defined as the ratio of pressure and volumetric strain.

  • Poisson’s ratio \(\nu\) is the negative ratio of transverse to axial strain.

• Plasticity is the property of the material because of which the material is able to retain (maintain) the deformed shape even after removal of deforming forces. Clay, polyethylene, etc.

• Hardness is the resistance to plastic deformation (e.g., a local dent or scratch). Scratch hardness is the measure of how resistant a sample is to fracture or permanent plastic deformation due to friction from a sharp object, whereas indentation hardness measures the resistance of a sample to material deformation due to a constant compression load from a sharp object.

• Stiffness is also called as the rigidity and is the ability of the material to resist the deflection or Elastic deformation. Stiffness is generally related to the springs, thicker springs are stiffer.

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Solved Example: 50-1-01

Toughness of a material is equal to area under _______ part of the stress-strain curve.

A. Elastic

B. Plastic

C. Both

D. None

Toughness refers to the capacity of a material of absorb energy prior to failure. Its value is equal to the entire area under the stress-strain curve.

Correct Answer: C

Solved Example: 50-1-02

The hardness is the property of a material due to which it:

A. Can cut another metal

B. Can be drawn into wires

C. Can be rolled or hammered into thin sheets

D. Breaks with little permanent distortion

Hardness is the ability of a material to resist deformation, which is determined by a standard test where the surface resistance to indentation is measured. The most commonly used hardness tests are defined by the shape or type of indent, the size, and the amount of load applied.

Correct Answer: A

Solved Example: 50-1-03

For a ductile material, toughness is a measure of:

A. Resistance to scratching.

B. Ability to absorb energy up to fracture

C. Ability to absorb energy till elastic limit

D. Resistance to indentation.

For a ductile material, ability to absorb energy upto fracture.

Correct Answer: B

Solved Example: 50-1-04

Mechanical properties include all of the following, except:

A. Strength

B. Elasticity

C. Fatigue

D. Texture

Correct Answer: D

Solved Example: 50-1-05

Ductility of a material can be defined as:

A. Ability to undergo large permanent deformations in compression

B. Ability to recover its original form

C. Ability to undergo large permanent deformations in tension

D. All of the above

Correct Answer: C

Solved Example: 50-1-06

The property of a material which enables it to resist fracture due to high impact loads is known as:

A. Elasticity

B. Endurance

C. Strength

D. Toughness

Correct Answer: D

Solved Example: 50-1-07

Resilience of a material is important, when it is subjected to:

A. Fatigue

B. Thermal stresses

C. Wear and tear

D. Shock loading

Correct Answer: D

Solved Example: 50-1-08

Malleability of a material can be defined as:

A. Ability to undergo large permanent deformations in compression

B. Ability to recover its original form

C. Ability to undergo large permanent deformations in tension

D. All of the above

Correct Answer: A

Solved Example: 50-1-09

Isotropic materials are those which have the same:

A. Identical elastic properties in all directions

B. Identical stresses induced in all directions

C. Identical thermal properties in all directions

D. Identical density throughout

Correct Answer: A

Solved Example: 50-1-10

A material is known as allotropic or polymorphic if it:

A. Has a fixed structure under all conditions

B. Exists in several crystal forms at different temperatures

C. Responds to heat treatment

D. Has its atoms distributed in a random pattern

Correct Answer: B

Solved Example: 50-1-11

Which of the following represents the allotropic forms of iron:

A. $\alpha$ iron, $\beta$ iron and $\gamma$ iron

B. $\alpha$ iron and $\beta$ iron

C. body centred cubic $\alpha$-iron and face centred cubic a-iron

D. $\alpha$ iron, $\gamma$ from and $\delta$ iron

Correct Answer: D

Solved Example: 50-1-12

What is the amount of energy required to fracture a given volume of material?

A. Impact strength

B. Endurance limit

C. Creep strength

D. Stress rupture strength

Correct Answer: A

Solved Example: 50-1-13

What mechanical property of a material which is a time-dependent permanent strain under stress?

A. Elongation

B. Elasticity

C. Creep

D. Rupture

Correct Answer: C

Solved Example: 50-1-14

What is the maximum stress below which a material can theoretically endure an infinite number of stress cycles?

A. Endurance state

B. Endurance test

C. Endurance limit

D. Endurance strength

Correct Answer: C

Solved Example: 50-1-15

What is the resistance of a material to plastic deformation?

A. Hardness

B. Stiffness

C. Creep

D. Rigidity

Correct Answer: A

Solved Example: 50-1-16

The property of a material which allows it to be drawn into a smaller section is called:

A. Plasticity

B. Ductility

C. Elasticity

D. Malleability

Correct Answer: B

Solved Example: 50-1-17

The property of a material by virtue of which it can be beaten or rolled into plates is called:

A. Malleability

B. Ductility

C. Plasticity

D. Elasticity

Correct Answer: A

Learning Objectives:

• To understand basic electrical property of the engineering materials.
• Define electrical properties of a material such as electrical conductivity,semi- and super-conductivity, resistivity and their importance in calculation of resistance.
• To understand the energy-band model for electrical conduction in materials.

• Resistivity Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current.

Electrical conductivity Electrical conductivity or specific conductance is the reciprocal of electrical resistivity, and measures a material’s ability to conduct an electric current.


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• An isotropic material has identical values of a property in all directions. An opposite behaviour will be referred as anisotropic behaviour. Wood is an example of anisotropic material.

• Allotropy is the property to exist in two or more different forms. Graphite and diamonds are allotropes of Carbon. Pure iron can exist in three different forms alpha iron, gamma from and delta iron depending upon the temperature.

Solved Example: 50-2-01

What physical property of a material refers to the highest potential difference (voltage) that an insulating material of given thickness can withstand for a specified time without occurrence of electrical breakdown through its bulk?

A. Thermal expansion

B. Conductivity

C. Dielectric strength

D. Electrical resistivity

Correct Answer: C

Solved Example: 50-2-02

With the rise of temperature, the conductivity of a semi-conductor:

A. Remains unchanged

B. Decreases

C. Increases

D. Nothing is certain

Correct Answer: C

Learning Objectives:

• To understand basic electrical property of the engineering materials.
• Define electrical properties of a material such as electrical conductivity,semi- and super-conductivity, resistivity and their importance in calculation of resistance.
• To understand the energy-band model for electrical conduction in materials.

• Specific Heat the ratio of the heat added to (or removed from) an object to the resulting temperature change.

• Coefficient of thermal expansion measures the fractional change in size per degree change in temperature at a constant pressure.

• Thermal Conductivity, which is used in Fourier’s law of heat conduction, is the measure of ability of a material to conduct heat.

Solved Example: 50-3-01

What physical property of a material that refers to the temperature at which ferromagnetic materials can no longer be magnetized by outside forces?

A. Melting point

B. Thermal conductivity

C. Thermal expansion

D. Curie point

Correct Answer: D

Solved Example: 50-3-02

What physical property of a material that refers to the rate of heat flow per unit time in a homogeneous material under steady-state conditions per unit area, per unit temperature gradient in a direction perpendicular to area?

A. Thermal expansion

B. Thermal conductivity

C. Heat distortion temperature

D. Water absorption

Correct Answer: B

Solved Example: 50-3-03

What physical property of a material refers to the ratio of the amount of heat required to raise the temperature of a unit mass of a substance 1 degree to the heat required to raise the same mass of water to 1 degree.

A. Specific heat

B. Latent heat

C. Heat of fusion

D. Heat of fission

Correct Answer: A

Learning Objectives:

• To describe chemical properties of material.
• To learn the indicators that convey whether a chemical change has taken place.
• To disctinguish between chemical and physical changes.

Chemical property can be broadly defined as ability to produce a change in the composition of the matter. They can be observed only when one substance in a sample of matter is changed into another substance.

Important Chemical Properties:

• Flammability: The ability to burn in the presence of Oxygen.
• Reactivity: How easily a substance combines chemically with another substance.
• Corrosion Resistance: Ability of metal to react with air to produce metal oxides.

Solved Example: 9237-02

Which of the following metals can displace the rest from their salt solutions?

A. Copper

B. Iron

C. Silver

D. Zinc

Correct Answer: D

Solved Example: 9237-03

Food cans are coated with tin and not with zinc because:

A. Zinc is costlier than tin

B. Zinc has a higher melting point than tin

C. Zinc is more reactive than tin

D. Zinc is less reactive than tin

Correct Answer: C

Solved Example: 9237-04

Metal A displaces metal B from its salt solution, but not able to displace metal C from its salt solution. Metal B displaces metal D from its salt solution. Which of the following depicts correct order of reactivity of metals.

A. A > B > C > D

B. B > C > A > D

C. C > A > B > D

D. C > A > D > B

Correct Answer: C