Material Science

Question 1

What are primary bonds?

Answer 1

A bond formed by the direct transfer or sharing of electrons (ionic / covalent / metallic)
Strongest bonds.

Question 2

What are secondary bonds?

Answer 2

Secondary bonds do not involve the valence electrons at all. They are weak intermolecular bonds formed as a result of dipole attractions. (unbalanced distribution of electrons in molecules) Weak bonds associated with determining properties of many non-metallic materials

Question 3

What is an ionic bond?

Answer 3

A primary bond arising from the electrostatic attraction between two oppositely charged ions.
Ion: a charged atom or group of atoms form by addition or removal of electrons.

Question 4

What is a covalent bond?

Answer 4

A primary bond arising from the reduction in energy associated with the sharing of pairs of electrons by several atoms.

Question 5

What are metallic bonds?

Answer 5

A primary bond arising from the attraction between the positive ion cores and the negatively charged electrons of the “electron cloud” within an aggregate of metallic atoms.

Question 6

What does crystallise mean?

Answer 6

Crystallization: The forming of solid material (crystals) during cooling

Question 7

What are the three systems (structures of metals) into which the important metal will crystallize.

Answer 7

Body centred cubic (BCC)
Face centred cubic (FCC)
Close packed hexagonal (CPH)

Question 8

Describe an atom by naming the parts.

Answer 8

Electrons have a negative charge
Protons have a positive charge
Neutrons have no charge
Protons and Neutrons are about the same size and make up the mass of the atom

Question 9

Find the stress in a bolt which resists a tensile load of 6.5 KN with a diameter of 12 mm.

Answer 9

Stress = force/area
Force = 6500 N
Area = pi x r2 = 3.14 x 0.006x 0.006 = 0.000113

Stress = 6500/ 0.000113
Stress = 57.5 MPa

Question 10

Find the strain if the tensile test piece had an original gauge length of 80mm and a final length of 102mm

Express this as percentage elongation

Answer 10

Strain = extension/original length
extension = 102 - 80 = 22
original length = 80

Strain = 22/80 = 0.275

% elongation = extension/original length x 100
% elongation = 22/80 x 100 = 27.5%

Question 11

How does an elastic material behave?

Answer 11

Returns to its original shape when the load is removed.

Question 12

How does a plastic material behave?

Answer 12

Remains deformed when the load is removed.

Question 13

How does a brittle material behave?

Answer 13

Cracks and breaks without plastic deformation.

Question 14

Describe a tough material.

Answer 14

Does not readily crack; can withstand dynamic loads such as shock or impact.

Question 15

Describe a ductile material.

Answer 15

Can be deformed plastically under tension; can be pulled or drawn into a wire.

Question 16

Describe a malleable material.

Answer 16

Can be deformed plastically under compression; can be hammered into a sheet.

Question 17

Describe a hard material.

Answer 17

Not readily scratched or indented.

Question 18

Describe a stiff material.

Answer 18

Requires a large force to produce a small deformation.

Question 19

Describe a smooth material.

Answer 19

Low friction surface.

Question 20

Describe a durable material.

Answer 20

Properties do not worsen with repeated loading and unloading.

Question 21

What did Hooke discover?

Answer 21

If you apply too big a force then a material will lose its elasticity.

Hooke discovered that the amount a spring stretches is proportional to the amount of force applied to it.

Question 22

What information does the spring constant give us?

Answer 22

The spring constant measures how stiff the spring is.

The larger the spring constant the stiffer the spring.

Question 23

Why is yield stress important?

Answer 23

Yield stress is very important to the designer because all machines, structures, bolts, etc. should all be loaded in service below the yield point.

Question 24

What is yield stress?

Answer 24

The yield stress is defined as that stress at which some marked increase in strain occurs without a corresponding increase in stress (e.g. mild steel has a definite yield point).

Question 25

What is the elastic limit?

Answer 25

The elastic limit is defined as the greatest stress that a material can endure without taking up some permanent set (plastic deformation).

Question 26

What is the proportional limit?

Answer 26

The proportional limit is defined as the greatest stress that a material can endure without losing straight-line proportionality between stress and strain. Most materials exhibit the proportional limit within the elastic limit. Thus for all practical purposes the proportional limit can be regarded as identical with the elastic limit, and is often known as the proportional elastic limit.

Question 27

What is ultimate tensile strength?

Answer 27

The ultimate tensile strength (U.T.S.) of a material is the maximum stress that the material is capable of developing. Once the (UTS) is exceeded, the load appears to drop away to failure, and the greatest amount of „local necking‟ occurs in ductile materials.