Materials

Question 1

Stiff

Answer 1

Small extension per unit of force

Question 2

Elastic

Answer 2

returns to unstreched form when stresses are removed

Question 3

Plastic

Answer 3

Permanent deformation

Question 4

Ductile

Answer 4

Can be drawn into wires

Question 5

Malleable

Answer 5

Can be formed into shapes

Question 6

Hard

Answer 6

Resists indentation upon impact

Question 7

Brittle

Answer 7

Undergoes little or no deformation before fracture

Question 8

Tough

Answer 8

Absorbs a lot of energy (deforms plastically) before fracture

Question 9

Strong

Answer 9

Can withstand high stress

Question 10

Ceramics properties

Answer 10

Hard, stiff, brittle

Question 11

Metal properties

Answer 11

Pure: ductile, large plastic region, stiff, tough
Alloys: strong, less tough, stiff

Question 12

Polymers

Answer 12

Man made: Kevlar, Teflon, polythene. Has similar properties to glass.
Natural: DNA, wool, cellulose, starch, proteins. Can absorb more energy before breaking.

Question 13

Composites

Answer 13

When two or more material are bonded together. Has a reinforcing material that provides strength and bonding agent (the matrix)

Question 14

Young’s modulus

Answer 14

A measure of stiffness of a material, rather than an individual specimen

Question 15

Young’s modulus equation

Answer 15

Stress/strain
E=FL/AX

Question 16

Young’s modulus and spring constants

Answer 16

Doubling the area doubles the K
Doubling the length halves the K

Question 17

Force extension graph

Answer 17

Initial gradient- spring constant
Area under graph- work done / energy required to break the spring
Area under curve- energy stored
Elastic limit- end of initial gradient

Question 18

Strain

Answer 18

Change in length/ initial length
Unit less

Question 19

Stress

Answer 19

Force/ cross sectional area
Pa or Nm^-2

Question 20

Dislocation

Answer 20

An extra half plane of atoms. Makes plastic flow easier as only one set of bonds need breaking at one time.
If it’s easy material is ductile.
If it’s hard material is brittle.

Question 21

Alloys dislocations

Answer 21

Dislocations are pinned, slip is more difficult

Question 22

Crystals

Answer 22

A region of atoms all oriented in the same direction
Eg quartz

Question 23

Amorphous

Answer 23

No long range order
Eg glass

Question 24

How to get an amorphous state

Answer 24

Rapid cooling tends to trap particles in an amorphous state, resembling the disordered arrangement in a liquid

Question 25

How to get a crystal state

Answer 25

Slow controlled cooling of a liquid can lead to a single pure crystal

Question 26

Polycrystalline

Answer 26

Lots of grains oriented differently to one another but with an ordered , regular structure within each individual grain

Question 27

AFMs

Answer 27

Atomic Force Microscopes Move a needle over a sample to detect the contours of the surface

Question 28

Diamond

Answer 28

Strong covalent bonds Directional bonds break by cracking

Question 29

Copper

Answer 29

Strong metallic bonds Non-directional bonds Malleable

Question 30

Ceramic bonds

Answer 30

Directional bonds, so extremely difficult for atoms to move as they are locked in place

Question 31

To make polymers stiffer

Answer 31

Add bulky side groups, inhibits chain rotation

Question 32

Stretching a rubber band graph

Answer 32

1) bonds rotating 2) chains slide over each other 3) pulls along bonds

Question 33

Stretching a rubber band

Answer 33

Initially stiff bonds rotate, elongating the molecules. Area decreases, so feels less stiff. Finally rubber feels stiff again because the crosslinks are holding the molecules together

Question 34

Directional bonds in ceramics

Answer 34

Directional bonds make it difficult for directional bonds to glide. A crack concentrates the stress, the bigger the crack the bigger the stress. Bonds break one row at a time

Question 35

Cracking in metals

Answer 35

Plastic flow More energy needed to break metal Metals are more tough