material defs

Question 1

Define brittle

Answer 1

A material that breaks by fracture propagation with hardly any plastic deformation

Question 2

Define ductile

Answer 2

Undergoes large plastic deformation under tensile (pulling) forces

Question 3

Define malleable

Answer 3

Undergoes plastic deformation under compressive (pushing) forces

Question 4

Define hard

Answer 4

A material which is resistant to scratching

Question 5

Define tough

Answer 5

A material that can absorb a lot of energy by plastic deformation before fracturing

Question 6

Define stiff

Answer 6

A material that requires a large amount of force for a small deformation

Question 7

Define strong

Answer 7

Requires A LARGE FORCE to break

Question 8

If a builder tries to bend a tile and it doesn’t deform, what property does the tile have?

Answer 8

its stiff

Question 9

If glass can’t be scratched, what property does it have?

Answer 9

its hard

Question 10

How is the statement “brittle materials are easy to break” incorrect?

Answer 10

Brittle materials are easy to FRACTURE

Not break

Question 11

What properties do ceramics have?

Answer 11

Stiff

Hard

Brittle

Question 12

What properties do metals have?

Answer 12

Malleable

Ductile

Pure metals are soft

Alloyed metals are harder

Question 13

What properties do polymers have?

Answer 13

Glass-like polymers are brittle

Semi-crystalline polymers are tough

Question 14

What defines a ceramic?

Answer 14

A material which has been heated to get its properties

Question 15

What defines a composite?

Answer 15

A mix of materials on a macroscopic scale

Question 16

What are the 3 types of material structure?

Answer 16

Crystalline
Amorphous
Polycrystalline

Question 17

Describe the crystalline structure

Answer 17

Atoms are arranged in a rigid three-dimensional fixed regular structure

Question 18

Describe the amorphous structure

Answer 18

Atoms are bonded with no regular structure

Resembles the structure of a liquid

Question 19

Define polycrystalline structure

Answer 19

Made of many interlocking crystals with no regular arrangement relative to each other

Question 20

Describe the polycrystalline structure

Answer 20

The material consists of a number of grains all orientated differently

The particles inside each grain are arranged in a regular pattern

Question 21

Explain why glass is brittle

Answer 21

Glass is strained elastically

Around the small cracks in the material, the stress concentration is much higher than the applied stress

At the tips of the small cracks in the material, 2 neighbouring atoms are pulled apart and then the next 2 and so on

The crack moves through the material (propagates)

Glass fractures easily (it is brittle)

Question 22

Why are metals tough?

Answer 22

Metals are ductile

Applying stress causes the cracks to deform plastically

This makes the cracks wider

So the stress concentration around the cracks decreases

And the atoms form bonds with different atoms

So the cracks don’t propagate

Question 23

What is often used instead of toughness and why?

Answer 23

Fracture energy is used instead

Toughness is hard to measure accurately

Question 24

Define fracture energy

Answer 24

Energy required per unit cross-sectional area to break the material

Question 25

How do you calculate fracture energy?

Answer 25

Fracture energy = used energy to fracture / cross-section area Fracture energy = W / A units: J m^-2

Question 26

Define tensile strength

Answer 26

Tensile (pulling) force required per unit cross-sectional to break the material

Question 27

How do you calculate tensile strength?

Answer 27

Tensile strength = breaking force / cross-sectional area Tensile strength = F / A units: Pa

Question 28

Why are metals ductile?

Answer 28

There are dislocations in the arrangement of atoms (mismatches) The dislocations move through the arrangement This allows rows of atoms to move 1 at a time relative to each other The reduces the energy to deform by a given amount massively

Question 29

Explain why alloys are less ductile than pure metals

Answer 29

Regular close packed planes of atoms can slide over each other due to the movement if dislocations in pure metals But in alloys, dislocations are pinned down and slip is prevented so the layers can't slide over each other so it is less ductile

Question 30

What are the 4 main properties of metals?

Answer 30

Conductors Shiny Stiff Ductile

Question 31

What are the 3 properties of ceramics?

Answer 31

Insulators Stiff Brittle

Question 32

What are the 2 properties of polymers?

Answer 32

Insulators Flexible

Question 33

The restoring force of a spring is always less than the loading force in an example What does this mean? What happens after loading and restoring the spring many times?

Answer 33

Energy returned is less than the work done stretching the spring Energy must be conserved so the internal energy of the spring must increase So the spring will become warmer

Question 34

What happens to the spring constant when 2 springs are put in parallel and why?

Answer 34

Putting them in parallel (side by side) doubles the spring constant because the load is shared between the two springs so the springs extend half the amount compared to what would have happened to just one. -each spring gets half the extension, therefore needs double the spring constant. f=kx

Question 35

What happens to the spring constant when 2 springs are put in series and why?

Answer 35

Putting them in series (end on end) halves the spring constant because both springs extend the same amount and the total extension is double what it would have been with just one spring. since f=kx

Question 36

define stress

Answer 36

force acting per unit area (Nm^-2) (pascals)

Question 37

define strain

Answer 37

extension per unit initial length (no units) (extension/ length) cancel each other out

Question 38

define young modulus

Answer 38

the ratio of stress to strain for a material (E= stress/ strain) (E=Fl/Ax)