3.4 Materials

Question 1

Define elasticity

Answer 1

The property of a body to resume its original shape or size once the deforming force or stress has been removed

Question 2

Define plastic deformation

Answer 2

Material does not return to original length when force is removed

Question 3

Why don’t plastic materials return to their shapes?

Answer 3

Has exceeded its elastic limit

Question 4

What is A on a force-extension graph?

Answer 4

Limit of proportionality

Question 5

What is B on a force-extension graph?

Answer 5

Elastic limit

Question 6

What is C on a force-extension graph?

Answer 6

Plastic behaviour

Question 7

What is D on a force-extension graph?

Answer 7

Fracture

Question 8

What is elastic limit?

Answer 8

Beyond this point it will not show elastic behaviour but plastic

Question 9

What is the limit of proportionality?

Answer 9

The point at which extension is no longer directly proportional to the force
Material behave elastically still
Stops obeying Hookes law

Question 10

What is fracture?

Answer 10

When the material breaks

Before this happens the material undergoes creep

Question 11

What type of graph is used to show the difference between plastic and elastic behaviour?

Answer 11

Force against extension

Question 12

What is Hookes law?

Answer 12

States that extension of an object is proportional to the force that caused it, provided the elastic limit is not exceeded

Question 13

What is the equation for Hooke’s law?

Answer 13

F=kx

Question 14

What is the unit of the force constant?

Answer 14

Nm-1

Question 15

When do you stop using the force constant?

Answer 15

When deformation becomes plastic

Question 16

Why do we unconventionally plot force on the y axis and extension on the x axis?

Answer 16

Because then the gradient of the line is equal to the force constant

Question 17

What does the work required to stretch a wire depend on?

Answer 17

Stretching force and extension

Question 18

How do you find work done from a graph?

Answer 18

Area underneath

Question 19

Define stress

Answer 19

Force per unit cross sectional area.

Nm-2 or Pa

Question 20

Define strain

Answer 20

Extension per unit length

No units and is dimensionless

Question 21

What is young modulus?

Answer 21

Stress/strain

Or Fl/eA

Question 22

What type of young modulus do stuff materials have?

Answer 22

Large

Question 23

What are the two ways to calculate you gs modulus?

Answer 23

Gradient of stress/strain graph

Calculate value directly from equation

Question 24

What is ductile?

Answer 24

Can be drawn into wires and will show plastic deformation under tensile stress before breaking

Question 25

What is malleable?

Answer 25

Can be hammered or beaten into flat sheets and will show extensive plastic deformation when subjected to compressive forces

Question 26

What is brittle?

Answer 26

Break with little or no plastic deformation

Question 27

What is a hard material?

Answer 27

One that will resist plastic deformation by surface indentation

Question 28

What is stiffness

Answer 28

The ability to resist tensile force

Question 29

What is a polymeric material?

Answer 29

Made of long chains of polymers and can withstand large strains

Question 30

What is the ultimate tensile strength?

Answer 30

The maximum stress it can withstand while being pulled or stretched, before it breaks

Question 31

Precision of micrometer

Answer 31

Micrometer to the nearest 0.01mm

Question 32

What's important when plotting the graph?

Answer 32

Through origin | Lobf

Question 33

How to reduce error in Young's modulus experiment?

Answer 33

0 error on micrometer or ruler | Remove by adding or subtracting error

Question 34

Typical Young's modulus value of a metal?

Answer 34

50-100 *10^9 Pa

Question 35

What is the unit of Young's modulus?

Answer 35

Pa

Question 36

What does a stress strain graph for brittle materials look like?

Answer 36

Doesn't curve

Question 37

What does the area under a polymeric material curve?

Answer 37

Amount of energy converted to heat per unit volume

Question 38

Why are the losing and unloading curves for rubber different?

Answer 38

Energy released when the rubber is unloaded is less than work done to stretch it as some is converted to heat