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Flashcards in 3.4 Materials Deck (38)
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1

Define elasticity

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

2

Define plastic deformation

Material does not return to original length when force is removed

3

Why don't plastic materials return to their shapes?

Has exceeded its elastic limit

4

What is A on a force-extension graph?

Limit of proportionality

5

What is B on a force-extension graph?

Elastic limit

6

What is C on a force-extension graph?

Plastic behaviour

7

What is D on a force-extension graph?

Fracture

8

What is elastic limit?

Beyond this point it will not show elastic behaviour but plastic

9

What is the limit of proportionality?

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

10

What is fracture?

When the material breaks
Before this happens the material undergoes creep

11

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

Force against extension

12

What is Hookes law?

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

13

What is the equation for Hooke's law?

F=kx

14

What is the unit of the force constant?

Nm-1

15

When do you stop using the force constant?

When deformation becomes plastic

16

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

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

17

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

Stretching force and extension

18

How do you find work done from a graph?

Area underneath

19

Define stress

Force per unit cross sectional area.
Nm-2 or Pa

20

Define strain

Extension per unit length
No units and is dimensionless

21

What is young modulus?

Stress/strain
Or Fl/eA

22

What type of young modulus do stuff materials have?

Large

23

What are the two ways to calculate you gs modulus?

Gradient of stress/strain graph
Calculate value directly from equation

24

What is ductile?

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

25

What is malleable?

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

26

What is brittle?

Break with little or no plastic deformation

27

What is a hard material?

One that will resist plastic deformation by surface indentation

28

What is stiffness

The ability to resist tensile force

29

What is a polymeric material?

Made of long chains of polymers and can withstand large strains

30

What is the ultimate tensile strength?

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