Topic 4 - Materials 2

Question 1

What’s energy density?

Answer 1

It’s the work done in stretching a specimen per unit volume of the sample
= 1/2 x stress x strain

Question 2

If a material can absorb a lot of energy before it’s fracture what does this mean?

Answer 2

It’s a tough material

Question 3

Little plastic deformation means what about a material?

Answer 3

It’s brittle

Question 4

What’s the hysteresis loop?

Answer 4

On a stress-strain graph it represents the energy per unit volume transferred to internal energy for each cycle

Question 5

How do you calculate the extension?

Answer 5

New length - original length = extension

Question 6

If you want to compare 2 different materials what do you use force-extension or stress-strain?

Answer 6

Stress-strain

Question 7

If a force stretches a material it’s called …

Answer 7

Tensile

Question 8

If a force squashed a material it’s called?

Answer 8

Compressive

Question 9

Compressive forces tend to be?

Answer 9

Negative

Question 10

What’s breaking stress?

Answer 10

When the stress becomes too much the atoms separate completely and the material breaks

Question 11

What comes first on a stress-strain graph the UTS or the breaking stress?

Answer 11

UTS

Question 12

Name one thing that can effect UTS and breaking stress?

Answer 12

Temperature

Question 13

What does the area under a force extension graph represent?

Answer 13

Elastic energy strain

Question 14

What’s the equation for elastic strain energy?

Answer 14

Elastic strain energy = 1/2 x spring constant x extension*2

Question 15

What’s the equation for work done?

Answer 15

Work done = 1/2 x force x extension

Question 16

Up to the ………. …… ………… the stress and strain of a material are proportional. After this point you can no longer use the equation to calculate the young modulus

Answer 16

Limit of proportionality

Question 17

From a stress-strain graph how would you calculate the energy per unit volume?

Answer 17

Energy per unit volume = 1/2 x stress x strain

Question 18

What are the different point on a stress-strain graph?

Answer 18

1. limit of proportionality
2. Elastic limit
3. Yield point

Question 19

The stronger a material the higher the ………. ……. on the stress-strain graph

Answer 19

Breaking stress

Question 20

Stiff materials have a large ………. ……… . And for a given stress a stiff material will have a lower ……….. than a less stiff material

Answer 20

Young’s modulus

Strain

Question 21

What’s the difference between stress-strain & force-extension?

Answer 21

• F-E are specific for the tested object and depend on its dimensions
• S-S describes the general behaviour of a material, they’re independent of the dimensions

Question 22

What’s on which axis of the stress-strain graph?

Answer 22

Y axis - stress

X axis - strain

Question 23

What does it mean if a material is elastic?

Answer 23

Regains original dimensions when the deforming force is removed
-example rubber