Properties of materials and structures

Question 1

What is the equation for stress?

Answer 1

stress = force/cross-sectional area

Question 2

What are the units for stress?

Answer 2

N m*-2 / Pa

Question 3

What is the equation for strain?

Answer 3

change in length/ original length

Question 4

What are the units for strain?

Answer 4

no units - ratio

Question 5

What is the relationship between change in length and the original length of the material?

Answer 5

they change in proportionality to each other

i.e. a bar twice as long stretches twice as much

Question 6

What is the proportional limit?

Answer 6

the end point of the stress-strain curve where the relationship is linear

Question 7

What is the elastic limit?

Answer 7

the greatest stress that can be applied to a material so that when the stress is removed, it will return to its original shape.

Question 8

What is elastic behaviour?

Answer 8

a material which exhibits elastic behaviour will deform instantly and return to its original shape as soon as the load is removed

Question 9

What is plastic behaviour?

Answer 9

a material which exhibits plastic behaviour will deform instantly and when the load is removed, it will retain its new shape

Question 10

what is the yield point?

Answer 10

the point which once passed, the material will undergo considerable elongation without a corresponding increase in stress

Question 11

What is the stress at the yield point known as?

Answer 11

the yield stress

Question 12

What happens during strain hardening?

Answer 12

the material undergoes changes in its atomic and crystalline structure resulting in an increased resistance to further deformation

Question 13

What is the ultimate strength?

Answer 13

the highest point on the curve after which stretching occurs and necking or waisting of the material occurs whereby the cross-sectional area is reduced

Question 14

What is the rupture point?

Answer 14

is the point at which the material breaks

Question 15

Describe a brittle material

Answer 15

a material that can only survive a limited strain before breaking - e.g. glass

Question 16

Describe a ductile material

Answer 16

a material that deforms plastically before breaking e.g. copper

Question 17

Describe the differences between a brittle and ductile material

Answer 17

a brittle material only requires a small strain before breaking

a ductile material behaves plastically before breaking

Question 18

Describe the phenomenon of necking

Answer 18

after the ultimate strength point is passed, the material stretches and its cross-sectional area is reduced.

Question 19

What does the Young’s Modulus of a material indicate?

Answer 19

stiffness - how difficult a material is to deform under loading

Question 20

What is stiffness?

Answer 20

a measure of how difficult a material is to deform under loading

Question 21

What is the formula for Young’s Modulus?

Answer 21

stress/strain

Question 22

What are the units for Young’s Modulus?

Answer 22

Pa

Question 23

Describe a material with a small young’s modulus

Answer 23

such a material requires only a small amount of stress to produce a large strain (flexible)

Question 24

Give an example of a material with a small youngs modulus

Answer 24

rubber

Question 25

Describe a material with a large Young’s Modulus

Answer 25

such a material requires a large stress to produce even a small strain (stiff)

Question 26

Give an example of a material with a large YM

Answer 26

diamond

Question 27

what is rigidity? what is the equation?

Answer 27

A materials ability to resist axial deformation

rigidity = YM x cross-sectional area

thus, rigidity increases with cross-sectional area

Measured in Newtons

Question 28

What is stiffness?

Answer 28

the force required to produce a unit deflection

Question 29

What is the equation for stiffness?

Answer 29

k = EA/change in length

Question 30

What is the opposite of stiffness? What does it mean?

Answer 30

Flexibility - deflection under a unit load