Materials

Question 1

Hookes law

Answer 1

The relationship that the force F experienced by an extensible object is proportion to its extension ΔL

Question 2

Limit of proportionality

Answer 2

Hookes law is a relationship between two quantities. But, this relationship does not always hold. When a force-extension graph is non-linear, Hookes law does not apply

Question 3

Elastic limit

Answer 3

The maximum force the spring can sustain and then return to zero extension

Question 4

Gradient of force extension graphs

Answer 4

The gradient of a force-extension graph is the value of the constant of proportionality, k. For springs, this is the spring constant

Question 5

Area under a force extension graph

Answer 5

Elastic potential energy/elastic strain energy

Question 6

Density

Answer 6

Measure of how much mass an object has per unit volume

Question 7

Tensile forces

Answer 7

Forces that stretch an object

Question 8

Compressive forces

Answer 8

Forces that squash the object

Question 9

Stress if force is tensile

Answer 9

Positive

Question 10

Stress if force is compressive

Answer 10

Negative

Question 11

Strain if force is tensile

Answer 11

Positive

Question 12

Strain if force is compressive

Answer 12

Negative

Question 13

Tensile stress

Answer 13

The tension force per unit cross-sectional area of a material

Question 14

Tensile strain

Answer 14

The extension per unit length of a material ie change in length

Question 15

Young’s modulus

Answer 15

A measure of the stiffness of a material, the tensile stress per unit tensile strain

Question 16

Stiffness

Answer 16

The extent to which a material under stress experiences a strain

Question 17

Ultimate tensile strength

Answer 17

The maximum stress a material can withstand before fracture

Question 18

Elastic limit

Answer 18

The value of stress or force beyond which elastic deformation becomes plastic deformation; the material will not return to its original shape and size when the stress or force is removed

Question 19

Elastic region of stress-strain graph

Answer 19

Removal of stress or force will return the object to its original shape

Question 20

Limit of proportionality

Answer 20

The value of stress beyond which the stress is no longer proportional to the strain

Question 21

Plastic region

Answer 21

Removal of the stress or force will not return the object to its original shape
; the change in shape of the material is irrecoverable

Question 22

Yield point of stress-strain graph

Answer 22

The point beyond which the material extends rapidly for a small change in stress

Question 23

Brittle

Answer 23

The material distorts very little even when subject to a large stress and does not exhibit much plastic deformation

Question 24

Ductile

Answer 24

Materials that have a large plastic region and can therefore be drawn into a wire

Question 25

Polymeric materials

Answer 25

A material comprised of long chain molecules, for example, rubber, which may show large strains

Question 26

Tough

Answer 26

Needs a large energy to break and create a new fracture surface

Question 27

Stiff

Answer 27

The extent to which a material under stress experiences a strain

Question 28

Strong

Answer 28

The extent to which a material resists breaking under stress; it has a high ultimate tensile strength and a high breaking stress

Question 29

Hard

Answer 29

A measure of the difficulty of scratching or denting a material

Question 30

Area of hysteresis loop

Answer 30

The energy transferred per unit volume

Question 31

Describe the behaviour of rubber under stress

Answer 31

The stiffness of rubber gradually decreases as it is initially stretched. When the polymer chains have uncoiled fully, the rubber becomes stiffer

Question 32

Hysteresis loop

Answer 32

A loop-shaped plot obtained when, for example, losing and unloading a material produce different deformations