3.4 Matierals

Question 1

Define brittle

Answer 1

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

Question 2

Define compression

Answer 2

The result of two coplanar forces acting into an object. Compression usually results in a reduction in the length of the objects shape

Question 3

Define compressive deformation

Answer 3

The changing of an objects shape due to compressive forces

Question 4

Define ductile

Answer 4

A material is ductile if it can undergo very large extensions without failure. Ductile materials can be stretched into wires.

Question 5

Define Elastic deformation

Answer 5

If a material deforms with elastic behaviour, it will return to its original shape when the load is removed. The object will not be permanently deformed

Question 6

Define Elastic potiental energy

Answer 6

The energy stored in an object when it is stretched.

Question 7

How can you find the elastic potienal emergy from a force-extension graph?

Answer 7

The area under the graph

Question 8

Define extension

Answer 8

The increase in an objects length

Question 9

What is hookes law?

Answer 9

The extension of an elastic object will be directly proportional to the force applied to it up to the objects limit of proportionality.

Question 10

What is the equation for the extension of a spring?

Answer 10

Force = spring constant x extension
F=kx

Question 11

What is the equation for stress?

Answer 11

Stress = force/ area
ó = F/A

Question 12

What is the equation for strain?

Answer 12

Strain = extension / length
E=x/L

Question 13

What is the equation for youngs modulus?

Answer 13

young modulus = stress / strain
E=ó/E

Question 14

What are the 2 equations for elastic potential energy?

Answer 14

Energy = 0.5 x force x extension
E = 0.5 x F x X

Energy = 0.5 x spring constant x extension^2
E = 0.5 x k x X^2

Question 15

What is ultimate tensile strength?

Answer 15

The maximum stress a material can withstand before fracture

Question 16

What is the elastic limit?

Answer 16

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 17

What is the plastic region on a stress / strain graph?

Answer 17

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 18

What is the limit of proportionalityin regards to a stress/strain graph?

Answer 18

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

Question 19

What is the elastic region on a stress/ strain graph?

Answer 19

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

Question 20

What is the yield point?

Answer 20

Yield Point—the point beyond which the material extends rapidly for a small change in stress

Question 21

Why can ductile materials be drawn into a wire?

Answer 21

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

Question 22

What is a polymeric material?

Answer 22

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

Question 23

Define tough

Answer 23

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

Question 24

Define stiff

Answer 24

The extent to which a material under stress experiences a strain

Question 25

Define hard

Answer 25

A measure of the difficulty of scratching or denting a material

Question 26

Define strong

Answer 26

The extent to which a material resists breaking under stress; it has a high Ultimate Tensile Strength and a high breaking stress

Question 27

What is the area of a hysteresis loop equal to?

Answer 27

The energy transferred per unit volume