Intro

Question 1

What is density

Answer 1

The density of an object is the measure of mass per unit volume and is measured in Kg/m^3

The more dense an object is the heavier it will be

Question 2

When would fatigue occur

Answer 2

When a metal is subjected to cyclic loadings, it will (after sufficient repetitions) start to crack. This type of failure is known as fatigue and affects all metals

Question 3

What is elasticity

Answer 3

A body is said to be perfectly elastic, if after it has been deformed by external forces, it returns completely to its original shape when the forces are removed

Question 4

What is the definition of stress

Answer 4

Force per unit area.

SI units measured in N/m^3 or pascals both have equal value

Question 5

What is the definition of tensile stress

Answer 5

Forces trying to stretch or lengthen the material

Question 6

What is a compressive stress

Answer 6

Squash or shorten a material

Question 7

What is a combined stress

Answer 7

Tensile and shearing

Compressive and shearing

Question 8

What is a simple stress

Answer 8

When only one type of stress is acting on a body

Question 9

What is unit strain

Answer 9

The amount of deformation of a dimension of a body resulting from the application of a load divided by the original dimension of the body

Question 10

What is poissons ratio

Answer 10

As a material gets stretched it gets thinner and as it gets compressed it gets fatter

Question 11

What is a body’s elastic limit

Answer 11

The maximum stress to which a material may be subjected and still return to its original shape upon release of the load

Question 12

What is a body’s yield strength

Answer 12

The maximum stress that can be applied to a material with out permanent deformation of the material

Question 13

What is ultimate tensile strength

Answer 13

Maximum value of tensile strength that a material can withstand with out breaking

Maximum tensile force divided with original cross sectional area

Question 14

What is the modulus of elasticity

Answer 14

The ratio of stress to strain

Question 15

For airframe structures many light materials are required, what do they normally have to be lighter than

Answer 15

5kg/dm^3

Question 16

What are the 3 most important light weight metals used in aircraft structure

Answer 16

• Aluminium and aluminium alloys (density 2.7kg/dm^3)
• Titanium and titanium alloys (density 4.5kg/dm^3)
• Magnesium and magnesium alloys (density 1.74kg/dm^3)

Question 17

On aircraft structure where high weights or high strengths are needed, heavyweight metals and their alloys are applicable. What density do they range between

Answer 17

7.85 and 9.5kg/dm^3

Question 18

What is the basic building block of a crystal called

Answer 18

A unit cell

Question 19

How many atoms does a (BCC) Body Centred Cubic have

Answer 19

9 total

Question 20

How many atoms do (FCC) Face Centred Cubic have

Answer 20

14

Question 21

Is iron BCC or FCC

Answer 21

Iron is BCC below 910°c and FCC above 910°c

Question 22

How many atoms do HCP have

Answer 22

17

Question 23

What metals would have a FCC form

Answer 23

Aluminium, gold, copper, nickel, silver

Question 24

What metals would normally have a HCP arrangement

Answer 24

Cobalt, magnesium, titanium and zinc

Question 25

What should the selection of materials be a compromise between

Answer 25

The quality of the material to forfil the required function, and all costs

Question 26

What are the characteristics of iron in its pure form

Answer 26

Soft, malleable, ductile which is easy to form and shape

Question 27

What main element is iron alloyed with to prevent rust

Answer 27

Carbon

Question 28

Why does cast iron have limited uses in the aircraft industry

Answer 28

Low strength to weight ratio and brittleness