Intro Flashcards
What is density
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
When would fatigue occur
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
What is elasticity
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
What is the definition of stress
Force per unit area.
SI units measured in N/m^3 or pascals both have equal value
What is the definition of tensile stress
Forces trying to stretch or lengthen the material
What is a compressive stress
Squash or shorten a material
What is a combined stress
Tensile and shearing
Compressive and shearing
What is a simple stress
When only one type of stress is acting on a body
What is unit strain
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
What is poissons ratio
As a material gets stretched it gets thinner and as it gets compressed it gets fatter
What is a body’s elastic limit
The maximum stress to which a material may be subjected and still return to its original shape upon release of the load
What is a body’s yield strength
The maximum stress that can be applied to a material with out permanent deformation of the material
What is ultimate tensile strength
Maximum value of tensile strength that a material can withstand with out breaking
Maximum tensile force divided with original cross sectional area
What is the modulus of elasticity
The ratio of stress to strain
For airframe structures many light materials are required, what do they normally have to be lighter than
5kg/dm^3
What are the 3 most important light weight metals used in aircraft structure
- 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)
On aircraft structure where high weights or high strengths are needed, heavyweight metals and their alloys are applicable. What density do they range between
7.85 and 9.5kg/dm^3
What is the basic building block of a crystal called
A unit cell
How many atoms does a (BCC) Body Centred Cubic have
9 total
How many atoms do (FCC) Face Centred Cubic have
14
Is iron BCC or FCC
Iron is BCC below 910°c and FCC above 910°c
How many atoms do HCP have
17
What metals would have a FCC form
Aluminium, gold, copper, nickel, silver
What metals would normally have a HCP arrangement
Cobalt, magnesium, titanium and zinc
What should the selection of materials be a compromise between
The quality of the material to forfil the required function, and all costs
What are the characteristics of iron in its pure form
Soft, malleable, ductile which is easy to form and shape
What main element is iron alloyed with to prevent rust
Carbon
Why does cast iron have limited uses in the aircraft industry
Low strength to weight ratio and brittleness
