Material properties

We’ll focus on:
Elasticity and plasticity
Stages in elastic and plastic deformation(tensile testing)
Hardness
Fatigue , fracture toughness and creep(materials problems in aircraft construction)
Basic thermal properties(ex)

Types of force and deformation
When vertical members can no longer resist a load they either crush or buckle (bending out of shape)

How are the springs(in car suspension)made springy?
Spring act like a cushion , providing comfort and performance, allowing the wheel to maintain contact with road surface when travel over a bump. Spring must be
elastic.

Elasticity and plasticity
Elasticity-ability to extend significantly, but still return to their original shape(rubber)
Low elasticity , strong => stiff
Low elasticity , weak => brittle (glass)
Plasticity-ability to change shape significantly, but DO NOT return to their original shape
Can be plastically deformed by hammering or rolling=> malleable(lead , Pb)
Can be stretched into a long length=> ductile(Cu)

Stages in elastic and plastic deformation
Point 0-1:
The extention of the bar is proportional to the increase in tension.
Point1:
The limit of proportionality
Point2:
The elastic limit

Stages in elastic and plastic deformation
Point 3:
The Yield point
Point 4:
UTS-the Ultimate Tensile Strength
Point5:
The fracture point

Heat treating metal
The properties of a metal can be changed by heat treating it – that is , heating and cooling the metal.

The main types of heat treatment
Quenching(quenched metal is harder , but tends to be more brittle)
Annealing(annealed metal is generally softer and more elastic)
Tempering(tempered metal possesses a balance between hardness and elastisity)
Age hardening,surface hardening

Hardness
Affects a material’s durability
Can be defined in two ways:
-Scratch hardness
-Indentation hardness

Fatigue / creep
There are two important problems:
Fatigue(caused by cyclic loads)
Creep(components
Become permanently
damaged)

Springs are made from wire(wire made from ductile metal)
When the wire manufactured , it is stretched beyond its elastic limit and even yield point
To put back the springiness to a spring , it is tempered

Comparing copper or aluminium
as materials for electrical wires
The thermal conductivity of copper is 40% greater than that of aluminium. Copper is a much more effective thermal conductor.
Copper has a coefficient of thermal expansion apprx. 40% lower than that of aluminium.