Слайд 2We’ll focus on:
Elasticity and plasticity
Stages in elastic and plastic deformation(tensile testing)
Hardness
Fatigue ,
![We’ll focus on: Elasticity and plasticity Stages in elastic and plastic deformation(tensile](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-1.jpg)
fracture toughness and creep(materials problems in aircraft construction)
Basic thermal properties(ex)
Слайд 3Types of force and deformation
When vertical members can no longer resist a
![Types of force and deformation When vertical members can no longer resist](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-2.jpg)
load they either crush or buckle (bending out of shape)
Слайд 4How are the springs(in car suspension)made springy?
Spring act like a cushion
![How are the springs(in car suspension)made springy? Spring act like a cushion](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-3.jpg)
, providing comfort and performance, allowing the wheel to maintain contact with road surface when travel over a bump. Spring must be
elastic.
Слайд 5Elasticity and plasticity
Elasticity-ability to extend significantly, but still return to their original
![Elasticity and plasticity Elasticity-ability to extend significantly, but still return to their](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-4.jpg)
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)
Слайд 6Stages in elastic and plastic deformation
Point 0-1:
The extention of the bar
![Stages in elastic and plastic deformation Point 0-1: The extention of the](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-5.jpg)
is proportional to the increase in tension.
Point1:
The limit of proportionality
Point2:
The elastic limit
Слайд 7Stages in elastic and plastic deformation
Point 3:
The Yield point
Point 4:
UTS-the Ultimate Tensile
![Stages in elastic and plastic deformation Point 3: The Yield point Point](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-6.jpg)
Strength
Point5:
The fracture point
Слайд 8Heat treating metal
The properties of a metal can be changed by heat
![Heat treating metal The properties of a metal can be changed by](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-7.jpg)
treating it – that is , heating and cooling the metal.
Слайд 9The main types of heat treatment
Quenching(quenched metal is harder , but tends
![The main types of heat treatment Quenching(quenched metal is harder , but](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-8.jpg)
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
Слайд 10Hardness
Affects a material’s durability
Can be defined in two ways:
-Scratch hardness
-Indentation
![Hardness Affects a material’s durability Can be defined in two ways: -Scratch hardness -Indentation hardness](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-9.jpg)
hardness
Слайд 11Fatigue / creep
There are two important problems:
Fatigue(caused by cyclic loads)
Creep(components
Become permanently
damaged)
![Fatigue / creep There are two important problems: Fatigue(caused by cyclic loads) Creep(components Become permanently damaged)](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-10.jpg)
Слайд 12Springs are made from wire(wire made from ductile metal)
When the wire manufactured
![Springs are made from wire(wire made from ductile metal) When the wire](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-11.jpg)
, it is stretched beyond its elastic limit and even yield point
To put back the springiness to a spring , it is tempered
Слайд 13Comparing copper or aluminium
as materials for electrical wires
The thermal conductivity of copper
![Comparing copper or aluminium as materials for electrical wires The thermal conductivity](/_ipx/f_webp&q_80&fit_contain&s_1440x1080/imagesDir/jpg/377356/slide-12.jpg)
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.