Materials for Machine Design Flashcards
Food of design
Materials
one that performs well,
is good value for money and gives pleasure to
the user - uses the best materials for the job,
and fully exploits their potential and
characteristics: brings out their flavor, so to
speak
Successful product
6 broad classes of materials
Metals
Glass
Polymers
Elastomers
Ceramics
Composites
The classes are classified based on common features like
Similar properties
Similar processing routes
Similar applications
Classes of engineering materials that have relatively high moduli.
They can be made strong by alloying and by
mechanical and heat treatment, but they remain
ductile, allowing them to be formed by
deformation processes.
Metals
Characteristics of the fracture that a high strength alloy produce
Tough ductile fracture
Like metals, they too have high moduli, but these materials are brittle
Ceramics and glasses
‘strength’ in tension of ceramics and glasses means
Brittle fracture strength
Strength in compression of ceramics and glasses
Brittle crushing strength
Materials that have no ductility.They
have a low tolerance for stress concentrations
(like holes or cracks) or for high contact
stresses (at clamping points, for instance).
Ceramics
______materials accommodate stress concentrations by deforming in a way which
redistributes the load more evenly; and
because of this, they can be used under static
loads within a small margin of their yield strength
Ductile
_______materials always have a wide scatter in
strength and the strength itself depends on the
volume of material under load and the time
for which it is applied
Brittle
They are stiff, hard and abrasion-resistant (hence their use for bearings and cutting
tools); they retain their strength to high temperatures; and they resist corrosion well
Ceramics
They have moduli which are low, roughly 5O
times less than those of metals, but they can
be strong - nearly as strong as metals
Polymers and elastomers
combine the attractive
properties of the other classes of materials
while avoiding some of their drawbacks.
They are light, stiff and strong, and they
can be tough
Composites
define the behavior of materials under the action of
external forces called loads.
Mechanical properties of materials
Enumerate the mechanical properties of materials
Strength
Elasticity
Plasticity
Hardness
Toughness
Brittleness
Stiffness
Ductility
Malleability
Cohesion
Impact strength
Fatigue
Creep
mechanical property that
enables a metal to resist deformation load. It is its capacity to
withstand destruction under the action of
external loads
Strength
the ability
of an object or material to resume its normal
shape after being stretched or compressed.
Elasticity
ability to
undergo some permanent deformation
without rupture(brittle)
Plasticity
The resistance of a material to force penetration or bending. It causes materials to resist scratching, abrasion, cutting or
penetration
Hardness
the ability of materials to oppose the scratches to outer surface layer due to
external force
Scratch hardness
It is the ability of materials to oppose the dent due to
punch of external hard and sharp objects
Indentation hardness
also called as dynamic hardness.
It is determined by the height of “bounce” of a
diamond tipped hammer dropped from a fixed height
on the material
Rebound hardness
It is the property of a material which
enables it to withstand shock or impact.
Toughness
Mechanical properties of materials which enables it to withstand
permanent deformation. Causes materials to break rather than bend under shock
or impact.
Brittleness
the resistance of a material to
elastic deformation or deflection
Stiffness
a property of a
material which enables it to be drawn out
into a thin wire
Ductility
a property of a material which permits it to be hammered
or rolled into sheets of other sizes and
shapes
Malleability
a property of a solid
body by virtue of which they resist from
being broken into a fragment.
Cohesion
ability of a metal
to resist suddenly applied loads
Impact strength
the long effect of repeated
straining action which causes the strain or
break of the material
Fatigue
slow and progressive deformation of
a material with time at a constant force.
Creep
reaction with oxygen in water and air.
Oxidation or rusting
Metals are hard, non-adhesive, cold and
smooth,they are very often shiny and strong.
They are also ductille and malleable, do not
break easily. Metals are very good conductors
of electricity, sound and heat. When
temperature rises they expand, and when it
falls, they always contract. They can be easily
welded to other metals
Physical properties
Most metal are recyclable and some metals
such as lead or mercury are toxic and they
are a danger for humans being and for the
environment.
Ecological property
Metals with iron
Ferrous metal
Areas of weaknessess
Dislocation
An alloy of carbon and iron
Carbon steels
mixture of two or more chemical elements and the
primary element is a metal.
Alloy
carbon content between 0,1%
and 0,3%
Mild steel
less ductile but
harder and tougher than iron, grey colour,
corrodes easily.
Mild steel
Contains 0,3% and 0,7% carbon.
Medium carbon steel
it’s used
for the manufacture of products which
have to be tough and hard wearing like
gears, tools, keys, etc
Medium carbon steel
contains between 0,7%
and 1,3% carbon
High carbon steel
Very hard and brittle material
High carbon steel
It’s used for
cutting tools and products which have to
withstand wear such as guillotine, springs,
etc.
High carbon steel
iron and chromium alloys, chromium
content between 13% and 27%.
Stainless steel
______ prevents rusting with an oxide film
Chromium
Used for cutlery, sinks, pipes,
car pieces, etc
Stainless steel
94% Fe, 3% Si, 2% Mg, S, P
Grey Cast Iron
brittle but
extremely hard and resistant, it corrodes by
rusting
Grey Cast Iron
pistons, machinery parts, streets
lamps, drain covers, tools
Grey Cast Iron
makes the alloy magnetic and improves
elasticity.
Silicon
makes the alloy harder and heat-resistant.
It’s used to make stainless steel.
Manganese
Chemical element added to alloy to improve strenght and prevents corrosion
Nickel
makes the steel harder, more heat-resistant
and prevents corrosion
Tungsten (W)
makes the alloy harder and tougher and
more rustproof.
Chromium
It’s the most abundant metal in the earth’s crust
Aluminum
Silvery white color, light, highly resistant
to corrosion, soft, malleable and ductile, low
density, good conductor of both electricity and
heat.
Aluminum
high voltage power lines, planes, cars,
bicycles, light metal work. roofing and windows
and doors units, decoration, kitchen tools and
drink cans.
Aluminum
It’s a pure metal that is the world’s third most
important metal, in terms of volume of
consumption.
Copper
a reddish-brown metal, ductile and
moderately strong, very good conductor of
electricity and heat,It corrodes very easily
Copper
Copper and zinc alloy
Brass
It’s gold in color. It has very
good anticorrosive properties and it’s
resistant to wear
Brass
It’s shiny and silvery white.
Magnesium
It’s very light, soft and
malleable, but not very ductile. It reacts
very strongly with oxygen
Magnesium
Fireworks, aerospace industry, car
industry.
Magnesium
It’s a shiny white metal.
• Properties: It doesn’t oxidize at room
temperatures, it’s very soft.
• Uses: Soft-soldering, tin foil and tin plate.
Tin
It’s a silvery grey metal.
• Properties: Soft and malleable. It’s toxic
when its fumes are inhaled.
• Uses: Batteries, it’s use as an additive in
glass for giving hardness and weight.
Lead
It’s an alloy of copper and tin.
• Properties: High resistant to wear and
corrosion.
• Uses: Boat propellers, filters, church bells,
sculpture, bearings and cogs.
Bronze
bluish grey shiny metal
Zinc
Anticorrosive, not very hard,
weak at low temperatures
Zinc
These materials are used for their electrical and thermal
conductivity, corrosion resistance, appearance and
color, and ease of working.
• They have the highest conductivity of the engineering
metals and are very ductile and easy to braze, and
generally to weld.
Copper
contain small amounts of
various alloying elements such as beryllium,
chromium, zirconium, tin, silver, sulphur or
iron.
High copper alloy
Element added to brass to enhance machinability
Lead
Added to brass to enhance strength
Tin
Copper zinc alloys are _______ up to about 37% zinc in the
wrought condition.
Single phase
Alloys with more than about 37% zinc are___________, and have
even higher strength, but limited ductility at room temperature
Dual phase
alloys of copper with
nickel, with a small amount of iron and
sometimes other minor alloying additions
such as chromium or tin.
• The alloys have outstanding corrosion resistance in waters, and are used extensively
in sea water applications such as heat exchangers, condensers, pumps and piping
systems, sheathing for boat hulls.
Copper nickel
contain 55 – 65% copper
alloyed with nickel and zinc, and sometimes
an addition of lead to promote machinability.
Nickel silver
Manufacturing process that is used in creating basic forms
Primary processes
Manufacturing process used to alter or add features
Secondary process
creates complex shapes from molten
metal
Casting
Metal casting that uses permanent molds into which low
melt point metals such as zinc are injected under
pressure
Die Casting
creates intricate wax patterns
that are coated with slurry, the wax melted out,
then filled with molten metal.
Investment casting
The process was originally invented for making
jewelry and, sometimes referred to as the lost-wax
process, has become a method for casting complex
parts such as turbine blades.
Investment casting
Type of casting machine for low melting metals such as zinc,
tin, and lead.
Hot chamber
Type of die casting machine for metal melted in a chamber
separated from the machine.
Cold chamber
Forging uses hydraulic die sets or open dies
and hammers to plastically deform usually hot
metal into net shapes, oftentimes starting with a rough approximation of the finished shape
called a blocked preform
Bulk/metal deformation
transforms mill products into finished
raw materials such as I-beams, plates, and
sheets. The process may be performed hot or
cold,
Rolling
Can produce moderately complex
shapes in parts that are up to 3 ft. long.
Forging
used to further reduce bar stock and
improve surface characteristics and strength
through a cold, die puling process.
Bar drawing
continues the process of bar drawing
by pulling ductile materials through increasingly
smaller dies to wind up with steel, aluminum, and
copper wire.
Wire drawing
Sheet metal is cut into smaller straight-edged pieces
by ______
Shearing
Sheet metal working /metal forming that gradually pushes the material into a die
cavity that deepens with each step through the die.
Drawing
Sheet metal working /metal forming that creates holes and slots where needed
Punching
Sheet metal working /metal forming that creates tabs and other features that run
perpendicular to the plane of the original material.
Bending
Sheet metal working /metal forming that shears the finished part from the
remaining coil material that has served to carry the forming part through the die
Blanking
Manufacturing process that uses various cutting tools, abrasive
wheels, as well as some unusual media such as
water or sparks, to remove material from
round and bar stock, castings, etc. to produce
accurate finished good
Machining
include sawing, turning,
boring, reaming, etc. and are oftentimes
performed as secondary operations to clean
up parts or to create surfaces that are suitable
for assembly.
Machining
one such process, where ductile metals
such as copper and aluminum are forced through
dies to produce common shapes such as copper
tubing or aluminum angles.
Extrusion
Major categories of machining
Cutting, abrasives, non-traditional
involves the forming of both
thermoset and thermoplastic materials usually by
molding but also by subtractive methods such as
machining.
Polymer processing
In __________ of polymer processing, an elastomer charge is placed
between heated die halves which are subsequently
closed to force the material into the shape of the
cavity.
Compression molding
________ uses an auger to soften plastic
pellets in a barrel and inject the resulting “shot”
under high pressure into a usually multi-cavity
mold.
Injection molding
another polymer
processing method that shapes sheets or
films of thermoplastic into cavities or over
plugs usually using vacuum or air to pull or
push the softened material against the
mold surfaces.
Thermoforming
common method for making
plastic bottles.
Blow molding
used to produce large
hollow shapes such as kayaks by relying on
the centrifugal force imparted to molten
plastic as it spins within a rotating mold.
Rotomolding
encompasses many final operations
that make a part ready for assembly
Finishing
where the different parts that
compose a finished product come together.
Assembly
Materials Selection Process
- Identify product design requirements
- Identify product element design requirements
- Identify potential materials
- Evaluate materials
- Determine whether any of the materials
meet the selection criteria - Select materials
