School of Biomedical Engineering
International University – Vietnam National Universities HCMC
Machine Design
Engineering Materials
and their Properties
Contents
1
Classification of Engineering Materials
2
Physical properties
3
Mechanical properties
4
Chemical properties
Materials Science and Engineering
structure • arrangement of internal components
• subatomic
• atomic
• microscopic
• macroscopic (bulk)
characterization
properties
processing
• method of
preparing material
performance
• behavior in a
particular
application
• material characteristic
• response to external
stimulus
• mechanical, electrical,
thermal, magnetic,
optical, deteriorative
Classification of Materials
Metals
Ceramics & Glasses
Polymers
• good conductors of
electricity and heat
• lustrous appearance
• susceptible to
corrosion
• strong, but
deformable
• thermally and
electrically insulating
• resistant to high
temperatures and
harsh environments
• hard, but brittle
• very large molecules
• low density, low weight
• maybe extremely
flexible
Classification of Materials: A Few
Additional Catagories
Biomaterials
Semiconductors
Composites
• implanted in human
body
• compatible with
body tissues
• electrical properties
between conductors
and insulators
• electrical properties
can be precisely
controlled
• consist of more than
one material type
• designed to display
a combination of
properties of each
component
Intel Pentium 4
fiberglass surfboards
Why study materials?
❖ applied scientists or engineers must make material choices
❖ materials selection
▪ in-service performance
▪ deterioration
▪ economics
BUT…really, everyone makes material choices!
aluminum
glass
plastic
Classification of Materials
Classification of Engineering Materials
The engineering materials are mainly classified as :
1. Metals and their alloys, such as iron, steel,
copper, aluminium, etc.
2. Non-metals, such as glass, rubber, plastic, etc.
The metals may be further classified as :
(a) Ferrous metals,
(b) Non-ferrous metals.
Selection of Materials for Engineering
Purposes
The following factors should be considered while
selecting the material :
1. Availability of the materials,
2. Suitability of the materials for the working conditions in
service.
3. The cost of the materials.
Classification of Engineering Materials
Metals
Semiconductor
Steel reinforced
concrete
Polymers
Ceramics
Concrete
Physical properties
❖colour –light wave length
❖specific heat – the heat required to
raise the temperature of one gram of a
substance by one degree centigrade
(J/kg K)
Physical properties
❖density – mass per unit volume
expressed in such units as kg/cm 3
❖thermal conductivity – rate at
which heat flows through a given
material (W/m K)
Physical properties
❖melting point – a temperature at
which a solid begins to liquefy
❖electrical conductivity – a measure
of how strongly a material allows the
flow of electric current (Ω⋅m)
Physical properties
❖Optical properties – response to light
▪ index of refraction – bending of light
▪ transparent – light passes through
▪ translucent – some light passes
through but no distinct image
▪ opaque – no light passes through
Physical properties
❖coefficient of thermal expansion –
degree of expansion divided by the
change in temperature (m/°C)
Mechanical properties
❖tensile strength – measures the force
required to pull something such as rope,
wire, or a structural beam to the point
where it breaks
❖ductility – a measure of how much strain
a material can take before rupturing
Mechanical properties
❖malleability – the property of a material
that can be worked or hammered or
shaped without breaking
❖brittleness –breaking or shattering of a
material when subjected to stress (when
force is applied to it)
Mechanical properties
❖elasticity – the property of a material
that returns to its original shape after
stress (e.g. external forces) that made it
deform or distort is removed
❖plasticity - the deformation of a material
undergoing non-reversible changes of
shape in response to applied forces
Mechanical properties
❖toughness – the ability of a material to
absorb energy and plastically deform
without fracturing
❖hardness – the property of being rigid
and resistant to pressure; not easily
scratched
Mechanical properties
❖machinability – the property of a
material that can be shaped by
hammering, pressing, rolling
Chemical properties
❖corrosion resistance - a material's
ability to resist deterioration caused by
exposure to an environment
Properties of Materials
Which properties do the following materials possess?
Material
Properties
Aluminium
lightness; strength
Rubber
elasticity; insulation
Ceramics
thermal resistivity
Steel
strength
Copper
conductivity; corrosion resistance
Lead
high density; ductility
Nylon
strength; toughness
Cast iron
damping capacity
Wood
insulation; environmental friendliness
Properties of Materials
Find application for the following engineering materials:
Material
Applications
Aluminium
foil; aircraft; window frame
Rubber
tyres; seal; gasket
Ceramics
furnace; brick
Steel
section; pipe
Copper
pipe; cables
Lead
storage battery; radiation protection
ballast; bullets
Nylon
rope; clothing
Cast iron
engine block; valves
Wood
furniture; deck
Physical Properties of Metals
Physical properties of metals
Material with greatest density
Tungsten - 19300 kg/m3
Uranium - 19100 kg/m3
Lead - 11340 kg/m3
Steel - 7800 kg/m3
The strongest material
Material
Tensile Strength
UTS (Ultimate Tensile
Strength)
Carbon nantotubes
62000 MPa (theoretical
300000 MPa)
48000 kNm/kg
Carbon fiber
5650 MPa
3200 kNm/kg
Glass fiber
4700 MPa
1340 kNm/kg
Spider web
1000 MPa
900 kNm/kg
high-strength steel
1200 MPa
154 kNm/kg
The best conductor
Material
Silver
Conductivity
63 x 106 S/m (1/ohm)
Copper
59.6 x 106 S/m (1/ohm)
Gold
45.2 x 106 S/m (1/ohm)
Aluminium
37.8 x 106 S/m (1/ohm)
The best insulator
Material
Specific resistance
Polyethylene terephthalate (PET)
1020 ohm
Glass
1014 ohm
Rubber
1013 ohm
Material Strength and Stiffness
The standard tensile test is used to obtain a variety of material
characteristics and strengths that are used in design. The load is
converted to stress by the calculation
Material Strength and Stiffness
The deflection, or extension of the gauge length, is given by l − l0 where l is
the gauge length corresponding to the load P. The normal strain is calculated
from
Stress-strain diagram obtained from the standard tensile test
(a) Ductile material; (b) brittle material.
Material Strength and Stiffness
Material Strength and Stiffness
Hooke’s law
where E is called Young’s modulus or the modulus of elasticity
True strain is the sum of the incremental elongations divided by the current gauge length
at load P,
Classification of Engineering Materials
The maximum shear stress τmax is related to the angle
of twist θ by
where
θ is in radians,
r is the radius of the specimen,
l0 is the gauge length,
G is the material stiffness property called the shear modulus or the modulus of
rigidity.
Classification of Engineering Materials
The maximum shear stress is also related to the applied
torque T as
where
J = ½ πr4 is the polar second moment of area of the cross section.
Processes
Forging - a manufacturing process where
metal is shaped by plastic deformation
under great pressure into high strength
parts.
Casting – pouring or injecting molten metal
into a mold containing a cavity with the
desired shape
Processes
Hot-Working Processes
Hot working: such processes as rolling, forging, hot extrusion, and hot
pressing, in which the metal is heated above its recrystallation
temperature.
Cold-Working Processes
Cold working: the forming of the metal while at a low temperature (usually
room temperature).
In contrast to parts produced by hot working, cold-worked parts have a bright
new finish, are more accurate, and require less machining.
Cold-Working Processes
General Classes of Materials
Young’s modulus E versus density ρ
for various materials.
School of Biomedical Engineering
Thank You !