ME 224: MATERIALS SCIENCE
& ENGINEERING
Properties of Materials
By: Escarda, Donne Derick S. | Manliguis, Mel Ryan
Properties of Materials
There are, it is said, more than 50,000
materials available to the engineer.
In designing a structure or device, how
is the engineer to choose from those vast
menu of materials which best suits the
purpose?
1
Classes of Materials
Components such as metals and
alloys, polymers, new ceramics
2
Composite Materials
Combining the best properties of
the materials to make new
materials (such as fiberglass).
3
Natural Materials
Like wood and leather which
have important properties that is
still hard to beat in today’s
materials
Plastic-Handled Screwdriver
A typical screwdriver has a shaft and blade made of a highcarbon steel, a metal.
1
Steel; high modulus
modulus measures the resistance of material to
elastic deflection or bending. The Shaft should yield
high modulus to resist blending and twisting.
2
Handle; polymethylmethacrylate
Otherwise known as PMMA, plexiglass or perspex.
Easy to mold when hot (compared to wood).
aesthetic reasons: appearance, feel, texture, low
density.
ease of frabrication
cheaper
Turbofan Blades
Are made from a titanium alloy, a metal. This has a
sufficiently
good
modulus,
yield
strength,
and
fracture
toughness.
The metal should resist:
1
Fatigue; due to rapidly fluctuating loads.
2
Surface wear; from striking everything from
water droplets to large birds.
3
Corrosion; important when taking off over the
sea because salt spray enters the engine
Other important consideration: Density
The heavier the engine, the less the pay-load the
plane can carry.
Carbon-fiber reinforced polymers (CFRP) - density less
than one-half of that of titanium
Spark Plug Materials in Internal
Combustion Engines
1
Electrodes
-made of tungsten alloys due to their
resistance to:
• Thermal fatigue from fluctuating temperatures.
• Wear from spark erosion.
• Oxidation and corrosion caused by upper-cylinder
gases with sulfur and lead.
2
Insulation
-made of alumina (a ceramic) because it:
• Provides electrical insulation.
• Resists thermal fatigue, oxidation,
and corrosion.
The Classes of Engineering Materials
from which articles are made.
1
Metals and Alloys
They are often used in combination with other materials
to form composites (e.g., steel-cord tires).
2
Polymers
They are sometimes reinforced with fibers to create
composites, such as CFRP (Carbon Fiber Reinforced
Polymer) and GFRP (Glass Fiber Reinforced Polymer).
3
Ceramics
They are used in composite materials such as wirereinforced cement.
The Classes of Engineering Materials
from which articles are made.
4
Composite
Composites are materials that combine two or more of these
classes to improve mechanical properties.
How the properties of engineering
materials affect the way in which
products are designed
1
Intrinsic
These are inherent properties of a material that are
independent of external factors
2
Polymers
These are properties related to the practicality, economic
feasibility, and aesthetic aspects of a material
3
Design
Both types of properties must be balanced in the design
process to create functional, cost-effective, and visually
appealing products.
Metals
Metals are opaque, lustrous elements that are
good conductors of heat and electricity. Most
metals are malleable and ductile and are, in
general,
denser
substances.
than
the
other
elemental
Model Traction Engine
A fully working model, one-sixth full size, of a steam traction
engine of the type used on many farms a hundred years
ago. The model can pull an automobile on a few litres of
water and a handful of coal
The use of metals in the traction engine:
1
Mild steel; yield strength σy of around 220 MPa;
easy to cut, bend or machine to shape; cheap
2
Gear-wheel teeth or drive shafts; made from
medium-carbon, high-carbon or low-alloy steels
to give extra strength
The use of metals in the traction engine: Fire grate
3
4
Stainless steel is used in several places.
Cast Iron; Although this is rather brittle, it is
fine for low-stressed components like the
cylinder block; has several advantages over
mild steel.
The use of metals in the traction engine: Valves
5
Brass; stronger than copper, fairly corrosionproof, easier to machine
6
Nickle; The superb creep resistance of the
nickel-based superalloys is a key factor in
designing the modern gas-turbine aeroengine.
Drink Cans
Alluminium-base metals is the driving material for
this because:
To avoid seams
Can must not leak
Recyclable
Non-toxic
Light
Aluminium is the best choice for this.
Artificial Hip Joints
The titanium alloy implant for a replacement hip joint.
The long shank is glued into the top of the femur. The
spherical head engages in a high-density polythene socket
which is glued into the pelvic socket.
Data for Metals
Table 1.6 Properties for Generic Metals
ME 224: MATERIALS SCIENCE
& ENGINEERING
Properties of Materials
By: Escarda, Donne Derick S. | Manliguis, Mel Ryan