Download Materials and their Properties

Chapter 12
404
p. 386-421
• Since the time of prehistoric Man, humans have
been manipulating different materials to build
tools and structures to live in. The most
common materials are:
• Wood
• Ceramics
• Metals
• Alloys
• Plastics
• Modified Wood
• Composites
HISTORY of MATERIALS (do not copy)
• Different types of rock were used to build
initial tools and wood was most likely one
of the first materials used to build
dwellings and furniture.
• Ceramic structures have been found in
many historical digs. The earliest ceramics
were pottery articles made from clay.
HISTORY (Continued)
• The arrival of plastics many centuries later
were very significant in the advancement
of the use of material.
• With time, composites were added to the
mix allowing the advancement of the
manufacturing of technical objects.
WOOD p. 390-391
•
Primary material used by man for construction
and heating.
• 2 types of wood:
– Hardwood
– Softwood
• The following properties greatly influence the
choice of wood for construction:
– Hardness * low thermal/electrical conductivity
– Elasticity * pliability and ability to be shaped
– Colour & shades * texture and grain
– Resilience and toughness * weight
• Modified wood consists of
wood and additional products
such as glue, plastics and
preservatives. Some
examples:
• Plywood
• Particle board
• Fiber board
• Since wood is an organic
substance it tends to degrade
very rapidly.
• Products such as paint, stain,
hardeners and varnish, protect
the wood from weathering and
infestation.
CERAMICS p. 392-393
• Ceramics have low
electrical conductivity
properties, thus making
great insulators for
electrical circuits.
• Their durability and
hardness make them very
useful for construction bricks, ceramic tiles,
carbide blades, etc.
• Ceramics are very heat resistant and this makea
them appropriate for kitchen appliances such as
ovens and heating dishes.
• Ceramics do not corrode and therefore are very
useful for ducts and drains.
• Just the same, ceramics are fragile and can be
easily broken. Care must be taken in the choice
of raw material and the method for baking.
• Certain acids and bases (sulfuric acid and
calcium hydroxide) can degrade ceramics.
• Extreme changes in temperature may also crack
and destroy ceramics.
METALS p. 394-395
• Metals are made from extracts from mineral ore and are
often shiny.
• This material displays good thermal and electrical
conductivity.
• Many are valued for their malleability (pliability) and
ductility (deform under tension - stretch).
• Since metallic substances are rarely pure in nature, they
are often classified as alloys.
• They are produced because of their density, reactivity,
electrical and thermal conductivity, and tensile strength
and shear strength.
• Corrosion is caused by oxidation of the substances.
• Coating and surface treatments usually increase the life of
the material and decrease degradation.
Alloy: A
mixture of a
metal with
one or more
other
substances,
which can be
metal or
nonmetal. copper, magnesium, manganese, silicon and
zinc.
PLASTICS p.396-397
•
Plastics are often produced from fossil fuels such as
petroleum and natural gas.
•
Plastics can be molded because they are malleable.
•
Thermoplastics
–
–
–
–
–
Do not undergo chemical change when heated
Can be molded over and over again
Can be manipulated (molded) when heated
When cooled, the structure holds its shape
Not biodegradable but most can be recycled
• Thermosetting plastic
–
–
–
–
–
–
Always remains hard even when heated
Once it take shapes its form can not be altered
If overheated it will decompose
Melamine and polyesters (nylons) are examples
Harder and more resilient than thermoplastics
In Quebec cannot recycle thus have negative effects
for the environment
– Poor conductors
• Degradation
– Appears as cracks or change of color
– Degradation is irreversible
– Affected by certain liquids like acids, oxidation and
ultraviolet rays from the sun
– Addition of waterproof coatings, antioxidants and
pigments can reduce degradation and protect the
plastic
COMPOSITES p. 399-400
•
Made from two or more materials from different
categories.
•
Two main components:
– Matrix (original material) that forms structure
– Reinforcement (inserted into matrix to strengthen it)
•
Degradation
– Deformation or fracture
– Avoid extremes: shocks, impact, repeated stress
– Do not survive in corrosive solutions
MECHANICAL PROPERTY
p. 388
• The term Mechanical Property defines how a material will respond
when subjected to different forces and constraints. The most
common mechanical properties are:
• Elasticity
• Malleability
• Stiffness
• Hardness
• Resilience
• Ductility
• Other properties are also very important to consider when choosing
a material for construction:
Electrical
Thermal
Resistance to corrosion
• Ex: If a car company is planning a new model of vehicle they will try
to choose a material for the body structure that will be resistant to
road salt and therefore rust. The use of different metalloids for
hubcaps is a good example.
• The study of stress factors and their
effects on materials will help determine the
suitability of a particular material for a
specific manufacturing project.
• Manufactures refer to the word constraint
when considering stress factors.
Main types of Constraints
•
•
•
•
•
•
Tension or tensile (pulling)
Compression (pushing)
Torsion (twisting)
Shearing (cutting)
Deflection (bending)
Temperature(which can cause
deformation)
p. 387
Types of Deformation p. 387
• FRACTURE: is when the force being applied is
large enough to break the object.
• ELASTIC: The constraint changes the form of
the material but once the force is removed the
materials returns to its original shape.
• PLASTIC: the force causes a permanent
deformation that remains even when the the
force is removed.
Mechanical Properties of Materials
Mechanical Property
Definition
Hardness
Ability to resist indentation or
abrasion
Elasticity
Ability to return to original shape
after undergoing a constraint
Resilience
Ability to resist shocks without
breaking
Ductility
Ability to be stretched without
breaking
Malleability
Ability to be flattened or bent
without breaking
Stiffness
Ability to retain shape when
subjected to various constraints
**Degradation
of a Material:
Is the decline
in some of its
properties due
to the effects
of the
surrounding
environment.
**Protection
of a
Material: Is
the
application
of
procedures
that prevent
or delay its
degradation