1. business and industrial
2. chemicals industry
3. plastics and polymers

16/04/2015
The Technological World -Manufacturing technical
objects
Manufacturing technical
objects
• when building a technical object we must
consider the stresses the object will be
subject to and properties of materials
• 3 things to consider:
– 1. Constraints and deformations
– 2. Properties of materials
– 3. Types of materials, characteristics,
degradation and protection
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16/04/2015
Constraints and Deformations
• Technical objects are often subjected to
external forces
• Constraints are used to describe the
different types of forces that an object can
undergo
• A deformation describes the change in
shape that may occur as a result of
exposure to a constraint
Types of Constraints
Type of Constraint
Description
Compression Crushing
force
Tension
Stretching
force
Torsion
Twisting
Force
Bending
force
Deflection
Shearing
Cutting force
Symbol
Example
Squeezing a can
rock climbing
tug of war
· wringing out a
towel
· a fish bending a
fishing rod
· scissors cutting
paper
· hedge cutters
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Types of deformations
Types of
Deformations
Description
Elastic
Temporary change in shape,
returns to original shape when
stress is removed
Plastic
Permanent change in shape even
when constraint is removed
Fracture
Constraint causes material to
break
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Properties of Materials
• Mechanical Properties describe how a
material will react when subjected one or
more of the constraints:
• 1) Hardness – is the ability to resist dents
or marks
• 2) Elasticity – able to return to its original
shape (reverts back to original after
compression, deflection, tension or
torsion)
• 3) Resilience – resists shocks without
breaking
• 4) Ductility – can be stretched without
breaking; ie. into wires
• 5) Malleability – can be flattened or bent
without breaking
• 6) Stiffness – able to keep its shape
(Resists deflection especially; not elastic)
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• Other important properties of materials
are:
• 1) Resistance to corrosion – will not react
with water, oxygen, acids, salts or bases,
resists rusting or colour changes
• 2) Electrical conductivity – allows
electricity to flow
• 3) Thermal conductivity – able to allow
heat transfer
Materials, characteristics,
degradation and protection
• all materials degrade at different rates
• degradation occurs due to environmental factors
• some procedures allow a material to be protected
in order to slow down degradation
• there are 5 categories of materials:
–
–
–
–
–
A) Wood and modified wood
B) Ceramics
C) Metals and alloys
D) Plastics
E) Composites
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• A) Wood and modified wood
• Characteristics
– Different woods have different properties
• Deciduous trees – hardwood
• Coniferous trees – soft, elastic woods
– used for hardness, resilience, elasticity
– low thermal and electrical conductivity
– light weight
• A) Wood and modified wood
• Protection
– degradation happens due to living organisms
(fungus, insects etc) and water (wood rots)
– can be coated in basic solution containing
copper (green)
– Pesticide treatments
– can be heated to a high temperature (more
expensive)
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• B) Ceramics
• Characteristics
– often made with sand or clay
– Produced by heating and cooling
– used for their low electrical and thermal
conductivity
– hardness, resistance to corrosion
– Can be brittle
– extremely resilient if baking process is
controlled
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• Protection
– ceramics are very resistant
– avoid exposure to acids, bases and excessive
thermal shock
• C) Metals and alloys
– ductile, malleable, good conductors of heat
and electricity
– alloys are metals mixed with other metals or
non-metals to make them more useful
• Protection
– most damage is due to rusting (oxidation)
– metals can be coated to protect them (paint,
grease, other metals, phosphates)
– we can also make metals harder by "quench
hardening" or "tempering them" (rapidly
heating or cooling them)
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• D) Plastics
– plastics are made from fossil fuels
– Can be heated and moulded
– Poor conductors of heat and electricity
– other substances can be added to obtain
specific properties
– thermoplastics soften when heated and
harden when cooled
– thermosetting plastics remain hard even when
heated(cannot be recycled)
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• Protection
– damage occurs due to 3 main reasons:
• 1. water absorption (use a waterproof
coating)
• 2. oxidation (add antioxidant materials to
plastic)
• 3. uv rays (add pigments that absorb uv
rays)
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• E) Composites
– a combination of materials from different
categories
– The properties of the composite are better
than the individual materials
• contains 2 parts:
– 1. a matrix (skeleton, gives shape)
– 2. a reinforcement (fills the matrix to give
strength)
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• Protection
– both the matrix and the reinforcement need to
be protected (depends on type of material)
– strong holding between the two parts is
important
• Uses
– used in airplane wings, engines, brakes
– used in sporting equipment (hockey sticks,
helmets)
– used in bullet proof vests
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