Transcript of Parts of objects can be subjected to one or more external FORCES Remember forces? An action that...
- Slide 1
- Slide 2
- Parts of objects can be subjected to one or more external
FORCES Remember forces? An action that can change the motion of an
object, or deform the object, by pushing or pulling on it.
- Slide 3
- Materials tend to be deformed by forces A constraint describes
the effect of external forces on a material Compression, tension,
torsion, deflection, shearing
- Slide 4
- Other types of compression: Compression shorts for sports
Squeezing a wet sponge Crushing a pop can
- Slide 5
- Other examples: Copper stretched into a wire Two teams of
tug-of-war
- Slide 6
- Slide 7
- Examples: An earthquake twisting a bridge Hands wringing a wet
towel
- Slide 8
- What other examples can you think of?
- Slide 9
- Scissors and metal cutters
- Slide 10
- Slide 11
- Three types: elastic, plastic, fracture ELASTIC: temporary
change in shape PLASTIC: permanent change FRACTURE: breakage
- Slide 12
- Slide 13
- Plastic deformation of piece of railway track
- Slide 14
- before and after
- Slide 15
- Slide 16
- The mechanical properties of a material describe how it reacts
when subjected to one or more constraints Hardness, elasticity,
resilience, ductility, malleability and stiffness
- Slide 17
- Hardness is the ability to resist indentation or abrasion
- Slide 18
- Elasticity is the ability to return to their original shapes
after undergoing a constraint
- Slide 19
- Resilience is the ability to resist shocks without
breaking
- Slide 20
- Ductility is the ability to be stretched without breaking The
opposite of ductile is brittle
- Slide 21
- Malleability is the ability to be flattened or bent without
breaking
- Slide 22
- Stiffness is the ability to retain shape when subjected to
various constraints
- Slide 23
- Resistance to corrosion electrical conductivity thermal
conductivity
- Slide 24
- Ability to resist corrosive substances (water, salt, fumes)
which can cause damage like rust
- Slide 25
- Ability to carry an electric current
- Slide 26
- Ability to transmit heat
- Slide 27
- Degradation of a material is the decline in some of its
properties This is due to the effects of the surrounding
environments climate, humidity, chemical Examples : old
photographs, rust on cars What else degrades over time?
- Slide 28
- We can protect material by treating the material Rust-proofing
of cars 2 ways
- Slide 29
- Slide 30
- Wood Ceramics Metals and alloys Plastics Composites
- Slide 31
- Wood comes from trees! There are 2 types of wood : hardwood and
softwood Categorized based on their hardness Hardwood : maple, oak
(deciduous trees) Softwood : pine or spruce (conifers)
- Slide 32
- Considerations: Species of tree used Speed of growth and
injuries Water content
- Slide 33
- Hardness, elasticity, resilience and toughness Low thermal
conductivity
- Slide 34
- Made from wood, glue, plastics and preservatives Modified wood
is treated wood or a material made from wood mixed with other
substances Plywood, particleboard and fibreboard Why do we need
modified wood? Arent the trees good enough?
- Slide 35
- Resistance to cracking, shrinking and twisting/warping, it is
very strong Layers are glued together, grain opposite
(perpendicular grain)
- Slide 36
- Made from wood particles like wood chips and shavings and
sawdust Pressed together with resin Cheap to make, very dense, not
as strong as plywood
- Slide 37
- sometimes called MDF for medium density fibreboard Made from
wood fibers by breaking down the hardwood or softwood and mixing it
with wax and resin It is denser than plywood Used in manufacturing
of furniture More dense than particle board
- Slide 38
- Wood can degrade quickly because it is organic We treat wood to
prevent it from rotting The wood can be dipped in an alkaline
solution containing copper : greenish wood Also can heat wood to a
very high temp, expensive treatment
- Slide 39
- Dipped wood for deck building Heat treated wood for
flooring
- Slide 40
- Made from heating oxides like SiO 2 When the raw material is
heated, the water evaporates and the bonds between the compounds
are rearranged Ceramics are always solid at room temperature
- Slide 41
- Traditionally clay and sand
- Slide 42
- Low electrical conductivity, used as insulators High degree of
hardness used for bricks & building materials like tiles and
also as cutting tools Heat resistant and low thermal conductivity
so used a lot in the kitchen, dishes, ovens Resistant to corrosion
Fragile, can break easily unless treated
- Slide 43
- Quite durable, think archaeological digs Strong acids and
strong bases can degrade ceramics significantly (Breaking Bad
season 1 bathtub scene?) Can deteriorate with sudden thermal shock
Glass is a type of ceramic
- Slide 44
- Pot-in-pot refrigerator Zeer fridge Easy to make, very
efficient, cheap!
- Slide 45
- METALS METALS are made from mineral ore, shiny Good thermal and
electrical conductivity Some are ductile and malleable ALLOYS
ALLOYS are a mixture of a metal with one or more other substances
which may be metallic or non-metallic Metallic materials are rarely
pure metal
- Slide 46
- Ferrous means with iron, examples are cast iron and steel
Nonferrous without iron, examples are aluminum alloys, brass,
bronze
- Slide 47
- Main degradation is oxidation which causes corrosion They are
treated with coatings Coating can be metallic (zinc, chrome, gold,
silver, nickel, aluminum, lead) Coating can be non-metallic (paint,
enamel, grease, resin)
- Slide 48
- Slide 49
- An alloy made mostly from iron and carbon Heat treated
- Slide 50
- Made from petroleum and natural gas Made of polymers and other
substances Two types THERMOPLASTICS and THERMOSETTING PLASTICS
- Slide 51
- Plastic that becomes soft enough when heated to be molded or
remolded and that hardens when cooled to hold its shape of plastics
are thermoplastics Containers Recyclable (codes 1-6)
- Slide 52
- What else can you think of?
- Slide 53
- These plastics remain hard even when heated If heated to its
decomposition temp (max temp) then it will decompose Melamine,
polyester Harder and more resilient than thermoplastics Not
recyclable Kayaks, cafeteria trays
- Slide 54
- Famous Kingston Penn escape done with cafeteria trays!
- Slide 55
- Cracks can form over time along with colour fading Slow
degradation but irreversible Different methods of protection
include waterproofing, antioxidant additions, pigmentation
- Slide 56
- composites
- Slide 57
- Formed by combining materials from different categories to
obtain material with enhanced properties 2 main components : matrix
and reinforcement
- Slide 58
- No not the movie The matrix is the skeleton of the material and
gives it shape It surrounds and supports the reinforcements The
reinforcements are inserted into the matrix to strengthen it
- Slide 59
- Plastic reinforced with fiberglass is used in airplanes:
plastic is the matrix and fiberglass is the reinforcement The
properties of the two are combined to obtain a material that is
stiff and resilient
- Slide 60
- Aerospace Sports arts/music instruments Engines and braking
systems for high performance Military and police bullet
proofing
- Slide 61
- Deformation or fracture of matrix Loss of adherence between
matrix and reinforcement Protection by testing for correct material
mix and testing for adherence in conditions present
- Slide 62
- worksheet