Topic 4 - pt.2 Flashcards
physical properties
- mass = amount of matter contained within a specific material
- weight
- hardness = resistance of a material to penetration or scratching (affected by strength and plasticity of mat.)
mechanical properties
- tensile strength = ability of a material to withstand pulling forces (important for ropes, cables, etc)
- compressive strength = capacity of a material or structure to withstand forces trying to reduce size
- toughness = ability of a material to resist cracking (a material’s resistance to fracture when stressed)
aesthetic characteristics
- taste
- smell
- appearance
- texture
- colour
composite
reinforcing (strands, particles, poles) + matrix (e.g. glue)
- an example is concrete: poles are placed (reinforcing) to shape the structure and concrete is poured in the middle (matrix)
timber general knowledge
Man-made: plywood, MDF, particle boards (all composites)
- limited recycling so not sustainable
- more even
- can be as big as you want
Natura: oak, pine, beech
- looks natural (grew like that & a certain size)
- more sustainable and recyclable
- can shrink due to temp & moisture
- splitting, cupping, warping, bowing
metals
Ferrous: iron, steel
- contains iron –> rusts & magnetic
Non-ferrous: copper, gold, silver, aluminum
- doesn’t contain iron so doesn’t rust
- not magnetic
plastic
Thermoplastics: PET, PP, PS
- once set it can be reset/changed bc there are no cross-links (chains can move freely when heated)
- physical structure / molecular structure
- can be recycled
Thermosets: polyester, epoxy resin, urea-formaldehyde
- once set it can’t be reset or changed
- chemical structure = strands that hold it together (cross-links)
- limited recycling
metal crystals
- smaller crystals = harder but more brittle (grains packed closer) + cracks move easily across metal
- larger crystals = softer, more malleable metal + cracks take longer to cross the metal
- more dense = more brittle
- grain boundaries are weak spots
heat treatments
Annealing: heating metal to high temps & then cooling slowly –> large crystals form
- malleable & softer
Quenching: heating metals to moderate temp and cooling them quickly
- small crystals form –> harder but more brittle
Tempering: reheating quenched metal but to a much lower temp –> reduces brittleness but keeps hardness
- gets the best of both annealing and quenching
- more impact resistant
alloys
- mixture of metals
- e.g. brass = copper + zinc
textiles
Natural: cotton, wool, silk
- fibre –> stands –> weaved into longer strands –> yarn –> big sheets of fabric
- very ductile
Synthetic: polyester, nylon, lycro
- plastic (oil based)
- not sustainable
toughened/tempered glass
- heat treated to make it tougher
- shatters into small pieces
- used for car glass, furniture
seasoning of timber
Seasoning of timber:
- Air Seasoning (natural) –> no expensive equip. needed, small labour cost, env. friendly bc little energy used BUT takes longer than Kiln, large area needed
- Kiln Seasoning –> kills insects, requires little stacking space, dries quickly BUT expensive, requires supervision by skilled operator, uses lots of energy, gives weaker timber
why straws are hard
Straws need to resist deformation when force is applied, especially if someone bites or squeezes them slightly. A straw that is too soft can easily deform, blocking the flow of liquid or making it uncomfortable to use.
finishes - timber
- aesthetics: to improve the natural beauty of material
- function: to protect it from environmental impact, heat, moisture
- finished timber needs to be sanded with abrasive paper
