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
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
