Chapter 1: Materials and their properties Flashcards
Definition of strength
the amount a material can withstand a force applied to it
Definition of ductility
the amount a material can be deformed
Definition of toughness
the amount a material can withstand an impact without breaking
Definition of hardness
the amount a material can resist wear and abrasion
Definition of stiffness
the amount a material can resist bending
Definition of brittleness
the potential for a material to shatter when in contact with a force
Definition of malleability
the amount a material can be deformed without rupturing
What is Young’s Modulus
The ratio of stress to strain of a material. it shows how stiff a material is
FORMULA: STRESS/STRAIN
Formula for stress
Stress = force/cross-sectional area
units for stress is in* N/mm^2*
Formula for strain
Strain = change in length/original length
no units!
Type of strengths
Tensile: ability to resist a pulling force
Compressive: the ability to resist a squeezing force
Torsional: the ability to resist a twisting force
Give examples of ferrous metals, and non-ferrous
Ferrous metals and alloys:
* cast iron
* low and high carbon steels
* steel alloys (stainless steel).
Non-ferrous metals and alloys:
* aluminium
* copper
* lead
* zinc
* alloys (brass and bronze).
What is annealing?
-modifying the structure of metals-
A heat treatment that makes a metal softer and easier to work with (more malleable/ductile)
* metal is heated to specific temp/colour, allowed to cool down after
What is hardening?
a heat treatment that increases the hardness & strength material (due to changed in arangement of atoms)
* Heat to a temp a bit above the lower critical point, soaks (often oil/brine) at that temp so grains have time to rearrange
* tempered: to remove some of the brittleness
* quenching: rapid cooling of a hot metal by immersing in a liquid (oil)
What is normalising?
A heat treatment that results in metal that is tough, with some ductility.
* Metal is heated to temp under melting point, cools in the air
What is cold working?
A process of strengthening metals through plastic deformation.
Metals become harder to resist any further change.
-non heat process-
eg: hammering
What is corrosion?
a reaction between the surface of the material and the environment that consumes some of its material.
* often possible to alter effects of environment by managing corrosion or adding/subtracting carbon (to change structure of surface. )
How to add or subtract carbon in steels?
Adding:
* heat the steel part until it becomes cherry red, then dip it into the carbon powder. Do this a few times and some of the carbon powder will be absorbed into the steel surface.
* Using a wire brush, clean off the excess carbon
* (complete hardening process): heat to cherry red, and quench in oil. (tempering is not needed)
Difference between thermoplastic and thermosetting polymers
Thermoplastic: recyclable, can be reshaped and reheated
thermosetting: not recyclable, cannot be reshaped and reheated
ABS
thermoplastic
recycling number 9:
* strong
* rigid
* harder and tougher than polystrene
1.plastic pipes
2.children’s toy
Polystyrene
thermoplastic
recycling symbol 6:
- good toughness
- good impact strength
1. packaging
2. foam cups
Acrylic
thermoplastic
Recycling symbol 7:
* transparent
* hard wearing
* not shatter
1. plastic windows
2. bath tubs
Polyester resin
thermosetting
- stiff
- brittle
- good strength
1. suitcases
Nylon
thermoplastic
Recycling number 7:
* ductile
* durable
1. gear wheels
2. bearings
melamine resin
thermosetting
- stiff
- hard
- strong
1. kitchen worktops
Epoxy
thermosetting
- stiff
- brittle
1. printed circuit boards
CRP
composite
- carbon fibres in resin matrix
- low density
- high strength
1. aircraft structure
GFP
composite
- glass fibres in resin matrix
- high strength
- low density
1. water tanks
Plywood
composite
- layers of wood bonded at right angles
- uses adhesives
- smooth surface
1. furniture making
MDF
composite
- wood fibres and adhesive matrix
- smooth
- able in veneered form
1. furniture, internal panelling
OBS
composite
- strands of wood compressed with adhesive matrix
- more uniform
- lower cost
1. walls, roof decking
structural concrete
composite
- most common
- concrete reinforced with steel bars to increase tensile strength
1. bridges
