https://padlet.com/matthew_slark/vslftgo70qwa Revision for Unit 203 en-us 2017-09-18 17:55:31 UTC 2026-01-30 08:13:25 UTC hello@padlet.com https://padlet-assets.s3.amazonaws.com/icons/Terminator.png matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/187489932 F ∝ x
Force is directly proportional to Extension
F = kx
k is a constant it is the force constant or Stiffness constant . unit is Nm^-1]]> 2017-09-14 10:29:50 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/187489932 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/188601166 P is the limit of proportionality, this is where the object i.e. a spring no longer obeys hooks law
Just after the limit of proportionality is the elastic limit this is where the object will be permanently deformed and no longer will return to its original shape ]]> 2017-09-18 17:58:02 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/188601166 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/188626077

]]> 2017-09-18 18:46:25 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/188626077 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/188631839  Strength   | Strong is the ability to resist forces without breaking. Different types are; tensile strength, compressive strength and torsional strength
Density  | A dense material has a large mass per volume. Density is dues to the weight and the size of a materials atoms and how compact it is.
Stiffness  | Stiff means that a material is hard to stretch or bend. A metal sheet is stiffer than a polythene (plastic bag) sheet with the same dimensions.  Stiffness is measured by Young's modulus 
Hard  | A Hard material means that it is difficult to dent the surface. (i.e. steel knife is harder than a plastic one) a lot of ceramic materials are very hard
Brittle  | Brittle is if it breaks cleanly leaving very few or no jagged edges. Glass is brittle due to cracks which propagate easily through its structure.
Tough  | Tough the material does not break cleanly; a tough material is resistant to crack propagation. Tough is opposite to brittleness a tough material absorbs a lot of energy before it breaks.
Elastic  | An Elastic material will return to its original shape after stretching. Rubber bands are elastic and metals can be when the gap between atoms extends slightly.
Plastic  | Plastic is a material that goes through permanent deformation when stretched.
Ductile  | Ductility is when a material is easily drawn into a wire. E.g. cooper is more ductile than tungsten. Metals are ductile due to their non-directional metallic bonds allowing atoms to slide past one another.
Malleable   | A malleable material means it is easily formed into another shape by hammering it or pressing it. ]]> 2017-09-18 19:00:59 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/188631839 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/193356510 Quenching the steel in oil, water or molten baths. after heating it up to its ICP( upper critical point)
This form martencite ehcih is very hard and brittle]]> 2017-10-03 11:29:44 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/193356510 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/193357156 Internal stress casued by rolling, bending and forging steel. this stress is removed by heating the steel above its UCT ( upper critical temperature) then it is quenched then cooled in air over a long period of time.
typical heat range is 830-960 degrees C.
normalizing enhances machineability it also minimises the amount of distortion in the future ]]> 2017-10-03 11:32:22 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/193357156 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/193358399 Alters physical and/or chemical structure of a material. increasing ductility and reducing hardness.
this makes the metal more workable. (softens it
To anneal a material you heat it above its recrystalisation temperature and then cooled ]]> 2017-10-03 11:36:53 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/193358399 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/193359427 tempering is used to increase toughness.
Performed after hardening,  it is used to reduce excess hardnsss. done by heating the metal to just below the critical point for a period of time. then allowing it to coo in air.


]]> 2017-10-03 11:40:20 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/193359427 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/204779807 Vickers: This test is used for 'micro-hardness' like small parts or thin sections for aircraft parts. it uses diamond indenter. the material needs to be highly polished. the angle between the sides is 136 degrees.
a test force is applied  for 10-15 seconds.
HV = force/ area of indentation

Brinell: generally used for materials with a rough surface and does not require polishing. like castings and forging. a Spherical indenter  with a fixed diameter is applied. the indentation is measured by a Brinell microscope. a major error is the diameters measured due to the jagged edges.
HB = 2F/PI (D-(D-d)^1/2)

Rockwell:  Most common hardness tests and is very accurate. Rockwell measurs the Periment depth of indentation is uses a Spherical or Diamond indenter.
is pre loads a force to break the surface with a depth e then adds a secondary force with another depth E.

HR = E - e]]> 2017-11-08 13:09:19 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/204779807 matthew_slark https://padlet.com/matthew_slark/vslftgo70qwa/wish/204780046 2017-11-08 13:10:00 UTC https://padlet.com/matthew_slark/vslftgo70qwa/wish/204780046