3.4 materials

• what is a tensile force?

  a force that produces extension
• what is a compressive force?

  a force that shortens an object
• when does tensile deformation occur?

  when a tensile force is applied
• when does compressive deformation occur?

  when a compressive force is applied
• what is Hooke's law?

  when the force applied to a material is directly proportional to its extension
• what is the spring/force constant?

  k , measure of stiffness of a material
• what is elastic deformation/limit ?

  material will return to its original shape after force is removed. materials sometimes follow hooke's law up to the elastic limit
• what is plastic deformation?

  material has undergone permanent structural changes and therefore will not return to original shape after force is removed
• what does area under a Fx graph represent?

  work done
• what graph is this?

  loading and unloading graph for a metal wire

  
• what graph is this?

  loading and unloading graph for polythene

  
• what does change in area under a loading-unloading graph represent?

  thermal energy transfer to surroundings
• what is tensile stress?

  stress = force / cross-sectional area
• what is the unit of tensile stress?

  Pa
• what is tensile strain?

  strain = extension / original length
• what is the unites for tensile strain?

  no units
• what does this graph represent?

  stress strain graph for a ductile material

  
• what doe the points on this graph represent?

  P = limit of proportionality

  E = elastic limit

  Y1 = upper yield point (where material expands rapidly)

  Y2 = lower yield point (where material expands rapidly)

  UTS = ultimate tensile strength

  B = breaking point (point of fracture)

  
• what is UTS?

  ultimate tensile strength is the maximum stress a material can withstand before reaching its breaking point
• what is a strong material?

  material with a high UTS
• what is young's modulus? 


  ratio of stress to strain

  young modulus = tensile stress/ tensile strain
• what are the units for young modulus?

  pascals
• what is this graph?

  stress strain graph for a polymeric material - polythene

  
• what is this graph?

  stress strain graph for rubber

  
• what is this graph?

  stress strain graph for brittle material

  
• what is this graph?

  loading and unloading graph of a rubber band

  
• how to work out force/spring constant of springs in parallel?

  add them together
• how to work out force/spring constant of springs in series?

  add their inverses together to give 1/Ktotal