Mechanical Properties

• What is a mechanical property?

  How a material performs when different forces are applied to it
• Fatigue strength

  refers to the maximum number of stress cycles a material can withstand.
• Shear strength

  force that acts parallel or tangential to a surface, causing it to deform or slide.
• In what situation does shear occur?

  when directional forces cause the inner structure of a material to slide against itself
• Tensile strength

  amount of load a section of a material can withstand before breaking.
• What is tensile strength measured in?

  Newtons per square millimetre (N/m*2) or megapascals (MPa)
• Yield strength

  the point where a material under load will no longer returns to its original position or shape. The deformation moves from elastic to plastic.
• Toughness

  ability to withstand shock loading (impact resistance) without fracture.
• Hardness

  ability to resist permanent indentation. It also refers to its resistance to scratching, abrasion or cutting.
• What tests can be used to measure a material's hardness?

  Brinell, Rockwell and Vickers
• Ductility

  ability to be stretched, pulled or drawn without breaking. The material will retain its new shape when a load is removed.
• Young's modulus of elasticity

  The ratio of tensile stress to tensile strain. It can be used to determine how easily a material can stretch and deform. (stiffness)
• What can a tensile test be used to determine?

  Young's modulus of elasticity
• What is the formula for Young's modulus?

  E = FL/A(delta)L
• The units in the Young's modulus formula are?

  E = young modulus (Pa)

  F = force in newtons (N)

  L = original length in metres (m)

  A = area in square metres (m*2)

  Delta L = change in length in metres (m)
• Malleability

  ability to be deformed under pressure without breaking.
• Elasticity

  tendency to return to its original size and shape when a distorting force (causing deformation) is removed.
• Plasticity

  ability of a solid material to permanently deform under stress. Once a force is removed the shape cannot be changed.
• Brittleness

  a material's tendency to fracture when placed under stress. It can also be defined as a having a low tendency to deform before breaking. (sudden failure)
• Stress

  ratio of applied force to the cross-sectional area of the material. Stress will try to resist any change in dimension as a response to any applied forces.
• How does the cross sectional area of material impact the stress value?

  • A larger cross sectional area will experience less stress, as the force is distributed over a larger area. This reduces pressure over one part of the material or object.
  • A smaller cross sectional area will experience the opposite. The force will be concentrated over a smaller area, increasing the stress it undergoes.
• What is the formula for stress?

  (sigma) o = F/A
• What are the units in the Stress formula?

  o = stress (N/m*2) or Pa

  F = force (N)

  A = area (m2)
• Strain

  deformation of a material from stress. It is also defined as the ratio of the change in length to the original length.

  • There are 3 types of strain: normal, volumetric and shear.
• What is the formula for Strain?

  (epsilon) e = (l-lo)/lo
• Stress strain curve

  Shows how a material will behave when subjected to increasing loads. In ductile materials, the curve is split into 3 stages:

  • Linear elastic region - where the material undergoes elastic deformation.
  • strain hardening region - test material is subjected to the maximum stress it can sustain. (This is also called the ultimate tensile strength/UTS)
  • necking region - the ability to sustain stress rapidly decreases. At this point the material is rapidly approaching its breaking point. (fracture)

  
• what is fracture? (stress-strain curve)

  point of material failure
• what is yield strength? (stress-strain curve)

  limit of a material's elastic behaviour
• What does the term load mean?

  Application of force onto an object. A material's performance is dependent on the type of load it is subjected to.
• What are the 5 loading forces?

  1. Compression
  2. Tension
  3. Shear
  4. Torsion
  5. Bending

  
• units featured in Strain formula

  lo = original length

  l = stretched length

  • both are in mm
• Flexural strength

  a material's ability or structure's ability to withstand bending.