materials definitions

• Strength


  • A strong material that needs a large amount of force to break it
• Stiffness


  • Does not deform very much when force is applied
  • Includes tensile stiffness and compressive stiffness
• Brittle


  • Prone to cracking
• Tough


  • Resistant to cracking
• Malleable


  • Can be hammered into shape
• Ductile


  • Can be drawn into a wire
• Density


  Mass per unit volume
• Stiffness


  Independent on its dimensions, depends on length and area
• Hooke's law


  The strain of the material is proportional to the applied stress within the elastic limit of that material
• Elastic potential energy


  Energy stored when wire behaves elastically
• Stress


  • Internal resistance offered by the body to the external load applied to it per unit cross sectional area
  • Can be tensile or compressive
• Strain


  Extension per unit length
• Young's Modulus


  Measurement of mechanical properties of linear elastic solids, stress over strain
• Elastic deformation


  1. Metal atoms are joined by little springs (interatomic bonds)

  2. The springs stretch

  3. When force is removed the metal returns to its original length
• Plastic deformation


  1. If load is big enough, bonds are broken

  2. In ductile metal, layers of atoms slide over each other

  3. This is permanent deformation
• Fatigue


  • Process in which small cracks in a component initiate and grow under the influence of a repeated loading, possibly to a final failure
• Creep


  • A form of slow mechanical deformation that occurs when a material is exposed to high stress levels for a long time
  • Creep is time dependent
  • High temperature and stresses can cause creep in metals
• Hysteresis


  Energy transferred as heat a the molecules side past each other
• Viscosity


  Amount of internal friction in a fluid