Mechanical properties of materials

• Elastic deformation


  An elastic deformation is one where the object will return to its original shape, once the deforming forces are removed
• Plastic deformation


  A plastic deformation is one where the object remains permanently deformed, even once the deforming forces are removed
• Condition for an object to experience tension

  There must be a pair of forces, acting on the object in opposite directions, causing it to stretch
• Condition for an object to experience compression

  There must be a pair of forces, acting on the object in opposite directions, causing it to compress
• Yield stress


  The stress at and beyond which the object will undergo plastic deformation
• Fracture stress


  The stress that causes the material to break
• Stiff


  A stiff object is one that only produces a small extension per unit force
• Ductile


  If an object is ductile, it means that it can be easily stretched into wires
• Brittle


  If an object is brittle, it will undergo very little plastic deformation before a fracture occurs
• Tough


  A tough object is one that can absorb a lot of energy before fracture
• Hooke's Law


  The extension of an object is directly proportional to the force applied to it, up to the limit of proportionality, given that external conditions remain constant
• Hooke's Law (equation)


  Force = Spring Constant x Extension

  F = kx
• Limit of proportionality


  The point beyond which the object will no longer obey Hooke's law
• Energy stored when an object is stretched or compressed

  Elastic potential energy
• Area under a force-extension graph


  The area under a force-extension graph is equal to the energy stored
• Equation for energy stored when a spring is stretched

  E = 1/2 kx^2
• Stress


  Stress is the force per unit area applied to an object
• Strain


  Strain is the ratio of extension to original length
• Young Modulus


  The Young Modulus is the ratio of stress to strain. It is a measure of a material's stiffness.
• Unit of stress


  Stress is measured in Pascals
• Unit of Young Modulus

  Since stress is measured in Pascals and strain doesn't have a unit, the unit of Young Modulus is Pascals
• Rayleigh's Oil Drop experiment was designed to estimate the size of an atom