1.5 Solids Under Stress

1.5 Solids Under Stress

1. Stress/Strain/Young Modulus

   • Stress, σ
     • The tension per unit cross sectional area [σ] = Pa or Nm^-2
       • σ = F/A
         • Where F is the force/tension and A is the cross-sectional area
   • Strain. ε
     • The extension per unit length due to applied stress [ε] = none
       • ε = Δl/l
         • Where Δl is extension and l is original length
   • Young Modulus, E
     • The ratio of stress to strain for a material in the Hooke's Law region [E] = Pa or Nm^-2
       • E = σ/ε

2. Key Terms

   • Tension - The magnitude of the force that a stretchedf object exerts on whatever its ends are attached to. This is eqaul in magnitude to the force apploied to the object to keep it stretched
     • Extension - The increase in length of an object when put under tension
       • Elastic - When a material returns to its original shape and size when tension is removed
         • Elastic limit - the point at which the object/deformation ceases to behave elastically/can be considered elastic
           • Hooke's Law - Provided the elastic limit is not exceeded, the extension of a spring is directly proportioanl to the tension
             • F = kx
               • Where k is the spring constant and x is extension
   • Elastic potential energy or Strain energy - The energy stored within a specimen which is being deformed elastically
     • Work = 0.5Fx = 0.5kx^2
   • Crystalline - consisting of crystals, which are regular arrays of particles (usually ions)
     • Polycrystalline - consisting of a large number of interlocking crystals

3. Classes of solid materials

   • Crystalline
   • Amorphus
   • Polymeric