MECH 4: MODULE 2

• Unit strength of a material is defined as the stress in the material
• Stress formula: σ =
• Units of stress:

  • Pascal, Pa = N/m^2
  • Megapascal, MPa = N/mm^2 or MN/m^2
  • Kilopascal, kPa = kN/m^2
  • Pound per square inch, psi = lb/in^2
  • Kilopound per square inch, ksi = kips/in^2
• 1 psi = 6.895 kPa
• Normal stress occurs when a member is loaded by an axial force in tension or compression
• Normal stress formula: σ = P / A; where P = applied normal load, A = area
• Shear stress is produced when applied loads cause one section of the body to slide past its adjacent section
• Shear stress formula: τ = V / A; where V = shear force, A = area
• Classification of Shear:

  • Single Shear: A = πd^2 / 4
  • Double Shear: A = 2πd^2 / 4
  • Punching Shear: A = dt
• Bearing stress refers to the contact pressure between separate bodies and can be classified as normal stress
• Bearing stress formula: σb = Pb / Ab; where Pb = applied normal load, Ab = bearing area
• Tangential stress in thin-walled vessels: σt = pD / 2t or (pD / 4t) - (poD / 4t) if there is external pressure
• Longitudinal stress in thin-walled vessels: σL = pD / 4t or (pD / 2t) - (poD / 2t) if there is external pressure
• Stress in thin-walled sphere: σ = pD / 4t or (pD / 2t) - (poD / 2t) if there is external pressure