Bolt Stretching

Bolt stretch according Hookes Law

Bolt stretching according Hook's Law can be expressed as

dl = F L / E A (1)

where

dl = change in length of bolt (inches, mm)

F = applied tensile load (lb, kN)

L = effective length of bolt where tensile strength is applied (inches, mm)

E = Young's Modulus of Elasticity (psi, N/mm²)

A = tensile stress area of bolt (square inches, mm²)

Tensile stress area can be expressed as

A = 0.7854 (d - 0.9743/n)² (2)

where

d = nominal diameter of bolt (inches, mm)

n = number of threads per inch (pitch)

Example - Bolt Stretching

• stud diameter : 7/8 inches 
• thread pitch : 9
• Young's Modulus : 30 10⁶ psi
• design bolt load : 10000 lb
• effective length : 5 inches

Tensile stress area can be calculated as

A = 0.7854 (7/8 - 0.9743/9)²

    = 0.46 (in²)

Change in length of bolt can be calculated as

dl = 10000  (lb) 5 (in) / (30 10⁶ (psi) 0.46 (in²))

    = 0.0036 (inches)

Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Web The Engineering ToolBox