Bolt Stretching

Bolt stretch according Hooke's 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 lbs
• effective length : 5 inches

Tensile stress area can be calculated as

A = 0.7854 ((7/8 in) - 0.9743/9)²

    = 0.46 (in²)

Change of length can be calculated as

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

    = 0.0036 (inches)

Engineering News

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