Stress in Bolts

Calculating the stressed area in UN and UNR bolts

The weakest points in a bolt is the stressed area in the thread root. The stressed area depends on the type of threads - coarse threads will reduce the stressed area compared with fine threads.

The stressed area can be calculated as

A = π / 4  (d_n - 0.9743/ n)²         (1)

where

A = stressed area (square inch)

d_n = nominal bolt diameter (inch)

n = 1 / p = number of threads per inch

p = pitch (length per thread)

Despite that reduced area reduces the braking load, coarse threads are used for clamping. Fine threads are weaker due to the reduced thread height.

Engineering News

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