Maximizing Thread Strength: Stress Analysis on M10 Bolt with 100 kg Load

[Aerstz]

Homework Statement

Calculate the stress in a screw thread resulting from a known force

Relevant Equations

Stress = Force / (0.25 * pi * (nominal thread diameter - 0.93194 * pitch)^2

A load of 100 kg acting in the axial direction is applied to a nut coupled with a standard M10 bolt. The nominal thread diameter is 10 mm; pitch is 1.5 mm. Thus, the stress acting on a single thread in the bolt is:

1000 N / (0.25 * pi * (10 mm - 0.93194 * 1.5 mm)^2) ≈ 17.21 MPa

17 MPa seems rather low. If a nut covers 5-threads, the total stress is therefore just 3 MPa (17/5), translating to a maximum load acting on the steel nut (assuming proof strength of ~200 MPa) of approximately 10-tons.

10-tons seems a lot of weight before a loaded M10 nut will strip a bolt of its threads, which is why I'm posting this to request clarification/verification, please?

 

[Lnewqban]

Please, see:
https://www.engineeringtoolbox.com/metric-nut-proof-load-d_2029.html

https://www.engineeringtoolbox.com/metric-bolts-minimum-ultimate-tensile-proof-loads-d_2026.html

https://www.engineeringtoolbox.com/steel-bolts-metric-grades-d_1428.html

 

[Aerstz]

Please, see:
https://www.engineeringtoolbox.com/metric-nut-proof-load-d_2029.html

https://www.engineeringtoolbox.com/metric-bolts-minimum-ultimate-tensile-proof-loads-d_2026.html

https://www.engineeringtoolbox.com/steel-bolts-metric-grades-d_1428.html

Thanks. Judging by the information in these links, my calculation is about five-times out. What confuses me is that the formula I used I took from a report I produced years ago, and I cannot recall where it came from, and I am unable to find it anywhere online (I even asked an AI bot). In my report, the predicted stress was verified by FEA, so why my result here is so disagreeable with the tabulated values you linked me to I have no idea.

 

[deajohn]

Thanks. Judging by the information in these links, my calculation is about five-times out. What confuses me is that the formula I used I took from a report I produced years ago, and I cannot recall where it came from, and I am unable to find it anywhere online (I even asked an AI bot). In my report, the predicted stress was verified by FEA, so why my result here is so disagreeable with the tabulated values you linked me to I have no idea.

You may have your answer by now but you are confusing tensile thread stress in the bolt and nut shear stress. The tensile stress is force/area independent of thread number.

The nut shear stress is force/ nut shear area which is pi x D x nut depth, usually three thread engagement