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

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A 100 kg axial load on an M10 bolt results in a calculated thread stress of approximately 17.21 MPa, which appears low. When considering a nut engaging five threads, the effective stress reduces to about 3 MPa, suggesting a maximum load capacity of around 10 tons before potential stripping occurs. This raises questions about the accuracy of the initial calculations, particularly in relation to established proof strength values. The distinction between tensile stress in the bolt and shear stress in the nut is crucial, as tensile stress is independent of the number of engaged threads. Clarification on these calculations and their discrepancies with established values is sought for better understanding.
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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?
 
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Lnewqban said:
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.
 
Aerstz said:
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
 
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