Bolt Tightening Torque
A bolted joint only works if the bolt reaches the right preload. Under-tightened joints loosen; over-tightened bolts yield. This tool calculates the tightening torque for ISO metric coarse-thread bolts with the simplified VDI 2230 relation and checks the equivalent stress during tightening.
Tightening torque M_A74.8N·m
- Preload F_M
- 37.8 kN
- Thread torque M_G
- 39.1 N·m
- Under-head torque M_K
- 35.7 N·m
- Stress area A_s
- 84.3 mm²
- Yield load F_0.2 = Rp0.2 · A_s
- 54 kN
- Equivalent stress σ_red
- 545 MPa
- σ_red / Rp0.2 = 85 % — VDI 2230 assembly limit 90 %
METHOD
How it is calculated
F_M = ν · Rp0.2 · A_s M_A = F_M · (0.16·P + 0.58·μG·d₂ + μK·D_Km / 2) d₂ = d − 0.6495·P D_Km = (s + d_h) / 2 σ_red = √(σ_M² + 3·τ²) ≤ 0.9 · Rp0.2
ASSUMPTIONS & NOTES
- Friction coefficients range from 0.08 to 0.20 depending on finish and lubrication; 0.12–0.14 is typical for dry, uncoated steel.
- The mean under-head diameter uses ISO 4017 across-flats and ISO 273 medium clearance holes.
- Torque-wrench scatter (±10–25 %) and embedding losses are not included; use a full VDI 2230 analysis for critical joints.
Results are for preliminary design and checking; base the final design on the governing standard and safety factors.
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