Maximum tightening torque to preload a metric bolt
Tightening torque (thread + head friction), resulting preload and stress relaxation for a metric bolted joint tightened to a prescribed equivalent stress.
Tightening torque, M_A = M_G + M_WD84.21 Nm
Preload, F_i35.08 kN
Load reserve, P_b = F₀.₂ − F_i18.85 kN
Stress relaxation, (σₑ−σₜ)/σₑ27.72 %
Thread friction torque, tightening, M_G43.16 Nm
Thread friction torque, loosening, M_G−-23.03 Nm
Head friction torque, M_WD41.05 Nm
Equivalent stress, σₑ576 MPa
Torsional stress, τ229.8 MPa
Tensile stress, σₘ416.36 MPa
Tensile stress area, Aₛ84.26 mm²
Ultimate tensile strength, Rₘ800 MPa
Yield strength, Rₚ₀.₂640 MPa
Pitch, P1.75 mm
Pitch diameter, d₂10.863 mm
Root diameter, d₃9.853 mm
Method & references
- Maximum tightening torque to preload a metric bolted joint to a prescribed equivalent (von Mises) stress.
The computation is a literal port of the original client-side JavaScript from /calculators/e3_6b.htm. Results are verified equal to the original by an automated golden-master test. No formula has been re-derived or “improved”.