Explore an axial bolted joint under an external tensile load cycling from zero to a maximum. Compare bolt stress amplitude, mean stress and a Goodman index, including joint separation. This is not a life prediction or code-compliance check.
Bolt Specification
Bolt grade
Nominal diameter d
Joint Conditions
Joint stiffness ratio Φ
External load Fa
kN
Tightening factor αA
Fatigue Safety Factor
―
While paused, moving a slider updates the results immediately.
The external load acts on one bolt and cycles from 0 to Fa. Φ is the bolt load fraction; αA controls the assumed preload scatter. Fatigue reference values of 30/50/60/70 MPa are educational assumptions, not guaranteed properties of the selected bolt class.
Reproduce a result
Select the property class and size. Diameter indices 0–6 correspond to M8, M10, M12, M16, M20, M24 and M30.
Enter Φ, peak external load Fa in kN and αA. Fa is the maximum of a zero-to-peak cycle, not its alternating amplitude.
Read amplitude, mean stress and the index. Check separation and yield warnings independently of the Goodman index.
Worked example
Class 8.8, M12 (As=84.3 mm²), Φ=0.20, Fa=20 kN and αA=1.40 give Fi=0.7×640×84.3/1.4=26,976 N. Separation starts at 33,720 N, so the joint remains clamped. Fb,min=26,976 N and Fb,max=30,976 N give σa=23.7 MPa and σm=343.7 MPa. With the assumed Se=50 MPa, n=1.11. Reducing Φ to 0.10 halves σa to 11.9 MPa.
🙋
What should I check in this example?
🎓
Change one input at a time and compare the formula with the displayed result. Read amplitude, mean stress and the index. Check separation and yield warnings independently of the Goodman index.
Limits and interpretation
After separation, Fb,max=Fa preserves force balance. Contact details, bending, prying, loosening and local plasticity are not solved. Without an S–N curve and load history, the tool cannot predict failure cycles or remaining life. An index above one is not a safety certification.
Frequently asked questions
No. At zero external load the bolt carries Fi. Fi−(1−Φ)Fa is the remaining compression in the clamped members at peak load, not the minimum bolt tension.
The spring model gives Fsep=Fi/(1−Φ). At or above this external load, the interface opens and the bolt is assumed to carry the entire external load.
No. The fatigue reference values are assumptions. Thread geometry, finish, temperature and stress ratio require appropriate fatigue test data.
No. It reduces assumed preload and mean stress, but also lowers the separation threshold. Check separation, yield and fatigue separately.
Checks cover displayed units, reference calculations, input sensitivity, boundary conditions and cross-language results. They do not certify code compliance or real-world accuracy.