KEVOS® MAKEOS · Fasteners
Bolted Joint Fatigue Check
Will the bolt in this preloaded joint survive the fluctuating external load?
Alternating and mean bolt stress for a preloaded tension joint under a load cycling between zero and a maximum, and the Goodman fatigue safety factor using the bolt’s endurance strength.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Tensile stress area | mm² | Tensile stress area of the bolt (see the metric thread tool). |
| Preload | kN | Installed preload. |
| Maximum external load (cycling from zero) | kN | Peak external tensile load per bolt; the load is assumed to cycle between zero and this value. |
| Joint constant C = kb ÷ (kb + km) | Joint constant from the bolted joint tool (stiff joints have small C). | |
| Bolt endurance strength (fully corrected) | MPa | Fully corrected endurance strength of the bolt, including thread effects (published values for rolled threads are about 129 MPa for class 8.8, 162 MPa for 10.9). |
| Bolt tensile strength | MPa | Minimum tensile strength of the bolt. |
| Required fatigue safety factor | Required factor of safety against fatigue. |
Method and formulas
- σa = C P ÷ 2At; σm = σa + Fi ÷ At; σi = Fi ÷ At.
- Goodman (load line from preload): n = Se (Sut − σi) ÷ [Sut σa + Se (σm − σi)].
- Example: the default joint has σa = 11.862 MPa and a fatigue factor of 4.7039.
Limitations
- Concentric joint without separation; bending and prying raise bolt stress amplitudes.
- The endurance strength must already include thread stress concentration.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check cylinder head, flange and con-rod bolts under cyclic loads
- Show how preload and joint stiffness protect the bolt
- Compare rolled and cut threads
Who it is for
- Design engineers
- Maintenance engineers
What you get
- Alternating and mean bolt stress
- Preload stress
- Goodman fatigue safety factor
Interpreting the result
- A stiffer joint (smaller C) or a softer bolt (longer, reduced shank) cuts the alternating stress.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 1521–1535. Topic reference; no source tables or recommended settings are reproduced.
- VDI 2230 Part 1
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