KEVOS® MAKEOS · Springs
Torsion Bar Spring
What rate, twist and shear stress does this torsion bar spring have?
Torsional rate, angle of twist, arm-tip deflection and shear stress of a solid round torsion bar loaded through a lever arm.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Bar diameter | mm | Diameter of the active (twisting) part of the bar. |
| Active length | mm | Length between the fixed end and the arm. |
| Shear modulus | GPa | Shear modulus of the bar steel. |
| Force at arm | N | Force at the end of the lever arm. |
| Arm length | mm | Lever arm length from the bar axis. |
| Allowable shear stress | MPa | Allowable shear stress for the spring steel and duty. |
Method and formulas
- T = F × arm; J = π d⁴ ÷ 32.
- Twist θ = T L ÷ (G J); rate = G J ÷ L.
- τ = 16T ÷ π d³; arm-tip deflection ≈ arm × θ (small angles).
- Example: 1000 N on a 200 mm arm twists the default bar 7.3595° with τ = 127.32 MPa.
Limitations
- Solid round bar; end fittings and transitions add stress concentrations.
- Small-angle arm deflection approximation.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Size a torsion bar for a counterbalance or suspension
- Check stress at maximum twist
- Find arm deflection
Who it is for
- Design engineers
- Spring buyers
- Maintenance engineers
What you get
- Torque and twist
- Torsional rate and linear rate at the arm
- Shear stress
Interpreting the result
- Preset (scragging) and shot peening raise the usable stress of torsion bars.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 295–303, 344. Topic reference; no source tables or recommended settings are reproduced.
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