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CALCULATORS / SHAFTS, COUPLINGS AND ROTATING ASSEMBLIES

Combined shaft bending and torsion calculator

Solid circular shaft bending and torsion; von Mises screen.

shafts-combined-load.napkin / editable
✓ checks pass

SCENARIO COMPARISON

Compare the numbers.

This source describes an analytical model. Its quantities and checks are the view.

ScenariobendingMPashearMPaequivalentMPa
30.18057.5451232.8884
24.14447.5451227.4543

All calculated quantities are listed with the inputs. Switch to Source to inspect the equations.

SCENARIOS / CALCULATED VALUESSAME SOURCE

Change an input to see the consequences.

equivalent stress budget32.89 MPa✓ passes

BASELINE INPUTS

CALCULATED

bending30.18 MPa
shear7.5451 MPa
equivalent32.888 MPa

Edits change the baseline source.

Calculated from your source · not saved
Baseline · Baseline
equivalent stress budget32.89 MPa ✓ passes
alternative · alternative
equivalent stress budget27.45 MPa ✓ passes

Illustrative first-order example. Checks are editable requirements, not design standards. The broader topic may require additional equations, data, and validation.

Formula and units

This example uses the following equations. Input names and units match the editable source above.

bending
bending = 32*moment/(pi*diameter^3) [MPa]
shear
shear = 16*torque/(pi*diameter^3) [MPa]
equivalent
equivalent = sqrt(bending^2+3*shear^2) [MPa]

Original worked example

These are the baseline values in the downloadable source. Edits above let you test your own values.

Given

moment
10 N*m
torque
5 N*m
diameter
15 mm

Calculated

bending
30.1805 MPa
shear
7.54512 MPa
equivalent
32.8884 MPa

Assumptions and limits

Solid circular shaft bending and torsion; von Mises screen.

The requirement checks use the limits written in this example. Passing a check does not establish that the model covers every load, material behavior, or operating condition in a real design.

Download this .napkin example ↓

Take it further with your agent

Napkin keeps the inputs, equations, checks and assumptions together in one study. Your agent sets it up; you change the numbers.

Try with Claude ↗

codex 'Use Napkin (https://napkin.engineering/mcp, or the local Napkin plugin) to build a study: Combined shaft bending and torsion. Inputs: bending moment; torque; geometry. Outputs: combined stress; diameter screening. Model scope: Elastic shaft models and specified supports. Read napkin_capabilities and the current snapshot. Ask me for the values that matter, label assumptions with units, author .napkin source, validate it and apply it with napkin_source using the current revision, then open the study. Add checks for the limits I supply. Keep unsupported analyses explicit.'

Claude needs the Napkin connector; Codex needs the Napkin plugin. Set up your agent ↗

The broader study

The topic brief below describes the broader scope. The worked example above states the particular calculation it implements.

  • Inputs: bending moment, torque, geometry
  • Outputs: combined stress, diameter screening
  • Modes: calculate, compare, sweep
  • Drawing: Shaft load diagram

EXECUTABLE WORKED EXAMPLE · FIRST-ORDER MODEL · CHECK THE SCOPE & ASSUMPTIONS

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