Chapter 25
Approximate Shaft Dimensioning According to Niemann 2001, 3rd Edition, Page 742

The required dimensions for the design of shafts and axes with full circular cross-section will be estimated with an approximate calculation. It is assumed that the main load is well-known.

‘The permissible nominal torsional stress is set so low that the neglected bending stress will be considered as well as increasing stresses due to impact forces (external forces), notches, cross-sections, etc. The basis for the design of axes under bending stress is the nominal stress’ (from Niemann 2001, 3. Edition, p. 741).

The material can be selected for the calculation from the database. It is also possible to use individual material by the default of the maximum permissible torsion and bending tension.

25.1 Material Selection

For the calculation the material can be selected from the following listbox.

25.1.1 Define your Own Material

In case you cannot find the material you are looking for in our extensive database, simply define your individual material. You will find the entry ‘User-defined’ in the listbox. If you select this option, the input fields will be enabled, so that you can enter your own input values.

25.2 Material Number

Every material has a material number. With the material selection, the material number is displayed automtically. If you have specified an user-defined material, then ‘0.0000’ appears in the listbox ‘Material number’.

25.3 Load Types

Four different load types are available for the calculation:

• Idle axle (bending)
• Circulating axle (bending)
• Shaft (torsion)
• Shaft (torsion and bending)

• Idle axle: Usually repeated load and impact load are superimposed to the static base load, therefore a fluctuating stress is assumed for the dimensioning and the permissible bending stress is derived dependent upon the alternate strength.
• Circulating axle: For the determination of the permissible reversed bending stress, superimposed repeated and impact load have to be considered as well.
• Shaft: Bending and torsional moments are the main factors influencing shaft design. For the dimensioning you have to differentiate between shafts where only a torsion acts on the shaft or shafts that transmit also bending stresses. Accordingly, the permissible nominal tension has to be estimated differently.

After the input of the load - bending and torsion load or both - as well as the desired safety factor, the required minimum diameter of the axle or shaft is determined.

Our manual is improved continually. Of course we are always interested in your opinion, so we would like to know what you think. We appreciate your feedback and we are looking for ideas, suggestions or criticism. If you have anything to say or if you have any questions, please let us know via telephone +49 (0) 531 129 399-0 or email www.tbksoft.eu.