Stress Concentrations on Shafts

Any abrupt change in parts can capture internal stresses and cause stress concentrations. Examples of these changes are the following:

  • grooves
  • holes
  • notches
  • shoulders
  • keyseats
  • threads
  • splines

 

The stress concentrations are localized and in some occasions can cause microcracks which then can propagate and form bigger cracks with eventual machine breakdown.

A stress concentration factor is defined by the following

 

Lets take for example the following shaft:

 

This shaft is expected to have stress concentration on the vicinity of the key seat formation, shoulder, notches, etc.

 

A 3D FEA analysis can show the problematic areas. Typical types of these analyses include the following loads

  • rpm
  • thermal
  • interference fitted parts
  • Dynamic loads

 

Figure below shows results of such simulation with stress concentration on the vicinity of the key

 

 

The response of the shaft on the loads applied onto it is a very complicated mechanism and FEA tools are strongly recommended to drive the design process, especially for keyed shaft connections.