Analysis tipsTips-Tricks

Tips & Tricks - Choosing Sections for Torsion Loading

Torsion Loading - The type of section chosen will greatly influence the torsional stiffness of a component or structure. Where possible use closed sections, as the stresses are distributed more evenly over the total area, allowing a greater load. We show using hand calculations just how much better closed sections are, and give a helpful tip on measuring angular deflection in SolidWorks Simulation.

Comparing Section Torsional Properties

sections
1. Round closed sections are the best for resisting torsion 2. Square closed sections are the next best, followed by rectangular closed sections 3. Open sections are no good in torsion!
Note also that in a round section, the maximum stress occurs at the outermost fibre, whereas in a rectangular section the maximum stress actually occurs at the closest point to the centroid on the outer surface.

Getting Angular Displacements out of FEA

When checking Finite Element Analysis (FEA) results, the displacement plots available in SolidWorks Simulation don't give an angular displacement plot. However, the angular displacement can be calculated and verified by dividing the circumferential displacement by the shaft radius.

When plotting displacements relative to an axis, make sure to select the axis as reference geometry; then the following notation applies, despite apparently inaccurate labelling:

  • UX corresponds to the radial displacement (in mm etc.)
  • UY corresponds to the circumferential displacement (in mm etc.)
  • UZ corresponds to the axial displacement (in mm etc.)

You can download a worked example here.

fea1

HANDY TIP!

Sections which have an open seam are up to 100 times less stiff in torsion than closed sections - so run a stitch weld down the seam for a simple solution for split pipes.

See the difference in the displacement plots below...

weldtip comparison

For complex problems where the stresses are difficult to derive accurately, there are a number of approximate methods available to the advanced analyst - give Greg a call on 03 382 5282 or email him to discuss further training or analysis options.