Applying a Bolt Pretension Load

Bolt Pretension

Analyzing a bolted flange used to be a serious undertaking, in part because of difficulties in including pretension loads produced by the installation torque of tightening the bolt. The bolt pretension load option available in ANSYS Workbench allows the analyst to more readily specify known axial loads or adjustments to bolt bodies or bolt cylindrical faces.

A coordinate system is required when applying a bolt pretension load to a bolt body. The Z-axis of the coordinate system must be in the direction of the bolt axis.

There are four bolt pretension load options:

  1. Load - Applies a compressive axial load to the bolt (T=0.2*DF)

    T = Torque; D = Bolt Diameter; F = Axial Load

  2. Adjustment - Applies a compressive axial displacement to the bolt
  3. Lock - Fixes preload displacement for subsequent load steps
  4. Open - Opens the bolt load so that no load is applied to the bolt in a particular load step

Note: Contact settings are critical when applying a bolt pretension load.

Applying a Bolt Pretension Load

Apply Bolt Load

Apply a bolt load to a cylindrical bolt face or bolt body. If the load is applied to a cylindrical face, the program will slice the body mesh at the centroid of the applied face and create pretension elements in the direction of the cylinder axis If the load is applied to a body, the program will slice the body mesh at the origin of the local coordinate system and create pretension elements in the direction of the local coordinate system Z-axis.

Contact Settings

Contact between the bolt shaft and nut should be bonded. Contact pairs that run the length of the bolt should be changed to No Separation or Frictionless to allow the two components to slide in relation to one another. Bonded contact could block the ability of the bolt pretension from deforming properly.

Mesh Settings

A sufficiently fine mesh on the face or body that contains the bolt pretension loads should be used so that the mesh can be correctly partitioned along the axial direction of the bolt.

 

View Animation of Bolt Pretension Model (Turn on speakers to hear audio)

View ANSYS Advantage Article - "Analyzing Bolt Pretension in ANSYS Workbench Platform"