MET 425 - FEA Applications II

Nonlinear Behavior: Bolt Preload/Contact

Prof. Dave Johnson, psuprofdj@psu.edu, Penn State Erie, The Behrend College

Homework Assignment 5

A steel bracket is firmly attached to a wall on the vertical, right face.  All dimensions are given in mm. The bracket is 20 mm deep, extruded from the 2D sketch, above.  
This assembled modeled is provided to you as a ParaSolid Text File   Use a Right-click on this link, then "Save Target As...", then "Save as type: All Files", and use a file name like: "bolt-bracket.x_t" 

A simplified steel bolt is assembled through the bracket holes.  
The bolt is initially tightened such that the axial tensile preload is 2500 N.

Reference: ANSYS Help > Mechanical Applications > Mechanical Applications User's Guide > Features > Applying Boundary Conditions > Types of Loads > Bolt Pretension

After assembly, the bolt shank is loaded with a force load of 1000 N directly away from the bracket web and a component of 500 N parallel to the web and normal to the bolt shank.  The bolt heads may slide (friction coefficient = 0.2) and the bolt shank OD may come in contact with the ID of the bracket holes. 

Reference: ANSYS Help > Mechanical Applications > Mechanical Applications User's Guide > Features > Analysis Settings > Steps and Step Controls for Static and Transient Analyses

Anticipating the final bolt shank loading, the bolt is initially positioned forward in the holes, away from the bracket web, just contacting (line contact) the bolt holes ID.

Turn in:

  1. A plot showing all contact regions.  Specify the contact type and options used for each.
  2. A plot showing the environment (loads and constraints)
  3. A plot of the finite element mesh - Use "Contact Sizing" for better mesh in contact regions.  Document the number of nodes, elements, and ALL element types used.
  4. Estimate the torque necessary to create a preload of 2500 N in the bolt.  Identify the source of the calculation formula and all terms used to estimate the torque.

    For the bolt preload ALONE:

  5. a plot of the total deformation
  6. a plot of the equivalent stress
  7. a plot of contact pressure under the bolt heads
  8. a plot of the axial stress in the bolt.
  9. Does the axial stress in the bolt agree with the preload force level ?  (Hand calc & compare)

    After the bolt shank load is added:

  10. a plot of the total deformation
  11. a plot of the equivalent stress
  12. a plot of contact pressure under the bolt heads
  13. a plot of the contact pressure between the bolt shank OD and the bracket holes ID
  14. a plot showing how much sliding occurs between the bolt heads and the bracket flanges
     
  15. Explain: 
    1. How is the bolt preload treated in later load steps, when other loading acts on the model ?
    2. Are large deformation effects important ?  WHY ?
    3. Is plasticity needed for this simulation ?  If so, show the stress-strain data you used and present the equivalent plastic strain plots at the end of each load step.
    4. Should symmetry be used for this assembly ?  If so, document the loading used and include a plot to show the symmetry regions.