Spring 2007, MET 415 - FEA Applications I

Prof. Dave Johnson, dhj1@psu.edu, Penn State - Erie, The Behrend College

Homework 4A:  3D Solid Modeling

Concepts:

• 3D Modeling (Volumes, Booleans, Area Fillets, Merging)
• Topological Degeneracy (ANSYS, not WBE)
• Solid element types
• Tetrahedral meshing
• Element size control
• (ANSYS)Listing Data: Keypoint locations, Edges of areas, Faces of Volumes
• Concentrated Force/Moment Loading
• 3D Stress State evaluation
• Error evaluation on large 3D models and around singular points
• (ANSYS) Use of Multiple Display Windows

Problem Description:

A common steel link for the steering of a Cub Cadet lawn tractor is shown above.   A tie rod is attached by a bolt through the hole at the right end of the link.   The solid cylindrical protrusion on the left end transmits the load from the tie rod to the front wheel as a torque on the cylinder.  Part dimensions are given (in inches) in the figure below.

The loading to be considered for this part includes:

• A torque of 210 inch-lb_f CCW about the Z-axis acts from the hole about the axis of the cylindrical protrusion.
• A torque of 120 inch-lb_f CCW about the Y-axis acts from the hole on the right end

For these loading descriptions, the Z-axis is the centerline of the cylindrical stub, and the X-axis runs from the center of the cylinder to the center of the hole.

Decisions you must make:

Does this model exhibit symmetry ?  Is this a linear, static analysis ?  Must you use a 3D model ?  What element type should be used ?   What are appropriate material properties ?

How should the loads be introduced, i.e., where the tie rod bolt interacts with the hole in the right end of the link ?
Constrain the hole and load the stub - or - constrain the stub and load the hole ?

Turn in:

• An element plot showing your final mesh.  (ANSYS) Use two windows to show ALL sides/faces of the model.
• An Environment plot showing ALL the loads and constraints
• A hand calculation (from Strength of Materials) of the maximum equivalent stress on the cylindrical protrusion, just past the fillet on the +X axis side.  (This is a state of combined stress; use Mohr's circle for your calculations)
• A stress plot to compare to your hand calculations and to illustrate the maximum stress on the part.  Note the global mesh error (SEPC) on your plot.
• Plots of deformed shape (incl. SEPC) and the element mesh error (SERR), selecting only the nodes and elements around the fillet and cylindrical stub (to determine if you can have any confidence in the stress calculations)
• A printout of the ANSYS, FSUM result for forces and moments about the post centerline, at the end face of the post (SPOINT).  Use the FSUM output to confirm proper loading has been applied to the model.
• (ANSYS) Include a session log file, to which you have added comments describing the process of modeling and loading the steering link.  "Write a DB Log File" after you have constructed and successfully solved the original part mesh.  Comments are not needed on graphical picking commands (FLST, FITEM), but should be on the action command that follows the picking.  For example: 
  ASBW,P51X        !  Divide areas by WP based on graphical picking, above
  You can view a SAMPLE LOG FILE.