Spring 2006, METBD350 - FEA Applications I

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

Project 1: Connecting Rod

Concepts:

  A connecting rod is to be analyzed as an idealized, two-dimensional system shown above. This part has two materials: stainless steel (AISI 301 cold worked) for most of the section, and brass (C26000) for the bushing in the smaller hole at the left end.
  This structure also has two different thicknesses:  the main body is 0.060" thick, and at the small end, it is 0.120" thick.  (This means some of the steel section is 0.060" and the rest is at 0.120" thick.  The brass bushing is 0.120" thick.)
  Also, notice that there is a 0.075" fillet between the thinner and thicker stainless steel sections at the small end of the con-rod.

ANSYS:  The boundary conditions inside the holes are intended to simulate the presence of a pin or shaft in each hole.  The load is assumed to be distributed over a 90^o arc and is more intense at the center of that span.  Similarly, the constraint on the right side acts over a 90^o arc, opposing the load.  This approach is a common approximation for cases with a pin through a hole when the load bearing side is obvious.  Some analysts use a 60^o arc rather than a 90^o arc for this assumed behavior.
Workbench:  Investigate cylindrical supports, bearing load, and compression-only support

  The ultimate strength of the stainless steel is 185 ksi. and of the brass is 76 ksi.  Using a "design factor" of 8 (for repeated loading), evaluate this design.   If necessary, modify the design to reduce the maximum stress below the allowable level.  However, you may NOT change the inside diameter of the bushing or of the inside diameter of the hole in the right end of the con-rod, and you may not change the thickness of the part.  Use the same materials.  Don't be "excessive" in your corrections.
ANSYS: Consider using the model's command log file for any small redesign modifications.
Workbench: Use "Update: Use Geometry Parameter Values" to synchronize the DesignSimulation model to the DesignModeler model

Report:

• Include plots showing the model (different materials and thickness) and the boundary conditions.  Investigate the /ESHAPE command for presenting the model thickness.
• Include plots which illustrate the maximum deflection and stress in the original design,
• Show and comment on the level of FEA mesh error of your analysis (in each region of the geometry),
• Hand calculation of axial force in the connecting rod compared to ANSYS results (SFx)
• Also, do a hand calculation estimate of the maximum normal stress in the fillet area based on a stress concentration factor, K_T, compared to the appropriate ANSYS stress results
• Describe any design modifications (in detail) required to bring the stresses within the allowable levels
• Present the stress results of the modified design, to show that acceptable stress levels have been achieved
• Append a session log file, to which you have added comments describing the process of modeling and loading the connecting rod.  "Write a DB Log File" after you have constructed and successfully solved the original part design.  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.
  A word of advice:  the comments you add to the logfile should make it read like a story of the process you followed in creating the model.  Log file comments are NOT simply ANSYS command definitions.

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Reminder: All project reports will be typed, and include:

• a cover page with course name, project name, team names, and date
• a brief objective statement (2-3 sentences, maximum, of engineering objectives)
• a summary of procedures (bulleted items)
     a complete list of:
  • assumptions, 
  • given data, 
  • modeling and analysis steps
• a conclusion statement (what was learned about the part or device, an evaluation of the design, and an interpretation of the results)
• a copy of the project statement (this web page) may be attached.

[1] a possible Workbench command object could include:

/SHOW,PNG      ! send plots to PNG file
/GFILE,350     ! plot file resolution
/RGB,INDEX,100,100,100,0   ! switch the
/RGB,INDEX,0,0,0,15        ! B/W colors

prerr          ! print error for entire model

esel,s,mat,,1  ! select one body by material ID number
nsle,s         ! select the nodes attached to those elements
prerr          ! print error for that body of model
pldisp,2       ! plot the deformed shape of that body

esel,s,mat,,2  ! select one body by material ID number
nsle,s         ! select the nodes attached to those elements
prerr          ! print error for that body of model
pldisp,2       ! plot the deformed shape of that body

esel,s,mat,,3  ! select one body by material ID number
nsle,s         ! select the nodes attached to those elements
prerr          ! print error for that body of model
pldisp,2       ! plot the deformed shape of that body

ALLSEL         ! select everything

/SHOW,TERM     ! direct plots back to the screen