Fall 2007, MET 425 - FEA Applications II:
3D Solid Modeling/Mapped Meshing

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

Homework Assignment 3B

Concepts:

Workbench DesignModeler: Freeze, Slice, multi-body parts DesignSimulation: Mesh Method: Sweep vs. Hex-dominant

ANSYS Top-down modeling: primitive shapes and boolean operations Mesh Controls (spacing ratio) Concatenation and Mapped Meshing ANSYS macros

A carbon steel (1045 HR) bearing bracket is shown in the figure above. Young's modulus is 30e6 psi, Poisson's ratio is 0.3

• The base is 6 x 3 x 1 inches. The four holes in the base are 0.75" diameter and are positioned 0.75" from the blocks edges.
• The bracket is 3" wide, 0.75" thick. It is centered on the 6" dimension of the base, flush to the back edge.
• The centerline of the hole and counterbore are 1.75" from the top of the block. (The bracket edge is straight up for 1.75", then begins the 1.5" RADIUS of the outer edge).
• The through hole is 0.85" RADIUS, the bushing counterbore is 1" RADIUS and is 0.1875" deep.
• The two triangular brace plates are 0.15" thick and extend from the forward edge of the base to the 1.75" elevation on the bracket.
• Model the bracket EITHER using the ANSYS solid modeling or Pro/ENGINEER.
• All fillets have been ignored to simplify the construction - this is primarily a meshing exercise

Workbench: slice the part into many simpler bodies - bodies with 4, 5, or 6 faces.  Consider all surface and hidden features as you plan your slicing operations - look at top, front, and side views to visualize necessary cuts.
Try to use a "SWEPT" mesh.  If that fails, try "Hex Dominant."  Swept mesh success requires more, simple volumes.

ANSYS: Create volumes that can be mapped meshed with ALL brick-shaped (hexahedral) finite elements.

ANSYS: This is an opportunity to use/create an ANSYS macro to assist in processing volumes for mapped meshing.  A useful macro might be:

VSEL,S,,,arg1      ! select a volume (user gives 'arg1')
ALLSEL,BELOW,VOLU  ! select all entities with the vol.
/out,vdata.txt     ! print to a scratch file
VLIST              ! list areas around the volume
ALIST              ! list lines around the areas
/out               ! close the scratch file
*uilist,vdata.txt  ! display the file in the UI
/sys,del vdata.txt ! delete the file
/eof

This small example is not perfect (does not check for the existence of the volume), but you may find this to be a handy utility during model development

• Constrain the nodes on the bottom of the entire base in the vertical direction. Also, constrain the nodes on the I.D. of the holes in the base, only at the bottom surface, in the two horizontal directions. Finally, apply a pressure load of 10000 psi. to the base of the bushing counterbore, i.e., its a bearing thrust load.
• Solve, and evaluate the equivalent stress and deflection for the model.

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  Turn in:

• a solid model geometry plot (i.e., either an ANSYS volume plot or a Pro/ENGINEER shaded image plot)
• an element mesh plot,
• an environment plot showing the loads and constraints,
• a plot showing the highest equivalent stress on the part (and any plot(s) needed to justify the mesh error)
• also, a plot of the equiv. stress with the user-defined contour bands to clearly identify and material which exceeds the yield stress (60 ksi).

  In Summary:

  Report the mesh statistics (element type, no. of nodes and elements, mesh error %), solution time, solver choice

  Discuss the results on the "user-specified," 0 - 60 ksi contour range plots.  How do you interpret the contour bands ?  Why would you want to present results this way ?

  What comment can you make regarding the F.E. mesh error for the analysis of this bracket?  What causes the mesh error to be so high ?  
  Comment on variations in the graphical display of results (i.e., PowerGraphics ON or OFF) for the stress results plot.

  In Workbench, a useful Solution Command Object for this would 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
  /VIEW,1,1,1,1        ! set the viewing direction
  PLDISP,2              ! plot deformed shape w/undeformed edge
  
  /GRAPH,FULL      ! Deactivate PowerGraphics
  PLNSOL,S,EQV   ! plot vonMises stress
  /GRAPH,POWER  ! Reactivate PowerGraphics
  PLNSOL,S,EQV   ! plot vonMises stress
  /SHOW,TERM       ! direct plots back to screen
   
  PRERR           ! Print global error, SEPC

   

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