Spring 2008, MET 415 - FEA Applications I

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

HW-10A:  3D Modeling with Shells & Solids

CONCEPTS:

• 3D Modeling: Solid and Shell Elements
• Import of Assembly Geometry
• Modify imported geometry
• Symmetry features
• BETA features in ANSYS 11.0 WBE
• NON-Linear Solution:
  • small or large deformations ?
  • gradual load application (substeps)
  • automatic time stepping
  • iterative solution, (equilibrium) convergence
  • results controls
• Contact Element Settings

A tool for forming sheet metal is show in the image, above. The die is 4"  x 4" with a 2.0" diameter spherical cavity.  The punch is also 4" x 4" cross-section and its spherical protrusion is 1.9" diameter. 

Between the punch and die is a square piece of sheet metal (translucent in the image) which is 0.050" thickness.

The 3-part assembly geometry is available as a Parasolid file, tool.x_t  Use a Right-click on this link, then "Save Target As...", then "Save as type: All Files", and use a file name like: tool.x_t

Import this assembly into ANSYS Workbench DesignModeler (DM):

• Divide it for symmetry -  use DesignModeler > Tools > "Symmetry"
• Compress the sheet metal solid body to a mid-surface - use DesignModeler > Tools > "Mid-Surface"
• Add a round feature 0.2" RADIUS on the sharp edge of the die - [use DesignModeler > Create >Fixed Radius Blend]
• [Optional - only if we were to fully close the punch/die] Add a round feature 0.25" radius on the sharp edge of the punch

Move the assembly model to Simulation:

All bodies are structural steel (you need 2 structural steel materials)

• the punch and die will not yield
• the sheet metal can yield (S_Y = 36000 psi, E_T = 1E6 psi)

For ANSYS WB 11.0, activate BETA features - [Options... -> Common Settings -> User Interface, you may want to set the "Show Beta Options" switch to "Yes" (to see and use beta features)].  We'll need this for contact regions btw solid and surface bodies.

Insert Manual Contact Regions btw:

• the sheet metal and the punch, lower surfaces
• the sheet metal and the die, upper surfaces
• use frictionless contact behavior
• include "offsets" to account for the sheet metal thickness
• Adjust contact regions to "Update Stiffness" more frequently 

MESH (~12k nodes for reasonable solution time):

• Use high relevance, large overall element size (0.25") and aggressive shape checking
• Add "contact sizing" for both contact regions (0.15")
• Add a face sizing on the round edge of the die (0.1") to keep the mesh smooth

Environment:

• Fixed base on the die
• Move the punch (top face) down 0.25" (gradually - substeps)
  [The actual process would move the punch down 1" and then lift it up again - but for a classroom exercise, proper setup and solving just a portion of the downward stroke is useful without requiring overnight solving]
• If the sheet metal appears to move away from the center, CORRECT symmetry definition for edges of surface bodies

Analysis Settings:

• Automatic Time Stepping
• multiple Substeps
• Weak Springs: OFF
• Large Deflection: ON

• the element mesh
• a plot showing all the symmetry regions on the assembly
• the "environment" [ALL constraints and loads on the model]
• the reaction force history for the process of moving the punch down (Probe: Reaction)
• final deformation of the sheet metal
• final equivalent plastic strain in the sheet metal
• final vonMises stress in EACH body