Spring 2007, MET415 - FEA Applications I

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

Sample Problem for Exam 2

Model and solve the problem below in ANSYS and answer the questions at the bottom of the page.

The lid of a plastic CD case is loaded in a manner which may cause the tabs to break off.

• Modulus = 1x10⁶ psi
• Poisson's Ratio = 0.35
• The load, F, is 5 lb_f
• Distribute the 5 lb_f load equally over the (nodes along the) edge of the tab.

What element type was used ?

What element options were used ?  (element behavior)

What real constants were used ?

How many nodes and elements were created ?

What is the % error (SEPC) for your solution ?

What is the maximum deflection (in inches) ?

What is the maximum vonMises stress (psi) ?

Where does the maximum vonMises stress occur ?

What is the sum of forces on the model ?
 S Fx =         S Fy =         S Fz =
     (Get the Reaction Solution from the General Postprocessor)

What happens to the maximum stress as you refine the mesh ?

The model above is created in ANSYS, using 1/2 symmetry: SHELL93 - default options, 0.05" thickness (real constant), 4643 nodes, 1486 elements.  The mesh error, SEPC, was 45.3% (singularity exists at sharp corner).  The max. stress is not reliable since it occurs at the singularity and will increase indefinitely as the mesh is refined.

ANSYS Workbench model: symmetry could NOT be used in WB 10.0 since edges of surface bodies cannot be constrained as frictionless surfaces.  The WB model was solved with NO constraints - weak springs were permitted to support the part.  3925 nodes and 3747 SHELL181 elements were meshed.  The mesh error, SEPC, was 19.3% (singularity exists at sharp corner).  The max. stress is not reliable since it occurs at the singularity and will increase indefinitely as the mesh is refined.