The default failure criteria for ANSYS is Von Mises, however you have been asked to complete a FEA on a brittle material, what failure criteria would be more appropriate and why? How would you apply this criterion if there is no option for it within the program? A colleague of yours has come to you with a question about their mesh, they have a general mesh on most of the object with refinement around the sharp edges. They find that as they increase the refinement level the stress keeps increasing and is now beyond the failure stress of the material. What sort of loading could cause this to happen and why? Consider two objects made of different isotropic materials (Aluminium and Steel) but with the same geometry, loads and boundary conditions. Which of the materials would have a higher stress and why? When meshing you have two options; free and mapped. Explain the advantages and disadvantages of each of the methods? Give an example of when you would use each method and justify why? Observe the two stress distribution plots below, what is the difference between the two plots?
1.convergence failure
2.Concentrated load
3.steel will have higher stress when compared to aluminium..
4.Free Meshing
•ANSYS has a free meshing routine and its easy to use
Will it give good results when compared with mapped meshing
•Create the Geometry
•Good-
-easy to create the geometry
-meshing is fast
•Bad-
-some triangular elements are used
-some elements may have poor aspect ratios
Mapped Meshing
•Create the Geometry
-create the geometry in smaller sub areas using key points and lines
•Concatenate Lines
-sub areas must be bounded by 3 or 4 lines
-concatenate lines around areas until each sub area has no more than 4 boundary lines
•Good
-Lots of control over meshing and elements
•Bad
-takes a lot more time to create the geometry
5.Stress is more in 1st when compared to 2nd.
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