Solution for cracks in turbine housing using modal analysis

- December 16, 2018 at 12:13 pm
  
  Shaikashique88
  Subscriber
  
  I have created a crack in a turbine housing , while i am using modal analysis its not validating the results as it does not have an option for crack creation. How to solve yhe problem for finding natural frequencies with crack in an object.
- December 16, 2018 at 4:15 pm
  
  peteroznewman
  Subscriber
  
  Edit the geometry and model the crack in the solid (or surface) body. Make sure when meshing to turn off mesh defeaturing, then a Modal analysis will include the effect of the crack.
  
  Regards,
  Peter
- December 19, 2018 at 5:59 am
  
  Shaikashique88
  Subscriber
  
  But i would also like to know about the stress intensity factors for the problem.If i create a crack in the solid body itself then how would i evaluate the SIFS values in solution. My problem is to calculate natural frequencies, Von missses stresses , and SIFS for a turbine blade with and without crack . So i would like to get a deatiled procedure.
- December 19, 2018 at 12:10 pm
  
  peteroznewman
  Subscriber
  
  In Static Structural, create a Coordinate System inside the crack, insert a Fracture branch, then insert a Pre-Meshed Crack. You will need the Coordinate System to help ANSYS to know the direction of the Pre-Meshed Crack. In the results you can insert Fracture Tool and you can evaluate SIFS.
  
  If the crack is closed in the geometry, so there are just two faces touching, one idea that would make comparing with and without a crack easier is to either have Bonded Contact (type MPC) or Mesh Merge to remove the crack from the model, without editing the geometry.
  
  Please reply if you need more details, or mark this post with Is Solution if you have everything you need.
  
  Regards,
  Peter
- December 20, 2018 at 4:52 am
  
  Shaikashique88
  Subscriber
  
  Thank you for your reply.I have done what you just mentioned already, the problem i am facing is with finding out natural frequencies with crack in my component.
  
  it has been showing the error - "Fracture cannot be sent into solver " , in "MODAL ANALYSIS" there is no fracture option . i am getting the same frequencies with and without crack, actually the frequencies should be different.
- December 20, 2018 at 1:27 pm
  
  peteroznewman
  Subscriber
  
  Duplicate the Static Structural, delete the Fracture branch from the outline and the Loads, then convert it to Modal. That way you will keep all your mesh controls and supports.
  
  The lower frequency modes might be almost identical with and without the crack in the geometry. You might need to request some higher frequency modes. Did you look for motion of material across the crack? I expect if you probe for displacements on each side of the crack geometry, you might see a difference.
  
  Regards,
  Peter