General Mechanical

General Mechanical

Fracture mechanic – cracks results interpretation

    • momidor
      Subscriber

      Hello, 


      It seems I've got a problem. The calculated Ki value is rather strange, i.e. when deep of the crack is decreasing the Ki value is increasing. Thus  for zero crack KI would be maximum... 


      Load combination is pure stretching ~ 80% of yield


      Does anyone know what went wrong ?


      Thanks in advanced


      Jurek


       


       

    • peteroznewman
      Subscriber

      Hello Jurek,


      I would have thought the crack propagation direction, the X axis in the image, would be pointing down, not along the length of the sample as shown below.



      Regards,
      Peter


       

    • momidor
      Subscriber

      Hello Peter, 


      Thanks. Well... I got minus KI now. It seems to be strange too. How to interpret negative value ? 


      I enclosed the quote from "The stress analysis of cracks handbook NY 2000 Hiroshi,Rankin,Irwin". Obviously it's not exactly the same crack because my is not going through the hole body.




       

    • peteroznewman
      Subscriber

      The coordinate system for a pre-meshed crack should be in the gap behind the crack front, not in the material.


      Maybe the crack is going to grow in the global +/- Z direction.  What if you make two more cracks, one on each side of the slot?

    • momidor
      Subscriber

      Yes ! Similar to my hand calculations... 


      Happy New Year Peter !


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