Calculating failure load from stress/strain results

- January 9, 2019 at 2:29 pm
  
  leticiacampello
  Subscriber
  
  Hi All,
  
  I'm currently working on a project in which I have to simulate a spontaneous humeral fracture in young children. I have finished all my simulations, but I'm struggling to calculate the failure load from the stress/strain contour plots. I'm using the principal stress/strain theory and I would like to know if anyone has any tips on how to get a value for failure load from results?
  
  I would much appreciate any help on this topic. Thank you in advance.
  
  Regards,
  
  Leticia
- January 9, 2019 at 2:40 pm
  
  peteroznewman
  Subscriber
  
  Hi Leticia,
  
  The failure load is when the Maximum Principal Stress = Ultimate Tensile Strength.
  
  What value of Tensile Strength are you using? This reference shows the Ultimate Tensile Strength of bone is 60-70 MPa.
  
  How is load defined in the model?
  
  Make a chart of Max Principal Stress in the bone vs Load and draw a horizontal line from the Tensile Strength to the curve, and a vertical line from the intersection down to the load. That is your failure load.
  
  This should be done after you have completed a Mesh Refinement Study to show that the Maximum Principal Stress is not dependent on the mesh element size.
  
  Regards,
  Peter
- January 9, 2019 at 2:42 pm
  
  jj77
  Subscriber
  
  Perhaps you can use the stress safety tools within ansys, there are different types. For instance the maximum tensile stress safety tool, can be used for brittle materials.
  
  For more info on this, see the help manual (just copy and paste the link below into your browser that comes up after accessing ansys/help).
  
  https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v192/wb_sim/ds_Stress_Tool_o_r.html?q=safety%20factor
- January 9, 2019 at 3:06 pm
  
  leticiacampello
  Subscriber
  
  Thanks for you reply,
  
  for my previous simulations, i did not included the tensile strength. I have done it now in the engineering data and ran the simulations again.
  
  My model is very very simple, so it's a cylinder with one end fixed and in the other end i've added a point load (upwards) as to simulate bending. I have also done with a moment on the cylinder. So I should just get the values from max principal stress and plot against the load?
  
  I didn't quite follow what I have to do with the tensile strength curve (the horizontal and vertical lines you explained)
  
  thank you so much!
  
  Leticia
- January 9, 2019 at 3:16 pm
  
  leticiacampello
  Subscriber
  
  Also, the load applied is about 71.6N and the other scenario with moment, I simulated as a value of 11.1Nm.
  
  BW
  
  Leticia