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General Mechanical

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Withdraw test

    • Ken Ng
      Subscriber

      Hi,

      I am trying to make a simulation to match the experimental result with some data from another program

      This is my model, a 4.5 × 50 mm screw (modelled as smooth surface) inserted into a predrilled orthotropic block is the hole diameter slightly smaller than the screw's diameter (overlapping diameter from another program's data is 1mm) to create the friction contract (the blue part is the surface of the hole, the red part is the surface of the screw).

      The table is the orthotropic block material:

      Density (kg/m3)

      500

      Young's Modulus X direction (MPa)

      14700

      Young's Modulus Y direction (MPa)

      737

      Young's Modulus Z direction (MPa)

      1000

      Poisson's Ratio XY

      0.449

      Poisson's Ratio YZ

      0.292

      Poisson's Ratio XZ

      0.374

      Shear Modulus XY (MPa)

      1150

      Shear Modulus YZ (MPa)

      942

      Shear Modulus XZ (MPa)

      103

      The following are the screw material changed properties, other properties remain unchanged of the default structure steel material

      Density (kg/m3)

      8000

      Young's Modulus (MPa)

      200000

      Yield strength (MPa)

      215

      Ultimate strength (MPa)

      450

      Poisson's Ratio

      0.29


      The graph of force reaction for the displacement vs the displacement is plotted to do the comparison. 

      the frictional contact is set as mu = 0.3 and with the command

      et ,cid, 174
      RMODIF,cid,21, 5.3
      RMODIF,cid,22, 4

      but I am encountering some problems:

      1. I wonder why the simulation failed to run the overlapping diameter is 1mm.

      When I set the hole diameter is 3.5mm (overlapping diameter is 1mm), the simulation goes error and gives me these messages. Why would this happen?

      2.  The DC coefficient failed to function or function weirdly

      So as the 1mm overlapping diameter can't work, I changed the overlapping diameter to a smaller value. but the DC coefficient would either cause errors like that shown in the previous image or give out a strange result that does not decay exponentially. What do I miss for the dynamic friction formula to work properly?

      3. How to insert the Hashin failure criterion into the model?

      I have checked this post (/forum/forums/topic/hashin-failure-results/) and the guide but I am still confused about where and how to input the Hashin failure criterion into the material. These are the data I have for the Hashin failure criterion

      Failure criteria:
      Parallel tension = 108 MPa
      Parallel compression = 29.8 MPa
      Matrix tension = 2.3 MPa
      Matrix compression = 5.5 MPa
      Longitudinal shear = 7.8 MPa
      Transverse shear  = 7.8 MPa
      Fracture energy 
      Longitudinal tension = 1.6 N/mm
      Longitudinal compression = 60 N/mm
      Transverse tension = 0.06 N/mm
      Transverse compression = 0.2 N/mm

      Thanks

       

       

       

       

    • Ashish Khemka
      Forum Moderator

      Hi,

      The error message indicates rigid body motion. What if you perform a modal analysis and see if any of the part seem to be unconstrained?

      Regards,

      Ashish Khemka

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