General Mechanical

General Mechanical

3 Point bending test for different thickness of material (co-polyester PETG)

    • chaebinkim1127
      Subscriber

      Hi,


      I'm currently trying to simulate the 3 point bending test (based on ASTM D790) with ANSYS.


      I tested four different thickness of copolyester PETG plastic: 0.06'' 0.122'' 0.236'' 0.325'' with Instron in physically and got the flexural stress and modulus from the test.


       


      I tried to simulate this with ANSYS but I have some issues.


      First, I'm not sure which stress I need to look for the flexural stress. Should I see the equivalent stress? or normal stress?


      Also, as I increase the thickness of the test specimen (i.e) from 0.06'' to 0.122''), it gives me less normal stress value.(the equivalent stress goes up, but ridiculously high) 


       


      Here are the settings I've tried:


      I use the flexural modulus as the young's modulus of the material since I want to get the similar value of flexural stress from ANSYS.


      Connection: I add contacts to three fixtures (one top, two bottom) and set them as frictional


      Mesh: Add contact sizing for three fixtures and add edge sizing for the contact line that I created in geometry section 


      Setting: Add displacement for the top fixtures and use tabular data with time (i.e.) 0.05 in/min), and add cylindrical support for the two bottom fixtures


      I add one of the result I got with thickness of 0.122''


       


      Thank you for your help! 

    • Sandeep Medikonda
      Ansys Employee

      Hello,


        Please refer to the examples listed in the Cornell learning module. It talks of a 4point bending test.


        There are also solved examples ob bending in the verification manual. Please see here.


        Peter also demos how to do this in this discussion and the video below:



      Note that you calculate bending stress in Mechanical:



      A word of caution here, ideally flexural or bending modulus of elasticity is equivalent to Young's modulus, however, this might not be true for polymers.


      Regards,
      Sandeep
      Guidelines to the Student Community

    • jaymin0002
      Subscriber

       

      Hello Sandeep Medikonda, 

      Could you please guide me on how we can define the flexural modulus of elasticity and Young’s modulus differently for polymers in ANSYS? 

      Thank you in advance. 

       

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