3 Replies Latest reply on Apr 2, 2014 3:45 PM by Jared Conway

    Nonlinear unloading problem.

    Stefo Peev

      Hi again, I have made a simulation of cylindric rubber model ( d=10 mm, l=50 mm) with F=100 N force, but i have problem with the damping. When I load the force, the stress-strain curve is nonliear, that is OK. When I unloading the stress-strain curve is very close to the curve of loading, and that is not right, even if I set damping (stiffness coefficient = 0.5). When you load-unload a rubber-like materials the material absorbs energy and the stress-strain curve of unloading have to be different of the loading curve. Even when you unload all that force can be seen small deformation, that deformation goes to zero if you get more time for relaxation. My question is where is my error? I want to get correct curve of unloading for 1 cycle of load-unload.

       

      I use:

       

      1. Nonlinear dynamic study;

      2. Mooney-Rivlin model with stress-strain curve, taken from experiment (Poisson's - 0.4995, TEC - 0.0006699, Mass - 1020 kg/m^3, Tensile Strenghth - 14 MPa);

      3.10 seconds loading of 100 N force and immediately unloading the same force for another 10 sec.;

      4. Autostepping - increment 0.2, max 20, № of adj. 10;

      5. Large displacement;

      6. Direct Sparse Solver;

      7. More accurate;

      8.Step/Tolerance - 1,30,0.01,0.01,0.5;

      9. Newton-Raphson method;

      10.Integration - Newmark;

      11. Mesh element size - 2,.8 mm;

      12. Damping stiffness coefficient = 0.5;

       

       

      Thank you in advance.