General Mechanical

General Mechanical

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some problem of defining prony shear relaxation parameter

    • Zhenhao Qian

      When I fitting the shear relaxation curve, I found I must define the elastic modulus, but I don't know which modulus should I define, Instantaneous modulus or equilibrium modulus?

    • John Doyle
      Ansys Employee

      Assuming this is a small strain application, the base material can be defined with the instantaneous linear elastic modulus and Poisson's ratio.

      If this is a large strain application for a polymer type material, consider defining  base material as a hyperelastic strain energy density function.

      • Zhenhao Qian


        Thank you for your reply! And I’ m sorry about my late reply.

        I also have some questions


        1. Would I interpret small strain as the part before plastic stage? 
        2. Before I do stress relaxation test about my material, I do uniaxial compression test to confirm its linear elastic stage. Because as far as I know, the stress relaxation test must ensure that it is within the linear elastic stage of material. Due to limitations, I can only apply load at a low speed (about 10mm/min to 60mm/min), I ‘m not sure how to confirm the linear elastic stage, because before 0.2 strain, the uniaxial curves don’ t seem to be completely ‘ linear‘ . I’ m not sure whether my understanding is correct.
          The figure shows the uniaxial compression curves. Red line = 10mm/min, Blue line = 60mm/min.
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