10.4.2. Fitting Procedure in Ansys Polymat

Start Ansys Polymat by typing polymat. Then follow the procedure described below to perform the fitting for the data presented in Experimental Data.

Note:  The fitting calculation for this example will take significant time, due to the transient elongational curves added for the fitting.

 

10.4.2.1. Step 1: Define the Fluid Model Type

  Select Fluid Model

  1. Choose Differential viscoelastic model.

      Differential viscoelastic model

  2. Return to the top-level menu.

 

10.4.2.2. Step 2: Specify the Material Data Models

  Material Data

  1. Enter the Differential viscoelastic models menu.

      Differential viscoelastic models

  2. Specify the first viscoelastic model.

      1-st viscoelastic model

    1. Select the Giesekus model.

        Giesekus model

    2. Accept the current values.

        Accept current values

    3. Return to the Differential viscoelastic models menu.

        Upper level menu

  3. Specify the second, third and fourth viscoelastics models of type Giesekus.

      Addition of a viscoelastic model

    Note:  You do not have to change values of the different modes. They will be fitted automatically later.

  4. Return to the top-level Ansys Polymat menu.

 

10.4.2.3. Step 3: Read in and Draw the Experimental Data Curves

  1. Enter the Automatic Fitting menu.

      Automatic fitting

  2. Enter the List of Experimental Curves menu.

      Add experimental curves

  3. Add the first experimental curve (visc.crv).

      Add a new curve

    1. Select the curve named visc.crv.

        Enter the name of the curve file

    2. Specify that the curve is a shear viscosity curve.

        Modify the curve type

      1. Choose steady shear viscosity (the default).

          steady shear viscosity

      2. Return to the List of Experimental Curves menu.

  4. Add the second experimental curve (g1.crv).

      Add a new curve

    1. Select the curve named g1.crv.

        Enter the name of the curve file

    2. Specify that the curve is a storage modulus curve.

        Modify the curve type

      1. Choose storage modulus G’.

          storage modulus G’

      2. Return to the List of Experimental Curves menu.

  5. Add the third experimental curve (g2.crv).

      Add a new curve

    1. Select the curve named g2.crv.

        Enter the name of the curve file

    2. Specify that the curve is a loss modulus curve.

        Modify the curve type

      1. Choose loss modulus G".

          loss modulus G"

      2. Return to the List of Experimental Curves menu.

  6. Add the fourth experimental curve (stress_01.crv).

      Add a new curve

    1. Select the curve named stress_01.crv.

        Enter the name of the curve file

    2. Specify that the curve is a transient extensional flow curve.

        Modify the curve type

      1. Choose transient extensional flow.

          transient extensional flow

      2. In this menu, choose uniaxial mode, stress vs. strain [ln(l/lo)], and constant extensional velocity.

      3. In the menu Experimental curve #4, modify the initial strain rate (V/lo) and set it to 0.1.

          Modify the initial strain rate (V/lo)

      4. Return to the List of Experimental Curves menu.

  7. Add the fifth experimental curve (stress_1.crv).

      Add a new curve

    1. Select the curve named stress_1.crv.

        Enter the name of the curve file

    2. Specify that the curve is a transient extensional flow curve.

        Modify the curve type

      1. Choose transient extensional flow.

          transient extensional flow

      2. In this menu, choose uniaxial mode, stress vs. strain [ln(l/lo)], and constant extensional velocity.

      3. In the menu Experimental curve #5, modify the initial strain rate (V/lo) and set it to 1.

          Modify the initial strain rate (V/lo)

      4. Return to the List of Experimental Curves menu.

  8. Add the sixth experimental curve (stress_10.crv).

      Add a new curve

    1. Select the curve named stress_10.crv.

        Enter the name of the curve file

    2. Specify that the curve is a transient extensional flow curve.

        Modify the curve type

      1. Choose transient extensional flow.

          transient extensional flow

      2. In this menu, choose uniaxial mode, stress vs. strain [ln(l/lo)], and constant extensional velocity.

      3. In the menu Experimental curve #5, modify the initial strain rate (V/lo) and set it to 10.

          Modify the initial strain rate (V/lo)

      4. Return to the List of Experimental Curves menu.

  9. Return to the Automatic Fitting menu.

  10. Plot the six experimental data curves.

      Draw experimental curves

The curves will be presented in two graphics: In the first one, you can see the steady shear viscosity, G’ and G"; while in the second, you can see the extensional curves.

 

10.4.2.4. Step 4: Set Numerical Options and Run the Fitting Calculation

  1. Set the numerical parameters for the calculation.

      Numerical options for fitting

    1. Limit the range of relaxation times to be from a minimum of 0.01 to a maximum of 100.

        Modify the range of relaxation times

    2. Return to the Automatic Fitting menu.

  2. Specify a name for the material data file (for example, example4.mat).

      Enter the name of the result file

  3. Start the fitting calculation.

      Run fitting

 

10.4.2.5. Results

The results of the fitting calculation are as follows: 

RESULTS 
nb. of modes = 4
 
 mode # 1 - Giesekus model
 T = T1 + T2
 (1+alfa*trelax/visc1*T1)*T1 + trelax*T1up = 2*visc1*D
 T2 = 2*visc2*D

 where - visc is the viscosity
       - visc1 = (1-ratio)*visc
       - visc2 = ratio*visc
       - trelax is the relaxation time
       - T1up is the upper-convected time derivative of T1
 
 visc   = 0.1940853E+04 [auto]
 trelax = 0.1000000E-01 [auto]
 alfa   = 0.7392697E+00 [auto]
 ratio  = 0.2350520E-04 [auto]
 
 mode # 2 - Giesekus model

 T = T1 + T2
 (1+alfa*trelax/visc1*T1)*T1 + trelax*T1up = 2*visc1*D
 T2 = 2*visc2*D

 where - visc is the viscosity
       - visc1 = (1-ratio)*visc
       - visc2 = ratio*visc
       - trelax is the relaxation time
       - T1up is the upper-convected time derivative of T1
 
 visc   = 0.1129548E+05 [auto]
 trelax = 0.2154435E+00 [auto]
 alfa   = 0.6407529E+00 [auto]
 ratio  = 0.0000000E+00 [fixed]
 
 mode # 3 - Giesekus model

 T = T1 + T2
 (1+alfa*trelax/visc1*T1)*T1 + trelax*T1up = 2*visc1*D
 T2 = 2*visc2*D

 where - visc is the viscosity
       - visc1 = (1-ratio)*visc
       - visc2 = ratio*visc
       - trelax is the relaxation time
       - T1up is the upper-convected time derivative of T1
 
 visc   = 0.4098902E+05 [auto]
 trelax = 0.4641589E+01 [auto]
 alfa   = 0.4906601E+00 [auto]
 ratio  = 0.0000000E+00 [fixed]
 
 mode # 4 - Giesekus model


 T = T1 + T2
 (1+alfa*trelax/visc1*T1)*T1 + trelax*T1up = 2*visc1*D
 T2 = 2*visc2*D

 where - visc is the viscosity
       - visc1 = (1-ratio)*visc
       - visc2 = ratio*visc
       - trelax is the relaxation time
       - T1up is the upper-convected time derivative of T1
 
 visc   = 0.4973851E+04 [auto]
 trelax = 0.1000000E+03 [auto]
 alfa   = 0.4113689E+00 [auto]
 ratio  = 0.0000000E+00 [fixed] 

The computed and experimental curves are shown in Figure 10.4: Computed and Experimental Curves for Steady Shear Viscosity, Storage Modulus and Loss Modulus and Figure 10.5: Computed and Experimental Curves for Stress vs. ln(l/lo) at Different Initial Strain Rates (0.1,1, and 10)..

Figure 10.4: Computed and Experimental Curves for Steady Shear Viscosity, Storage Modulus and Loss Modulus

Computed and Experimental Curves for Steady Shear Viscosity, Storage Modulus and Loss Modulus

Figure 10.5: Computed and Experimental Curves for Stress vs. ln(l/lo) at Different Initial Strain Rates (0.1,1, and 10).

Computed and Experimental Curves for Stress vs. ln(l/lo) at Different Initial Strain Rates (0.1,1, and 10).