Learning Forum

[Aswin]

Hi ,

I need to model the non linear behavior of the base material for the flexible pavement. The parameters provided by the literature provides non linear constants K1, K2 and K3 as shown in the picture below. I looked at the engineering tool box in ANSYS and could not find any matching selection to input these values. What is the best way to model the non linear behavior of the base material based on these parameters from the literature? Also once, I am successful in creating the material properties, how do I perform Non Linear analysis in Model? Do I just solve similar to linear model or do I need to change parameters in Analysis setting or other tools? I am new to ANSYS and will greatly appreciate your response.

 

 

Thanks,

 

Aswin Karki

 

 

[peteroznewman]

Aswin,

The table includes the authors and year the paper was published that had the material model they used in the paper. You should obtain the original paper and read it to understand their material models.

Once you understand their models, you can map them to the material models available in ANSYS.

Once you use a nonlinear material model, ANSYS will automatically use iteration to solve the model. You can control the iteration using various settings under Analysis Settings. You might also turn on other sources of nonlinearity such as Large Deflection if needed.

Regards,
Peter

[Aswin]

I was not able to map those in ANSYS. As they usesd these paramenters directly in the software. They have used different software than ANSYS. My project must use ANSYS.

[peteroznewman]

I was suggesting you show what the equations are for these material models, which I have done below.

This nonlinear behavior of unbound granular material was defined using the model developed by Witczak and Uzan (1988) which recommended the following formula: 

where MR is resilient modulus, k1, k2, and k3 are constants, sigma 3 is isotropic confining pressure, sigma d is the deviator stress, and pa is atmospheric pressure. 

Below is the form of the bilinear material model in the Thompson and Robnett 1979 paper. 

 

It has been observed that the granular layer of a pavement shakes down to a resilient (elastic) state via compaction during construction and under repeated wheel loads during the early stages of its service life. Resilient triaxial test (Allen and Thompson 1974; Karasahin et al. 1994), designed to mimic the stress state in granular layers, indicate that the inelastic deformations quickly shake down under cyclic loading and subsequently the response is essentially elastic (albeit nonlinear), as shown schematically in Fig. 1.

By showing the information above, I hope someone can suggest how to create this material model in ANSYS. Attached is a pdf with another paper.

[Aswin]

Hi Peter,

Thank you for your detailed response. I went through more literatures and found that the Mohr Coulomb parameters can be used for non linear analysis. When I tried to solve the model for the nonlinear effect,it would not complete the solution. I tried many different ways by changing solver step and mesh but nothing helped. Then I saved the file to different name and run it again and it is giving me error "The license used for the solution does not support  a specified non linear model. Either use a higher level license, switch to linear material model or suppress." I am using STUDENT VERSION of software. I am not sure if it has limitation for nonlinear analysis. If it has then I am not sure why it is still trying to solve without convergence on the another copy of the model. 

 

Thanks.

[peteroznewman]

Aswin,

You have two discussion topics going on the same model.

In the other discussion topic, I address the problem you created by using inappropriate values for the Mohr-Coulomb material model. The problem solving has nothing to do with using a Student license.

Please use only one discussion, the other one, to address one model, and stop using this discussion.

Thanks.