Getting large maximum principal stress in my bar (Exceeds the yield limit)

to2020

Hi,

I am doing a bond test with the rebar and concrete. When I apply 5mm of displacement on the rebar (over 200-300 substeps), I get the following result for the maximum principal stress:

My properties for the rebar is 500MPa yield strength and 560MPa ultimate tensile strength.

The way I modelled is that I have inputted a steel plate with high elastic modulus to make it a fixed support (shown in green in the picture above), the concrete surrounding the bar is of 40MPa in strength.

I have tried running simulation for bonded contact between the steel rebar (I have also modelled the ribs as I am analyzing this) as well as frictional (with a coefficient of 0.45). I get very high maximum principal stress for both the cases.

I have used a 3mm mesh because it is the lowest I could go on the student version (if I make it smaller, the solver won't run). Would anyone know why this is happening?

I have attached the link to the file (https://drive.google.com/file/d/1nO1G7UuOlhgvOGsRfXG6CFqnUBEcYWmv/view?usp=sharing)

I just want to get the load vs displacement graph. Hope someone can suggest what I am doing wrong/give guidance to what I can do instead.

Thanks in advance!

rkumbhar

Hi @to2020

Just to check have you turned ON large deflection in Analysis setting? What nonlinear material properties are you using for rebar?

to2020

Hi @rkumbhar

Thank you for the response.

No, I haven't turned on the large deflection.

I just used the default material property given in ANSYS library for the structural steel (I then changed the tensile yield strength and ultimate tensile strength values to 500MPa and 560MPa respectively). I then did inputted bilinear law with yield strength of 500MPa and Tangent Modulus of 560MPa. I realised there was a typo in the value I inputted previously. But with the following updated settings:

Structural steel properties:

Concrete Properties:

I then applied 5mm displacement on top of the rebar and the maximum principal stress I get is what is shown below:

rkumbhar

Hi @to2020

Great! Please Turn ON the large deflection and try again.

to2020

Hi @rkumbhar ,

Sorry for the delay in getting back to you.

I was getting the following error, so I was increasing the substeps and still get this error:

Here are my settings:

I am using 3mm mesh size. If you could please suggest what to do, it would be great.

Thanks again!

to2020

@rkumbhar Could you please help or anyone who has an idea of what is causing the above error please reply :)

akhemka

Hi @to2020 ,

The error above is element distotion error and the error message gives instructions on what to do:

Excessive distortion of elements is usually a symptom indicating the need for corrective action elsewhere.

1. Try incrementing the load more slowly (increase the number of substeps or decrease the time step size).
2. In the Mesh task, change the setting for the Aggressive mechanical control that will create better aspect ratios. This approach is applicable only if you are using manual meshing.
3. Consider the behavior of materials and review the contact pairs.

Please see if you can try implementing these changes.

Regards,

Ashish Khemka

to2020

Hi @akhemka,

1. I have initially incremented the load between 200-300 steps. I have tried to increase this as per the recommendation but was getting the same error.
2. I haven't done manual meshing - just let the program create a mesh for me after specifying the contact sizing between rebar and concrete as well as the rib size (Both are set to 2mm because if I go any smaller, the program won't run as it exceeds the academic limit).
3. I have modelled the contact as friction (Between rebar and concrete).

Is there anything else I can do instead?

Thanks!

akhemka

Hi @to2020 ,

Did you check the element 78254 for which part is showing this error. Also, are you seeing this ina bilinear model with zero tangent modulus? If yes then you can expect this behavior as the material will behave as perfect plastic. Please let me know.

Regards,

Ashish Khemka

to2020

Hi @akhemka

Yes, it is a bilinear model. How can I check the individual elements?

Thanks!

akhemka

Hi @to2020 ,

Instead of bilinear model try using a multilinear model. For checking individual elements try using worksheet tab in the NAmed Selection:

https://www.padtinc.com/blog/beyond-clicking-named-selections-move-to-the-worksheet/

For motr details on plasticity model please refer to the link below:

https://forum.ansys.com/discussion/9394/bilinear-multilinear-curve-fitting-for-plasticity-modelling

Regards,

Ashish Khemka