Learning Forum

[Maximilian Löchte]

hey guys,

 

i try to simulate the material behaviour of epoxy resin under compressive strength. I have got data from material tests which were made according to ISO 604.

The following curve shows the relationship between the load and the deformation.

 

 

I already worked on the first part of the curve (untile maximum strength). For this i used Isotropic Elasticity and Bilinear- or Multilinear Isotropic Hardening. I think that these material models are best for the plastic part, aren't they?
But now i'm struggling with the rest of the curve? My question is: How to simulate this part? Or in generell: Is it even possible to simulate it? It would be nice if you can give me some advise about this! Please tell me also if you would choose other material models than the two mentioned above.

It's my first time to work with ANSYS, so my skills aren't that good. :(

 

Greetings from Germany
Max

[peteroznewman]

Hey Max, yes, you would use a plasticity material model. Yes, you only take data from the force-displacement curve up to the maximum value. The stress-plastic strain data table will use the last value for larger values of plastic strain in a simulation where the plastic strain exceeds the last value in the table. In a tensile test specimen, that model is sufficient to see the typical necking behavior which reduces the force output at large displacement. See what happens in your compressive simulation.

I recommend the following two courses:

https://courses.ansys.com/index.php/courses/topics-in-metal-plasticity/

https://courses.ansys.com/index.php/courses/topics-in-metal-plasticity/lessons/how-to-define-a-multilinear-hardening-plasticity-model-lesson-1/

[Maximilian Löchte]

Hi Peter, thank you for your answer. I worked on this the last days and it seemed to fit quite good. But with this my task hasn't finished, because now i try to model the material behaviour of a confined specimen which is also made of epoxy resin.
My professor told me that i should try to use the Drucker-Prager-Model for modelling the material behaviour for both tests (unconfined/confined). I think i read a lot about it, but i still don't know how to work with it in ANSYS. How do i get the necessary parameters for Ansys? I couldn't find any helpful information for using this model in ANSYS.

I still only got the experimental data which i mentionend in my first post.

Thank you for your help!

Max

[peteroznewman]

When you say "don't how to work with it in ANSYS", what do you mean?

In the ANSYS Help, go to Mechanical APDL and look at the Technology Showcase section. Chapter 49 uses Drucker-Prager.

Read the Theory manual section on Drucker-Prager.

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v231/en/ans_thry/thy_mat1.html%23capmodel

It includes literature references that you can also read.

[383] Sandler, I. S., DiMaggio, F. L., & Baladi, G. Y. (1976). Generalized cap model for geological materials. Journal of the Geotechnical Engineering Division. 102, 683-699.

[384] Pelessone, D. (1989). A Modified Formulation of the Cap Model. Gulf Atomic Report GA-C19579, prepared for the Defense Nuclear Agency under Contract DNA-001086-C-0277.

[385] Schwer, L. E. & Murray, Y. D. (1994). A three-invariant smooth cap model with mixed hardening. International Journal for Numerical and Analytical methods in Geomechanics. 18, 657-688.

[386] Foster, C. D., Regueiro, R. A., Fossum, A. F., & Borja, R. I. (2005). Implicit numerical integration of a three-invariant, isotropic/kinematic hardening cap plasticity model for geomaterials. Computer Methods in Applied Mechanics and Engineering. 194, 50-52, 5109-5138.

 

[387] Liu, R., Lin, G., & Bhashyam, G. (2010). Transformation of the Sandler and Rubin nonsmooth cap model to the Pelessone smooth cap model. ASCE Journal of Engineering Mechanics. 136, 680-685.

[Maximilian Löchte]

Thanks for your quick reply. I forgot to tell that i am using Ansys Workbench, so i don't have any skills in APDL. What i meant above was that i don't know how to use my data for the material model. After choosing the Drucker-Prager model in the engineering data, workbench asks for data like uniaxial tension/compression strenght and the biaxial compression strength. If i choose the additional softening option for the DP Model, there will be more necessary data. For all these points i don't know how to transform my data from the compression test into the necessary data for workbench. Generally i don't know how to use this material model in workbench and i couldn't find any help in the internet. Maybe you can give me some advise how to work with it. Thanks a lot Max

[peteroznewman]

It is useful to have a good understanding of the basic failure theories. Below is a good introductory video. I will look for a good explaination of the DP model for my next post.