Help needed with crack growth simulation implementing CZM

[Denis Pryadko]

Help needed with crack growth simulation in Ansys implementing CZM

Hello, everyone!

Could you, please, help me with the following issue?

I’m trying to simulate a crack growth in an anisotropic media using cohesive zone model (CZM), and the results I get do not agree with my expectations, based on a common sense and simple estimations.

As I don’t yet feel myself on a safe ground with APDL, I make use of Ansys Mechanical, implementing command objects where needed.

At the moment the model is looking like a two beams (meshed with 20-node bricks) bonded together with a surface-to-surface contact, being separated from each other.

In the Contacts branch I create a bonded Solid to Solid contact, and attach a command object to it. Here is the text from the command object:

ESEL,S,REAL,,4

EDELE,all

ESEL,ALL



tb,czm,3,,,cbde

tbdata,1,1e4,5e-8,,,1e-8



About the first 3 lines: if I get it right, because of the symmetry of my model Mechanical automatically creates two contact sets, with real constant ID 3 and 4, respectively. Thus, I believe, it makes sense to delete one of these sets.

The elastic properties of the material in use are: linear anisotropic elasticity with 11, 22, 33 components of the elasticity matrix around 1e11 Pa .All faces of the beams are perpendicular to the relevant coordinate axis, the separation traction is applied along one of coordinate axis, normal to the contact plane (to be precise, I impose on two faces of the different beams not the force, but ramped displacement).

You can see that the maximum normal contact stress is set to be 1e4 Pa, which is not much, considering the elastic properties of the material. I estimate that if I set this value to 1e10 Pa, the model should crack after deformation of less than 15 %. On the practice, if this value is greater than 1e4, the body deforms until the deformation causes instabilities, without cracking. How could these be? Where is my mistake?

Some additional information about my model:

The pinball radius is set to be program controlled, large deflection = 0n, Augmented Lagrangian method , Physics type: structural, Analysis type: transient.

Thank you very much for your attention!

 

[Achy47]

Thank you for reaching out for help with your crack growth simulation in Ansys using CZM. I understand that you are facing some discrepancies between your expected results and the ones obtained from the simulation, and you are looking for some guidance on how to improve your model. I am happy to assist you in this matter.

Based on the information provided, it seems like you have a good understanding of the concepts and theory behind CZM and its implementation in Ansys. However, there are a few things that may be causing the discrepancies in your results:

1. The use of two beams in your model: While it is possible to simulate a crack growth between two bonded beams, it may be more accurate to use a single beam with a pre-existing crack. This will eliminate any potential issues with the contact between the two beams and provide a more realistic simulation of crack propagation.

2. The contact conditions: It is important to ensure that the contact conditions used in your simulation are accurate and representative of the real-world scenario. Any discrepancies in the contact parameters can greatly affect the results of your simulation.

3. The material properties: The elastic properties of your material may also play a significant role in the results obtained. It is important to ensure that the material properties used in your simulation are accurate and representative of the real material. Any errors or discrepancies in the material properties can greatly affect the behavior of the crack and its propagation.

I would suggest reviewing these aspects of your simulation and making any necessary changes to improve the accuracy of your results. Additionally, it may be helpful to consult with other experts in the field and seek their advice on your model and simulation setup.

I hope this helps and wish you the best of luck with your simulation. Please feel free to reach out for any further assistance or clarification.