Hi Tsambani,

                Firstly, thanks for your reply. I will check your document. But, I have already seen some of your videos. You have some examples with 2D pre-meshed crack and 3D surface cracks which I clearly understand. I was wondering if I could have a 3D pre-meshed crack or an interface crack between bodies/parts of 2 different properties.

Regards,

Shree

Hello,

I`m afraid I can´t help you concerning the pre-meshed crack object. However, could the CZM approach be a suitable alternative for your issue? With that you could simulate a bimateral crack at a given plane modelled as bonded contact and expanded with a detaching condition. As input parameters you can for example apply the cohesive strength and the critical energy release rate. 

Kind regards,

Alexandra

Hello Alexandra,

                      Thanks for pointing that out. I shall check 'Interface crack' and 'Delamination' options available in the newer Ansys versions. Thanks again for your suggestion.

 Regards

Shree

look at this code that i have wroten

http://weld-ing.blogspot.com/2015/11/ansys-mechanical-apdl-code-for.html

https://www.researchgate.net/post/How_do_I_create_crack_in_any_structure_in_ANSYS_APDL

https://www.researchgate.net/post/Fracture_Mechanics_How_can_I_make_geometrical_model_of_a_Double_cantilever_beam_with_a_crack_inserted_in_between_the_layers_in_Ansys_Mechanical

Hello Shree,

I am working on something similar which your question intents to. I hope you might have successfully achieved the results. I am working on crack growth in DCB specimens, in Ansys 19.0 workbench. I am facing a problem in creating a mesh at the crack surface. I created a semi-elliptical crack at the surface of the body with its respective coordinate system. When I try to generate mesh on the crack surface under fracture tool, it shows an error. Error: The object is not valid with adaptive mesh refinement.

If I am missing something, could you help me in finding the mistake. Any other suggestions would be helpful too. Thanks,

Karun

Hi Karun,

In Ansys R19.0, some of the above mentioned limitations do not exist anymore. With respect to your question,

• Are you using any adpative remeshing technique? SMART feature of the newer Ansys versions?
• Is the crack between two cantilevers with different material properties? OR are they modeled as two separate bodies?

It would be nice if you can add some images of your model. Easier option would be to send me an archive if you wish. I can have a quick look at it.

Good luck :)

Hello Shreeraman,

Sorry for the late reply.

I am using DCB samples and loaded as Mode-1 plain strain (2D).

I think I am not using any Smart feature of adaptive meshing. I refine the mesh near the crack tip using sphere of influence. Yes, the crack is in-between the two beams with different material properties. The geometry has two different bodies. I am trying to find the bond strength between two different materials by using the critical force (using w.r.t unit thickness in 2D model) found experimentally.

In order to validate the model, I tried to find K1, J-integral between the similar material and I got the reasonable values. But, in dis-similar materials, I am not getting reasonable values.

Apart from this, I am facing another problem of shear stress in both the models. Even the model is constraint to load in Y-axis, shear stress occurs near the crack tip and through out the sample, which gives some K2 value too. I can post some screen-shots to explain the problem. Thanks,

Karun

Karun Kalia

I did not get the first part completely. Are you trying to obtain the fracture toughness from simulations or are you using experimentally determined value in Ansys? To describe an interface crack. you need an additional parameter (mode mixity) together with the conventional SIF (K) or ERR (G) and such.

Your second problem (having shear stresses also when loaded only in pure mode-I) is typical of interface cracks. That is because of the oscillatory behaviour of field variables due to their complex nature, when the crack is between materials of different properties. Look out for literature on mode-mixity and interface cracks

Maybe, I can suggest some if you could tell me what your end goal is?

Regards

Hello Shreeraman,

Thanks again for your help. I am trying to find fracture toughness between two dis-similar materials using Ansys simulation (K1,K2 and J-integral). Both the materials are bonded and then under Mode 1 loading, the critical force is found experimentally (Load vs displacement). I apply this critical force under plane strain condition (2D) in the model.

I apply pre-meshed crack tool at the crack-tip (notch) interface of the dis-similar materials. Thank you for giving me insight on the mode mixity. With this, I suppose that I might need to apply some other type of crack at the interface with some additional parameters?

However, I face the shear stress problem (K2) in similar material model as well (under pure Mode 1 loading). Could this be due to unrefined mesh or type of elements at the crack tip. I use total Quad elements and refined mesh near the crack tip.

Regards,

Karun