Modelling Material Random Distribution in Ansys WB

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jacks3215 posted this 2 weeks ago

I would like to carry out simulation of fiber reinforced concrete material under three point bending load in Ansys workbench. Since concrete is a brittle material therefore addition of fibers alters the brittle nature of concrete to ductile. I have already carried out the experimental tests and would like to verify the results with that of finite element simulation.

I would like to request the experts here to guide me on how can I model the random distribution of fibers in Ansys workbench? Since in reality the fibers are randomly distributed with in the given block or space therefore I need to process the same in simulation work.

Thank you

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peteroznewman posted this 2 weeks ago

There are two kinds of simulations that are possible, but they have different objectives.

One kind is an extremely detailed model that tries to replicate the physics of concrete fracture, fiber breakage, fiber-concrete bond failure, fiber friction, etc to model at a very fine level what is happening to the components in the material under load. The model tries to predict what the experimental data will be, even before it is measured. This is the type of simulation a material researcher might build.

Another kind of simulation is much simpler, taking an existing mathematical material model with some adjustable parameters, and attempting a best fit of those parameters to the experimental data of a three point bending test, so that other more complicated shapes of reinforced concrete structure can be modeled and predictions made for the load carrying capability of those shapes that were never tested. The model of the three point test is going to reproduce the previously measured three point experimental data when the values of the parameters have been properly chosen. This is the type of simulation a structural engineer might build.

Which type of model are you trying to build?

If it is the the second type, then there are several plasticity models that have parameters you can adjust to match your experimental data.

jacks3215 posted this 2 weeks ago

Thank you for your reply.

I am a research student and simple verification of experimental results would be fine.

I also intend to simulate single fiber pullout from the concrete specimen. I have the specifications of concrete, fiber and interface parameters (chemical bond, frictional bond). These parameters I have taken from pullout experiments. From the simulation I could verify the experimental results. If these can be joined together in to the bending simulation, like the first way you mentioned in your answer, then is also ok for me.

For the bending I intend to carry out two simulations, with and without the addition of fibers. Since concrete without fibers will have brittle fracture therefore I could have the maximum strength and the crack and crush from the simulation. With the addition of fibers there will have different behavior resulting in multiple cracks and could have bendable concrete until fracture.

All of my concrete designs are simple, rectangular beam for bending, cubic block for compression. I wont be using any of the complicated structural shapes/designs in my experiments or simulations.

peteroznewman posted this 2 weeks ago

Jack, you may find some of my posts on this site relevant.

Here is a simulation of pullout of ribbed rebar from concrete and here is the question about the pullout force result.

Here is a simulation of compression failure of a concrete cylinder without rebar and the post below is with rebar.

Those simulations were using Explicit Dynamics models and are more for post failure illustration than calculating results.

There are many material models available in ANSYS to predict the load when failure would occur, without actually seeing the post failure behavior.

jacks3215 posted this 1 weeks ago

Thank you for the links. I will follow the links and get back in case of any problem.

I would like to confirm, please correct me if I am wrong, in case I model three point bending simulation of concrete (without reinforcement i,e, brittle fracture), static structural model would be a better choice.

But if I try to carryout three point bending simulation of fiber reinforced concrete in static structural then will the static structural be able to get the post cracking behavior as well? or I must use explicit dynamics for such purpose?

In addition, could you please guide me how could I model fibers random distribution with in a concrete block in Ansys workbench?

peteroznewman posted this 1 weeks ago

I'm having a problem replying, but I can paste an image of the text that the webite gave me an error typing!

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peteroznewman posted this 1 weeks ago

Attached is a zip file with an Excel spreadsheet, a text file and an ANSYS 18.2 project.

The spreadsheet creates 100 randomly oriented straight fibers with a random length between 0 and 5 mm, randomly distributed in a volume of 15 x 25 x 55 mm. You could modify the spreadsheet to create fibers of a minimum length.

The text file is a copy paste of columns O-S of the spreadsheet, which is read into DesignModeler.

After reading that file in and creating a volume, you can see the result shown in the image below.

This is not a complete solution, just an example of how to create random line bodies in DesignModeler.

I have used line bodies as steel rebar to reinforce concrete columns in Explicit Dynamics. Not sure how to use this in Static Structural.

 

Attached Files

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pgl posted this 1 weeks ago

Test reply.

jacks3215 posted this 3 days ago

Thank you for sharing the files. With reference to the attached files I would like to ask following queries,

I will be drawing the mold size to 400x400x1600 mm. I can assume that fibers are straight. I would like to ask is it possible to keep the fiber length constant at desired value, say 12 mm? Instead of using random length between 0-12 mm? With in the experimental work I have kept fiber length constant so if the values in simulation are different/varying then I might get different result in simulation. 

I have checked values of the text file and the Excel spreadsheet, columns from O to S, but the values of the columns Q-S differ from those mentioned in the text file. Could you please re-check this?

Thank you

peteroznewman posted this 3 days ago

I chose to randomize the fiber lengths because it was easy to do.  I can randomize the orientation of fixed length fibers, I just have to do a bit more math. This is all being done outside ANSYS using functionality in Excel.  The reason the text file and the Excel spreadsheet are different is because each time you open Excel, it creates 600 new random numbers to fill the cells.

There is more work to be done to figure out how to have the fibers bond to the concrete in a Static Structural model. I only know it is simple to do in Explicit Dynamics.

I will attach an Excel file example with the 12 mm fibers once I have got the equations worked out.

peteroznewman posted this 3 days ago

Attached is a zip file with an Excel spreadsheet to calculate the text file used in the ANSYS 18.2 model with 12 mm long randomly positioned and oriented fibers. I only put in 49 fibers and the solid because there is a 50 body limit on the Student license.

Attached Files

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