Finite Element Modeling - Science topic

The CDP model in Abaqus can be used for geopolymer concrete, but it requires careful calibration. Geopolymer concrete differs from ordinary concrete in tensile behavior, fracture energy, and ductility, often showing higher tensile strength but lower ductility. Parameters such as dilatancy angle and damage evolution must be adjusted based on experimental data to reflect these differences accurately.

from abaqus import *

from abaqusConstants import *

import random

def replace_material_randomly(percentage, model_name, part_name):

print('------------------replace_material_randomly-----------------')

try:

# Access the part from the model

p = mdb.models[model_name].parts[part_name]

# Define the new section

mdb.models[model_name].HomogeneousSolidSection(name='New-Section', material='MATERIAL2')

# Ensure the 'All_solids' set exists

if 'All_solids' not in p.sets:

raise ValueError("The set 'All_solids' does not exist in the part.")

elements = p.sets['All_solids'].elements

num_elements_to_replace = int(len(elements) * (percentage / 100))

if num_elements_to_replace == 0:

raise ValueError("Percentage too low; no elements selected for replacement.")

# Randomly select elements to replace

indices_to_replace = random.sample(range(len(elements)), num_elements_to_replace)

elements_to_replace = [elements[i] for i in indices_to_replace]

# Create a set of the elements to replace

region = p.Set(elements=elements_to_replace, name='Elements_to_replace')

# Remove previous section assignments

p.sectionAssignments.remove(region=region)

# Assign the new section to the selected elements

p.SectionAssignment(region=region, sectionName='New-Section', offset=0.0, offsetType=MIDDLE_SURFACE, thicknessAssignment=FROM_SECTION)

print("Material replacement completed successfully.")

except Exception as e:

print(f"An error occurred: {e}")

# Example function call

replace_material_randomly(10, 'Model-1', 'Part-1')

Did you solve your problem? I also want to use regurlar contact and cohesive contact concurrently.

If I consider the problem domain to be the entire CT specimen. What will be the boundary conditions? In that case do I have to restrict the Uy in the middle portion along the direction of crack?

Maxim Naumov What do you mean when you say grid settings?

My mesh is finer than that of the paper. The number of elements in my model is about 3 times that of the paper. I used C3D8R elements only.

Congratulations to you! Could you please share your thesis?

Dear Doctor

"Material damping can be defined:

Rayleigh damping

In direct-integration dynamic analysis you very often define energy dissipation mechanisms—dashpots, inelastic material behavior, etc.—as part of the basic model. In such cases there is usually no need to introduce additional damping: it is often unimportant compared to these other dissipative effects. However, some models do not have such dissipation sources (an example is a linear system with chattering contact, such as a pipeline in a seismic event). In such cases it is often desirable to introduce some general damping. Abaqus provides “Rayleigh” damping for this purpose. It provides a convenient abstraction to damp lower (mass-dependent) and higher (stiffness-dependent) frequency range behavior.

Rayleigh damping can also be used in direct-solution steady-state dynamic analyses and subspace-based steady-state dynamic analyses to get quantitatively accurate results, especially near natural frequencies."

Joshua Depiver Hello , can you please help me with this concern ?

i use USDFLD to compute phase fractions (3 phases) , law kinetics are written in SDVs , everything seems working good except the fact that i have negative values in the middle of my axsymmetric model , negative values are displayed also in the legend of SDVs which is not reasonable at all ?

As Samy said i would agree that this seems that the node/element for which you are trying to see results has some boundary constraints issue like it just seems like that contact surface restraints between small element and column are not defined correctly its just not behaving like a rigid connection. And with applied loads it seems like element is slipping inside the column element which is resulting in decreased strain with applied stresses.

In Abaqus software, a concrete failure point typically refers to the point at which the material model representing concrete reaches a state of failure or damage. Abaqus is a finite element analysis (FEA) software commonly used for simulating and analyzing complex engineering problems, including the behavior of structures and materials under various conditions. Concrete is a brittle material, and its failure can be characterized by different failure criteria, such as: Compression Failure: This occurs when the concrete is subjected to high compressive stresses, leading to crushing or cracking. Abaqus can simulate this failure using appropriate material models and failure criteria for concrete under compression. Tensile Failure: Concrete is weak in tension, and Abaqus can simulate the initiation and propagation of cracks under tensile loading. Shear Failure: Concrete can also fail in shear, especially in regions where there is a combination of compression and shear stresses. Abaqus allows for modeling shear failure using appropriate material models and failure criteria. Combined Modes of Failure: Abaqus supports modeling the interaction of different failure modes, considering the complex behavior of concrete structures under various loading conditions. To define a concrete failure point in Abaqus, you need to choose an appropriate material model for concrete and specify the failure criteria and parameters associated with the selected model. Abaqus provides several concrete material models, such as the Concrete Damage Plasticity (CDP) model, the Concrete Damaged Plasticity (CDP) model, and others, each with its own set of parameters to define the material behavior and failure.

I used the Tekla, Revit and 3D Solid and other softwares

Chase Mortensen, the surface to surface interaction with smaller slave surface mesh density will solve the problem. For more, let's connect on WhatsApp to discuss; https://wa.me/+923440907874

To the followers of this post, I did some more digging and with the help of other fellows, it turns out that applying periodic and symmetry BC is possible at the same time to the volume elements, as described in the following paper. Please note that BCs differ for tensile and shear loading in this manner. This means that applying mixed-mode loading is not possible in the setup.

Whitcomb, J. D., Chapman, C. D., & Tang, X. (2000). Derivation of boundary conditions for micromechanics analyses of plain and satin weave composites. Journal of Composite Materials, 34, 724–747.

Dear Mustafa Shqair I didn't see your reply before sir, I will review it and see if with this information I can solve the problem.

Thank you !

When you are writing an ABAQUS UMAT or USDFLD subroutine, you have access to certain information from the current and previous increments.

If you need access to a history of SDVs, you must implement that functionality yourself. For example, you could use an array of SDVs and, at each increment, "shift" the array, discarding the oldest value and adding the newest one.

This method could be implemented as follows:

Remember that these modifications must be thoroughly tested to ensure they work as expected.

As always, when working with complex subroutines like these, it is a good idea to refer to the ABAQUS documentation and consider contacting ABAQUS support or an experienced ABAQUS user for guidance.

Please download the code from iVABS from wenbinyugroup.github.io which include codes for cross-sectional analysis, and general-purpose linear/nonlinear analysis of beams made of arbitrary cross-section and arbitrary material.

For your specific project, you'll need to do some research to determine the best method of coding and programming in order to finish the analysis of the cantilever composite plate. The method of finite element analysis (FEA) is often used to model and solve complex engineering problems such as those involving the analysis of complex fluid dynamics. FEA allows for a highly accurate approximation of physical problems based on discretization and numerical integration of the equations of motions. Some popular software packages for FEA application are MSC Patran for the modeling language, Hawk-I for the computational engine, and Abaqus for the post-processing tasks. You can then look up tutorials online that provide step-by-step guidance on how to code a finite element analysis (FEA) of a cantilever composite plate. Most examples will involve employing a computational grid to discretize the problem into elements with associated properties, using a stiffness matrix to relate force and displacement, and expressing the equations of motion in terms of a numerical integration. Once you've completed the FEA analysis of the cantilever composite plate, you can then turn your attention to the next step of flutter analysis. Flutter occurs when an aerodynamic force causes a structure to become dynamically unstable. The process of flutter analysis involves using post-processors such as ABAQUS to analyze the data from the FEA procedures and to calculate the critical speed at which the structure can become unstable. I hope this information has been of help to you and good luck with your project!

Hi Amir,

I checked your input file and it seems that you are using MC material def. for your soil. So, my guess was that the strain concentration is caused by discontinuity in the material behavior. Your soil block is pulling the infinite region and since it is less deformable, you get the stress concentration and plasticity in the interface region. But I tried to run your input file and in fact, the plasticity already occurred during the static step.

So, there are 2 concerns here from my pov:

1. The way you create the model. First, there is no infinite elements in the bottom of the soil. I understand what you are trying to simulate but by modelling it this way, you have no representation of the static and dynamic behavior in the vertical direction.

2. The geostatic state is missing. As you know, the soil behavior is governed by its confining stress. And it is paramount in nonlinear soil simulation. In your static step, you apply the gravity loading to the soil but there is no predefined stress in the soil. This yields incorrect nonlinear behavior because the soil strength is underestimated. Any deformation beyond this point would be considered invalid. If you are unfamiliar with this, please check the abaqus manual regarding geostatic step.

So, for your model, I recommend to apply the infinite elements surrounding the main study area. You can imagine the interface to be like a half-ellipsoid. The interface here is the line between regular and infinite elements.

And then apply the correct geostatic step. I know it can be a challenge to implement a geostatic step on a model with irregular surface. How I usually solve it is by having a preliminary geostatic computation. In this preliminary model, I apply the geostatic computation while applying fixed boundary condition to all soil (finite) region and record the reaction forces. These reactions are then used as input in the true geostatic step in the main model to stabilize the result. I don't know whether you want to go this far, so I'll stop with the details.

Cheers and good luck with the model.

Hi

Does that mean you want to compare different bodies with a fixed underbody? If so, can't you consider the underbody rigid in your software? If not, can you ask your question more clearly?

You are welcome.

Thank you very much for your answer. I would also like to know whether the extended finite element in abaqus can be simulated when two or three natural fracture geometry parameters are known.

Hello!

This paper might be helpful for the reflection coefficient calculation

Dear Ali, I hope you find your solution already.

For those who come to this page, the solution is by having one part for all layers. Thus, no interaction definition is required between the layers. The layers are then created using partition. But before partitioning the finite box, you should create the solid for the infinite region using extrude from each face of the box as you required (vertical, horizontal, etc.) The extrusion is along the normal of each face, no need for draft angle. Afterward, partition the box and the infinite region to create all layers.

Just as discussed in other page about infinite element, the infinite elements need to be meshed with a sweep in the direction away/outward from the box. You can control this using the "assign mesh control" tool and then "redefine sweep path", which is available for hex or hex-dominated mesh. Along these outward directions, make sure that the number of element is one, using "seed edges" tool. In CAE, you can use the acoustic element (AC3XXX) as a place holder. Remember that the infinite elements must have a rectangular face inward, so you cannot mesh the box with tetrahedral elements. Afterward, write the input file, open it, edit the acoustic AC3XXX into the CIN3XXX, create a new job based on this input file, and run it.

Best regards.

hello

unfortunately is not mu skill.

What solver do you use,and where do you make your post processing, is it in ansys or in Autodyn?

This problem generally happens when Lagrange solver used. The time step is calculated from diagonal of the smallest cell divided by its surface and the local sound velocity of the cell. During impact the part will deformed and the time step will decreases until become less than minimum time stop option and problem stopped. Simply you can decrease the the minimum time stop in control such that from 10^-6 to 10^-8 and the problem will continue.

Such time time step like 10^-8 is too small and the problem well not go further. Changing time step is a just technique overcome the problem but to avoid the problem of very small cell generated during impact you have to eleminate their effect by checking the three erosion boxes in Autodyn Interactions menu.

If you are working with modal bases, it is more straightforward to change the order of an element. This means that the existing basis functions do not change. Some people enjoy this because it is easier to work with. Some antialiasing techniques require modal bases to be filtered directly, but this is not a performance bottleneck. Modal commands can also highlight sparsity within an element for special operators. This means that the savings are small for the modest order typically used in 3D. Nodal bases simplify the definition of element continuity and simplify the implementation of boundary conditions, contact, and the like. They are also easier to plot, leading to better ḥh-ellipticity in discretized operators. This, in turn, allows the use of less expensive smoothers/preconditioners. This means that people who create ways of solving problems can more easily use terms like "rigid body modes" and "multigrid methods," and they do not have to change how they think about things when they are using these methods. Discretization is a way to turn an ongoing problem into a discrete one that a computer can solve. An embedded discretization is one where the discretization is done in a way that makes it easy to access and use later on.

Without using COMSOL, you can solve fourth-order or higher-order equations in Matlab easily using the explicit method (forward in time and central in space) or the implicit method and vice versa with the crank-Nicolson method or other numerical methods finite difference method with consistency and stability with Dirichlet boundary conditions.

In our example, we used planar finite elements with two displacements per node (x and y) and therefore considered only the first 7 bending modes in the xy plane. For the expansion process, the numerical mode shapes were further reduced to 29 displacement DOFs in the y-direction.

From your description, I assume you are trying to use spatial linear finite elements. In this case, bending modes in the xz-plane (and possibly torsional modes) are also present in the numerical solution.

In our experimental model, the excitation was only performed in the y-direction, and the response was also measured in the y-direction using uniaxial accelerometers. Thus, only xy-plane bending was excited and observed.

Due to the lack of observability and controllability for the xz bending and torsional modes, an expansion to a spatial FEM model is unlikely to be successful.

If you are interested in a comparison of different expansion methods (SEREP, SEMM, and M-SEMM), open-source code and an example can be found in the Python library pyFBS (https://gitlab.com/pyFBS/pyFBS/-/blob/master/examples/21_expansion_methods.ipynb).

Hello, Tilmann Allzeit

When you impose in your model scale factor, what you are analysing is "almost" an unrealistic motion. The scale factor is based on the node displacement, so if the nodes are connected, for instance using "tie" constraint Abaqus can predict quite well the deformation. On other hand, when you have contacts, the nodes are unconnected, when you introduce the scale factor visually you may observe some penetrations, which is quite normal and this does not mean that you model is wrong. In order to verify if the contact is behaving as you want, I suggest you to analyse the CPRESS or the COPEN, as Raffael Bogenfeld mentioned.

You can try the tips given in this thread:

Here is the latest published Modelling Guide for Timber Structures developed by more than 100 global experts: https://web.fpinnovations.ca/modelling/. Chaper 4.1 discusses the constitute models for wood-based products and key modelling considerations, and Chaper 4.3 discusses how to simulate the lumber-, veneer-, and strand-based wood products.

Dear Raheel,

For your GFRP part, the Hashin Damage in Abaqus (both initiation and evolution) can be used only with Continuum Shell elements (and not the 3D Stress/C3D8R elements). You need to create a new Section with category of Shell and Type of Homogeneous or Composite. Then you need to replace this newly created section with your existent GFRP Section for your RHS Part. Next, you need to change your Element Type (in Mesh Module), for your RHS part only, to Continuum Shell/SC8R (you can find it in the Family list in the Element Type window).

I hop this helps!

I agree with the answers of Vincenzo Minutolo and G.R.Reddy. For quite some years, I used a post processing program to collect stresses in solids and integrate them, to get axial and bending components, across full thickness. Though, 2 elements across thickness, with three levels of nodes (top, middle and bottm) should give P & M, theoretically, I prefer to use not less than 3 elements as bare minimum. Four (4) elements are good enough to get any non-linear variation of stress across the thickness in a better manner.

If anybody have the code for standard problem of (Non-Linear Transient 2D problem) mentioned in JN Reddy Non-Linear FEA book, please share the code. Any help will be helpful.

Hi,

You may be interested in our new article on modeling FGM in ANSYS APDL.

please take a look through its DOI link:

We are eager to have your feedback.

best regards.

Ahmed Hassan Ahmed Hassan

Hi sir thanks for your response, but what I mean is that, is there a way to extract the equation behind a certain finite element analysis simulation in order to validate the results numerically?

You can use partition in 2D case. I attach an example.

Hi Towhid Faraji ,

In order to achieve this you need to define a material with tabular values of density vs field 1. In the Edit material increase the field variables to 1 and fill in the density vs Field 1 table. Then in the vusdfld you have to update the field values and the formulation in abaqus will handle the variation in density. The vusdfld should be something like that:

(*I haven't compiled or tested the subroutine, it is only for demonstration)

subroutine vusdfld(

c Read only variables -

1 nblock,nstatev, nfieldv, nprops, ndir, nshr,

2 jElem, kIntPt, kLayer, kSecPt,

3 stepTime, totalTime, dt, cmname,

4 coordMp, direct, T, charLength, props,

5 stateOld,

c Write only variables -

6 stateNew, field)

c

include 'vaba_param.inc'

c

dimension jElem(nblock), coordMp(nblock,*),

1 direct(nblock,3,3), T(nblock,3,3),

2 charLength(nblock), props(nprops),

3 stateOld(nblock,nstatev),

4 stateNew(nblock,nstatev),

5 field(nblock,nfieldv)

character*80 cmname

c

c Local arrays from vgetvrm are dimensioned to

c maximum block size (maxblk)

c

parameter( nrData=6 )

character*3 cData(maxblk*nrData)

dimension rData(maxblk*nrData), jData(maxblk*nrData)

jstatus = 1

c Collect strain values

call vgetvrm("LE", rData, jData, cData, jstatus)

c Update the field value with the strain value you need

call setField(nblock, nfieldv, nrData, rData, field)

return

end

subroutine setField(nblock, nfieldv, nrData, strain, field)

include 'vaba_param.inc'

dimension field(nblock, nfieldv), strain(nblock, nrData)

do k = 1, nblock

c For demonstration first strain component is used

strain11 = abs(strain(k,1))

field(k,1) = strain11

end do

return

end

Hello all,

At first open Abaqus Command from the start menu.

Its default address is C:\temp>. Change its address to your directory folder or copy your .inp file in C:\temp.

Next run a data check with the .inp file using following command:

"C:\temp>abaqus job=job-name.inp datacheck unconnected_region=yes interactive"

Enter (keyboard command)

If it asked for "Overwright?", answer: y

Enter (keyboard command)

After that datacheck completed with "Abaqus JOB job-name COMPLETED" message in the command window, open .odb file.

All unconnected regions can be viewed from following address:

Tools>display group>manager>create>Item:Elements, Method:Element sets, MESH COMPONENT 1, 2, 3, ...

Highlights items in the viewport.

Now you can find unconnected regions and fix them.

Regards,

M. Khodaei

Hi,

I have the same problem with displacement outputs in my model. Would you please tell me how could you solve your problem?

James Bayley

Martin Veidt : Thank you for your comment, but there is no density dimension in the VUSDFLD subroutine nor Strain.

Based on what dimension density can be changed or assumed?

Can you please explain a bit specifically?

I didn't work on this model, sorry.

Hi Yunus Rezvanifar,

The best way to do this is to use a subroutine. If the ABAQUS has your material equations, it’s easier to use the USDFLD; otherwise, use the UMAT subroutine. Check the links below. They are articles that can help you write the UMAT subroutine.

Best wishes.

Dear Yunus Rezvanifar ,

Field variables in abaqus are quantities that are used to perform calculations when running user subroutines. They do not describe a specific

physical quantity but are often used to describe solution dependent material properties.

Integration points are referred as material points to distinguish between the

Langragian and Eulerian approach.

Dear Mustapha,

Thank you for your answer.

Can you share your Abaqus model (.inp)?

Good afternoon! If the model solution stops, it is desirable to check the boundary conditions, it is also possible to increase the size of the computational grid. The pile is usually monolithic and the moment of inertia is evenly distributed.

The answer to your question could be pages. I will suggest few things assuming the definitions of the material models and boundary conditions replicate the given specimens in the test (in case you are trying to validate your model with experimental results).

0- Apply displacement rather than forces.

1- Turn off the force convergence criteria and only keep the displacement.

2- Exclude the extra displacement shapes for SOLID65 (Keyopt 1).

3- Use finer mesh as SOLID65 is mesh dependent.

4- Use bond-slip relation by employing COMBIN39 element.

NOTE: check the value of uniaxial tensile strength as it seems too small for the given concrete strength. You may use ACI or any other code to find that value.

Let me know.

Good luck.

I have created 44 Video Lectures for ABAQUS Python Scripting:

suitable for beginners and experts.

The corresponding Code can be found at github:

The cycle load module can completely solve this problem

Hi Manuel Urueña Palomo

I have found a solution for the above said problem. Bodies grouped under a single part in Design modeller can have selective shared topology using the option of 'Connect'. You may refer to this under the section of 'Selective Shared Topology: Using Connect after Share Topology' in Design Modeller User's Guide for further information.

Thanks.

Hi,

Mfront can be used for the analysis. see attached a helpful document

Regards

Dear Sina,

Watch this video it may help you.

Best regards.

Dear Ana,

Check that if your model fully supports these outputs. Make sure that the analysis type, material properties, and element type are defined in a way to produce these outputs.

Dear all,

Probably it is too late to respond to this question. However, I wanted to put my two cents here.

Selecting interior nodes is always a challenge and simply selecting a surface and the nodes attached to a surface is not always going to work. The best way of selecting nodes is selection based on a coordinate system and a geometry referred to that coordinate system (as also suggested by ). In Mechanical (by default) you can select nodes based on a cube geometry which is related to a Cartesian coordinate system (in the background). You can developed algorithms that uses different shapes e.g. cylinder, sphere and etc. based on either Cartesian or Cylindrical coordinate systems.

I developed an ACT sometimes back that enables selecting nodes in ANSYS Mechanical based on different shapes and coordinate systems. This ACT is available in ANSYS app store right now. I put a pdf document here hat shows the ACT capabilities.

Dear Hamed Sadaghian

Thanks for sending valuable papers. Papers focused on various topics.

Do you have a dataset that focuses on a specific topic in Cross Laminated Timber?

Best regards

Mehdi

The simplest solution you can use in an Abaqus simulation is to place viscous dampers at the boundaries of your model as described by Lysmer and Kuhlemeyer (1969) and make sure your boundaries are not too close to the structure and foundation. This works well in the presence of a homogeneous soil profile and perpendicular/tangential waves with respect to the sides of your model. The next step would be to look at more advanced approaches such as: infinite elements, absorbing layers (e.g., CALM = Calm Absorbing Layer Method), PML (Perfectly Matched Layers) or even hybrid approaches mixing FEM and BEM formulations. However, I do not know if these methods are available in Abaqus software (perhaps using user-defined elements?) nor the particular problems that may arise when calibrating their parameters, numerical stability, etc.