Finite Element Analysis - Science topic

Thank you Tufail Mabood , yes I encountered exactly the same problem when I was trying to calculate the gradient matrix, so I am wondering what techniques should be applied in order to address this problem? Is there a standard approach to deal with situations like this and even for more complicated element types?

Sarmed Wahab, Here are some documents and resources on the finite element analysis of self-compacting concrete (SCC) with varying proportions and new supplementary cementitious materials:

Beside, there are multiple publications available in the current domain.

Muhamad Alim basically, ANSYS manual and general notion related to nonlinear contact analysis prone to abrupt state changes, like from tension to slack. So, you may want to try prestressed stage first , so the link is taut and give it some compression properties, so the convergence is assured. it’s a trial and error. If it’s a dynamic analysis, Damping introduction should help.

Sadikbasha Shaik Yes, and much more. Here are the coordinates, areas, labels, and surfaces files for the Python outputs. You can use Python code in a similar domain to generate the resulting files for your project.

Here's a basic outline of how to define a nonlinear spring element in ABAQUS:

Wei Hao Koh The eigenvalues of the element stiffness matrix in static finite element analysis are the natural frequencies of the element. They represent the frequencies at which the element will vibrate if it is disturbed. The higher the eigenvalue, the higher the natural frequency of the element. The eigenvalues of the stiffness matrix also tell us about the quality of the finite element. A good finite element will have eigenvalues that are well-separated. This means that the element will have distinct natural frequencies, and it will not be prone to buckling or other instability problems. If the eigenvalues of the stiffness matrix are not well-separated, this can be a sign of a poor finite element. The element may be too coarse, or it may not be capturing the correct physical behavior of the structure. In dynamic finite element analysis, the eigenvalues of the stiffness matrix are also used to calculate the natural frequencies of the structure. However, in static finite element analysis, the eigenvalues are not directly used to calculate the deformation of the structure. Instead, they are used to calculate the stiffness of the element.

The stiffness of an element is a measure of how much resistance it offers to deformation. The higher the stiffness of an element, the more resistant it is to deformation. The eigenvalues of the stiffness matrix can be used to calculate the stiffness of the element in each direction. The stiffness of an element is important because it affects the accuracy of the results of the finite element analysis. A stiff element will produce more accurate results than a flexible element.

I hope this

Seems fine to me. Step 6 will tell you if you did it right. The residual should be small, and also shouldn’t show any low order structure that seems too similar to any of the fit zernikes.

In short, YES!!

Experimental validation is often considered an important aspect of scientific publications involving problems solved using Abaqus or any other simulation software. While simulations can provide valuable insights and predictions, experimental validation helps confirm the accuracy and reliability of the simulation results. Including experimental data and validation in your publication can enhance the credibility and impact of your research. However, the extent of validation required may vary based on the nature of the problem and the specific research goals, as pointed out by Yousef Bahrambeigi

In ABAQUS, the yielding and damage criteria for concrete materials are typically based on the principal stresses or the effective stress. ABAQUS uses the concept of effective stress for concrete materials, which takes into account the influence of tensile stresses on the material's behavior.

The effective stress, denoted as σ_eff, is calculated as:

σ_eff = σ - α * f_t

where σ is the total stress, α is the tension stiffening factor, and f_t is the tensile strength of concrete.

When checking yielding and damage in a concrete material in ABAQUS, the effective stress is compared to the material's yield strength and ultimate strength. The yield strength is typically used to determine the onset of plastic deformation, while the ultimate strength represents the maximum stress the material can sustain before failure.

In your case, where you are modeling a concrete cylinder compression test, ABAQUS considers the effective stress (σ_eff) to check yielding and damage for the concrete material. It is important to note that the effective stress can be different from the nominal stress (σ) due to the inclusion of the tension stiffening factor (α * f_t) in the calculation.

Therefore, when comparing the maximum σ_33 stress at the element centroid (78 MPa) to the ultimate concrete strength (58 MPa), it is essential to consider the effective stress (σ_eff) and the tensile strength of the concrete material. If the effective stress exceeds the yield or ultimate strength, it indicates that the concrete material may have reached or exceeded its capacity and may be subject to yielding or damage.

Dear Sushil

Hi Dr Mohd,

Thank you Mohd Redzuan Mohd Sofian for articulating the steps. I will definitely press the recommendation button on your paper. I do have a couple of questions about the contact element.

I am able to create a target and contactor properties for the contact element in which I assign the friction and penetration properties. But I am not able to associate the contact properties to the steel cubes. Whenever I assign the contact properties, the steel properties of the material gets deleted.

Should I create a new element between the steel cubes and assign the contact properties to the new element? Could you kindly give me a rough step by step instructions on how to associate the contact properties to the steel cubes?

Go under "Property" tab. In the two columns of functions, you will find "Assign beam orientation" (on the right, 4 down).

Now select the problematic beam and click "Done". Now it will ask you for a direction of a vector n1. If you look under "Profile manager" (right, 5 down)-> select the created profile and you will see vectors 1 and 2. Vector 1 points to the right.

So when you assign beam orientation you tell the program where that vector roughly points (blue arrow, when you hit enter after typing in the direction). Hope that helps.

Hi Konrad,

The Kocks-Mecking parameter (kf) quantifies how strain rate influences strain hardening during plastic deformation. Sample geometry, such as diameter, potentially impact kf. Smaller diameters can lead to strain localization, different stress distributions, and variations in dislocation densities in comparison to larger diameters.

Initial mechanical properties of samples also influence the material's overall strain hardening behaviour and its sensitivity to changes in strain rate, which in turn affects the kf parameter. Higher initial yield strength can lead to greater potential for strain hardening and increased sensitivity to strain rate changes, potentially resulting in a higher kf value. The initial stiffness of a material can influence how it responds to stress. Materials with faster work hardening rates tend to exhibit higher strain hardening responses. Ductile materials deform more uniformly, while less ductile materials may experience localized deformation. The initial microstructure, including grain size and distribution, can also impact dislocation mobility, deformation mechanisms, and consequently kf.

If you look in Materials Science and Engineering Textbooks, such as "Materials Science and Engineering" by William D. Callister and David G. Rethwisch; These text books often cover topics related to plastic deformation, strain hardening, and strain rate sensitivity. Look for chapters on mechanical behaviour of materials.

Hope this helps,

Kind regards

It looks like you're encountering a challenging problem while working with a 2D axisymmetric model of a threaded connection. The error you mentioned, where some nodes have negative coordinate values on the axis of symmetry, can be a subtle issue. Here are some strategies that might help you fix the error:

Remember that seemingly small differences or errors can cascade into significant problems in complex simulation models. It might require a systematic process of troubleshooting and comparison between the models to pinpoint the exact cause of the issue. If you continue to experience difficulties, working closely with a more experienced colleague, or even directly with software support, may help you resolve this challenging problem.

thanks...there was some error now it's working.

Is there any way to delete elements using element set in abaqus explicit?

I am trying both subroutines and python script but ideas on the internet are not working.

As you have mentioned displacement 2 that means total displacement is two, here, i am unable to figure out how the rate of displacement has been defined in your solution. please let me know.

You're correct that restarting simulations can save considerable computational time and resources if multiple simulations share common steps initially. Abaqus provides a restart feature that allows the restart of analysis from any previously completed step or increment in a preceding analysis.

As you are facing an issue due to the change in the blade's location in the sixth step, you need a solution that allows for the modification of your model (i.e., the blade's location) between the fifth and sixth steps, and yet still enables you to restart the simulation from the sixth step.

Abaqus allows for such model changes in a restart analysis, but there are restrictions on the kind of changes that can be made. Changes like modifications to boundary conditions, load magnitudes, or material properties are allowed in a typical restart analysis. However, changes to the model geometry or topology, like moving the blade in your case, are usually not allowed.

One possible workaround would be to model all 20 blade positions in your initial simulation but activate them in sequence in subsequent simulations. Here's how you might do that:

Remember, this is just a workaround and may or may not be feasible, depending on the specifics of your simulation. You might also need to modify the workaround based on your requirements.

In conclusion, while Abaqus allows for certain modifications during a restart analysis, the changes you're trying to make might not be compatible with this feature. You might need to resort to alternative modelling techniques to achieve your goal. If you're still facing issues, I recommend contacting Abaqus support or consulting the Abaqus user manual or user community for more specific guidance.

In my opinion, Python is a brilliant choice for scientific computing and numerical analysis. Also, I think C++ would work, but it’s a complicated and difficult to master it.

Follow the bellow link, I simulated the same model from this tutorial.

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 !

I can still offer some suggestions to help you address the issue you're facing with the Indentation Size Effect (ISE) in your ABAQUS simulations.

Here are a few potential reasons why you might not be observing the expected trend of decreasing hardness with increasing indentation depth:

It is worth noting that the Indentation Size Effect (ISE) can be influenced by various factors, including material properties, strain gradient effects, and surface roughness. It is possible that other mechanisms or phenomena are counteracting the expected trend in your specific simulation. Additional considerations may be necessary to capture these effects accurately.

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.

Dear Lee,

Could still be lifting up and just a scale issue in the picture. The collor yellow in the picture can be tension or 0. You can output the stress of the interface. stress total tracti to be sure. Or change the legenda with a 0 value in it.

Ab van den Bos

NLyseConsultants.com for all your FEA projects within the built environment.

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!

Dear Victória Geovana Hollanda do Amaral

When encountering a bilinear behavior in the displacement-force graph for GFRP bars instead of the expected linear behavior, several factors should be considered for correcting the model. Firstly, ensuring accurate material properties is crucial. Verify that the Young's modulus, Poisson's ratio, and tensile strength values are representative of the specific GFRP material being used, referring to reliable experimental data or material specifications if possible. Additionally, evaluate the material model employed for the GFRP bars, as the chosen model may not be appropriate. Consider using a material model specifically designed for fiber-reinforced polymer materials, such as the Composite Damage Model or Continuum Damage Mechanics model. The element type and size should also be reviewed. Wire elements (T3D2) commonly used for bars might not accurately capture the non-linear behavior of GFRP. Utilizing beam elements (B21) designed for reinforced bars could provide better representation. It is important to refine the mesh and adjust element sizes, particularly around the GFRP bars, to accurately capture their behavior. Checking the boundary and loading conditions is crucial to ensure they reflect the experimental setup or real-world conditions. Lastly, validate the model by comparing specific points along the displacement-force curve to identify the range of discrepancy and focus on improving the model in that region.

Also, you can seek guidance from relevant literature which can provide further insights into modelling GFRP bars accurately in structural analysis software.

you need to ensure that the mode shapes being compared are in the same format. Here's a suggested approach:

Once you have both mode shapes in the same format (real-valued), you can calculate the MAC using the standard formula. The MAC formula involves comparing corresponding displacement values at each node between the two mode shapes.

Remember to normalize the mode shapes before applying the MAC formula. Normalization helps in removing any scaling effects and ensures a fair comparison between the mode shapes.

I hope this explanation helps you resolve the issue and accurately calculate the MAC between your experimental and FEM mode shapes. If you have any further questions or need additional assistance, please feel free to ask.

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.

You might be interested in VisPER (Visual PERMAS).

You can easily import stl files in ASCII and binary format. Afterwards, a remeshing capability can be used.

A free education edition of VisPER is available at https://www.intes.de/edu

And why sparse matrix has computational benefits than diagonal matrix for large sizes ?

There isn't exact number of slices needed for making a good model. Maybe you should be concentrated on how thick the slices are. You can make a pretty decent 3D model with 1.5 mm slice thickness, but thinner the slice thickness, better the result :)

1) At first , you have to create the model by defining the properties and geometry of the model.

2)Then mesh the model and apply the appropriate boundary conditions to simulate the loading and constraints in your analysis.

3)After this for adding a deflection expression, you can use the Abaqus Expression Language (AEL) or Python scripting.

4)You can create an expression by navigating to the "Model" module and selecting "Expressions" from the drop-down menu.

5)Then in "Model" module, select "Output Requests" and create a new request such as displacements or strains, and set the "Component Scope" to the desired direction of deflection. In the "Expressions" section of the request, assign your deflection expression to the appropriate variable.

6) Then just run the analysis and post processing for extract the deflection result.

I think these steps helps you to solve your problem.

Kika VI

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?

Clearly, researchers will come down on both sides of this question. I go back about 40 years in the Computational Science field. My choice is to write my own solvers whenever possible. For me, it is very important to understand the details of how the solver operates so that I may identify any numerical pathologies that occur. All intricate computational physics algorithms have difficulties; that is their nature. I have worked on both the research and applications side of this field. What I find is that when people get into the habit of just "running the code", they steadily depart from an understanding of the code. Of course, there is a balance that is in need of achievement. An engineer is unlikely to write his own code for the CFD or CSM analysis of a full aircraft, yet he or someone on the "team" must understand how to judge a commercial code's behavior. With that in mind, I will stand my ground, the best way to learn is to study the algorithms and write your own suite of computer codes.

Manar Naser If you are not going to change values of predefined field at material (integration) points during simulation, I think you can avoid using USDFLD. Presented .dat file (without lines pertained to USDFLD) is sufficient. From my experience, value of predefined field at any material point is equal to mean of element nodal values.

Thank you for a detailed response. I could not find the resources you've mentioned but I did find other papers on the MLS method.

Hi Neda,

The technique that worked for me was to output the coordinates of the surfaces in contact before any load was applied. After that, I developed a formula in excel to find the closest point between these surfaces and locate their nodes by indexing the position in the excel database. By this point the nodes that are closest from the formula, I considered them as matched.

After the load was applied, I looked again at the final coordinates of the nodes of the surfaces in contact, and substracted their final position from their initial position.

That enabled me obtain the relative motion in the three directions. The overall magnitude of relative motions was obtained as the square root of the sum of squares of the relative motions in the three directions.

I hope this helps.

Dear Kaushik Shandilya ,

Thanks a lot again. I appreciate your comments very much.

Aung Nyein Soe , your code is not correct and it is likely that your fortran compiler is not able to compile it. Indeed, according to Fortran 77 standards, all Fortran statements must be written in columns 7 to 72, which is not the case in your code (e.g. lines 20, 21 and 28).

Also, lines 56 to 61 do not make sense as you are trying to assign a value to an array, which is not possible for Fortran 77 (and also probably not what you want to do). The indexes of S11, S22... arrays are likely missing.

Before running an abaqus simulation, you should first try compiling your code to make sure no obvious programming mistake is present.

Charles

Why the step time is not change and the increment is too much?

Sir Ansys

For general simulation-driven design, I recommend ANSYS Workbench as it has a lesser learning curve then other software such as Altair HyperWorks, Abaqus or COMSOL. While they are good, it requires an expert in CAE to model and simulate your problem. If you have someone with a ton of expertise in solving PDEs, open-source codes like FEniCS can also do the job.

Dear Nekin Joshua

The below-mentioned links may be helpful to you.

Please look at the CT geometry. For a displacement control simulation, you may apply displacement at the upper (and lower) surfaces of the pin hole(s) and extract the load displacement curve. If the failure criteria is implemented, the load displacement curve should have a peak point, which is force corresponding to the UTS.

However, "UTS" is not really defined in this case like uniaxial tensile test.

Using an adaptive moving mesh method is one way to solve a 3D heat conduction equation involving a moving heat source, such as a laser. The main idea is to adapt the mesh to the changing heat source position so that the elements around the laser spot have a finer resolution.

using Model-based prediction, If the laser's motion is known, it can be predicted in advance using a mathematical model. The mesh can then be updated based on the predicted motion of the laser.

Yuhang Ding, I only faced this issue in ANSYS 22.

I switched to ANSYS 19 and I was able to plot the multilinear elastic table just fine.

It is possible that your simulation is not experiencing buckling because the material is behaving plastically before reaching the buckling threshold. In order to achieve buckling, you may need to increase the stiffness of the material or decrease the load applied to the specimen.

If you want to introduce a lateral load or perturbation to trigger buckling, you can do so by applying an initial geometric imperfection to the specimen. This can be done in LSDYNA by using the *INITIAL_IMPERFECTION keyword and specifying the magnitude and distribution of the imperfection.

You may also want to consider using an element type that is more suitable for simulating buckling behavior, such as a shell element or a reduced integration element.

Amir Mustakim Ab Rashid may use a statistical method to find the error in between the final answers.

There is no fixed amount like X/16. Optimal mesh size depends on the model geometry. It must assures that stress gradients are captured adequately

Hello.

Thanks for your response Farid SIr.

But, I am having difficulty in the simulation part in ABAQUS.

1. Im not sure if its logical, but as it is doesnt effect the stability slope much. If you predict it higher and repeat calculation, you could get much different results (less stable slope). So if you dont have any data and you want to play it safe, take into account higher level of water.

Questions 2 and 3 were already answered by others.

There are several possible reasons why the force at a given node might be zero when plotting a load-deformation curve in Abaqus:

It is difficult to determine the exact cause of the issue without more information about the model and the load-deformation curve you are trying to plot. It may be helpful to review the model setup and the loads applied to the model to ensure that they are set up correctly and to identify any potential issues.

There is probably cleaner way to do this, but you could also try varying temperature of the strand to "fake" prestress. This would of course complicate things if you need to also consider temperatures in the analysis.

Can you share your Abaqus model (.inp) format?

hello

unfortunately is not mu skill.

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The check of mesh quality has to do with the numerical integration of stiffness matrix [k] by Gauss quadrature in isoparametric formulation. In “full integration”, matrix [k] is computed exactly if the element has a perfect shape, i.e. cube for hexahedral elements, square for plane quadrilateral elements, etc. Any deviation from this ideal shape will introduce approximations in the numerical computation of [k]. If distortion is excessive, numerical integration may even become impossible (à problem with Jacobian). Of course, if distortion is limited to few elements far apart the critical location of interest, the mesh could be considered acceptable. However, no general conclusions can be drawn without seeing the mesh.

Try redefining your wrap properties and your analysis in a cylindrical coordinate system. You have one or both in a cartesian coordinate system.

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).

But in Ansys, I found that achieving solution convergence was difficult. Abaqus, I found that the solution convergence happening nicely and I could complete my work