Science topic

Finite Element Analysis - Science topic

A computer based method of simulating or analyzing the behavior of structures or components.
Questions related to Finite Element Analysis
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In 1D cases Hermite shape functions can be easily implemented. However, in 2D cases, if we want to use cubic Hermite triangle element (10 DOFs), then it is pointed out that the transformation between the physical triangle and the reference triangle is not affine-equivalent (or it is nonconforming). In this case, if calculating the gradient matrix directly then it will lead to wrong results.
The nonconforming nature of cubic Hermite triangle element is mentioned in Reddy's "An introduction to nonlinear finite element analysis" (see the attached figure), however, further discussion and examples of applying cubic Hermite triangle element are not presented in this book.
I am wondering if there are any available books/references that cover the details of the information related to this question.
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?
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I know FEA for simple concrete including the material testing and structural members testing. As of now, I have been searching for FEA of self compacting concrete with varying proportions and new Supplementary cementitious materials such as Non-ferrous metallurgy slags, bauxite residue.
Can you suggest some document or resource for this.
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.
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i am trying to simulate a tunnel under blast loading in abaqus , i am using coupled eulerian lagrangian, I find some difficulties,Any help (tutorial ,steps) would be highly appreciated.
1. Geometry and Meshing:-Create the geometry of the tunnel and the surrounding soil or rock. Mesh the tunnel and the surrounding soil/rock separately. Ensure that the mesh is refined enough to capture the important details of the simulation.
2. Material Properties: Define material properties for the tunnel structure and the surrounding soil/rock. These properties should include density, elastic properties, and strength properties if applicable.
3. Boundary Conditions: Apply appropriate boundary conditions to the tunnel and soil/rock domains. For example, fix the tunnel entrance or apply symmetry conditions if applicable.
4. Blast Loading: Define the blast loading. You can use a pressure-time history curve or other blast models available in Abaqus. Apply the blast load to the exterior of the tunnel entrance or the location where the explosion occurs.
5. Coupled Eulerian-Lagrangian (CEL) Setup: Create a CEL model to couple the tunnel and soil/rock domains. This involves defining the Eulerian region (soil/rock) and the Lagrangian region (tunnel). Set up the coupling parameters, such as friction, contact, and tie constraints between the Eulerian and Lagrangian regions. These parameters control how the two regions interact.
6. Analysis Settings: Define the analysis type (e.g., explicit dynamic analysis). Specify the time step size and other numerical parameters. Set up any additional features like output requests for monitoring specific results.
7. Run the Simulation:Submit the simulation for analysis. Abaqus will perform the calculations to simulate the tunnel's response to the blast loading over time.
8. Post-Processing: After the simulation is complete, analyze the results to study the tunnel's behavior, including deformation, stress, and damage. Visualize and interpret the results to draw conclusions about the tunnel's performance under blast loading.
9. Iterate and Validate: Depending on the results, you may need to iterate on the model, adjust parameters, or refine the mesh to obtain more accurate and meaningful results.
10. Simulating a tunnel under blast loading in Abaqus using the coupled Eulerian-Lagrangian (CEL) method can be a complex task, but I have given the basic steps needed.
11. All the best.
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I conducted pipe stress analysis using CAESAR II. And now I am trying to create similar analysis but in this case I use ANSYS APDL.
I find a problem while creating the boundary conditions, where in ANSYS APDL I can't model the Y+ supports because ANSYS APDL only has an option to restraint movement in both Y- and Y+ direction (the UY option, as can be seen in Figure 2).
Can anyone help me to model the Y+ support in ANSYS APDL?
I'd like to appreciate any responses.
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.
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I would like to develop 2D open cell foam models which can be further used in the FE modelling. Could anyone please suggest any modelling tool?
Thank you
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.
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Hello Everyone,
I am trying to define a non-linear spring element in Abaqus using the following values.
-8505.0193, -40
-6854, -30
-5514.401, -20
-4075.366, -10
0, 0
4075.366, 10
5514.401, 20
6854, 30
8505.0193, 40.
It is working fine with positive values. But when I define zero or negative values. it is showing an error as
"The independent variables must be arranged in ascending order. This error may have been caused by a possible empty line on the datacards in the property definition."
Here's a basic outline of how to define a nonlinear spring element in ABAQUS:
1. Define the Material Properties:For example, if you're modeling a nonlinear elastic material Define the Spring Behavior: *COHESIVE BEHAVIOR keyword.
2. Define the Spring Element: *ELEMENT keyword.
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What do the stiffness matrix's eigenvalues tell about the finite element's quality? I have read similar answers on ResearchGate, but many refer to dynamic analysis.
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
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Hi All,
I am trying to generate the 3D corneal surface from the Zernike Polynomials. I am using the following steps, can anyone please let me know whether they are accurate
Step 1: Converted the cartesian data (x, y, z) to polar data (rho, theta, z)
Step 2: Nomalised the rho values, so that they will be less than one
Step 3: Based on the order, calculated the Zernike polynomials (Zpoly), (for example: if the order is 6, the number of polynomials is 28 )
Step 4: Zfit = C1 * Z1 + C2 * Z2 + C3 * Z3 + ......... + C28 * Z28
Step 5: Using regression analysis, calculated the coefficient (C) values
Step 6: Calculated the error between the predicted value (Zfit) and the actual elevation value (Z)
Step 7: Finally, converted the polar data (rho, theta, Zfit) to Cartesian coordinates to get the approximated corneal surface
Thanks & Regards,
Nithin
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.
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For more details, see the link : https://zurl.co/roQB
The objective of the FMVSS222 standard is to enhance the safety of school bus occupants by reducing the number of deaths and the severity of injuries resulting from impacts with structures within the vehicle during crashes and sudden driving maneuvers. Finite Element Analysis (FEA) using Abaqus software allows to ensure compliance with the norms without conducting high-priced physical tests.
Specifically, the focus was on the passenger seat of the school bus, which has another seat in front of it. It was subjected to the application of force through loading bars.
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
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I am modeling a concrete cylinder compression test (see attached). Loading is applied along z direction, and I am checking the sigma_33 stresses. I am having maximum signma_33 at the element centroid around 78 MPa (see attached graph). I don't get it why it is higher than the ultimate concrete strength of concrete (58 MPa).
Which stress does ABAQUS consider to check yielding and damage for concrete material?
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.
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Can you please recommend me any useful material that will help me to understand CDP model generally used in ABAQUS for concrete materials? I have read some fundamental papers like Lee and Fenves, Lubliner et. al., etc. to understand the theory behind it. I got it to some extent. Now, I am looking for something that describes CDP from practical point of view. My main goal is to understand the output that I am getting from my analysis.
Any sort of information will be greatly appreciated.
Dear Sushil
Artcle: Calibration of a New Concrete Damage Plasticity Theoretical Model Based on Experimental Parameters.
• DOI:10.28991/CEJ-2022-08-02-03
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Hi all,
I am trying to model a contact problem in DIANA FEA. I went through the DIANA manual and found that DIANA has contact elements which imposes the contact constraint. But there aren't any tutorial or examples available online to do this.
The material property for the contact element has two options target and contactor. When I try to assign the contact element material properties to an existing steel object, the object loses its steel material properties and contains only the contact elements properties which is friction and penetration depth.
Could someone explain how can I assign the contact constraint in DIANA when two steel cubes are touching each other.
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?
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ABAQUS ERROR: ONE OF THE ELEMENT IS CLOSE TO PARALLEL WITH ITS BEAM SECTION AXIS, so I'd like to know how to solve this problem? The element property is beam element, so I should define the section oritention in all elements.
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.
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Below you can find equetion which express flow curve which describes the plastic deformation behavior of a material in a uniaxial tensile (or compression) test. I looking for books, articles which gives me information how values of C and n depends on geometry (eg. diamater and wallthicknes of drawn tube) as well as initial mechanical properties, before material work hardening. Do wires and rods of the same material but with different dimensions have a different form of the flow-curve, or does it depend only on the initial properties of the material?
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
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Hello dear colleagues
Hope you're fine.
I'm trying to model a threaded connection with a 2D axisymmetric model.
I need to make several models with slight changes and differences.
In some models, once the job is submitted, before the analysis gets started, it gets aborted due to "some nodes have Negative coordinate values" error.
When I check the error node set, they are all placed on the axis of symmetry.
I tried several ideas to work this out but none of them was successful like:
>changing element type,
>constraining the part in the direction prependicular to the axis of symmetry
>Using another datumn coordinate system
I appreciate it if you have any ideas to fix this error.
PS: some other models get solved without this error while these models are copied from one another and I couldn't see any difference seem to be related to this error between them
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:
1. Check Geometry and Meshing: Ensure that the axis of symmetry is correctly defined in your geometry. Examine the mesh near the axis of symmetry to make sure that there are no overlapping or misaligned elements that could be causing the negative coordinate values. Adjust the mesh density or quality if needed, especially around the area causing the error.
2. Review Boundary Conditions: Check the boundary conditions applied to the axis of symmetry. Ensure that you have applied the correct axisymmetric constraint or condition. Verify that other boundary conditions or constraints are not conflicting with the axisymmetric conditions.
3. Examine Units and Scaling:If you work with different units or scales between models, ensure that all parameters are consistently and correctly scaled. A mismatch in units might cause unexpected negative values.
4. Use a Different Solver or Algorithm:If available, try using a different solver or algorithm that might be more robust to the geometry and constraints in your model.
5. Look for Hidden Differences Between Models: Even though the models are copied from one another, there might be hidden or subtle differences causing the error. Compare material properties, boundary conditions, meshing settings, loads, and other model features to ensure consistency between the models.
6. Update or Repair Software:If it's a software bug or compatibility issue, consider checking for updates or patches from the software vendor that might address this specific problem.
7. Consult Support or Community Forums:If you are using commercial software, contacting their technical support with a detailed description of the issue (including the model files) could provide a solution. Community forums related to the specific software might also provide insights or solutions from users who have faced similar issues.
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.
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I am using VDFLUX for surface heat flux and VUSDFLD for element deletion.
I am just writing the two subroutines and submitting it during job. It's not throwing any error but it's not applying the surface heat flux load.
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.
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5. To set the displacement of the loading step to 2mm/min, click on the "Displacement" tab and enter "2" in the "Value" field.
Hello Sir
Rana Hamza Shakil
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.
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Hello everyone,
I am currently conducting a stencil printing simulation using ABAQUS. The simulation needs to be performed in 20 different locations on the stencil, requiring a separate simulation for each of these locations. In my case, all components remain fixed, and only the location of the blade changes across these 20 locations. The simulation consists of seven steps. Throughout these 20 simulations, all conditions remain identical from the first step until the fifth step. However, after the fifth step, I change the blade's location in the sixth step and continue the simulation in the seventh step.
Given that the first five steps are the same in all simulations, I would like to explore if there is a way to execute these steps only once and then reuse or restart the results for the remaining 19 simulations. In other words, I aim to find a method that avoids repeating the first five steps in the subsequent simulations. Although I have attempted to utilize the restart option, it did not prove successful due to the blade's location change in the sixth step.
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:
1. In your base model, define 20 different blades, one for each location, but only activate the blade for the first location. Define this as a model instance and create a step that activates the first blade.
2. In your subsequent simulations, you restart from the base model but activate a different blade in each simulation. In Abaqus, this can be done using the Model Change, Activate feature in a step.
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.
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Finite element method will be used to determine the stress-strain of a 3D composite material made structure.
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.
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I am a final year Masters's Student from Heriot-Watt University currently working on my dissertation project titled "A THEORETICAL ASSESSMENT OF THE STRUCTURE OF A LIQUID STORAGE TANK UNDER SEISMIC FORCES" with the following objectives:
1. Verification of Current Theories (Housner, Preethi, and Malhotra) of liquid Structure Behavior (sloshing wave height) under seismic forces for petroleum-filled storage tanks using Finite Element Modelling and Finite Element Analysis.
2. Assessment of the possible failure mechanism of the superstructure of the various liquid storage vessels under exposure to seismic forces using Finite Element Modelling and Finite Element Analysis based on the API 650 Design Standard.
3. Proposal and initial assessment of the effectiveness of a Bass Isolation System on the sloshing wave height using Finite Element Modelling and Finite Element Analysis.
Can the Ansys modal analysis module be used to model a fluid-filled storage tank and determine the sloshing wave height along with the impulsive and convective mass components of the fluid based on the application of specific Acceleration, Velocity, and displacement values?
Can I subsequently transfer the model to the Ansys Static Structural Module to determine the various resulting stresses that will develop within the tank structure due to the seismic forces and the fluid-structure interactions?
If not, can you guys offer any advice on what methodology I should take?
Follow the bellow link, I simulated the same model from this tutorial.
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Dear Researchers :
I will very much appreciate the help.
I have a 2D model in COMSOL. It's a plate, made of Polyethylene. An AC Voltage is applied on the upper electrode, the lower electrode is on V=0 (ground)
The sinusoidal function of the voltage is : Vo*Sin[wt + phi] where phi = 0 and V_o is equal to 2.4 kV
I am attaching an image of my 2D Geometry
I am solving the model in two steps
Step 1 : Using a Time Dependent Study (just to solve the physics of the electric currents module)
Step 2 : A stationary solver, to solve the Heat Transfer in Solids part.
I used the Multiphysics interphase of Electromagnetic Heating
I can correctly solve the Electric part of the model
But for the temperature, this is the graph that I get, which of course is not correct
Does someone might know where the mistake might be ?
Best Regards all :)
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 !
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Hello everyone,
I am currently investigating the phenomenon known as the Indentation Size Effect (ISE) using the Finite Element Method (FEM). My research involves conducting indentation tests through simulation using ABAQUS.
Here are some specifications of the model:
• It is a 2D axisymmetric model.
• The indenter is represented as a rigid body and possesses a semi-angle of 70.3°.
• The specimen material is assumed to be homogeneous and isotropic, characterized by an ideal elastoplastic model.
• Mesh is refined near the indenter tip to capture stress concentration accurately.
• Contact Interaction: Surface-to-surface contact, Tangential behaviour - Frictionless, Normal behaviour - Hard Contact.
I have conducted simulations at various depths, ranging from 500 nm to 5000 nm. To determine the hardness, I have employed the Oliver-Pharr Method. According to the concept of ISE, the hardness should decrease as the indentation depth or load increases. However, in my results, I have observed that the hardness remains almost constant regardless of the depth. Consequently, I am unable to observe the anticipated trend associated with the Indentation Size Effect in my findings.
For your convenience, I have attached the .cae file and the hardness vs indentation depth plot.
I would greatly appreciate any assistance or insights you can provide to help me address this issue.
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:
1. Material model: Verify that the material model you have assigned to the specimen accurately represents the behavior of the material under consideration. Ensure that the material properties, such as elastic modulus and yield stress, are appropriate for the specific material you are simulating. Consider consulting literature or experimental data to validate the material model.
2. Mesh refinement: Although you mentioned that you have refined the mesh near the indenter tip, it's important to ensure that the mesh is adequately refined throughout the entire contact region and beneath the indenter. The mesh should be able to capture the stress concentration accurately and provide sufficient resolution for accurate results. Try increasing the mesh density in the region of interest and re-run the simulations.
3. Convergence criteria: Check the convergence criteria you have set for your simulations. Ensure that the convergence criteria are stringent enough to achieve accurate results. Tightening the convergence criteria may improve the accuracy of the simulation results.
4. Indenter geometry and mesh: Confirm that the geometry and mesh of the indenter are accurately represented in your simulation. Ensure that the indenter semi-angle of 70.3° is correctly defined in the model. Additionally, double-check the mesh quality around the indenter tip and make sure it is appropriate for capturing the stress concentration accurately.
5. Contact behavior: Review the contact interaction settings between the indenter and specimen. Confirm that the settings accurately represent the desired behavior, such as frictionless tangential contact and hard normal contact. Any inaccuracies in the contact behavior could affect the simulation results.
7. Post-processing and analysis: Double-check your post-processing procedure, especially the implementation of the Oliver-Pharr Method for determining hardness. Confirm that you are correctly extracting the indentation depth and load values from the simulation results and accurately applying the method to calculate hardness.
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.
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Dear colleagues
I'm modeling bone healing around dental implants using Abaqus subroutines (UMAT / USDFLD).
I wonder:
1. How SDVs of current and previous increment can be accessed in the current increment through UMAT ?
2. and how SDVs of previous increments (eg. 10 previous increments) can be accessed in the current increment through USDFLD ?
Yunus.
PS: The value of SDVs at the beginning of the current increment can be accessed by GETVRM utility routine in USDFLD
When you are writing an ABAQUS UMAT or USDFLD subroutine, you have access to certain information from the current and previous increments.
1. For UMAT, the Solution-Dependent State Variables (SDVs) from the end of the last increment are passed into the UMAT as the array STATEV. At the start of the UMAT, STATEV contains the values at the end of the last increment. Your UMAT can then update the STATEV array as necessary based on the current increment's calculations, and these updated values will be passed to UMAT for the next increment.
2. For USDFLD, you can use the GETVRM routine to access the SDVs at the start of the current increment. However, accessing SDVs from multiple previous increments (like 10 increments ago) is not straightforwardly supported by ABAQUS.
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:
• Define an array of 10 SDVs.
• At the end of each increment, "shift" the array by moving all values one position down (SDV(2) to SDV(1), SDV(3) to SDV(2), etc.). The SDV value from the current increment would then be stored in SDV(10).
• In this way, SDV(1) will always contain the value from 10 increments ago, SDV(2) from 9 increments ago, and so on.
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.
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Could any one provide me with a MATLAB code for fixed-fixed beam that calculates the Mass and Stiffness matrices, Natural frequency, and mode shapes.
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.
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Hi,
I am modeling a reinforced concrete(RC) slab in DIANA FEA.
The RC slab is simply mounted on a steel girder (see config 1) Therefore, there is no bonding between the RC slab and the steel girder. In order to satisfy these interface conditions, it is set as shown in Figure 2. When a vertical downward pressing force (bending stress) from the center of the slab is applied, it is expected that the slab located on the girder will be lifted up (as in the principle of lever). See Fig 3). As expected, the upward displacement of the slab on the girder occurred, but in some sections it appeared as if it had been bonded and no lifting occurred (See Figure 4) Please advise why this is happening and what interface setting should be done.
Thank you.
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.
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What references do you recommend? What theory should I use to model unsteady aerodynamics? Is it better to use software or coding? Please share some insights.
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!
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I'm struggling to obtain the right behavior of gfrp bars, in the process of validating my model i achieve a bilinear behavior in the displacement x force graph when using gfrp bars as reinforcement, but in the research that i'm using the experimental behavior was linear. Even though i've tried to change a lot of parameters in my model I still couldn't obtain something close.
The model has steel stirrups and upper layer reinforcement and only the lower reinforcement uses GFRP bars.
The bars were modeled as wire T3D2 and the beam as solid c3d8r
For the properties data:
For concrete i'm using de young's modulus, poisson and CDP
For GFRP bars young's modulus, poisson and tensile strenght also rupture strenght
Anyone knows what can i do to correct the behavior that i'm having?
In the image i show the behavior that i need in black and what i am obtaining in the other colors
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.
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Hello everyone,
I have a problem calculating the modal assurance criterion (MAC) of a experimental mode shape and a FEM mode shape. I can calculate the AutoMAC for each mode shape, for which the values are all correct. Both matrices show that the same mode shape gets a value of 1, while the rest is near 0.
However if I now apply the same formula to the normal MAC nothing seems right. The sensors for the experimental mode shape can measure displacement in one DOF. So at each node the displacement is a complex value in the direction of one of the local X, Y or Z-axis. The FEM mode shape contains real values at each node and the displacement can occur in all 3 DOFs.
I hope someone can help me resolve this problem.
you need to ensure that the mode shapes being compared are in the same format. Here's a suggested approach:
1. Experimental Mode Shape: If the experimental mode shape has complex displacement values, representing motion along a single DOF, you can convert it to a real-valued format. For example, you can consider the magnitude of the complex displacement at each node as the mode shape value. This will result in a real-valued mode shape that represents motion in a specific DOF.
2. FEM Mode Shape: Since the FEM mode shape already contains real values representing motion in all three DOFs, no additional conversion is required.
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.
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I have modeled a two-dimensional plane strain embankment in Abaqus. I did not apply any forces, boundary conditions, or displacement to the infinite element, and I defined it as CINPE4. I defined two steps for the model: the first step is static to apply gravity load, and the second step is dynamic implicit. In the second step, I applied the time history of the Loma Prieta earthquake horizontally on the base of the model. Ultimately, I observe a concentration of shear strain at the boundary between the infinite and finite elements, as shown in the image below.
In addition, I have attached my model's .inp file to this question for reference.
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.
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I have some STL files describing the geometry I intend to use in FEA simulation in CalculiX code. I'm struggling to find resources on how I can do this. Any advice would be very much appreciated !
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
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Explicit scheme : By varying the mesh size, we see that for smaller sizes, the computation time for the usual mass matrix (not diagonal) exceeds that of the lumped mass matrix (diagonal). This I understand. But when the mesh size becomes large the computation time for the lumped mass matrix (diagonal) exceeds that of the usual mass matrix (not diagonal). Why ?
And why sparse matrix has computational benefits than diagonal matrix for large sizes ?
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I need to carry out a finite element analysis of the human foot. But I am not getting the CT scan file with more than 128 slices. Is it possible to model a human foot with 128 slices? How many slices at a minimum are needed for proper modeling and Finite Element Analysis?
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 :)
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Hi :),
I currently am doing a project where I have to analyse the deformation of a circular plate on abaqus , as loads I have added a pressure load and a body force and as boundary condition I have fixed ( encastre). How can I define a deflection on abaqus or what expression can I use in order to input in the software?
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.
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Hello,
I have several structures which is composed of an upper body and an under body. I want to compare different upper body with each other (therefore several different structures) with Finite element software. I also want to lower the stiffness of these under body to have the same stiffness on the different models and thus be able to compare upper body between them. For this the solution is to vary the Young's Modulus of these different under body. The problem is that some are longer than others in terms of length. How to take this parameter into account?
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?
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I'm looking to develop my knowledge to get hired as a stress engineer for my first job onwards. It seems like reinventing the wheel sometimes to try and understand how the software works. Is it bad / waste of time to do that?
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.
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I have made a model in Abaqus program. I want to define "E" as a constant value at each node in the part.
I have entered in inp. File
*Depvar
1,
*Elastic, dependencies=1
1000., 0.25, , 1000.
6e+09, 0.25, , 6e+09
*User Defined Field
and I have entered the constant values of "E" at each node like this .
*Initial Conditions, type=Field, Var=1
Part-1 . 1 , 22980538
Part-1 . 2 , 52880552
....... and all of nodes of the part
Moreover, I have defined a subroutine USDFLD as presented in this figure.
The problem is that after calling FV1 it is not equal to the values that I have interred in this command *Initial Conditions, type=Field, Var=1......How could I Solve this problem or is there any way to define "E" at each node of the part???
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.
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I am writing a FEA solver (using MATLAB) for computing stresses and stresses in a 2D rectangular plate with an elliptic hole (rotated to an angle). I computed the global stiffness matrix using Gauss quadrature (3 gauss points) and have also calculated stress and strain in each element.
How do I calculate the nodal stresses from the element stress values. I think the element stress values that I obtained are calculated at the centroid of each element. How do I extrapolate/interpolate these values to get nodal stress and strains?
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.
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Hi all,
I am trying to determine the relative motion between two surfaces in contact. Although I know how to calculate the relative motion, I don't know how to extract the paired nodes (closest nodes) of surfaces in ABAQUS when my geometry of study is undeformed.
For relative motion I will be using the following formula:
If there are contact surfaces named A and B, where there are i-th number of nodes:
X - Relative motion: square root( ( (X Deformed Node1B - X Deformed Node 1A) - (X Undeformed Node1B - X Undeformed Node 1A) )^2 )
Y - Relative motion: square root( ( (Y Deformed Node1B - Y Deformed Node 1A) - (Y Undeformed Node1B - Y Undeformed Node 1A) )^2 )
Z - Relative motion: square root( ( (Z Deformed Node1B - Z Deformed Node 1A) - (Z Undeformed Node1B - Z Undeformed Node 1A) )^2 )
Total relative motion: square root ( (X - Relative motion)^2 + (Y- Relative motion)^2 + (Z - Relative motion)^2 )
Please let me know if I can make my question more understandable or if there's more information required to make it clearer.
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.
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It seems that the most simple way to get both an infinite number of tessellated solids and lattices with periodic minimal surfaces in R3 consists on using a Pearce "saddle tetrahedron". The resultant convex solids:
1) Have configurations which tesselate the euclidean space. These tesselations are not Voronoi and have curved boundaries in a bcc lattice.
2) Define minimal surfaces for any 3 dimensional quadrelateral on the external closed surface of the solid.
Is there any topological description of such solids in the literature? How can we get a Weierstrass representation of the external surface of each polyhedron? How can we get the conjugate continous surfaces? Can we consider this to be a good design method for structural lattices?
Any comment will be wellcome.
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Hi,
I would like to apply a defined value of initial stress on 3D Shell elements in the initial step in Abaqus CAE. These shell elements are connected to a 3D Deformable Solid by a Tie Constrain. I have also tried to connect them through "shell-to-solid-coupling" constrain, but the same result. After the initial step, I provided a self-equilibrium step without any loading (Figure 4).
My problem is that after the next steps when loading starts a fast relaxation of this shell element (Figure 1) occurs without transferring the stresses to the tied 3D Solid shape (Figure 2). The tie properties are as shown in Figure 3.
My question is how to transfer a prestressing load (predefined field: stress) from a shell element to a 3D Solid, tied to each other since the main reason for this prestressing is to provide a negative deflection in the main structure?
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
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Abaqus provides the option to define the mode mix ratio based on energy or traction. The traction-based mixed mode response ( Mode I/II problem) where pure Mode I and II traction separation relation is already defined in the input file. Is the Abaqus interpolates for the intermediate mode mix ratios?
Thanks Kaushik
I was looking for the same in Abaqus documentation. It would be a great help, if you can share the link or refer the section in Abaqus documentation (if you have acces to).
Regards
Sailendu
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am working on static analysis on abaqus where friction coeff. is defined to be 0.01 and everything is going on well ....... on replacing the friction coeff. from 0.01 to 0.3 the job is being aborted even by changing the intial and minimum step time to EXTREME values .......
Any one had this problem before ???
Why the step time is not change and the increment is too much?
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I am looking to design and further running simulations and analyse a low speed shaft of a typical wind turbine. What should be the optimal shaft diameter and length for a given torque and rotational speed requirement in a transmission system of a wind turbine. Do you recommend any good software to run FEA simulations for validation analysis purposes.
Any suggestion, I will much appreciate.
Sir Ansys
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I am looking to design and further running simulations and analyse a low speed shaft of a typical wind turbine. In particular I am looking to design the shaft diameter and length and any other connection components such bearings, keys and so on, for a given torque and rotational speed requirement in a transmission system of a wind turbine. Do you recommend any good software to run FEA simulations for validation analysis purposes.
Any suggestions or comments, I will much appreciate.
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.
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I cannot find the PLA material in ansys. I tried to add PLA in library. After that also it shows error in PLA properties.
Please tell the way to add the PLA, ABS in Ansys workbench.
Thanking you.
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I am simulating the fatigue behaviour of Compact Tension (CT) samples using Ansys. I have to apply force which is calculated against any %UTS value it i cannot find which area will be used to accurately calculate the force for that ultimate stress value.
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.
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Dear sir or ma'am,
I am solving a 3D heat conduction equation involving a moving heat source (a laser). The goal is to get the thermal behaviour of the domain with time.
I am using structured grid and using the element size less than the dia of laser spot, which is way too small. It is computationally very heavy for my small laptop.
There is a method which uses adaptive moving mesh. A finer mesh surrounds the laser spot as it moves. But I do not have any idea how to implement that in my code.
Could you please recommed any thing where I can start? or how should I proceed?
Thank you and regards,
Ravi Varma
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.
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I get this error when I define material properties as nonlinear elastic
TB,MELAS
I cannot graph or plot the table.
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.
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I'm trying to simulate nonlinear compressive buckling of a material. However, it's not buckling as I would (theoretically) expect for lengths crossing the buckling threshold. It would just compress and fail at the failure strength/strain as specified in MAT024 - Piecewise Linear Plasticity. For further reference, I am using solid elements and it's a pin-pin configuration.
Theoretically, I'm thinking that a small lateral load/perturbation is needed to trigger the buckling and/or build the meshing with an out-of-straightness. I'm not an expert in FEA/LSDYNA, so any help with choosing the right keywords to get my specimen to buckle is appreciated.
I've already got the specimen to buckle elastically (eigenvalue), but struggling with nonlinear buckling.
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.
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Currently using Msc Marc Mentat for FEA. Now i conduct the mesh convergence/sensitivity analysis manually. So I need to know if there any automatic way to conduct the mesh convergence/sensitivity analysis
Amir Mustakim Ab Rashid may use a statistical method to find the error in between the final answers.
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I am using bone model in finite element analysis. There are not many references that emphasize on how their mesh convergence analysis was done in detail. What I assume is by finding the max Von Mises stress on one simulation having element size of X, and redo the simulation with element size of X/2 and get another max Von Mises stress. I'd do it repeatedly until X/16.
But is my assumption already correct? Or should I use something like root mean square calculation?
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
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Greetings to all.
I am trying to simulate heat transfer between 2 parallel plates.
The source plate have heat condition and I want to get temperature profile in upper plate, where heat flow through convection between the two .
Can someone assist me with some tips?
Hello.
Thanks for your response Farid SIr.
But, I am having difficulty in the simulation part in ABAQUS.
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I am an undergraduate student doing a thesis regarding slope stability analysis using PLAXIS 2D. My study area is at Kajang, Malaysia. I only assumed the phreatic water level because I don't have any borehole data. I have already done the model but I have questions regarding my model:
1. Is the water level that I have marked and assumed logical? (40 m above flat land)
2. What does the legend on the right represent, and is it the FOS? (The FOS that I obtained from the model is 1.780 as shown in the picture below)
3. Is the part that I have marked in the picture the critical slip surface (Picture 3)?
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.
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I have applied load axial to the column and pressure at beam but when i am try to plot x y data the reaction forces are zero at every node whereas in legend the reactions forces are showing.
#abaqus #FEA
There are several possible reasons why the force at a given node might be zero when plotting a load-deformation curve in Abaqus:
1. The node is not subjected to a load: If the node is not subjected to a load, then the force at that node will be zero. This could be due to the way the model is set up, or it could be because the loads applied to the model do not affect that particular node.
2. The element has zero stiffness: If the element connected to the node has zero stiffness, then the force at the node will also be zero. This could be due to a problem with the element definition or the material properties used in the model.
3. The load is applied at an incorrect location: If the load is applied at an incorrect location, it may not affect the node in question and the force at that node will be zero.
4. The model is symmetrical: If the model is symmetrical, the loads applied to the model may cancel each other out, resulting in a zero force at the node.
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.
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I am attempting to model a pretensioned concrete beam in ansys by varying prestressing force along the Straight Pre-Tensioning Strand.
During the experiment, the beam was fabricated segment by segment. The applied prestress was then released decrementally after each concrete segment.
The results of the distribution of prestress should be similar to the attached Figure 1.
However, in the finite model, the beam model is already been fully constructed.
I am trying to consider the prestressing force as push in pressure at the both ends of the strand.
Hence:
How do vary the pretensioning force for each concrete segment ?
Thanks
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.
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I exported the global stiffness matrix for my linear elastic instance in Abaqus, by attaching the following commands to the input file:
** Output Global Stiffness Matrix
*Step, name=Global_Stiffness_Matrix
*MATRIX GENERATE, STIFFNESS
*MATRIX OUTPUT, STIFFNESS, FORMAT=MATRIX INPUT
*End Step
However, the resulting matrix has most of the diagonal elements with very large values, for example:
1635,3, 1635,3, 1.000000000000000e+36
Why is this happening? And how could I solve?
Thanks!
Can you share your Abaqus model (.inp) format?
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Hello,
Recently, I am learning how to develop a full microstructure-resolved 3D model. And I want to use X-ray nano-tomography or focused ion beam/scanning electron microscope (FIB/SEM) to reconstruct the microstructure of commercial electrodes with sufficient nanoscale details. The microstructure-resolved models can be imported into computational programs to mimic the electrode behavior under the battery operation condition. But I encountered some questions. Firstly, how to add the current collector and separator into the segmented volume to construct a battery half-cell? Secondly, how to export the battery half-cell and import it into computational programs like COMSOL? Does any examples or source code about these questions?
I would appreciate it if you can help me.
hello
unfortunately is not mu skill.
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Hello. I am working on a project that investigates the stresses in severe scoliosis. Unfortunately, severe scoliosis has not been studied much using FEM. Can you help me to find the suitable Loading and Torque for the situation when the cobb angle is greater than 40 degrees? Or to Recommend me an article that has good information in this field.
Thank you so much for your attention and participation.
ApiFix® is committed to helping patients with adolescent idiopathic scoliosis (AIS) and their families make informed decisions about treatment options in partnership with their orthopedic specialist
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Help i am getting the following error message in abaqus
**WARNING: Surf-1 is ambiguously connected at node ###. This surface cannot be used with *CONTACT PAIR. ***ERROR: 1 improperly defined surface(s). Please check your surface definitions. Make sure that all surface normals point outward.
Note:
The mesh is an orphan mesh and is generated outside ABAQUS.
The mesh is fine and has a huge number of elements.
Element typr for the mesh is C3D4
i have defined the surface using ABAQUS CAE and it was generated automatically using the following commands
*elset, elset=surf-1-S1-1
*elset, elset=surf-1-S2-1
*elset, elset=surf-1-S3-1
*elset, elset=surf-1-S4-1
....
*surface,type=element,name=surf-1
surf-1-S1-1,S1
surf-1-S2-1,S2
surf-1-S3-1,S3
surf-1-S4-1,S4
As you will see, i have followed section 2.3.2 Element-based surface definition in abaqus user's guide.
if you read "Creating surface facets by specifying solid, continuum shell, and cohesive element faces" you will see i have followed it.
So what is the issue here?
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I have created a solid mesh of a flange model in hypermesh. However, only one of the mesh quality criteria is not satisfied. The max angle of some hexahendral elements is slightly higher than 135° (136°). How can this affect the final results?
Note: aspect ratio, jacobian, warping angle,skewness are fine
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.
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My question is that I'm wondering why my hoop stress in my composite pressure vessel is coming out to be non-constant throughout the ply layer. Wondering if it's in my composite layup or something else. Images below should show composite layup, encasture boundry conditions, and FEA Visualization of irregular hoop stress. Any help would be greatly appreciated.
Try redefining your wrap properties and your analysis in a cylindrical coordinate system. You have one or both in a cartesian coordinate system.
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If there is 2 DOF (Translational, Rotational) Cantilever beam, and it has 7 elements, I want to use System reduction technique to get rid of the rotational Dof, Do I expect to obtain the same first seven natural frequencies?
Because I tried to use SEREP technique and I did not get the first seven natural frequencies, I got the 1,3,5,7,9,11,13 natural frequencies?
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).
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