Plasticity - Science topic

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

Les neurosciences permettent une meilleure compréhension des fonctions cognitives telle que l'apprentissage support de l'éducation. L'apprentissage passe par certains processus pour l'apprenant : l'attention, l'engagement actif, le feedback et la consolidation des acquis. Cela permet de comprendre les difficultés des apprenants et d'orienter les méthodes pédagogiques pour un bon résultat.

Thank you for your answer. I will try this method@Joshua Depiver

I hope you find it useful

@ Anders Buen

Thank you for the article!

I've taken a closer look at it.

Unfortunately, as I feared, the article doesn't really help me any further. It also contains some weaknesses - for example in the evaluation of the measurements (CoR), which are ultimately interpreted exclusively with a viscoelastic model. For example, the importance of the bending wave (Zener) - although relevant here - is underestimated and adhesion is not included in the analysis at all.

With best regards

Ronny

Dear Deepika Kushwah ,

can you give some more details? Are those shell elements or solid elements?

How do you calculate the tangent stiffness matrix? Is the indexing of the stress/strain/stiffness tensor that you are using, correct?

For example if the shown model contains CPS4 (plane stress) elements, then you must specify a 3x3 stiffness tensor and 3x1 stress/strain arrays. In case of CPE (plane strain) elements then 4x4 and 4x1, and in case of solid elements 6x6 and 6x1 respectively.

No, there is no need for any other software to read the odb file. In simulating metallic foam materials in Abaqus, the choice between Crushable Foam Hardening and plastic strain with yield stress for hardening depends on the specific requirements of your simulation. Crushable Foam Hardening is used to model the behavior of compressible foam materials, while plastic strain and yield stress are more general parameters for hardening. In 2D cases, both approaches can be applicable, with Crushable Foam providing a more specialized model for foam materials. Ultimate tensile stress is crucial for failure criteria and can be used to assess material failure.

Dear Sarabjeet Kaur ，For more details please visit the conference website:

While achieving pinching effects in ABAQUS can be tricky, especially with just Concrete Damage Plasticity, It is possible to capture it by combining UMAT, ULE, and connectors Here it is showcased in my project model, where pinching is quite satisfactory. Check out this YouTube video for a demonstration: https://www.youtube.com/watch?v=-yMjWY7lWCk

It seems you are encountering non-convergence issues with your mesoscopic simulation of a three-point bending test in ABAQUS and the load-CMOD (Crack Mouth Opening Displacement) curves are not reflecting the expected results.

Non-convergence in ABAQUS can occur due to a variety of reasons, and here are some general troubleshooting tips that might help you resolve the issue:

If after addressing these points you still face convergence issues, it may be beneficial to review the results of a converged step to determine if there are any physical reasons for the non-convergence, such as unrealistic stress concentrations or unexpected material behavior.

you can slow down the loading amplitude rate

Hi is this something you want?

Here i have plotted the xx component of the logarithmic strain vs increment.

The boundary condition is uniaxial tension along the x-x.

The load file has also been attached.

Let me know if this is what you were looking for

Poly(3,4-ethylenedioxythiophene) (PEDOT) is a conducting polymer known for its high electrical conductivity and excellent stability. Modifying its properties, such as reducing elastic modulus and improving plasticity, can be achieved through the process of doping. Doping involves introducing additional substances (dopants) into the polymer matrix to alter its properties.

Here are steps to reduce the elastic modulus and improve plasticity of PEDOT through doping:

Remember that the choice of dopant and the doping process conditions will greatly influence the properties of the doped PEDOT. It's essential to carefully design and optimize the doping process to achieve the desired properties for the intended application.

hi Nayak,

did you find a solution to your problem? i am also trying to define solid wood in abaqus cae. i have elastic data but plastic data and i can't find how to define this data in abaqus. I have limited time left for my master thesis. I need serious help from you and other friends.

Regards.

Deleting or "killing" elements during a transient analysis in Abaqus, such as removing elements that exceed a melting temperature, can be achieved using the subroutine-based approach. Here's a general guide on how you can implement this method:

Remember that this approach doesn't physically remove the elements from the mesh, but it alters their properties so that they no longer contribute to the simulation. This can create numerical challenges in some cases, and careful validation and verification of your model will be important.

This is a high-level overview, and implementing this approach will require some expertise in writing and debugging user subroutines. The Abaqus documentation and various online forums can provide more detailed guidance tailored to your specific application and needs.

The UMATHT subroutine in ABAQUS lets users define their own constitutive model for a heat transfer analysis. It's used to define temperature-dependent thermal material behaviour. However, the code you posted appears to be for plastic deformation, not heat transfer, so it looks like it might be for a UMAT subroutine, not UMATHT.

The hardening curve equation that you provided is a common one:

Sf=Sy*(1.d0+E*eqplas/Sy)**xn

It appears to be using an isotropic hardening rule (specifically, a power-law hardening model) where 'Sy' is the initial yield stress, 'E' is the Young's modulus, 'eqplas' is the equivalent plastic strain, and 'xn' is the hardening exponent. 'Sf' is the flow stress. This formulation calculates the yield stress as a function of the equivalent plastic strain.

In the loop following this, Newton's method is used to solve for 'Smises' and 'deqpl' until a certain tolerance is met or the maximum number of iterations ('newton') is reached. 'Smises' is the von Mises stress, and 'deqpl' is the increment in equivalent plastic strain.

Please note that while this power-law hardening model is quite common, it may not be applicable or accurate for all materials. It's critical to use experimental data or data from the literature to calibrate the model parameters ('Sy', 'E', and 'xn') for the specific material you are studying.

For a better understanding of the UMAT or UMATHT subroutines and their intricacies, it would be useful to refer to the ABAQUS documentation and user manual or to reach out to Dassault Systèmes' support. Additionally, consulting with an expert in the field or someone with deep experience in using ABAQUS and user subroutines can be very beneficial.

Hello,

Adjusting the solution's setting could fix the issue. Try to use the fully-coupled solution, change the nonlinear solution to automatic, increase the number of iterations, and reduce the tolerance factor. These may fix the issue. In addition to that, you should be sure that the meshing is well adjusted.

Regards.

The best book that would suit your requirement is 'Fatigue of Materials' by Dr. Subra Suresh. The google book link is below:

Happy reading!

1. Start in the Ansys Workbench by selecting the Simulation tab and then click the "Materials" icon.

2. Select "Edit Material" from the drop down menu. A window will appear with several tabs. Make sure the "General" tab is selected.

3. Enter a name for your material, select the "User Defined" option under Material Model, and select "Nonlinear" in the Nonlinear Model drop-down menu.

4. Use the "Add Data" button to select your experimental data. Make sure to select the appropriate units for your data.

5. In the Data Settings tab, select the appropriate model type (i.e., Stress-Strain, Creep-Stress-Strain, etc.) and interpolation.

6. Select the appropriate units for your data and enter the Number of Data Points and Maximum Time for your data series.

7. Click the Apply and OK buttons to complete the material model definition.

In the Mohr-Coulomb model, plasticity can be incorporated by coupling temperature through the use of thermal softening or hardening parameters. Here's a general approach to coupling temperature in the Mohr-Coulomb model to predict plasticity:

It's important to note that the specific details of coupling temperature in the Mohr-Coulomb model may vary depending on the software or numerical method you are using for analysis. Additionally, obtaining accurate temperature-dependent material parameters and thermal loading conditions is crucial for reliable predictions. Consider consulting relevant literature or seeking expert guidance for your specific application to ensure proper implementation.

Put simply: In VPSC multiply grains are considered to live in one integration point, i.e. grains are not meshed explicitly, but their effect is only accounted for in terms of (homogenization) equations. VPSC is more suitable for larger scales in terms of calculation resource efficiency.

Thanks very much for your answer, Corentin Levard

@Tomas yeah it is intentionally done cause the idea is to fix one end and apply a displacement on the other side for 100 step

Hi!

Plastic deformation of the material is not associated with the modulus of elasticity, but with the yield point.

When determining the hardness, the material may already be in the plastic region.

Best regards

I will read it. Thanks a lot for your help Simon Smith

If you have compressive strength of concrete then you can find other parameter. If you have test data for the compressive strength of the concrete, you should use that data. It is important to note that the compressive strength of concrete is not the only material property that affects the behavior of concrete in the CDP model. Other important properties include the tensile strength, fracture energy, and tensile softening parameters. These properties should also be determined based on the specific type of concrete being modeled and the available data.

I think this video help you.

It seems that you are encountering convergence issues when you try to assign plastic properties to your soil layers in ABAQUS. Here are some additional, more specific suggestions that may help resolve the issues:

In addition, it may be helpful to review the solver output and error messages to identify specific issues that are causing convergence difficulties.

here you are

You could create an own excel according to the following article:

Hi,

Look for this book, chapter 7. They have tried to model the serration mathematically. It may help you to set some conditions to identify mathematically which type of serration (A, B, or C)

"The Three-Level Model to Describe Serrated Yielding: Structure, Algorithm, Implementation" by Dmitriy Gribov, Fedor Popov, and Eugenia Chechulina

Dear Shyam Kishor Sharma,

With respect to the description given by you in the question, let us consider that the material is made out of a single constant manufacturing process, and the stress-strain curve obtained from experiments is fixed.

Let us further consider that during service, there are no external physics involved such as temperature-changes, moisture absorption etc. and the load applied onto the component is purely mechanical.

Therefore, with the above considered points, the stress-strain curve would remain fixed just like a material-property or material-behaviour.

Now, let us come to the question of Tangent modulus.

I would try to explain from a generalized 3D concept of purely isotropic hardening.

Case-I : Let us assume that the stress-strain response is 'Linear Isotropic Hardening'. In this case, the hardening modulus ( H ) remains constant, just like the Young's modulus.

So, in the generalized 3D case, the expression of consistent tangent modulus matrix ( D-ep ) would be as shown in the attached file.

Here, we need to note that the tangent modulus matrix is dependent on a constant hardening modulus ( H ).

The response between equivalent total stress and equivalent total strain can be plotted as shown in the document with a linear behaviour.

But case-I is often not experimentally found. So let us move to case-II

Case-II: The stress-strain response follows Ramberg-Osgood hardening.

In this case, the tangent modulus matrix becomes a function of Ramberg-Osgood constant parameters (k , n) and also a function of varying values of equivalent plastic strain (epsilon-p) as shown in the attached document.

Therefore the expression of consistent tangent modulus matrix ( D-ep ) now incorporates a varying hardening modulus depending on the variation of equivalent plastic strain.

The response between equivalent total stress and equivalent total strain can be plotted as shown in the document with a non-linear behaviour.

---------------------------------------------------------------------------

Now let us come to the actual point of concern here.

In case-I, if simulation is performed, the iterative updating of variables would not incorporate any requirement of updating the Hardening modulus (since, it is constant in this case).

But, in case-II, if simulation is performed, the iterative updating of variables would compulsorily incorporate updating the Hardening modulus with every iteration (since, it is dependent on equivalent plastic strain in this case). This situation often leads to higher number of iterations required for achieving convergence, or sometimes even leads to non-convergence (if the stress-strain curve is too much non-linear).

Due to the above complexity in case-II, the computational effort is higher in there.

As such, many computational researchers assume that the hardening modulus is constant even though it shows a curved behaviour. In other words, they prefer an idealization of Case-II through Case-I. This often solves problems of non-convergence and also leads to faster convergence and less computational effort.

So, the fact which you are saying about 'some authors assuming approximate hardening modulus' is probably due to this reason.

Moreover, those authors might have probably done a little more tweaking. In order to accurately idealize the curved stress-strain response, they might have assumed a range of constant values of hardening modulus instead of one single approximate value.

This approach seems to have been by those authors mainly for faster simulations. In that process, they might have analysed the effect of the range of constant hardening values in their papers.

However, this does not mean the material-response or stress-strain curve is changing.

For any particularly manufactured fixed material, without any external influence of temperature, moisture etc., the actual stress-strain curved response and the dependence of hardening modulus / tangent modulus matrix on plastic strain would remain fixed.

Work hardening and strain hardening during service would not change it.

Only, if there is some alteration in the manufacturing process of the material, or if the material during service is subjected to high-temperature or other aggressive environments, the stress-strain curve and corresponding hardening modulus / tangent modulus would change.

You can separate elastic depth or elastic displacement from plastic depth/displacement in nanoindentation techniques using the Sakai model. I have used the model in my several papers as displayed below:

1. Alao and Yin, 2016. Assessment of elasticity, plasticity and resistance to machining-induced damage of porous pre-sintered zirconia using nanoindentation techniques. Journal of Materials Science and Technology 32 (5), 402-410.

2. Alao and Yin, 2015. Nanoindentation characterization of the elasticity, plasticity and machinability of zirconia. Materials Science and Engineering: A 628, 181-187.

3. Alao, 2019. Elasticity, plasticity and analytical machinability prediction of lithium metasilicate/disilicate glass ceramics. Journal of the Mechanical Behavior of Biomedical Materials 96, 9-19.

4. Alao et al. 2022. Effect of polymer amount on the mechanical behavior of polymer-infiltrated zirconia-ceramic composite at different pre-sintering temperatures. Materials Research Express 9 (8), 085401.

If you don't have access to any of the above papers, get in touch so that I can provide their soft copies for you.

Dear Mishra; First of all, thank you very much for your comments. I used the Mohr columb material approximation method for the soil environment. I noticed that because the cohessive yield stress value is zero, it gives this error. Increasing this value a little bit solved the problem.

Hi,

This happens a lot when contacts are not defined properly. I have faced this problem few years ago when I ran my first Ls-Dyna model.

The reason why it penetrates is because it doesn't read that there's another surface thru which it needs to interact.

I'm pretty sure you haven't defined surface to surface contact between these two surfaces. Define it and let me know if you still l face same issue.

You could find some key elements in the manuscript: Quantitative estimation of phenotypic plasticity: bridging the gap between the evolutionary concept and its ecological applications https://doi.org/10.1111/j.1365-2745.2006.01176.x.

Best regards,

Independent of which material model you take, you need to provide information on the hardening behavior in the post-necking regime in order to be able to simulate this region. Getting this information for a real material from experiments is not trivial. Though, there are established methods to extract true-stress vs. true strain data from the post-necking regime, e.g. using Bridgeman's correction or doing an inverse parameter identification (the latter is necessary definiely in case of complex stress states). A pragmatic approach is that you take the true pre-necking data and extrapolate them to the post-necking regime using an analytical law like a power law or a Voce law. Subsequently, the analytical law can be either rasterized to obtain the tabulated data for the built-in plasticity models of Abaqus or you implement it as a user-defined hardening law using the UHARD routine. Our GTN implementation (open source at https://tu-freiberg.de/nonlocalGTN ) supports power-law hardening by default.

Thank you very much Francesco Cervellera, as I'm still building the model and not focusing on a specific material, I'm using parameters of steel.

Therefore, I think it's rather a possible problem in the setup of simulation or some constraint of cohesive elements that I'm facing rather than the material definition that I described in the original post.

Domagoj

Hi Victor J. Аdlucky,

Just found out there was a reply. Thank you very much for your help. I will try to use your method and see if that works for me. Currently, I am using 2 connectors with different plastic rotation behaviours (arranged in parallel) between the 2 connecting points so that they can each handle the loading in the two opposite directions. If I am able to get what you suggest to work it would save 50% of the time for me!

Thanks again,

Heng

Dear Yasar Ameer Ali,

If you want to define CDP parameters such as eccentricity and dilation angle in Abaqus, it depends on the concrete used. So you shall calculate the parameters of the used concrete to define it correctly as it differs due to the additives used.

Dear Researchers,

There are mechanical models for conforming rough surfaces whose contacting asperities deform (i) elastically, (ii) plastically, or (iii) elastoplastically. To know whether the deformation will be plastic or elastic in a given situation of temperature and load, the concept of plasticity index is used. The “plasticity index” indicates the mode of deformation occurring in the contact [8]. The deformation of an asperity is said to be elastic up to some given load for a given hardness of the material above which plastic flow will occur.

Source: DOI:10.1098/rspa.1966.0242

Hi

It seems that this unfortunately is only available in Abaqus/Standard, so is not compatible with explicit.

For that thing you may try the following (but again in ANSYS, I hope similar options will be available in COMSOL):

1. Plot the radial deformation of nodes at the interface near the cavity in time history postprocessor it will show at what time point (or load step) diameter of cavity starts increasing.

2. If you are interested in understanding any leak through that cavity, contact pressure zero or contact status open may be used as the indication of the same.

Regards

The regular polygons of trigonal and hexagonal symmetry as yield criteria are summarized in Altenbach, H., Kolupaev, V. A., General Forms of Limit Surface: Application for Isotropic Materials, in Altenbach, H., Beitelschmidt, M., Kästner, M., Naumenko, K., Wallmersperger, Th. (eds.), Material Modeling and Structural Mechanics, Advanced Structured Materials, pp. 1-76, Springer, Cham, 2022. Both 24-gons are called the Rosendahl criteria.

Hi Saurabh Thakur,

When your model is temperature-dependent and has a high strain rate like impact, you should use the Johnson-Cook theory.

Depending on your simulation, you can define other variables as well. For example, in high-speed manufacturing processes where a large amount of inelastic strain exists, you need to define Inelastic Heat Fraction behavior, which indicates the energy dissipation rate as heat.

I recommend referring to the link below to see some examples and become more familiar with the Johnson-Cook theory.

Best wishes.

Hey Farshid Hajializadeh ,

I have the same problem, "Floating Point Exception detected in increment ...Friction Work is NaN ". I used a built-in VUMAT function.

I'd appreciate it if you could let me know how I can detect and solve the problem-caused variant.

Engr. Tufail yup. The data is extracted from Python. Hence, no equations are seen.

Check https://www.mdpi.com/2075-4701/8/11/955/pdf

That is a good question.

Es posible.

You can 1) decrease the initial time increment or 2 )go to:

Step>other>gneral solution controls>(choose the step you already defined)>Time incrementation>more>change(IA) from 5 to 10 or more based on your problem.

Amal Rai Unfortunately, I'm not familiar with Abacus. I saw this approach in many papers. Recently I'm trying to adopt the Discrete Element Method to simulate the FSW process.

The issue of stress in thin films and functional coatings is a persistent problem in materials science and technology that has congregated many efforts, both from experimental and fundamental points of view, to get a better understanding on how to deal with, how to tailor, and how to manage stress in many areas of applications. With the miniaturization of device components, the quest for increasingly complex film architectures and multiphase systems and the continuous demands for enhanced performance, there is a need toward the reliable assessment of stress on a submicron scale from spatially resolved techniques. Also, the stress evolution during film and coating synthesis using physical vapor deposition (PVD), chemical vapor deposition, plasma enhanced chemical vapor deposition (PECVD), and related processes is the result of many interrelated factors and competing stress sources so that the task to provide a unified picture and a comprehensive model from the vast amount of stress data remains very challenging. This article summarizes the recent advances, challenges, and prospects of both fundamental and applied aspects of stress in thin films and engineering coatings and systems, based on recent achievements presented during the 2016 Stress Workshop entitled “Stress Evolution in Thin Films and Coatings: from Fundamental Understanding to Control.” Evaluation methods, implying wafer curvature, x-ray diffraction, or focused ion beam removal techniques, are reviewed. Selected examples of stress evolution in elemental and alloyed systems, graded layers, and multilayer-stacks as well as amorphous films deposited using a variety of PVD and PECVD techniques are highlighted. Based on mechanisms uncovered by in situ and real-time diagnostics, a kinetic model is outlined that is capable of reproducing the dependence of intrinsic (growth) stress on the grain size, growth rate, and deposited energy. The problems and solutions related to stress in the context of optical coatings, inorganic coatings on plastic substrates, and tribological coatings for aerospace applications are critically examined. This review also suggests strategies to mitigate excessive stress levels from novel coating synthesis perspectives to microstructural design approaches, including the ability to empower crack-based fabrication processes, pathways leading to stress relaxation and compensation, as well as management of the film and coating growth conditions with respect to energetic ion bombardment. Future opportunities and challenges for stress engineering and stress modeling are considered and outlined

Hi Annah,

in order to induce plasticity in neuronal cultures you can pursue 2 different streets. The first one is the chemical induction using a modified external solution supplemented with glycine at saturating concentration for 3 minutes. The second approach could be the dual patch where you will identify 2 connected neurons and after that you stimulate the presynapse in order to potentiate the post. However, the first method is easier than the second one, and it works pretty well.

Good luck for your experiments

Luca

Dear Ayush Kumar Jaiswal

I assume you are using some kind of crystal plasticity model.

You can find parameters for the alpha phase here:

and see the crystal plasticity implementation here:

In crystal plasticity, you will need to use two different material models for the two phases. Normally in Abaqus you would define two different user materials and assign them to the different grains representing different phases (sections of the geometry).

Best Regards,

Nicolò Grilli

If you want to calibrate a model with a compression test (epoxy shows different response in tension and compression), just use j2 plasticity, available in ABAQUS. All you need is the evolution of the plastic strain and the yield stress.

Nanoindentation used to detect the shape recovery from the deformed one. In this way actuation property can be measured. Some of the following journals may help you:

https://www.nature.com/articles/s41598-017-13434-9

https://onlinelibrary.wiley.com/doi/abs/10.1002/adem.200900266#:~:text=Nanoindentation%20is%20a%20suitable%20tool,to%20study%20their%20pseudoelastic%20behavior.&text=The%20corresponding%20nanoindentation%20responses%20differ%20considerably%20in%20terms%20of%20pseudoelastic%20behavior.

etc.

Dear Mojtaba Abdolkhani,

It is preferable to use a modulus of plasticity in the simulation of samples made by selective laser melting of 316L in a vase. This way, the simulation results will be closer to your experimental data. The use of foreign data will lead to deviations, which you will then have to specify with correction parameters. The connections obtained from the laser fusion have a strong influence on the mechanical characteristics and plasticity of the obtained products. Therefore, make standard test specimens by selectively melting the 316L. The obtained data, plasticity model and reinforcement curves are included in the simulation.

Wishing you success in your research.

Sina Shokuhi This is your decision what you want to obtain. If you are interested just in the overall texture evolution you can use either a mean-field model like VPSC approximating rolling as a plane strain, see e. g. Eq. (7) in

Alternatively you can use finite element method to simulate the rolling process - in such a case you should provide the crystal plasticity model in each integration point. It can be either a single crystal model or a polycrystal (e. g. using Taylor or VPSC). This way you can obtain the spatial resolution of texture evolution but the simulation will be typically more costly.

Hi, This depends on the material response, i.e. the Stress - strain curve. If the material hardened after the yield, Hardening material properties should be considered, i.e. this depend in the slope of the curve after yielding however, elastic-perfectly plastic is most common in analysing to be safer for the design purpose.

Best wishes.

Hi!

Kinematic hardening is only a simplified model that is convenient for describing the Bauschinger effect. More realistic is the combined model that combines isotropic and kinematic hardening.

V.N.

Dear Yi Chen, no not only polymers, all materials that present accumutated strain under cycling show ratcheting. Please check this free access document. My Regards

Dear @Harrison stamoudis,

You can assume a cohesion of 0.01kPa for sand as an aparent cohesion.

Feel free to get in touch with me.

Cheers,

Ali Ahmadi