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Viscoelasticity - Science topic

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I would like to simulate temperature developments and shear rates of a plastic which is extruded through a nozzle.
In addition, a rod rotates in the nozzle to apply more shear (and heat energy) and to generate a mixture.
Important are:
- Material models: viscoelasticity, structurally viscous material, thermoelasticity
- To be able to model rotation well
- Temperature developments
- (mixing)
Ansys Polyflow:
- Specialised on extrusions
- Viscoelasticity
- Non Newtonian viscosity
- Rotation can be modelled well (according to a literature source)
- Unfortunately, thermoelasticity cannot be modelled (and I do not know if this can be modelled by myself).
Is Ansys Fluent the better choice, especially because of the thermoelasticity and the wider range of functions?
I hope you understand my case.
Thank you!
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I would try Polyflow first.
Maybe you could consider the temperature dependance of the viscosity by implementing a temperature dependance yourself.
You should consider what is more important/relevant for your problem: viscoelasticity (then Polyflow) or thermoelasticity (then Fluent).
Good luck and success with your challenging task !
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I have been using the ARG2 rheometer and conducting an Oscillatory amplitude using citrated whole blood. But I have never been able to get an LVR. Has anyone tried doing this and successfully had an LVR?
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Linear Viscoelastic Range in general corresponds to a low oscillation amplitude, when one is dealing with a frequency sweep rheological test. If you are working in controlled stress test, in which you specify the amplitude range of the stress amplitude, evolution of the dynamic rheological properties especially G' and G'' versus the stress amplitude allows you to determine the maximal amplitude stress under which the fluid shows a linear behavior. The range of the linear viscoelasticity corresponds to the stress amplitude range where G' and G'' remains constant. These later normaly should decrease beyond this maximal stress.
Good luck.
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Can somebody help me on how I can calculate the prony series parameters from the frequency domain DMA data to calculate g_i, k_i and tau_i to be able to use it in abaqus.
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I use abaqus. Thanks for your comments.
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I'm working on interconversions between viscoelastic functions. I'm finding it difficult to convert my creep stiffness data to dynamic modulus using the Prony series function. I need help please.
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Maciej Trzeciak Thanks for the reply Sir.
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Dear Researchers :
Does someone know something, or is acquainted with the issue of "Flow Lines" (also called "Flow Marks" or "Streaks") on the extrusion process of insulation layers on Electric Cables.
I am investigating about this defect,
Why cause them ? How can be eliminates ? What are the factors to make them appear on the cable ? Etc.
Kindly, Franklin U.
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Flow lines, streaks or flow marks are the result of flow instability that occur when the the rate of shear acting becomes higher that a critical value. Due to higher rate of shear the melt experiences higher normal stress differences causing die swell + sudden change in the temperature after melt comes out of extrusion + the adhesion between melt and die surface combine to give streaks.
Dr. B R Gupta
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I want to add Phan thein tanner constitutive relationship in a laminar flow through a 2-D channel in COMSOL 5.4. I have come across a viscoelastic flow (Oldroyd-B model) over a cylinder discussed in COMSOL documentation which I have attached here. Can anybody guide me on how to set up a PDE module for extra stress contribution? It would be a great help if someone shared an mph file.
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Dear sir:
You can benefit from this valuable Link about your topic:
#################
To add weak contributions to COMSOL::::::
Then, in the Model Builder, right-click the main interface node and, depending on the geometric entity level, select More>Weak Contribution at the domain or boundary level, Edges>Weak Contribution, Points>Weak Contribution, or Global>Weak Contribution.
############
Also the attached pdf files....
I hope it will be helpful...
Best wishes...
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Dear Abaqus expert:
I am conducting fully coupled thermo-mechanical analyses with large viscoelastic deformation in Abaqus. The model works well in Cartesian coordinates. But when I extend to a spherical case, there comes a problem on setting up spatially variable body (gravity) force. For simplicity, I assume axisymmetry so that a 2D model is enough. Please see the attached figure for the modeling domain (a quarter sphere in gray).
For the interior of a planet (e.g., the Earth or Moon), the direction of gravity acceleration/force is expected to vary with space, all pointing to the center of the planet's sphere (i.e., red arrows pointing to the center C in the figure). So I need to impose a body force whose magnitude and direction vary with space. In addition, as the model considers large deformation (with Nlgeom on), the body force is required to be updated at every step.
I have searched and tested a few potential methods:
1) Wrote a python code to automatically add expected body force load for all the elements under *DLOAD. The model runs, but as you may expect: the body force always stays the same for the elements when they move. I would instead expect the body force changes with element coordinate, especially when the element/material deformation is significant.
2) Created analytical fields for the two components of body force, and then added them as body force load. The model can run but has the same problem as the previous method.
3) I have also read the reference to the user subroutine DLOAD. It seems to be helpful at the first glance, until when I recognize that there is only one output variable - load magnitude. As I need to vary two components of the body force, it can not directly satisfy my requirement.
I am wondering if anyone of you has encountered a similar problem, and may provide some insight? Any related suggestion would also be welcome and appreciated.
Actually, I have tried for a few weeks but still cannot find a satisfying solution. If there is anything unclear for you to understand my problem, I would be willing to add more details.
Thanks for your attention and best wishes,
Min
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Hi Min,
make a python script that reads the position of each node in your model, it calculates the distance from the node to the centre and, with that information, you can estimate the force components that you want to apply on each node and then apply the force to the node.
Using this approach, you should have no issue in solving a large deformation problem.
I hope it helps.
Federico
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I have been working on a two-phase laminar phase-field method in comsol where my one phase is Newtonian whereas the second phase, a bubble, is taken as viscoelastic fluid. I want to know how to add the viscoelastic constitutive relationship to my momentum equation. If someone has any idea how to solve two-phase flow in comsol having a viscoelastic fluid even having a different approach from the phase-field method please share that too.
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Thank you Samuel Oyefusi for your reply,
I guess u got the question not the way I am planning to work so I am explaining the model (simpler version). I am taking a rectangular channel filled with Newtonian fluid (say, water), there I am having a circular bubble (viscoelastic). the bubble is made to move in the channel through a pressure-driven boundary condition. the interface tracking method I am using is the laminar phase-field (built-in comsol feature). since it handles only Newtonian or inelastic fluid, the polymeric stress component is not taken into account. i found in some literature that consecutive relations for that fluid extra stress term can be solved separately. if you have any idea regarding how to solve constitutive relationship for extra stress tensor (either as a pde or weak form in comsol) please let me know it would be a great help.
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I'm currently working in OpenFOAM as part of my research on two-phase viscoelastic flow. OpenFOAM version 9 supports viscoelastic flow models such as Maxwell, giesekus and PTT, listed under momentum transport models(Laminar). I don't know how to implement these models in the case file. If some case files of benchmark problems related to these(Twophase Visco elastic flow) exist, could someone guide me through those?
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The more stable solvers 'RheoTool' for viscoelastic fluid flow simulations is developed by Pimenta et al. The solver, along with tutorials, is available is https://github.com/fppimenta/rheoTool
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Hello, first off all my question may be badly formulated since this is my first interaction with viscoelastic behavior, from what I understand the creep compliance is somehow the equivalent of the compliance matrix in elasticity except for the fact that it is depended on time ( and maybe temperature) because it takes into account the the viscous behavior of the material.
From what i understand, in order to "separate" the viscous behavior from elastic behavior we need to subject our samples to constant loads over a period of time, thus we obtain strain vs time graphs for different loads which helps us see if the material is linear viscoelastic or nonlinear by analyzing the isochronals.
Now back to my question, it appears to me that the simplest way to determine the creep compliance tensor components, do we use the data obtained from the constant loading tests I mentioned earlier, specifically the isochronals obtained for every moment to calculate the every particular component of creep compliance tensor at that moment, and then use some kind of mathematical fitting (power laws for example) to obtain the creep compliance as a function of time.
Please tell me if the method that I explained is the way to proceed or if it's just nonsense.
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Please check this link
I hope it's useful for you
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I have prepared a blend of PP/SEBS and SEBS-g-MA. However, the storage modulus of blends increased at a lower temperature compared to pristine PP?
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about SEBS-g-MA effect on PP:
- "Effects of Crystallinity of PP and Flexibility of SEBS-g-MA Copolymer on the Mechanical Properties of PP/SEBS-g-MA Blends", Rishi Sharma, & S. N. Maiti , Polymer-Plastics Technology and Engineering, Volume 53, 2014 - Issue 3,
Pages 229-238,
- "PE-g-MA, PP-g-MA and SEBS-g-MA compatibilizers used in material blends",
A.Mengual, D.Juárez, R.Balart, S.Ferrándiz, Procedia Manufacturing, Volume 13, 2017, Pages 321-326
about nucleation of PP :
- "The PP nucleating agents and its effects on properties of PP" X. He, L. Wang, W. Pu, G. Zhang, C. Jiang, C. Wan, Int. J. Electrochem. Sci. 1(2006) 12
- "Advanced nucleating agents for polypropylene", Dima Libster, Abraham Aserin, Nissim Garti, September 2007, Polymers for Advanced Technologies 18(9):685 - 695 , DOI: 10.1002/pat.970
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I am trying to plot the attenuation coefficient vs wavenumber of SH wave through viscoelastic media from secular equation (c,k). But actually cannot do it. Any suggestion will be helpful here.
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While plotting the phase velocity, we took a real part and while attenuation, we take imagniary part. If you are unable to separate it. give the command to the imaginary part.
ContourPlot[Im[exp1] == 0 , {x, 0.1, 30}, {c, 5200, 6000}]
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Recently I've been trying to simulate a two-phase flow in Comsol. Comsol provides three methods for solving multi-phase flows.
1)two-phase (level-set)
2)two-phase (phase field)
3)two-phase moving mesh.
I need to include a viscoelastic fluid in this two-phase flow. But comsol only provide a viscoelastic flow option with single phase . So technically, level set and phase field methods aren't possible for me to use. I used viscoelastic module and then defined two deforming domains separately for viscoelastic fluid and the other Newtonian fluid. Now under viscoelastic module, i defined two fluid properties separately for two fluids and also a fluid-fluid interface. Along with all these, I also have to include electrostatics in to the system.
First of all, I would like to know whether my set-up is right or wrong. Some pictures related to my domain and set-up is attached below. While running, my interface is moving, but I'm getting inverted mesh after a while.
If someone could help me kindly reply.
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Hello Dear
send me the comsol file, i ll work on it
regards
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Hello! I would like to investigate viscoelastic behaviour of shape memory polymer in ANSYS.
As I understood from the literature, I need to set Prony series, WLF coefficients. That's it? Should I write some constitutive equations and how to implement it to ANSYS?
Thank you!
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Hello everybody,
         My task is to write a UMAT for non-linear viscoelastic material in Abaqus. When it comes to working in 2D and 3D, I see that there are places where I have to work with 4th order tensors. I understand that stresses and strains are stored as vectors in Abaqus - UMAT and are passed in and out the same way.
  • Now I don't understand how to handle the 4th order tensors accordingly.
  • Should I use them as 9*9 (81 components) matrix, or use them as (3*3*3*3) matrix or how to use them as vectors suitable to work with stress and strain vectors.?
It would be nice if any of you could help me understand it or refer me to a material that might help me. 
Thanks for your time
Regards
Shree
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I am currently learning about the preparation of UMAT for linear viscoelastic materials,which involves the PRONY series, but there are few materials for learning. The ABAQUS user manual is not very helpful, so ask for help.
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The field of education, teaching and thinking thank you.
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i ave developed a plastic vumat that doesn't work
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I apologize I'm not familiar with VUMAT, but offer this... It looks like you trying to simulate an extensional strain rather than a shear one, so I think it was right to not use corotational formulae. Is the material type interfering somehow?
Best
Phil
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I am presently researching about fatigue life prediction of short fibre thermoplastics under arbitary loading.Can someone suggest me how can I stabilize the cyclic behaviour considering viscoelastic material ?
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Really, the creep of polymer specimens is a reason of tests parameters variation. In order to stabilize the cyclic behaviour of viscoelastic thermoplastics under arbitary cyclic loading, you can try to enable feedback "actuator - extensometer" of test machine taking into account of criteria of this controlling.
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Hi, I am trying to create a histology based finite element model of human soft tissue. In order to model the viscoelasticity at the cellular level, I need to know the dynamic and bulk viscosity of the cell nucleus, cytoplasm, and extracellular matrix (ECM). I have looked through the literature. But I have not found any exact results. Could you please provide any information regarding this? Thank you.
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لاللزوجة الديناميكية (أحيانا تسمى أيضا اللزوجة المطلقة ) هو مشترك بين ... قد تظهر المواد الصلبة اللزجة اللزوجة كل من لزوجة القص واللزوجة السائبة
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What is the motive behind to analyze the structural performance with viscoelastic supports?
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I THINK THE BELOW ATTACHMENT HELP YOU
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I am trying to simulate the precision glass molding process. I am a bit confused with the viscoelastic properties on ABAQUS. I needed a few tips regarding the coefficients
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Time-domain viscoelastic behaviour refers to creep and stress relaxation while frequency domain viscoelastic behaviour refers to the response (stress/strain) of the material under sinusoidal excitation (strain/stress).
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I am wet spinning and have two syringe pumps. I want to run one pump at a time but as the syringe gets low on material start the second pump and turn the first pump off without interrupting the flow rate of the outlet. While the 2nd pump is running, I can fill up the first syringe and start that pump when the 2nd pump syringe gets low. So on and so forth. I would like to know if there is a directional valve that can help me achieve this. I was thinking a shuttle valve may work but I do not know if it will affect the outlet flow rate when I turn one pump off and another on
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Interesting
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I have read many publications using FE model to study interfacial behaviour. And Few of them considered matrix viscoelastic effect in the studies. I seems that most authors avoid to discuss about this.
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Follow
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It is my opinion that linear rheology oscillatory measurements performed with AFM may not be suitable for all viscoelastic materials/solids... whereas, different is the 'story' when performing stress-relaxation measurements with AFM... such as those reported in the following two articles:
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In this case,one ought to fix,keep constant,the distance between the filement tip of the AFM
and the surface of the viscoelastic sample in order to detect the attraction/ repulsion of the force field due to not only the applied stress and the corresponding strain but also the relaxation of the surface.
Again the above suggestion might not be suitable for all viscoelastic materials,especially if the filement tip of the AFM touches the dynamic surface during the examination
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There are different viscoelastic materials such as polymer, rubbers, etc. How to calculate the complex stiffness (K*=K(1+i*eta)) for such viscoelastic material ?
Is there any calculation steps available for certain polymer materials ?
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Dear Mukund A Patil, it is done via DMA. Please check the following attached files. My Regards
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Hello everyone,
I am trying to develop a model for soft tissue using fractional viscoelasticity in abaqus. I am using a springpot model defined using a VUMAT subroutine.
I am testing with a single solid element (C3D8) in a displacement controlled simulation. I am currently running a tension test with displacement control along x varying linearly from 0 to 0.1 at the end of the dynamic step. With VUMAT, the strain at the end of the time increment is already known and the corresponding stress has to be evaluated and updated.
However, when I run the model, within a few increments my simulation errors out with excessive element distortion. Upon printing the strains, I notice that the strains in the y and z directions (lateral strains) quickly blow up causing excessive distortion.
Has anyone encountered similar issues? if so, can you please suggest how to debug the problem.
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Hasanain Radhi Radeef , Thankyou for the response. I am using a single element for the test case. This is a viscoelastic model with small strains. So I should not be encountering large strains in the model. I had planned on using more elements for the test after the current test case worked.
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Hi everyone.
I am interested in studying the mechanical behavior of cells using nanoindentation experiments simulated by finite element analysis. Following the literature, cells usually show a viscoelastic behavior. For this reason, I would like to know what kind of viscoelastic model is more adequated for simulating the cells' response to indentation interaction.
Any comment or reference will be appreciated!
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Les modèles non locaux
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The image is taken From Callister's Materials Science and Engineering.
After glass transition, the polymer chains are mostly free to rotate and wiggle, but cannot slide past each other until close to melting point. So, with temperature, why there is no continuous decrement of viscoelastic modulus (for a fixed applied strain, after same time)? Is this because the chain "freeing for movement" and "fleeing for sliding past" are kinetically activated sharply beyond a certain temperature (say, Arrhenius kinetics), and in the plateau zone the glass-transition related chain "free to movement" activation is virtually close to 100% while melting related "free to slide past" activation is virtually zero?
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Hi Sumit,
the short answer to your question is yes I‘d think so. Obviously it’s material dependent as Martin mentioned and won’t occur similarly for every sample type.
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I have written a VUMAT for a viscoelastic material such that the VUMAT splits applied strain into viscous and elastic parts and calculates stress increment based on viscous part. This VUMAT is based on the material model from a paper attached to this question.
I created the JOB, did a data check, printed all values obtained from VUMAT, and compared them with the same model written as a stress update on MATLAB. The values are matching. But, when I submit the job, I get the error of excessive material distortion. I printed the straininc vector inside the VUMAT and certain components of it are of the order of 10^14 although the applied displacement load is very small.
I tried refining mesh, reducing applied load, changing material properties and, also enhanced hourglass control. I am unable to resolve it. Please help if you have a solution. I am attaching all supporting files.
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These links might be an asset, have a look:
Kind Regards
Qamar Ul Islam
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To study the bituminous mastic behavior, a test called stress relaxation is done it shows the solid or fluid-like behavior of mastic. By generalized maxwell model, one can predict the relaxation of mastic. How to enter a constitutive equation of model in the coding.
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Hi everyone.
I am looking for a guide (paper or book) that exhaustively explains how to model viscoelasticity in ABAQUS CAE.
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Hello,
Maybe you can use this work.
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Rubbers behave differently at different strain rates
So what input material properties are required to model viscoelastic materials subjected to impact? which material property such as compression, tensile shear need to be found from experimental techniques such as UTM? is there any standard for finding these properties?
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Hello,
I am building a material model for a nonlinear viscoelastic polymer in ABAQUS. For the beginning I just want to simulate an uniaxial tensile test. But now I want to know which damage criteria do I have to use? Which parameters do I need to simulate a real necking of the sample until damage. (dynamic explicit)
I already have the density, the E modulus, poisson's ratio, prony terms (viscoelastic).
Thank you!
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@Erencan Yildirim have you got the answer
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Need to perform finite element analysis on cortical bone using viscoelasticity properties. Require the values of prony series.
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anni fa facemmo questo studio con la prima MOC; io, lavoravo in ortopedia e portavo in reumatologia le teste di femore dei pazienti a cui avevamo applicato la protesi. Oggi non mi interessa piu' quella parte ma un'altra. L'osteoporosi si sviluppa in quando lo ione calcio non viene assorbito dalla cellula ossea perchè modifica la sua frequenza di ciclotrone per cui cambiando la frequenza di ciclotrone, se in canale del calcio con la pompa del calcio ha una frequenza normale, lo ione calcio non è piu' coerente. E' come dire che la cellula è la serratura e lo ione calcio è la chiave che deve entrare nella serratura. Se lo ione calcio cambia, cambia anche la chiave che lo rappresenta per entrare nella serratura. In questo caso si sottopone il paziente osteoporotico ad un apparecchio di ionorisonanza ciclotronica che gli trasmette il segnale corretto sfruttando l'effetto diapason, lo ione calcio ritrova la frequenza corretta e viene nuovamente inglobato nella cellula ossea. Si associa solo somministrazione di calcio e vit D per scrupolo anche se non è necessario. Megli si esegue il dosaggio calcemico. Dopo 3 mesi di terapia con ionorisonanza ciclotronica si esegue una M.O.C. o una osteosonometria e si verifica il miglioramento del grado di osteorporosi. La semplicità è la strada che ricerco. Questo è uno degli apparecchi di cui dispongo. https://www.quec-phisis.com/medicina/
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Many tools exist to determine the elasticiy or Young's Modulus of cells. However, sometimes when we compare data obtained by the same approach (By indentation using AFM for instance), we see data ranging from 1 kPa to 10s of MPa. I find it shocking that relatively similar samples can range by this order of magnitude depending on the work. How to know what is true and coherent with the community ? Whats the best approach for such mesuresments ?
I am an AFM specialist, and I'm considering many changes in my experiments
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It is a good question. There are a few serious reasons why the quantitative results of biological AFM-based mechanical measurements have very low reproducibility and sometimes they just don't make sense.
1. "Young's Modulus of cell" have no more sense than "Young's Modulus of car". Indeed, a living cell is not just a homogeneous "piece of something". It is an extremely complex dynamical system. Thus, the results (indentation curves) are dependent on lots of biological (age, stage of development, type, part of cell, etc.), chemical (pH, ionic strength, medium, etc.) and physical (temperature, pressure, irradiation, etc.) factors.
2. Lots of possible systematic errors: not accurate measurement of the force constant, contamination/breakage of the tip during the experiment (very common, have to be checked before and after), partial detachment or penetration of the cells, death of the cells, etc.
3. Limited statistics. Indeed, the cells cannot be kept in the AFM's liquid cell on forever. The number of curves per experiment is usually limited with this time factor and contamination/breakage of the tip (can be detected with the curves).
4. Interpretation problems. E.g. typically the tip has more complex shape than used in the model.
In view of the foregoing, it is better to avoid quantitative measurements when possible, and examine the relative differences, not absolute values. E.g. if one studies the influence of something to the cells, it would be better to put the cells into the AFM, take some control curves, then add something (chemical, radiation, etc.), and then take more curves. Of course, the control experiments should be done too, e.g. the measurements with at the same timings and conditions for the cells from the same line, but without the examined factor.
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Hi,
I am currently working on modeling a PEG-NFC hydrogel in ABAQUS using viscoelastic properties. However, I am having difficulties knowing how to determine the Prony Series for this. Can anybody help me out on how to do this? The data is given in the article provided.
Kind regards,
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I get the error: 'NO CONVERGENCE FOR ANY ORDER N FOR THE VISCOELASTIC SHEAR TEST DATA'. Do you know how I can solve this?
I used the shear test option as input with normalized values from the G' time graph.
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Hi all,
I'm testing the viscoelasticity of some gels with oscillatory tests (oscillation with strain sweep and frequency sweep). I am wondering what the normal force (the force that's compressing the gel, in the direction perpendicular to the oscillation) should be? Thank you!
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assuming you use a parallel plates measuring geometry, the aim of setting a normal force is to have ideal contact between sample and measuring geometry.
Therefore, it highly depends on sample properties. Both higher stiffness and slippery surface, e.g. oily or greasy, require higher normal force to maintain good contact.
However, a too high normal force will (1) squeeze the sample out of the measuring gap (will require trimming, if possible) and/or (2) will lead to an unrelaxed state of the sample, and this might also modify your measuring results.
As David Sturm mentioned, the values are typically something between 1 and 5 N (depends of course also on the plate diameter).
By the way, if your sample contains polymeric components you will observe an increase of the normal force during e.g. the frequency sweep, which is perfectly fine as it reflects the relaxation behavior of the unrelaxed sample state when measured (even if you measure within the LVE range).
Best wishes
Christopher
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Hi,
So, I have experimental data from DMA equipment of some samples containing CNT. I have plotted the storage modulus and loss modulus against temperature. But now I would like to compare these data with numerical data! Is there any possibility to simulate and obtain storage modulus as an output from any software? i.e. Abaqus, Ansys digimat etc.
I have come to a conclusion that is not possible, however, I would like to be 100% sure. Also is there any theoretical modelling to predict this viscoelastic modulus?
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ANNA PAULA IS CORRECT, YOU CAN EXPORT NUMERICAL DAT FROM TA UNIVERSAL ANALYSIS AS ASCCI FILE AND THEN OPEN IT USING EXCELL OR ORIGIN.
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Hello all,
I'm trying to model viscoelastic behavior in Abaqus. I have tried Hyperfoam + viscoelastic material model. the model need to capture both quasi static and dynamic behaviors. However, when I used Prony series to fit the viscoelastic behavior, this model cannot capture the dynamic behavior properly.
I think the key thing is to use a spring dashpot based viscoelastic model in Abaqus instead of the Prony series. As far as I know, If I choose viscoelastic material model in Abaqus, Prony series is the only option I can select. Anyone know how can I apply such model? I need to build something like a standard linear solid model but with a nonlinear spring.
Any help would be much appreciated!
Best,
Lejie
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I am working on modeling and simulation of biomecanical material behaviour, I have succeded on simulating skin using anisotropic hyperelastic material, on APDL and in our lab's finite element code. However, now, I want to perform this model, adding viscoelastic behaviour, (a strain rate depends on time). I just ask a help for the methodology of simulating a viscoelastic behavior on ANSYS APDL, and see the hysteresis of the stress-strain curve before
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It's better to formulate the problem mathematically. Then solved by using analytical or numerical techniques
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I am working on structural response of viscoelastic material  through prony series  and stress as part of my PhD work.Any body from this field please help me out  
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Thank you Omar. I developed custom built setup which performs tests at various speeds, relaxation test, creep test, ratcheting etc. comfortably.
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I am developing a solver to simulate compression of oil in shock absorber filled with viscoelastic compressible oil. The model will consider the loss due to viscosity which will decide the response of damper to the shock it experiences. Please include any link or document you think curucial for this.
I have made models for incompressible flows but I am having a hard time to find resources for this case.
Thank You!
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Thank you A.N.M. Mominul Islam Mukut ! This document gives serious insight to my problem as well as implementation.
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Hello everyone,
I am trying to model a damper in ABAQUS. I have obtained hyperelastic properties using a uniaxial tensile test and viscoelastic properties by relaxation test conducted in the tensile testing machine. The graph is attached below. After analysis, I am getting the following Hysteresis curve. I am unable to find the problem either in the model or in the rubber properties. In the animation is shown below the frame is stuck at the starting point. can anyone please help me with it?
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is this for human tendon replacement.
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I am studying about Impact load resistance property of Polyurea (Elastomer). With respect to this, I need to conduct tests on this material to evaluate its material model behavior as a hyperelastic material model and Viscoelastic material model. These material models are to be used in an FEA analysis to understand its impact resistance properties. I have researched some data mentioned below about the procedure to determine the viscoelastic properties and hyperelastic properties of an elastomer material.
Kindly review it and provide your valuable comments to improve it against discrepancies incurred by me.
Mechanical tests to be conducted for Hyper-Elastic model
1. Uniaxial Test  (ASTM D 412/ ISO 37)                        -       stress/ strain curve or table as output
2. Biaxial Test (ASTM D 6856 / ISO 16842:2014)        -      stress/ strain curve or table as output
3. Planar Test (                                                                   -      stress/ strain curve or table as output
4. Bulk Modulus Test (ASTM D 575 / ISO 7743)          -      pressure/ volume ration curve or table as output
Mechanical tests to be conducted for Visco-Elastic model
5. Creep test ( Shear, Volumetric and Combined )  (ISO 8013)            -        constant load/stress will be applied as input and  strain/ time curve  will be taken as output   
6. Relaxation Test (Shear, Volumetric and Combined) (ISO 3384)     -         constant deflection/strain will be applied as input and stress/time curve will be taken as the output
Test data derived from test no 1 to 4 shall be used to calculate Mooney-Rivlin hyperelastic material model parameters.
Test data derived from 5 & 6 will be used to calculate the following mechanical properties
a. long term normalized shear compliance or modulus
b. long term normalized volumetric compliance or modulus
c. normalized shear compliance or shear relaxation modulus vs. time
d. normalized volumetric compliance or volumetric  relaxation modulus vs. time
The data mentioned from points a to d are needed to derive the Prony series constant for the viscous elastic material model mentioned below:
1. Shear relaxation modulus ratio
2. Bulk relaxation modulus ratio  
3. Relaxation time
I have gone through ASTM/ ISO codes mentioned superficially but didn’t understand a few topics for some codes. I need your valuable guidance regarding the following points.
1. specimen preparation (Dimension and Shape)
2. Testing procedure. (Constant Load & Deflection required  in test no 5 & 6)
3. Determination of properties mentioned in points (a to d) from test data output received from test no 5 & 6.
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I have followed the procedure described in the file attached for property determination and conducted the test as per described codes.
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The dynamic mechanical analysis (DMA) test with frequency sweep is well known technique to characterize the viscoelastic properties.
I had gone through the different studies which had used DMA test to investigate the variation of storage and loss modulus with frequency for bone (compression mode) and soft tissue such as skin or cartilage (In tensile mode).
In literature it is reported that loss modulus decrease with frequency in bone but it increase for skin and cartilage.
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My clínical expertice it’s my opinion. However the diferents experiencies are very important. Thanks
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Hello everyone!
I have been thinking about extracting the storage and loss moduli (E’ and E”) of two viscoelastic materials -- namely PLA @200 C and PCL @90 C -- and use these values in modeling the materials’ viscoelastic behaviors using generalized Maxwell models.
I was hoping to do this with DMA (frequency sweeps with temperatures set constant at 200C and 90C, respectively). My original plan was to extract E’ and E” and use optimization/ curve fitting techniques to determine the elastic constants (E0, E1, E2, … n1, n2, …) of the Maxwell models. But now I am having a second thought about the validity of this approach given the materials would in molten states at the indicated temperatures.
My questions are:
  1. What is the best way to go about this?
  2. Can DMA be used to directly measure E’ and E” of molten polymers?
  3. Can DMA be used to indirectly determine E’ and E” at these temperatures? If yes, how?
I am kindly asking for your thoughts and guidance on this. I appreciate your time.
Thank you!
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Dear Abiy Wubneh, rheometry is the best tool. Please check the following Book and the attached file. My Regards
Structure and rheology of molten polymers: from structure to flow behavior and back again. Dealy, John M., Larson, Ronald G., Read, Daniel J., (2018, 2nd edt)
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I am working on a polyester which remains in sticky viscous state at room temperature. I want to check its shear modulus, viscosity and porosity. Most of the tensile testing needs mold to be formed which is not possible, also due to sticky nature AFM is also not possible. Which tests will be appropriate for there analysis.
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For measuring viscoelastic properties kindly cheak our following paperBio-Chemical Composition, Functional and Rheological Properties of Fresh Meat from Fish, Squid and Shrimp: A Comparative Study
March 2017International Journal of Food Properties 20(68)
DOI: 10.1080/10942912.2017.1308955
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I have started working on viscoelasticity (with very limited background) and our preferable model in this study is Giesekus. We have Capillary Rheometer and Rotational Viscometer accessible in the lab. For the Capillary test, single swell point measurement is also available. What other tests may be needed to fit the parameters of the model (we have very limited budgets). Furthermore, how can I fit the data? I appreciate a good reference (book/article).
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I don't know well about your field, but may attached articles are useful for you.
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I know that relaxation processes are extended to higher relaxation times because of the higher molecular weight in polymeric materials. However, why according to molecular arguments (Rouse, Zimm, tube model) elastic and viscous modulus are inversely proportional to molecular weight but experimentally the opposite is observed? For example, relaxation modulus of PS increases throughout the entire time scale (transition and glassy region) as molecular weight increases.
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There are many texts available via simple search. Thé following RG document deals with the answer. It is in accordance with my first contribution. My Regards
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For example ATF (Automatic Transmission Fluid).
I have noticed in my readings that they are only limited to measuring viscosity, but I cannot find studies of its viscoelastic properties.
To my understanding an ATF this working conditions is subjected to different levels of shear rate ans temperature.
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Hi all.
I did some rheological measurements to determine the viscoelastic properties of a commercial ATF (attachments).
I see that the ATF is Newtonian up to a shear rate 10^3 s-1 (equipment limit), also, the values of the storage modulus are low.
The service conditions of an ATF are much more extreme, shear rate> 10^3 s-1 and the starting temperature can be between -30°C to 20°C and in service between 80°C to 120°C on average.
Is the limitation of measuring equipment the little interest in the viscoelastic properties of ATFs?
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I want to covert creep data into frequency data as this may allow me to predict viscoelastic behaviour at very low frequencies e.g. 0.0001Hz. Low frequency data maps well microscopic structure. Can someone help me with this?
Thanks in advance.
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Thank you Florian. I will look into the paper. I was wondering do I need to do Fourier transform on my data. Thanks.
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Hello,
I'm currently trying to reproduce a relaxation test that I made in a lab on Abaqus.
I wanted to make this model works with Abaqus/Explicit since I need this type of analysis for further work.
I used my test data to evaluate Prony series coefficients and I found some with an average error of 5% between the model & test.
Then, I created a simple sample of rubber, with a surface linked to a RP on which I apply a specific displacement for few seconds and then I hold it for a while.
but, surprise, when I checked the results, I noticed that the Reaction Force of my RP was increasing, instead of decreasing as a Relaxation test would give us.
If you have any question or idea to help me, feel free!
Thanks,
Hugo
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Hugo Cadinot did you solve it? I am also figuring that out but I think that what you comment, it will probably be due to the creep curve which Abaqus is calculating itself although you have only introduced relaxation test data.
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In ABAQUS help I read the applications of direct solution in steady state dynamic analysis as follows , what are the examples of applications and where I can NOT use this method ? I would appreciate a comprehensive answer , thank youhttp://ivt-abaqusdoc.ivt.ntnu.no:2080/v6.11/books/usb/default.htm?startat=pt03ch06s03at09.htmlThe direct-solution steady-state analysis procedure can be used in the following cases for which the eigenvalues cannot be extracted (and, thus, the mode-based steady-state dynamics procedures are not applicable):
  • for nonsymmetric stiffness;
  • when any form of damping other than modal damping must be included; and
  • when viscoelastic material properties must be taken into account.
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Aha, I see.
Well, even with zero damping, you will get finite response as long as you do not hit exactly the resonance frequency.
To better understand, take a look here - the sdof system is key to all linear dynamics
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I was wondering what the difference is between the glass transition temperature and the ductile/brittle transition temperature? I know that Tg is the temperature where a polymer will go from a glassy state to a viscoelastic state. From my understanding when a polymer is under the Tg value it will be brittle and glassy. When a polymer is above the Tg value it will act rubbery and ductile. Is this correct?
I also know that the ductile/brittle transition temperature is the minimum temperature in which a material has the ability to absorb a specific amount of energy without fracturing. In other words it is the temperature in which a material will fail and crack because it has become so brittle.
I am just getting confused because I am trying to determine the temperature at which polyethylene will crack in the freezer and I don't know which value to use. For example, polyethylene has a glass transition temperature of -90°C, but it can crack if it is in a temperature of -70°C (DBTT). It does not make sense to me that polyethylene would crack while it is still in the viscoelastic state.
If anyone can explain the difference and clarify this up for me that would be great. Also, if anyone knows what value I should use to determine the cracking point of polymers due to freezing please let me know. Thanks!
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Dear Elizabeth,
There are some relations between glass transition and ductile/brittle transition which depends on the type of the polymers. They me be the same or there are some mathematical equations between Tg (glass transition) and Tb(brittle transition). It needs to explain with some graphs and mathematical equation.
I have attached some articles and one text which explain in details. I hope they would be useful.
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I am working on the dynamics of the fractionally damped viscoelastic materials. I have used Riemann–Liouville fractional derivative model in my analysis to characterize the viscoelasticity. In my seminar, people asked me that why did you select Riemann–Liouville model ? why didn't you select Caputo model? I was unable reply. What would be the right/logical answer ? Please give your comments.
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Dear colleagues
In models subject to initial conditions, Caputo (and its extensions), which has physical significance, should be used.
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How to study the normal and tangential combined loading effect on viscoelastic bodies?? Is there any formulations or general governing principles??
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In your question "normal" and "tangential" are not properly defined. Actually, all mechanical properties of isotropic bodies summarize into two coefficients (see eg. https://en.wikipedia.org/wiki/Lam%C3%A9_parameters), or two "elastic modulus". The response to any mechanical solicitations is a linear combination of them. For instance measurement of the propagation of longitudinal ultrasound waves is related to the compressibility modulus ("normal" ? in your terminology) and to the shear modulus ("tangential"?).
I hope this can help you.
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I have found some values for short and long term shear stress, decay constant and bulk modulus online for the ball. However, i am not sure how to use them.
Any help would be appreciated.
Thank you
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I agree with the link shared by Lamprini.
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I'm trying to simulate asphalt layers with Viscoelastic behavior in ABAQUS.
First of all, we must define a elastic property of asphalt, E and v (Poisson ratio).
After that must input viscoelastic coefficient of Prony series (g_i and k_i).
But I seen different expression of Prony series in term of define elastic module.
Many of them, they define prony series in term of E_infinite like below:
E(t)=E_inf + SUM ( E_i*e^(-t/tau_i) )
And E_inf=E0 - SUM(E_i)
And the additional problem is that the ABAQUS get viscoelastic property in term of dimensionless. It's mean that I must divide the E_i to E(infinite or zero).
the problem is that the i dont know what number must input. and when i try to calculate E_0 , i see the huge elastic module.
other question is when i want to compare elastic and viscoelastic material, when i want to define elastic module for elastic behavior, what elastic module must input? E_0 or E_infinite
Files that attached, is the different expression of prony series and abaqus defining of prony series
Please guide me
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Hi, I have done some stress relaxation tests to study the viscoelastic behaviour of hydrogels. I am just wondering how to use stress-time data to find prony series constants required for material characterization. Please help.
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Dear Arzmandi,
There are numerous methods for determining the Prony series from relaxation and/or creep data. An early method involved constructing log-log plots of relaxation data in which straight line approximations for the data on the log-log graph yield the time constants (i.e. torr i 's) from the slopes, and the exponential coefficients (i.e. alpha i 's) are obtained from the intercepts. Other methods have can be employed. For example, Johnson and Quigley determined a relaxation time constant for a nonlinear model which is similar to a one-term Prony series model.
The hereditary integral method can be employed to obtain an analytical representation of material response when it is subjected to rate dependent loading. it can be used for schedules in which the material is not allowed to relax between subsequent loading changes. The analytical representation can be used in a nonlinear regression analysis, with measured data, to evaluate the Prony series constants. Several regression analyses can be performed using different weight functions.
Load versus time test data for a sequence of different rate loading segments is least-squares fitted to a Prony series hereditary integral model of the material tested. A nonlinear least squares regression algorithm is employed. The measured data includes ramp loading, relaxation, and unloading stress-strain data. The resulting Prony series, which captures strain rate loading and unloading effects, produces an excellent fit to the complex loading sequence.
A common form for these constitutive equations N employs a Prony series (i.e., a series of the form N∑i αi . e-t/torri )
The Prony constants of the regression(Weighted Nonlinear Regression for Relaxation Test ) can be calculated.
Please follow these references for further understanding of creep relaxation prony step series
1.F10gge, W. "Viscoelasticity", Blaisdell Publishing Co. , Massachusetts, 1975.
2. Cristensen, R. M. "Theory of Viscoelasticity" 2 na Edition, Academic Press, New York, 1982.
3. Johnson, A. R., and Quigley, C. J., "A Viscohyperelastic Maxwell Model for Rubber Viscoelasticity", Rubber Chemistry and Technology, Vol. 65, No. 1, pp 137-153 (1992).
Hope it is useful for you.
Ashish
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How can I build a transverse isotropic viscoelastic material in ABAQUS? It will be very appreciated for an example!
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Thanks.
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Dear Colleagues,
I don't know how to add the viscoelastic term to the equation for the linear elasticity with thermal expansion (more details about the question are reported in the attached picture).
Can you help me?
Thank you very much for your help.
Best Regards.
Marco Gandolfi
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Thank you very much for your kind reply.
It clarifies a lot of things.
I understand that my naive model (based on the Kelvin-Voigt model) is too poor to be used for a general treatment of real materials. Instead, as you suggest, a system made by many springs and dashpots (Maxwell-Wiechert Model) should be used.
Anyway, is the Kelvin-Voigt model a subcase of Maxwell-Wiechert Model (when you have one spring and one dashpot in parallel) or do you need some other additional hypotesis?
Secondly, your instructions give me a reply to my last question. The expression to use for the strain is Equation (4) rather Equation (3) (I refer to my first screenshot).
Thank you very much again for your help.
Best Regards.
Marco Gandolfi
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Hello everyone,
I have the spring stiffness and damper coefficient for the Kelvin-Voigt model and I need to calculate/fit (by using Prony series) the Instantaneous/infinite elastic modulus and decay constant, which are generally derived from the stress relaxation response. Since the Kelvin-Voigt is not able to predict the stress relaxation behavior well, do you have any idea how can I calculate those constants?
Best regards,
Shahab
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Dear Dr.
Ijaz Durrani
,
Thank you so much for the references. I checked them .
As I understood, the instantaneous elastic modulus should be equal to spring stiffness+damper coefficient, and the infinite elastic modulus is equal to the spring stiffness only. Also, since the Kelvin-Voigt considers instantaneous shear relaxation, I need to set the decay constant as big as possible. Please kindly correct me if I am wrong.
Best regards,
Shahab
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I am trying to regenerate the Natural Frequencies of a clamped-clamped viscoelastic core via. ACM (Approached Complex Eigenmodes) method as is in the article : "Linear and nonlinear vibrations analysis of viscoelastic sandwich beams" (DOI: 10.1016/j.jsv.2010.06.012).I am trying to use semi analytical Galerkin method in order to do so. the problem with the use of ACM method for modeling the core my answers are close but when I increase the number of modes to solve the problem in more precise way my answer get worse! and also there is no convergence happening with increasing the number of the modes. what the problem could be? and would it be a better approach to solve the frequency dependent problems which wouldn't be highly costed in solving?
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Hi. There are two ways. the first one is to construct a mechanical model to describe the viscoelastic behaviour (in frequency domain) and include it in the stiffness matrix of the model (In this case, the Kglobal matrix will depend of the frequency and you will need use a recursive algorithm to compute the modal parameters). the second way is to express your model in a time domain and use the FFT.
I describe the fist way in my reseach
Uncertainty propagation analysis in laminated structures with viscoelastic core
WP Hernández, DA Castello, TG Ritto - Computers & Structures, 2016
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Hello all!
I am a beginner in Abaqus as well as Viscoelastic materials. So my question may sound like a very basic or rookie question.
I am trying to model a viscoelastic material which has one linear elastic spring with G1 and a spring in parallel with a dashpot, G2 and Viscosity, eta .
A value of time constant, Tau(s) = eta /(G1+G2) = 0.99 s
Other available parameters-
Time independent bulk modulus K
Time dependent Young's modulus E(0) and E(inf)
And Poisson ratio nu(0) and nu(inf) are available.
I am trying to develop this model in an attempt to simulate nanoindentation process.
First attempt made was with abaqus Prony series parameters,
g_i , k_i and Tau_i by using single set of values as follow-up
g_i = G1/(G1+G2) = 0.099, since g_i are normalized values
k_i = 0.99, K is time independent, but abaqus won't take values >= 1
Tau_i = 0.99 s, used as available
Used E(0) and nu(0) for initial deformations.
I got a set of results which don't seem reliable.
I think I have gone wrong with those parameters.
How should I calculate these parameters? Any other method than Prony series?
The values have been referred from this article:
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My solution is available on
Good luck
Frank
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nnow we have DMA test data of our sample PPS material and the storage module and loss module are so
so calculated
, but how to define our PPS material in some FEM tools like COMSOL ?I tried viscoelastic node under solid mechanics , using kelvin-viogt model but the result was not in good agreement with experiment
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You need to choose real material properties in model
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I am a Computer Engineer, so do not have any knowledge of FEA and have never used Ansys before. I have a 4x4 plain fabric weave model with properties of vectran and I want to do creep analysis on this model. But I am not sure which creep model to use and how to calculate the creep constants.
From one of the research papers, I have obtained some constant values (beta) for vectran (%elongation/log(t)). But I am not sure if I can make use of these values directly as C1 or C2 in Ansys.
This is the research paper for reference.
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Following the answers.
good question
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I am modelling a 3 point bending test of Asphalt Mixture beam . The beam is modeled as visco-elastic material . After peak load also the material gains strength as it ismodeled as visco elastic but I want to terminated the program once it reaches a yield point how to mention that in ABAQUS .
Please suggest some answers . thank you in advance
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