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Elasticity - Science topic

Resistance and recovery from distortion of shape.
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Hi everyone,
I ran a model in my ABAQUS CAE, however, when the simulation finished, the elastic modulus of the model appear to be higher that the elastic modulus of the material that I had assigned. Is this possible and what factors that affect the model to behave in such ways? Thank you in advance.
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The question sounds misleading and seems to confuse the concept of "elastic modulus" (which is a material property) and "stiffness" (which characterises a structure under certain BCs). It is indeed not possible that the elastic modulus changes in an analysis, as it simply defines the Hook matrix used in computation of element stiffness matrices
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I am trying to simulate low velocity impact on composite plates and every time I run the program it terminates and gives me this error. I am using MAT_ORTHOTROPIC_ELASTIC. Also, trying to understand the ABC directions. I understand that to get B you cross A into C. Do I define what I want ABC to be or does ABC direction correlate to XYZ?
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We're looking for a plugin for FIJ or ImageJ that could help us to quantificate the amount of elastic fibres in a tissues like aortha stained with orcein, but couldn't find any by now.
Thank you
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I will try to do it in that way.
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Hello all,
I am currently dealing with Abaqus and python and would like to solve the problem:
Since different geometries and different materials are considered, the Rp02 value of each material is used as a unit to keep the equivalent elastic-plastic stresses in a similar range, and the load range for the analysis has been set from 1*Rp02 to about 2.5*Rp02 for all different geometries and materials. Furthermore, the entire load range is divided into 6 load levels, as shown in the figure, and the equivalent elastic-plastic, and the corresponding equivalent elastic stress at each
load level is calculated.
How can I implement this with Python so that when I run the script in Abaqus, the loads are divided into 6 levels and between 1*Rp02 to about 2.5*Rp02?
I would be very pleased to receive your answer
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Walid Dhib Another option for developing scripts is to record them as a macro (open a file on Abaqus, select a macro manager and create a new macro). The first step is to save the model to the main directory and make it the working directory. Start the macro to build the Python script before generating the model.
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Hello everyone, 
I'm trying to calculate the elastic modulus tensor for a glass system based on MD simulation results. So far I believe I don't have any problem with Born term cB and I'm calculating it right :) but I am struggling with the stress fluctuation term cF. Has anyone here any experience with calculating elastic modulus tensor? Then I can explain into details what is the problem ...
Thanks
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Well I think after the NPT ensemble calculation, where you will find the equilibration volume, then you start running the calculation as NVT ensemble to calculate fluctuation in your system.
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explain to me the parameters that can influence the acoustic and elastic properties of materials
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The elastic properties are described by the youngs moduluses, the density, the poissons ratios and any twisting moduluses (G-modules), as well as the damping. Harder materials have higher moduluses and tend to have lower damping, but not necessarily.
Next, the geometry of the material play an important role, as well as the boundary conditions. Eg a thicker plate will be more bending stiff. It vibrational mode shapes depend on the boundary conditions. Free free, simply supported edges, clamped edges, or combinations of these. The resulting damping will depend on the boundary conditions too, as in general damping is mode shape dependant.
If the material is isotropic the description becomes simpler. For ortotropic plates eg more elastic parameters and direction dependant damping may occur, as for wood or wood composite plates.
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Hello,
I am working on a laterally loaded H-pile and trying to model it in Plaxis 2D. I am having difficulty converting the 3D to an equivalent 2D pile with the same elastic and flexural properties. any suggestion about which element I can use (ex: plate, embedded beam ) and any advice regarding the Parameters? and would be appreciated if there are any helpful resources for modeling such a system.
thanks
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Just need to correct the moment of inertia. Good luck
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Hello,
I am writing my thesis and I need to create a material database in a CAD program. I need to find a way to count mechanical properties of quasi-isotropic fiber laminates. I have found an algorythm to count elastic modulus and tensile strength but I need to know how the material would behave during twisting, too. How can I count Kirchoff' modulus or Poisson's ratio?
Please, help me.
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Good day!
As far as I understand, you need assessment of the averaged Poisson's ratio within the limits of homogeneous and anisotropic description of fiber-reinforced composite. There are several classic algorithms here, one of them is the approach of Whitney and Riley (Elastic properties of fiber reinforced composite materials. M.B. Riley, J.M. Whitney).
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I tried to perform tensile test in Deform 3D software but I faced some problems. Let me tell step by step.
Inputs given in tensile tests are
1. Elastic properties, 2. Plastic properties (Stress strain graph), 3. Failure criteria (Cockroft and latham failure criteria)
I have made one side (face) of tensile sample fixed and applied a constant velocity on the other side (opposite face) same as in experiment. I observed that very little thinning occurred near the opposite face where velocity was applied which was not matching with the experimental one (actually, failure location is close to centre). Also, No Effective strain contour generated during the simulation. Can anybody help me out in this ??
Consider this as urgent.
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Alireza Taheri Yes sir for simulation. Can you provide some suggestions regarding this, it will be very helpful.
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Hello my dear researchers
I use the elast package in wien2k and castep/materials studio to calculate the elastic constants of solids. I have a material with cubic structure, I make it a 2x1x1 supercell, so it becomes like tetragonal. My question is: to calculate the elastic constants, should I use the commands for cubic structure (C_set_elast_lapw) or those for tetragonal structure (T_set_elast_lapw).
And thanks in advance.
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Shahram Yalameha
ok sir thank you for your advice
i will try it
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Hi all,
I am trying to model a joint connecting 1D BEAM elements using ABAQUS connector element with the joint behaviour obtained in a separate 3D analysis. For example, I have a joint modelled in 3D SHELL element and after analysing this joint I obtained a moment-rotation relationship of this 3D joint. This moment-rotation relationship is then assigned to an ABAQUS connector element connecting the 1D BEAM elements in the 1D BEAM model.
My question is how do you correctly define the elastic and plastic range of behaviour in ABAQUS connector element?
1. Is the Elastic behaviour option only for the elastic range of my moment-rotation relationship or do I have to define the full elastic-plastic range in this behaviour option? If the latter is correct, I then need to tell ABAQUS in the Plastic behaviour option from what moment onwards in the full elastic-plastic range defined in the Elastic behaviour option where it should behave plastically?
2. I tried to define negative values in the Plastic behaviour option as my joint can have load reversal, however, it keeps giving me error. Is the Plastic behaviour option only allow positive values? If so is that mean ABAQUS assumed the onset of plasticity occurs at the absolute value of the number I specified for both directions? What if the onset of plasticity of my joint is different in 2 loading directions? Do I need 2 separate Plasticity behaviour options (1 for each direction) for it to work?
I know this is a long question, hopefully, there is someone out there who read through this and could provide me with some direction.
Many thanks,
Heng
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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
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Hello!
Biot poroelasticity describes elastic deformation coupled to fluid flow, the flow is transient. I assume one can also consider the steady-state case. Are problems of this type relevant? Transient problems can be more practical, like: "A well works for 1 year pumping with fixed rate, what stress does it induce?", while I can't think of steady-state analogues. Or are there any?
Thanks in advance!
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Thanks for the detailed answers! I'm sorry for the delayed response.
I think I need to specify a bit.
The poroelastic model I consider can be found, for example, here:
Its structure is broadly this:
  1. Diffusion-type equation for fluid pressure, which is transient
  2. Mechanical equilibrium equation for porous medium, which is steady-state (if I understand correctly, that's because mechanical response to water pressure change is relatively fast, and its dynamics can be neglected)
  3. Coupling terms that connect these two equations.
That describes fluid flow in porous medium, which elastically and fast (compared to flow process) responds to pressure changes. What are applications of this model to geomechanics? From what I see, they are the following. Various underground porous media cannot be fully described by elastic case, and one has to use more sophisticated models like plasticity. However, initial stages of processes sometimes can be described by elastic case, and poroelastic model can be used for, for example, estimation of time to reach critical stress or some other turning point.
If one changes fluid flow equation to steady-state, it can only predict the following: "A large amount of time has passed. Fluid pressure now has the following distribution. The medium, if it is still elastic, has this stress". However, there is now no predictive ability to estimate time of reaching critical stress. That is the main drawback which I see in the steady-state case
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Hello, I need help getting a code in python or Fortran for elastic stiffness to calculate the shear modulus at varying mean effective stress by the Hardin formula in Abaqus. Can anyone help regarding this, or else from where I can learn to code?
Regards,
Manisha
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Hello everyone,
I've written a rather simple linear elastic UMAT for orthotropic materials. I found that my output stresses are different from stresses should be.
For example:
In my model, I set a max load of 25 MPa and min load of 2.5 MPa (aka cyclic load ratio R=0.1). In my UMAT a wrote a line "write(*,*) "stress(2)=", stress(2) " to see how applied load matches outputs. I expect see alternation of 25 and 2.5 (when increment time=0.5), but I see the following:
stress(2)=0 - okay, initial step
...
stress(2)=-25 - okay
...
stress(2)=-49.99 ????
...
stress(2)=-2.5 - okay
...
stress(2)=-19.99 ????
then everything repeats
But in ABAQUS visualization stresses are as I set, 25 2.5 ...
Have you seen something similar? I'm bit confused, don't understand how it works.
If you have any ideas what can be wrong, let me know.
I have attached the UMAT subroutine file and inp file. Thank you.
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I found the answer. The problem was that I manipulated with stresses after the calculation of the ddsdde and a stress vector. I solved the problem by putting the stress vector calculation at the end of the subroutine. In other words, "the correct stresses" are at the beginning.
If you have similar issues, let me know.
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Dear all, I'm applying a given load to a spring. After compressing the spring, I will lock it to prevent any movement, and I will remove the load source. How can I estimate the load loss that will inevitably and gradually happen with time (elastic potential energy dissipation from the spring in an enclosed system)?
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Hi!
1) If there is dissipation, then the spring is inelastic.
2) Measurements are made in the same way as in stress relaxation in viscoelastic systems.
Valery N.
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Could anyone explain the difference between a linear elastic and linear viscous element?
also the meaning of parasitic viscous damping in an isolation system that results in a reduction of isolation system displacement demands
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Elastic means "recoverable deformation" : The ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed.
linear elastic behaviour can be expressed as: Stress = (stiffness) * (strain)
Viscous means : The resistance to the time-rate-of-change of strain. It is the induced stresses due to the rate of strain.
linear viscous behaviour can be expressed as: Stress = (viscosity) * (rate of strain)
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Good morning, greetings from Peru. I have a question. How is the critical elastic buckling load of a building calculated in Etabs or SAP 2000?
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buckling analysis based on eigenvalue is used in sap2000.
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I know how to plot Force versus total story drift hysteresis curve but I dont know how to subtract elastic part. I have attached a picture that clarifies my question.
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This is a good approximation,
Calculate the initial drift stiffness as a scalar , then use this equation in excel to modify the total drift vs force to plastic drift vs force
Plastic drift =Total drift -Force/Stiffness.
Thanks
Alaa
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Hello fellow abaqus users,
I try to solve the following problem:
I have 3 solid bodies (please see the attached file). The bodies are tied to their respective neighbor. Loads to be applied are a thermal load (thermal expansion) and a rotational load around the Z-Axis. The steel body is encastred.
I tried to model the adhesive as cohesive elements with elastic behavior type traction, but were not able to combine this element type with the thermal expansion. Is this even possible? If not, is there a workaround? I am really looking forward to any tips and hints.
Thanks in advance,
Adam
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Adam did you solve the problem. I am also trying to use this type of load in my simulation.
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  • Knowing that the Mathematical elastic model does not admit no analytical solutions. I would like to know, is there are some specific techniques for validation of the solutions for anisotropic linear elastic model, particularly analyticly, or with some numerical simulations.
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  1. Many thanks about your detail response. According to the literature, the mathematical elastic model means the divergence equation, -div(sigma) = 0, that consists in determining the stress tensor sigma satisfying this equation. The model is closed with imposing the boundary conditions of displacement field, or component stress tensor on the surface.
  2. Noting that the isotropic model and purely elastic stays easy to be validated with compression/traction tests. It consists in applying by defining from the force weighted by section on one face (face of cubic box microstructure). Are you sure about that the hexagonal point group approach could tackle this problem?
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Hi..all,
I have a horizontal beam(BEAM188) having length of 1m, cross-section area of BxH = 0.02mx0.025m. UDL (1 unit) is applied on horizontal beam. This beam ends are supported by concrete/steel foundation having the area of cross-section of 0.02mx0.025 and its vertical height is 0.05m.
Now, If the supporting structure having some flexibility then how can we include the foundation stiffness (N/m^3) for the supporting system in ANSYS APDL GUI/Command prompt?
Kindly, someone can give inputs here?
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You can use interface element such as COMBIN14 or 39.
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For thermal contact conductance estimation, selection of plastic or elastic deformation models is based on plasticity index. At lower pressure at the interface, the deformation of surfaces may be elastic even though the plasticity index is greater than 1. Plasticity index will not account for pressure.
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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
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Hello,
I'm havaing difficulty understanding the relationship between crystalline properties and mechanical properties of polymers.
I'm compounding two biodegradable semi-crystalline polymer 1) PLA and 2)PBAT.
I analyzed DSC, TGA, XRD, and mechanical properties of above polymers and have a couple of questions.
1) Through XRD analysis, PLA turned out to be amorphous while PBAT has crystalline dimensions. but it is known that these two polymers are semi-crystalline polymers(both have melting point, crystallization point in DSC analysis). Then why PLA is amophous in XRD analysis?
2) According to the previous reports, high crystallinity of polymer results in high elastic modulus and tensile strength because of brittleness. However, i got an opposite result that amorphous PLA(from XRD) has significantly high elastic modulus (about 2000 MPa) showing high brittleness while crystalline PBAT(from XRD) has significantly low elastic modulus and high elongation properties.
It would be really thankful if you share clear references or solutions!
Thank you in advance!
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1) PLA can be amorphous or semi-crystalline depending on your processing method. For example, a semi-crystalline PLA pellets can be transformed to amorphous PLA compounds or products if the cooling rate is too fast and the polymer chains don't have enough time to arrange themself into ordered state.
2) PBAT is a co-polyester with a very low glass transition temperature (Tg), which is below 0 degree. This means that the polymer itself is very ductile in room temperature as polymer chains are quite flexible.
PLA, on the other hand, has a high Tg, being around 55-60 C degree. It means that the polymer is rigid at room temperature.
Best regards,
Cuong
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I‘m going to run a crystal plasticity model with XFEM crack. the material properties are defined as USER MATERIAL. when the job was submitted, an error message was appeared :"39600 Elements are missing elastic property reference. The elements have been identified in element set ErrElemMissingElastic PropRef". I was confused by this message, because the elastic and plastic deformation were descripted in UMAT. but the job can't be submitted sucessfully.
Any response are appreciated, thanks you!
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Hi Wenjie Zhang,
This error could have two reasons:
The material you defined in the subroutine doesn’t match the geometry and the section you defined. For example, your model is solid, and the material properties you defined are for the shell model. the second reason is you may have assigned the wrong element type in the Mesh module. Check the simulation and see which one this is.
Also, I recommend checking the links below. They will help you write the UMAT subroutine and learn more about it. It’s worth a look.
Best regards.
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Looking for help regarding the calculation of elastic stiffness constant in N/m unit of a 2D material using energy-strain plot.
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Dipali Nayak , could you please elaborate each steps that how did you get elastic constant ? I mean how did you get strain energy ? I am interested to find the same.
Thank You
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Hi,
I am working on numerical simulation of ultrasonic wave propagation through an elastic medium without any defect. I calculated the velocity of wave by using time and distance relationship. But when i used model with void or crack, i got less time to detect the first wave, while it should be longer as there is hole in model and wave propagation through it should be more. Can anyone help me out this problem i.e. how wave velocity is calculated in the model with defect.
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I am trying to slove the standard rayleigh lamb frequency equation in isotropic plate using the newton Rapson method ( FORTRAN code ) but I am not able to capture all the root of the equation and modes, even not getting how to generate the data for plotting the dispersion curves... Kindly , please help.
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Hello everyone,
can anyone provide me the folowing values for Nano-Polycrystalline Diamond (NPD)?
- Young's modulus (elastic modulus (E))
- Heat Capacity
Thanks.
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Elastic modulus - 442-457 GPa. Thermal conductivity - >2000 W*m^−1*K^−1. Some references:
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How is possible to calculate Ruess Young's modulus for a composite with three layers? As I know the Ruess young modulus for two layers is calculated from the equation below:
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Filippo Piccini Can you explain it more specifically. Can I use the equation for the two first layers, then use it again for the result and the third layer?
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I am perfoming a simulation to determine the elastic/plastic behavior of a polymer material in abaqus.To simulate the plastic behavior of the material I am using a drukcer prager model. I have performed tensile and compression tests in order to determine the input parameters in abaqus (angle of friction, and hardening data). I have encountered convergence problem when I use the linear model, so I am trying to use the hyperbolic model but I do not know how to calculate the parameters for the hyperbolic model (angle of friction, Init Tension), any guideline in how to do it?
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Dear Christian Barona,
I recommend doing a hyperbolic curve-fitting on your data and obtaining the data you need. You can do this with MATLAB or Excel. Also, for more info, refer to this link: https://abaqus-docs.mit.edu/2017/English/SIMACAEMATRefMap/simamat-c-druckerprager.htm
Moreover, take a look at the links below. These are articles about the convergence issues and debugging in the ABAQUS.
Best wishes.
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Hello everyone,
Recently, I've been trying to conduct a vibration test to obtain the quality factor of a specimen. However, the support boundary inevitably affects the results.
I have tried elastic strips and EPE foams (supporting near the nodal points), but the quality factor varies (~10%) from test to test due to the slight difference in support. The quality factor of the specimen is about 10,000.
I wonder if there are practical treatments to minimize the variation of boundary effect so that the obtained quality factor can be more stable (~1%) during different tests?
Thanks a lot.
Hao
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I assume you are using flexural vibration of the specimen in this test. To get consistent results, the specimen must be vibration-isolated from the surrounding structures. This means that the natural frequency of the specimen bouncing on its supports as a rigid body should be much lower than the frequency of its resonance flexural vibration. For large structures, this kind of test is done by supporting the structure on soft pneumatic isolators with frequencies as low as 1 Hz. I understand your specimen is rather small, so pneumatics would be not suitable, but you can use the soft vibration-isolating elements such as long rubber strings suspended from above, or very soft "negative stiffness" springs. Vibration Control for Optomechanical Systems, by V.M. Ryaboy, ISBN 9789811237331, has some discussion of these issues, in particular, pages 76-85 and 130-132.
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I want to simulate the second harmonic in a nonlinear elastic material, so I choose comsol with murnaghan to describe the third-order elastic constants, but the received waves cannot have second harmonic and the frequency spectrum is the same as the elastic material. I don't know why? the mesh size have been chosed according to double frequency
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有呼吸裂纹才会出现非线性
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I am trying to solve a two dimensional elastic problem of following image to find out stress, strain, displacement of the body under the given condition. I intend to use finite difference method for solving the problem
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You can take it a step further from Haswellian and Hyperbola equations and CTCS discretization equations.
(∂V_x) / ∂t = 1 / ρ ((∂σ_xx) / ∂x + (∂σ_xy) / ∂y)
(∂V_y) / ∂t = 1 / ρ ((∂σ_yy) / ∂y + (∂σ_xy) / ∂x)
(∂σ_xx) / ∂t = (λ + 2μ) (∂V_x) / ∂x + λ (∂V_y) / ∂y
(∂σ_yy) / ∂t = (λ + 2μ) (∂V_y) / ∂y + λ (∂V_x) / ∂x
(_Σ_xy) / ∂t = μ ((∂V_x) / ∂y + (∂V_y) / ∂x)
∂f / ∂t = (f ^ (n + 1) -f ^ (n-1)) / 2∆t
∂f / ∂x = (f_ (i + 1) ^ n-f_ (i-1) ^ n) / 2∆x
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How to reasonably measure the elastic modulus of trees with different trunk heights, especially when the trunk is short and the crown is large?
Note: The tree must be measured intactly, therefore, we cannot cut the crown, we need the elastic modulus of the whole tree.
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Filippo Piccini Wow. Good. Thank you very much.
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*****************************************************************************
** UMAT FOR ABAQUS/STANDARD INCORPORATING NON-ELASTIC BEHAVIOUR FOR PLANE **
** STRAIN AND AXI-SYMMETRIC ELEMENTS. **
*****************************************************************************
*****************************************************************************
**
**
**
*USER SUBROUTINE
SUBROUTINE UMAT(STRESS,STATEV,DDSDDE,SSE,SPD,SCD,
1 RPL,DDSDDT,DRPLDE,DRPLDT,
2 STRAN,DSTRAN,TIME,DTIME,TEMP,DTEMP,PREDEF,DPRED,CMNAME,
3 NDI,NSHR,NTENS,NSTATV,PROPS,NPROPS,COORDS,DROT,PNEWDT,
4 CELENT,DFGRD0,DFGRD1,NOEL,NPT,LAYER,KSPT,KSTEP,KINC)
C
INCLUDE 'ABA_PARAM.INC'
C
CHARACTER*80 CMNAME
C
C
DIMENSION STRESS(NTENS),STATEV(NSTATV),
1 DDSDDE(NTENS,NTENS),DDSDDT(NTENS),DRPLDE(NTENS),
2 STRAN(NTENS),DSTRAN(NTENS),TIME(2),PREDEF(1),DPRED(1),
3 PROPS(NPROPS),COORDS(3),DROT(3,3),DFGRD0(3,3),DFGRD1(3,3)
C
C
PARAMETER (M=3,N=3,ID=3,ZERO=0.D0,ONE=1.D0,TWO=2.D0,THREE=3.D0,
+ SIX=6.D0, NINE=9.D0, TOLER=0.D-6, FOUR=4.D0)
C
DIMENSION DSTRESS(4), DDS(4,4)
DOUBLE PRECISION TRVAL, VOID, KAP, PMEAN, SVOLUME, DSVOLUME
C--------------------------------------------------------------------
C
C SPECIFY MATERIAL PROPERTIES
C
C
E = 210000.0
XNUE = 0.3
KAP= 0.01
C
C SET UP ELASTICITY MATRIX
TRVAL = DSTRAN(1)+DSTRAN(2)+DSTRAN(3)
VOID = STATEV (2)
SVOLUME = (VOID+ONE)
PMEAN = (STRESS(1)+STRESS(2)+STRESS(3))/THREE
DSVOLUME = (VOID+ONE) * TRVAL
SVOLUME = SVOLUME - DSVOLUME
EBULK3 = (PMEAN/TRVAL) * (EXP ((SVOLUME/KAP)*TRVAL) - ONE )
EG2 = E/(ONE+XNUE)
EG = EG2/TWO
EG1 = EG/THREE
EG3 = TWO*EG1
EG4 = FOUR*EG1
ELAM = EBULK3
C
C
DO K1 = 1, 3
DO K2 = 1, 3
DDS(K2,K1) = ELAM - EG3
END DO
DDS(K1,K1) = EG4 + ELAM
END DO
C
DDS(4,4) = EG
C
C
C DETERMINE STRESS INCREMENT
C
C
TRVAL = DSTRAN(1)+DSTRAN(2)+DSTRAN(3)
DSTRESS(1) = EG3*(TWO*DSTRAN(1)-DSTRAN(2)-DSTRAN(3)) + ELAM*TRVAL
DSTRESS(2) = EG3*(TWO*DSTRAN(2)-DSTRAN(1)-DSTRAN(3)) + ELAM*TRVAL
DSTRESS(3) = EG3*(TWO*DSTRAN(3)-DSTRAN(2)-DSTRAN(1)) + ELAM*TRVAL
DSTRESS(4) = EG*DSTRAN(4)
C
C UPDATE STRESS
C
DO K = 1,NTENS
STRESS(K) = STRESS(K) + DSTRESS(K)
END DO
C
C
C DETERMINE JACOBIAN
C
C
DO I=1,3
DO J=1,3
DDSDDE(I,J) = DDS(I,J)
END DO
END DO
DDSDDE(4,4) = DDS(4,4)
C
C
RETURN
END
**
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Dear Chathurika Jayasundara,
Hi
Thank you for sharing this with me if you come to a conclusion. I'm doing the same thing and I've had this problem.
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I have already written a LS Dyna UMAT code for a linear elastic isotropic material. Now I want to add element deletion to it.
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Add *MAT EROSION keyword?!
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I am simulating fracture using xfem czm for a material (which is ellipsoid in shape) that is inside another material (cuboid in shape).
A prestress is given to the inside material and as intuition says the fracture should initiate where stress concentration happens. And that will be in my case the is the tips of the ellipsoid.
But the maximum principal stress is higher in other regions of the ellipsoid than the tip of the ellipsoid which is not intuitive. Can anyone think of a better reason why this is happening and what can be the best way to initiate a fracture in the material?
Inclusion inside the host (3D model)
As you can see the maximum principal stress is not highest at the tips of inclusion but rather highest in other non-concentrated parts of the inclusion.
Please let me know why this is happening and if you know any other better crack initiation criteria other than maximum principal stress in xfem for quasi-brittle material?
The geometry of inclusion (the material inside the host):
----------------------------------------------------------------------------------------------
The x:y:z ratios are 4:1:1, so intuitively crack should have formed at the pointy part other than other parts.
This inclusion is indside the host as shown in the attachment and prestress is applied to the inclusion. According to me the maximum principal stress should be highest in the pointy part which is not happening as shown in the results (elastic simulation).
So my question is
1. Why maximum principal stress is not highest in the pointy (stress concentration part)?
2. What are other better criteria for fracture initiation in ABAQUS XFEM for quasi brittle material.
Kindly let me know,.
Regards
Biswabhanu Puhan
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Ductility Ende und Crack materialled , metal, plastid, composite ales materialled !!!!!
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What failure criteria can be more efficient for the analysis of cracked rock mass under linear elastic conditions?
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In my opinion, the Griffith failure criterion can be a good option, considering that it has been discussed in many sources ( e.g., Fracture Mechanics, (2011) by Chin-Teh Sun, Zhihe Jin ) it can be a suitable and complete criterion in rock masses.
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The calculation of a model took about 36 hours to solve and I did not select the option to calculate elastic deformations, now I need that parameter and I do not want to calculate everything again.
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Dear Cáceres,
As you may know, the total strain components(E) option is selected by default when you create a step, so if you deselect it manually, you should calculate the element displacement by accessing the ODB file, as our friend Mohammadreza Moeini said. However, as you mentioned that your analysis took about 36 hours, I assume that maybe there are a large number of elements in your model, so this method may cause some errors. I recommend you to rerun your job. But for accessing the ODB file by python scripting, there is a complete lecture in lesson 2 of this package: https://caeassistant.com/product/python-scripting-in-abaqus-part-2/.
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I am writing a small piece on the definition on long run price elasticities of gasoline/fuel and the length of measurement periods.
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Gasoline prices in my country, Libya, reach about half a dinar per liter, which is equivalent to a maximum of one dollar per barrel for Libyan consumers, and of course water is more expensive than oil in Libya.
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I have come across a few studies in the literature reporting unbelievably low elastic modulus for API 5L Grade B steel around 10 GPa while the lowest elastic modulus for this steel in reliable sources is around 180 GPa. Also, the yield strain in their reports is around 3.5% which is huge for elastic deformation in steel. Is this an error in their UTM experiments or something else?
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Ali:
The previous responses are dead right. This has to be an error of measurement. Yield strains in crystalline metallic materials are invariably way less than 1% and the Young's modulus of all steels is around 200 GPa. Unlike plastic properties, the elastic properties - elastic modulus and Poisson's ratio - are only marginally affected by factors such as small changes in composition and microstructure, as elastic deformation only involves the flexing of atomic bonds with no permanent change in atomic positions. As pointed out, as Fe is the dominant element in steels, it would be impossible for the modulus to drop to anywhere near 10 MPa.
The issue here is almost certainly one of measurement. Although we think of Young's modulus as the elastic slope of the uniaxial stress-strain curve, it is notoriously difficult to measure this way as the displacements are so small. These authors probably used the displacement transducer on their testing machine rather than a strain gauge mounted directly on the specimen itself, and thus their measured displacements would include those in the gripping system and the machine itself. The fact that their stress-strain curve has a "J" shape at the start is an indication of this as this phenomenon is almost certainly due to the specimen "seating" itself in the grips.
The best way to measure the elastic modulus is by measuring the propagation of a elastic wave through the material, e.g., using techniques such as the resonant ultrasound (RUS) method.
ROR
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Dear fellow contact mechanicians,
I just stumbled over a problem in analytic mechanics of plane Cattaneo problems in the presence of bulk stress.
It is said that the Ciavarella-Jäger principle for "small enough bulk stress" applies to this problem in the following form:
q(x) = \mu*(p(x; P, beta = 0) - p(x; P - Q/mu, beta)),
where q(x) is the tangential contact traction distribution, p(x) the pressure distribution, P the normal line load, Q the tangential line load, mu the friction coefficient and beta a "rotation angle" proportional to the bulk stress, which I will discuss in a minute.
The second term on the right side in above equation corresponds to a "fictious" normal contact problem of the same contacting bodies under the load (P - Q/mu) and with a relative rotation by beta.
The condition of "small enough bulk stress" is basically that the contact area for this "fictious" problem (which corresponds to the stick region in the actual Cattaneo problem), completely lies within the actual contact area. Moreover, a non-zero value of beta will increase the contact length on one side and decrease it on the other side. So, e.g., for Q = 0 the condition of "moderate bulk stress" is actually that beta = 0, i.e., there is no bulk stress.
Now, we know that tangential contact problems have a loading history. Even the Cattaneo problem has a history: first the normal load is applied, and then an increasing tangential load. However, when beginning to apply the tangential load, Q equals zero, so any (constant) bulk stress will violate the "moderate bulk stress condition".
Or to put it more generally: For any non-zero constant bulk stress, the "moderate bulk stress condition" is violated at the beginning of tangential loading.
Does that change anything about the final contact configuration at the end of the Cattaneo loading?
Or am I missing something?
Thank you very much for your help!
Kind regards,
Emanuel
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Well thank you, but that paper doesn't answer my question, as the authors just put moderate bulk stress ("We restrict attention to cases in which the direction of slip is the same at either end of the contact") and calculate from there. And for now, I am only interested in the Cattaneo loading, not the cyclic case.
My question is, what happens, if the contact switches from non-moderate to moderate bulk stress? Consider Q = 0. Then, the "moderate bulk stress condition" is that there is actually no bulk stress; you can look it up in Barber's book, but it is logical, as any bulk stress will lead to opposite slip directions at the two contact ends.
Now, does that change anything about the contact solution if Q gets large enough during the Cattaneo loading for the bulk stress to be actually moderate?
I guess, the point is, that slip will always just propagate inside from the contact edges, unless loading is reversed, even if the bulk stress is not moderate, and so, no point will ever switch from slip to stick (although at one edge the slip direction is continously reversed), but I am not able to prove that rigorously.
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I am calculating the elastic constants for a crystal with tetragonal symmetry,using VASP . In the INCAR file I have added the following tags :
NSW =1
IBRION =6
ISIF =3
POTIM =0.015
NFREE =4
I am getting 13 components in the elastic tensor instead of 6 . It will be really helpful if anybody can provide any suggestion .
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I tried testing the symmetry of your POSCAR in the Pymatgen software, and it returned a symmetry of monoclinic group #10, even with a fairly high symmetry tolerance of 0.1. Also looking at the Materials Project and ICSD databases for this material I see only monoclinic and triclinic structures, so I do not think that the material is actually tetragonal.
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Using the stress strain data obtained from compressive strength test of concrete cylinders how to define the points to estimate the final tangent Modulus of Elasticity and secant Modulus of Elasticity?
Is there any correlation between these two moduli?
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In addition to the answers already provided, you may find the following article useful:
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To determine the dynamic mechanical properties of PLA compounds it is important to understand their viscous nature (flow properties). Thus, dynamic mechanical analysis (DMA) is performed to evaluate the effect of temperature on the mechanical properties of elegant PLA. Three parameters were used to demonstrate the dynamic mechanical properties of the PLA, i.e. (1) the storage coefficient (E ') corresponding to the elastic response to deformation and related to the material rigidity (2) the loss modulus (E') corresponding to the slag fraction; and (3) the damping factor (tan). These parameters provided qualitative and quantitative information about the thermal behavior of the elegant PLA.
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What is the load and frequency we have to apply? Temperature ranges differs according to polymers,
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My opinion
The foundation of the wall has a large tread area, in order to distribute the loads on a large ground surface in order to increase the bearing capacity. This really happens when the construction is at rest and all the loads are directed vertically to the ground. When the construction receives lateral loads from the earthquake, the wall along the entire height of the floors, together with its base, tends to overturn. The beams with which it is connected to the nodes react and prevent the overturning of the walls in height. However, the cross sections of the beams are strained with torques and if the torques are large then they fail and we have the collapse of the construction. The weight of the base and the foot girders are not able to stop the overturning in large earthquakes, because the entire height of the walls are huge levers and lower huge torques that the foot girders are unable to receive. It is very important to stop the wall overturning if we want the beams and foot girders not to break We can only do this if we lock the sides of the wall with the ground, as we lock the steering wheel of the car so that it is not stolen from us.
When driving and wanting to turn one hand pushes one side of the steering wheel up and the other down. In the same way it turns the wall in the earthquake and breaks the beams and the foot girders. The vertical force of the side of the wall is received by the base and transmitted to the ground. The upward force of the other side is picked up by the beams and foot girders and they break. If we anchor the sides of the wall with the ground, we will stop the upward force and we will help the beams and the foot girders not to break. It is simple. We remove the base in width, and we make bases in depth, anchored to the ground, so that we receive the vertical forces and the forces that are directed upwards successfully, so that we do not strain the beams and foot girders and break them. The beams also break when the pillar or wall is deformed due to bending. To prevent the bend we use elongated walls with multidimensional cross sections so that they can receive all the horizontal directions of the earthquake.
The walls did not bend easily. If we want to reduce any bending of them, we impose on them by pre-tension compression in the cross section + anchoring in the ground. The pre-tension in the cross section of the wall also increases the elastic displacement, because the cracks that are created are not inelastic but close due to pre-tension and return the wall to its original position. On the other hand they increase the active cross section of the wall due to compression. The shear failure that exists at the concrete and steel interface in the relevance mechanism does not exist since there is no relevance to the prestressing. The foundation soil becomes stronger as the anchorage transfers loads to the lower and stronger compacted soils. The control of coordination and seismic duration is now possible because we control them with external forces coming from the ground.
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A typical foundation wall minimum thickness of eight inches applies to walls eight feet or less with no more than seven feet of soil pressing against it. Foundation walls taller than eight feet with more than seven feet of soil pressing against it requires a larger foundation wall 10 to 12 inches in width.
What is the Optimal Foundation Wall Thickness? | Fox Blocks
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Dear all,
Can anyone help me to apply an elastic clamping stiffness at a node in Abaqus?
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Possible solutions:
*ELEMENT, TYPE=SPRING2
elementID, node1, node2
*SPRING, ELSET=name
1000
or
*ELEMENT, TYPE=SPRINGA
elementID, node1, node2
*SPRING, ELSET=name
1000
or
*ELEMENT, TYPE=CONN3D2,ELSET=elset1
elementID, node1, node2
*CONNECTOR SECTION,ELSET=elset1, BEHAVIOR=name1
CONNECTOR BEHAVIOR,NAME=name1
*CONNECTOR ELASTICITY, COMPONENT=1
1000
You can specify in the Abaqus input file either of the above options and see which works best for you.
Best.
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Dear Colleagues
I am using a UMAT for modeling the hysteresis behavior of a Material.
It is a simple UMAT which modify the elastic modulus of the material at different strains in order to reproduce the hysteresis behavior.
I need to convert it into a VUMAT for Explicit Dynamic simulation in ABAQUS.
What should I change in My code?
I have attached my code.
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Code will be almost the same, only you need to change the function and variables as per VUMAT and there is no need for Jacobina calculation in VUMAT, after this change, I think it should work.
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Hi all,
I am working on Phase-Field UEL for hyperelastic materials. I am using codes of Dr Molnar ( http://www.molnar-research.com/tutorials_videos_3.html) to develop hyperelastic material. I have tried to replace the UMAT with my hyperelastic UMAT in the UEL and call the UMAT for stiffness but it's not working and resulting in negative Jacobian.
Any suggestions in implementing hyperelastic UMAT in UEL. Please let me know.
Thanks & Regards,
Sri Harsha
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Hi, not yet
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Iam trying to calculate the modulus for my kevlar yarn sample from the results i have obtained using the ASTM D2256, however, Iam not able to find the calculation procedure, can anyone please suggest any literature/material which may contain the details of how to proceed with the calculations.
Thank you in Advance
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The elastic modulus(E) E(MPa)=Stress(MPa)/Strain (Eq 1)
MPa=N/mm2
Applied several loads in increment on the cross area of the sample and obtained the Stress
Stress=F(N)/Area(mm2)
For each applied load estimate the length variation (L-Li ) based on the initial length (Li). Then calculate the strain=(L-Li)/Li
Calculate E describes in Equation 1
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Hi all, I'm new to Abaqus and trying to model a 1.4 kg weight laid on the buttocks. I have an imported buttocks model with element type C3D4H for the hyper elastic materials and C34D for bones. I assigned boundary conditions of encastre to the bottom part of the buttocks, and the weight can only move in direction toward the buttocks. I'm using prescribed displacement of the weight and measuring the RF2 on the top nodes of the weight and trying to get ~13.7N (1.4*9.81). I've assigned surface to surface contact with 0.8 COF between the weight and the area of the buttocks in contact. I cant seem to get convergence at other part rather then the middle of the buttocks, when the weight is above the peak height... I tried many things but cant get it to converge, It start to get really slow around 80% and diverge at around 95%, when the loads get to ~12N. Also the deformation seems a bit large for this small weight. I would really appreciate some help, I'm attaching the cae file with 3 locations of the weight I tried. Thank you, Tomer
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1) Reduce the load increment so that the loads and/or imposed displacements are applied to the model in very small steps
2) Try to run a *STATIC, RIKS analysis instead of a general static analysis
3) Try to use C3D8 elements and use the *ADAPTIVE MESH and *ADAPTIVE MESH CONSTRAINT options
Best.
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Can I know exact assumption for LASSO and Elastic Net? Since Elastic Net is a hybrid method for LASSO and Ridge Regression, did it have the same assumption as them?
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They work on hyper parameters. They will not have assumptions. They work with big data and when you have big data, they are rarely parametric.
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Hello Everyone, I have to simulate the piezoresistive cantilever of poly-silicon. During the selection of material in COMSOL, they ask for an Elasticity matrix. so which value should be entered. I am first time using the piezoresistive cantilever. If anyone knows the answer, kindly please reply.
Thank you
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you welcome Neethish Kumar Unnam.
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hello how to input materials parameter for the following
elastic - plastic material
I have the following parameters only
lame constants
yield stress
hardening parameter
young modulus and poisson's ratio
I know how to input everything except lame constants
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For what kind of materials?
Linear elastic: Its 3D plot has no special meaning
It is significant for materials with anisotropic and nonlinear properties.
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We know that the TERRATEST 5000 BLU is the Light Weight Deflectometer for dynamic plate load test to check compaction quality in earthworks and road constructions.
I am interested in is it possible to assess the strength of asphalt concrete pavements on highways and urban streets using the TERRATEST 5000 BLU (by definition of elastic deflection)?
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Dear Dr. Raximjon Soataliyev , Thanks for your helpful response!
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I am trying to model the impact element having non linear stiffness in Abaqus. I want to model the pounding force between two frames under earthquake excitation. For this I am using Axial connecter element and defined elastic behavior and reference length equal to gap. Under elastic behavior I have input the table of Force vs Relative displacement in such a way that force is zero in tension and remains zero until gap closes. But after running the analysis my pounding force value is comming less than expected.
My whole objective is to model the gap element and it should work in a way that when two frames collide, the gap element becomes active else it should transfer no force?
Please somebody tell me where I am doing wrong or if there is another way of modelling gap in abaqus?
Thanks in advance.
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What are the formulae of Voigt, Reuss and Hill Poisson ratio in terms of independent elastic constants (C11, C12, C44) or in terms of bulk and shear moduli for cubic ? Whether they are same or different for all?
PR= (3B-2G) / (6B+2G).
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I would like you to check this video based on Voigt and Reuss Notation in real world composite application
Regards
Paul Vizhalil
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Rocherulle's model and elastic properties
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S.O. Pillai, by SOLID STATE PHYSICS
look at 1st unit bonding in solids, you can how to calculate bond dissociation energy of all compounds
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so im modelling a brick wall on ABAQUS, i input elastic and plastic properties for my model and my vertical plastic strain value shows that my model has 0.25. obviously this is so big especially for materials like brick that is a brittle material not elastic, does anyone can help me to solve this problem?thanks in advance
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Dear Oryza, Before going for nonlinear analysis did you check the linear elastic analysis first? This check is just to confirm that your model is doing what it is supposed to do.
Once you check your model for linear analysis, to check why the strain is significantly large it is essential to check the boundary conditions. From the limited information you provided in your question, it's not easy to give you a suggestion why your model has a high strain value.
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Hi, image there is a case which in the elastic part Young's Modulus depends on the fields, let's say two.
Is it possible to define one field by USDFLD and another by UFIELD? How Abaqus manages this (Start with the USDFLD one or UFIELD one as Field 1)?
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How will temperature of submarine sedimentary strata change after it suffers from earthquakes? Will the elastic source give rise to a temperature field?
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See also the following useful link: https://www.jstor.org/stable/983382
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I was analyzing regression problems with some numerical datasets. Then I saw that the elastic net shows a bad results. But I do not understand why it shows bad results?
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In my masters' work, I noticed the same. Although I didn't mention this in my dissertation, I am curious to know the reason.
As per my understanding, when you enforce two regularisations (L1 and L2) in Elastic Net, you are overconstraining the problem often resulting in an ill-posed problem even though the coefficient matrix is not ill-conditioned.
For example, let us say the L1 regularised loss is bigger than the L2 regularised loss in each epoch and due to spectral bias you would end up fitting data on bigger loss (dominant frequency).
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I am trying to simulte tensile deformation of Cp Ti. I am using hooke's law for elastic region and phenological power law for plastic deformation. Do we have to use any other model to capture the grain shape changes during tensile deformation?
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Add deformation vector and use wrap by vector in Paraview to visualise the shape change
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I am just trying to model a concrete cube with a rubber layer on the top of it...both concrete and rubber layer has linear elastic properties...now when I am giving a pressure load on the top of the rubber, the rubber layer gets spreads to a large extent. How is it happening? I was under the impression that once the rubber gets compressed fully the concrete should come in to picture thereafter and get the pressure.
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The reason behind such behaviour of rubber with linear elastic properties is: The linear elastic properties of rubber do not take into consideration the volume incompressibility effect of rubber and hence this leads to the unrealistic behaviour of rubber (identified as a negative increase in its volume). The problem can be simply solved by considering the hyperelastic properties of rubber. Any other suggestions would be highly appreciated.
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Hi,
I have given input isotropic elastic properties with 1MPa of young's modulus, 0.48 Poisson's ratio, density 1300 to wall structure (0.5mm thickness).
For that, I am getting highest von mises stress after the stenosis region which is about 900Pa (0.0009MPa) and 1385Pa (0.001385Mpa) for systolic(0.4s) and diastolic(0.55s) conditions respectively. I 'ud like to know, how to correlate these results with the given inputs.
Tq in advance,
Regards
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The von Mises stress is an invariant of the stress tensor, related to the deviatoric part of stress (in contrast to hydrostatic stress of the bulk). If you dop an object in deep water for example, the hydrostatic stress will increase, but the von Mises stress will be zero. Von Mises stress is mainly used to check for yielding of ductile metals. I don't know if von Mises stress is a suitable measure to evaluate the state of artery tissue, but if it is then it can only be interpreted in relation to some limit values. The limit values need to be looked up in a text book or evaluated by experiments.
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There is a soft pneumatic actuator which is made of Hyper Elastic material that I am going to simulate it in Abaqus or Ansys. A fiberglass layer is attached to bottom of actuator. This layer prevents any elongation in both direction (Longitudinal & Transvers ) but allows actuator to bend. How can I simulate it in Abaqus or Ansys ? adding boundary condition or creating property?
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Dear Mr. Sina,
In Ansys, you have ACP option which gives laminate option. This might help you to build the required model and analyze...
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When the tube array is subjected to water cross flow, what is the effect of fluid flow direction on fluid elastic instability in the tube array? Consider the effect of flow direction, i.e., if the water flow is upward or downward or if the fluid flow direction is horizontal. Many researchers developed an experimental setup in which fluid flows in the horizontal direction; few developed a setup for fluid flow in the vertically upward or downward direction.
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It really dependent on the facts of the Source and circumstances.
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Hi,
Can someone please provide me experimental values of the longitudinal or Transversal sound speed for Single Crystal Tantalum and Copper, along with the directions (100), (110), and (111)? I have limited access to journals, and I'm no longer affiliated with a University. There is a paper titled Elasticity of BaFCl single crystal under hydrostatic pressure, which tells elastic constants are related to the speed of sound. It is also well-known people in Geophysics use the speed of sound to find the elastic constants (inverse process) https://www.hindawi.com/journals/mpe/2016/6762076/
Anyways, I need the experimental values of the speed of sound for the crystals mentioned above. I'm trying to publish a final paper of an algorithm for finding the speed of sound for any K direction and a given pressure P . It would be awesome if the results I obtain are close to the experimental data available. I presented part of my work a long time ago at https://meetings.aps.org/Meeting/TSF16/Session/H4.4
Thank you
Oscar Guerrero
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Dear Oscar, sorry to see that your very interesting question has not yet been answered by experts in this field of research. As a synthetic inorganic chemist I would not call myself an expert enough to give you a qualified answer. However, I can recommend to you the following potentially useful literature references which hopefully help answering your question.:
High Pressure Thermoelasticity of Body-centered Cubic Tantalum
This paper is freely accessible as public full text on RG.
For copper please see:
Atomistic shock Hugoniot simulation of single-crystal copper
In this case you can easily request the full text of the paper directly from one of the authors via RG (four of them have RG profiles).
Some basic information can also be found in the respective Wikipedia entry at https://en.wikipedia.org/wiki/Speeds_of_sound_of_the_elements
Good luck with your work!
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Dear all,
I wanted to ask how to resolve the error of getting some element negative or zero or small area, Like with the same mesh with simple elastic or elastoplastic analysis it (abaqus) is not giving the same error . Only when I am using phase field with subroutine I am getting this error .
Note: The specimen I am running the simulation is Compact tension (CT) specimen in 2D .
One of the probable solution I am gonna work on is to ,"Mesh the specimen in Hypermesh" but I do think that it can be done simply in abaqus cause CT specimen is not that complicated specimen to mesh in abaqus with good mesh quality to work with .
Thanks for any future help and also if i find the solution to my problem I will share it in here in the answer to my own question .
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