Hi, I tried a Linear perturbation analysis in ABAQUS with surface-to-surface contact. The parts that are defined as contacting surfaces are 0.2mm apart. They are also given a normal behavior with a pressure overclosure option using "hard" contact. However, in some modes where it is expected to be in contact, there is interpenetration. The problem is that it depends on the scale of deformation too. So my question is how to make this generalised, i.e., include no contact in case of tensile mode behaviour and include high stiffness in case of mode involving compressive type behaviour?

I found in a few articles that the contact condition in the base state cannot change which is, if two nodes are in contact they will continue to be in contact and if two nodes are separated, they will remain separated. This separation induces interpenetration. So in general terms, how to include contact non-linearity in a linear perturbation step in ABAQUS which includes different modes of vibration involving changing contact conditions from the base state?

Hi all

how can I make the local 1 direction to be the projection of the Z global axis in abaqus 2D model?

thank you

Hi all

this error keeps popping up " The third axis should be in the hoop direction" when modeling carbon fiber within matrix in 2D in abaqus.

Can you please help?

Thank you

Hi all

I was wondering about implementing carbonfiber properties (engineering constants) in 2D in abaqus.
This error keeps popping up "The third axis should be in the hoop direction".

I am adjusting material orientation so that the primary axis X sould be out of the paper. But in 2D the Z axis must be out of the paper.

Is there any solution to that?

Thanks

For 3D isoparametric elements, we could easily find evaluate x(r,s,t), y(r,s,t) and z(r,s,t) from (r,s,t). Given a global point (x,y,z), how could we find/derive the corresponding nature coordinate (r,s,t)? Is there any equation? Even for linear element, the coordinate transformation is not linear.

This is a practical FEM implementation issue, if a user wants to query a displacement at a given global point, how can we do that? If we know the (r, s, t), then we could easily find the U(r, s, t) = ΣNi(r, s, t)Ui

Do we have to solve a small nonlinear equation?

Thanks for your help.

Hi!

I am trying to apply a viscous pressure (VP) load to beam elements (B31) but I obtained thie error message: "INVALID LOAD TYPE ON ELEMENT * INSTANCE *. LOAD TYPE VP IS NOT VALID FOR ELEMENT TYPE B31"

Do you have any suggestion?

Thank you!

I have managed to adjust a material property to get the best fit to the experimental response using fminsearch in MATLAB, but I lost access to free MATLAB so I have to use something else. I like Scilab, it works for everything I did with MATLAB except this.

Scilab throughs and 'invalid handle' error when executing:

dos('abaqus cae -nogui response.py','-echo');

at the line inside response.py:

Job.submit(consistencyChecking=OFF)

It seems that Scilab opens a dos shell to execute abaqus but 'response.py' has this line inside it:

Job.submit(consistencyChecking=OFF)

and the echo option returns this:

Abaqus Error: cae exited with an error.

I look inside abaqus.rpy, where I found that the error is 'invalid handle' while executing line 361 in response.py, and line 361 is 'Job.submit(consistencyChecking=OFF)'

Needless to say, I verified that I can run:

abaqus cae -nogui response.py

at a black dos shell (dos prompt), no problem, and using MATLAB that used to work, and did not change anything in response.py, I just translated the minimizaion code in Scilab. I checked the new code line by line, all works except:

dos('abaqus cae -nogui response.py','-echo');

which I can write like this, but then I get no error message:

dos('abaqus cae -nogui response.py');

Does anyone know how to solve this? maybe another MATLAB-alike to use?

How does one define Element based surface for a User defined Element?

Dear iMechanica community,

Hi! I am trying to verify Abaqus VUMAT with simple examples so I wrote a VUMAT for orthotropic material and compare the result with Abaqus built-in material model (Elastic -> Engineering constants). The material constants are given in 1.png and 2.png. All other settings from part to mesh is identical. The stress distribution of built-in material model is in 3.png and the stress distribution of VUMAT is in 4.png. The discrepancy is not ignorable. The VUMAT code is also attached as a .txt file.

Is there anything that I miss in my code? I will appreciate your help. Thanks! If the problem were solved, I will write a tutorial for this and post it on iMechanica and Github.

Notes: The Fortran code is based on VUMAT from Rutger's repo: https://github.com/rutger-kok/composite_cdm_tan

I have differenet layups for cantilever beams. I run the static riks test from the eigen value in the first software ,giving values of initial arc increment of 0.005, mimumimum arc length increment as 1E-35 , maximum of 1000. The static riks gives good results for the notional loads for layup 30 -30 30 -30. However, keeping all other parameters same but for a different layup 30 -30 -30 30 ,the values from the staic riks are very very far from the experimental results. The values from the unique nodal for displacement is in the range 0f 10-3 while the values I get for lateral and vertical deflections are around 300 mm and 67 mm for the layups.

What parameters do I need to change so my values are close to the experimental results?

Hi,

I am wondering if someone could suggest a good book for learning about creep deformation.

Thanks,

Gyan

Hi I tried to code a basic phase field model for fracture in octave.

It doesn't seem to converge to the correct load. It fails later.

Also mesh refinement did not improve the results.

The link to the GIT is here

https://github.com/dontcallmesuren/Phase-field-modelling.git

Any idea where I am wrong?

Ping me. Thanks in advance.

Hi, everyone. I am considering the heat conviction during compacting simulation by Abaqus. I was wondering that how to define the sink temperature and film coefficient? Is there any references for the two parameters of different materials?Thank you so much for your help in advance.Sincerely

Hello every body,

I would like to use CDM (continuum damage mechanics) for modeling damage in my constitutive model and I need to incorporate a variable (or its effects) into my mechanical damage that doesn't evolve or change by time but changes by other factors (such as irradiation dose or etc..). Does anyone know of a paper which had been used the similar approach? I would really appreciate it if you can provide the link for me because I couldn't find any so far.

Regards,

Faezeh

Hello,

Does anyone know if Abaqus is able to calibrate/fit Johnson cook material parameters (A B n m & D1-D5) from uniaxial stress-strain curves at different strain rates.

I have these uniaxial stress-strain curves at different strain rates but i dont know how to generate the johnson cook parameters. Also i want to know how Johnson Cook is handeling different E-modules at different strain rates. I`m working with fiber reinforced thermoplastic which has different stiffness at different strain rate.

Appreciate you urgent help!

Best regards

Ali Khajehgani

Hi everyone.

I want to determine Fermi energy from the band structure of a conductor and a semiconductor.

I believe that for semiconductors, it is given by the average of highest energy in the valence band and the lowest energy in the conduction band. Please correct me if required.

I am wondering how to obtain fermi energy for conductors where those two bands are overlapping.

Thanks in advance.

I am interested in modelling low cycle fatigue damage growth in mild steel using Abaqus. Which model will best suit the ductile damage in steel?

I have the following questions.

1. How to model alloy in LAMMPS? How to automatically randomize the position of atoms of various types?
2. Also how to evaluate the mechanical properties such as Elastic modulus and Fracture toughness?
3. Is it possible to model interface fracture using LAMMPS?

I am looking to generate cohesive elements in a bulk (mesh input). Is there any efficient method/code available using any executable or in MATLAB?

I am building a big model to select some specific elements using Python script in Abaqus Cae. The script runs quickly and the result is as expected in a small model. However, the computational efficiency in a bigger model is very low. The script has run 18 days in a Linux workstation with noGUI command. Are there any methods to set parallel computation in Abaqus cae? Thanks in advance.

How to conduct nanoindentation simulation of a coating material (Substrate Ti material and Tantalum pentoxide (Ta2O5) as a coating material) by FEA software? What are the input parameters I need to consider for the simulation?

Hello,

I have defined general shell section properties in my model in Abaqus. When I run the simulation, there's no stress out put data available. What could be the reason for this?

Oi!

I am now using USDFLD to do my simulations. And I need to assign strength, that created by MATLAB, to element 1 to 33.

In the simulation, when the element stress equals the streength failure will happen.

Do you have any idea about how to assign the strength to element? Should I use NOEL or UEL?

Thank you!

HI , the query is related to FE modelling of 1d Euler bernouli beam for pipe

If a pipe is modeled as a beam ,how can we input or account for the internal pressure of pipe.

What is the quantity and the direction of nodal loads

Should a load = Pressure x Pipe sec Area be applied to all nodes??

Thank You.

I have been trying to analyse plate buckling by using Static Riks method in abaqus and I have been getting load factors greater than 1 at bifurcation. I have frist carried out the linear perturbation, buckling analysis and I am using its igen modes to introduce imperfections to the non-linear model. I have also defined self contact. Can someone tell me what would be the reason to get higher buckling loads for the non linear case?

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Hello,

I am performing high strain rate testing/dynamic testing in split Hopkinson pressure bar (SHPB). As part of validating my experimental results, I have created a numerical model in LS DYNA. The model consists of striker bar, pulse shaper made of copper and incident bar (Fig 1 and Fig 2 in the attached pdf). Copper pulse shaper typically filters out high frequency oscillations of the incident pulse and also increases its rise time. The size of pulse shaper is 2.5 mm thick *12 mm diameter. It is circular in shape. The output I am looking is z-stress on an incident bar element (typically its center of the bar where strain gage is installed). The incident stress vs time obtained numerically and experimentally must match each other. However, I am not able to achieve it. Refer to Fig 3.

From my quasi-static tests on copper specimen, I obtained A, B and n parameter. I had a sheet 1 ft by 1 ft by 2.5 mm thick from which 4 tensile test specimens were created (2 in one direction and 2 in direction perpendicular to it). My SHPB is suitable for testing rocks and not metallic specimens. Hence I was not able to do dynamic tests to obtain parameter C. Now since I am not able to match my experimental and numerical incident stress vs time curves, I have the following question. Please help me. I am stuck at this point from past many weeks.

1. The rise of incident pulse numerically is very slow more than double that of experimentally obtained pulse (Fig 3). This is most probably because the rate at which copper pulse shaper is deforming is also very slow. This I checked by obtained z stress vs time (Fig 4) and effective plastic strain vs time (Fig 5) curves for a element in pulse shaper. Now I am not able to find solution as to what parameter shall I change to get a good match. I have played with C parameter from 0.009 to 0.2 but the rate of loading in pulse shaper does not change and same holds for rate of loading of incident pulse. Are my A, B and n parameters incorrect? Please refer to engineering stress vs engineering strain curve of the copper (Fig 7) I have got from tensile tests. It might give you some idea if my parameters are right or wrong? If A, B and n are correct, I can at least be sure that I have to change C.

I have already done validations to check my contact and I think it is working fine. So all my attention is on material model parameters. I am using log linear Johnson Cook parameter C for strain rate sensitivity.

Hello everyone,

I have created a UMAT code for J2 elasto-plasticity with isotropic hardening for 3D solid elements.

At this point I would like to support also plane stress shell elements. What changes in the code are

suggested? The already implemented code, takes as input the strain tensor at time tn and the strain

increment tensor and updates the stress at time tn+1 and calculates the material Jacobian and

achieve quadratic convergence. The stress and strain tensors are manipulated as 6x1 vectors and the

material Jacobian as a 6x6 tensor. I know that in case of plane stress the vectors should be 3x1 and 3x3

respectively. What else should i take into consideration? The strain tensor as used by the umat contains

olny the values of ε = [ε11, ε22, ε21] in case of CPS4R elements. What about the ε33? This should not

be zero as it is calculated from the incompressibility condition and from the plane stress constraint where

σ33 is zero. Is ε33 used by ABAQUS at all, or should I keep it only as state variable?

What about the material jacobian in plane stress? Is it calculated as in the 3D case? Any thoughts or

suggestions would be highly appreciated.

Dear Community,

I have a model in which I would like to alter the geometry to account for local buckling/imperfection. Since, the CAE is not that flexible in modifying the geometry, I do it externally.

For this, I extract the mesh (node coordinates) from abaqus -> undeformed shape, and modify it externally -> deformed shape.

After that, if I import back the new mesh to abaqus in the Part module and continue the analysis, it works fine.

But, would it be possible to work in the Assembly module?

I would like to be able to import the new mesh (deformed) to Assembly, to have it directly independent.

The editNode() cmd used for Part is not working for Assembly:

Error: AttributeError: 'PartInstance' object has no attribute 'editNode'.

Any ideas/suggestions?