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fatigue crack propagation in Abaqus

 

How can i simulate fatigue crack propagation in Abaqus?

I want to simulate propagation of an edge crack in a rectangular steel plate using XFEM method in abaqus.
I know i should use Direct Cyclic step but i have lot of problems with this.
Thanks in advance.
 
Regards,
M.Sc Student of Mechanical Engineering
Mechanical Department of Ferdowsi University of Mashhad ( the 3rd University of IRAN )
Sincerely yours , AMIN
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ABAQUS/explicit excessive mesh distortion problem

 

I'm modeling a friction based welding process which involves a rigid tool being inserted into a deformable (Aluminium alloy) workpiece. I've used Johnson-cook plastic hardening with Johnson-cook rate dependency (initially it was the plasticity) to see if has some +ve effects on my model, but it didnt. I have used C3D8RT elements for both tool and workpiece.I've used a fine mesh for the interaction region (for tool and workpiece) and coarse mesh otherwise. The tool has an angular velocity of 400 rads/sec with a feed rate of 0.5 mm/sec whereas the bottom surfaces of workpiece are encastre'd. I've given the movement to the tool by us ing 'tabular' amplitude increasing in paced manner. In the step, i've specified non-linear geometry with mass scaling for the concerned interaction (tool & workpiece) region (factor-10^8) at the beginning of step (it does increase the stable time increment). I've used ALE adaptive meshing with a frequency of 1 and remshing sweeps as 50-75, I've chosen frequency of 1 so that I can specify ALE mesh constraint for the workpiece (only the region where tool is inserted). I even tried element deletion, although I didnt specify any damage criteria in material module (dont know if it's necessary). the total time period of my analysis is 4 seconds and a pressure of 80Mpa is applied on the tool. I would like to clarify that I've checked the units of the material pro perties 'n' number of times and there's no worry over there. Whenever i run the analysis, the model reaches a time period of only 0.7594 seconds with stable time increment of 1.0E-6. the mesh gets excessively distorted and analysis is aborted.

 please anyone with any helpful suggestion, give your inputs !!  I can share more info if needed

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How to view the distribution of plastic strain values?

 

Hi,
I am facing a difficulty in viewing the distribution of plastic strain in my
RC beam model in Abaqus. When I select the PE option in Visualization
module, all the contours are displayed in blue colour, although the results
show deformation and I have inserted all the materials plastic strains.

Thank you.

Regards
Ismail

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Concrete Damaged Plasticity input parameters in Abaqus‏

 

Hi, 

I am trying to calculate the parameters necessary for Concrete Damaged Plasticity Model in Abaqus. Could anyone please let me know how, step by step, to obtain the "Yiel d stress" vs"Inelastic strain" for Compressive Behaviour; and the "Yield stress" vs"Cracking strain" for Tensile Behaviour? 

I am basically confused about what values I need from the stress-strain curves and how to obtain the above parameters to be input in software. 

Thank you 

Regards 
Ismail
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Contact of rigid bodies

 

Hi to everyone,

I am trying to model contact between two rigid blocks of the same geometry. In the tangential direction a Coulomb friction behaviour is needed while in the normal direction a "hard contact" should be applied; however, the standard surface-to-surface contact may not be applied for rigid bodies in Abaqus. Thus, I have tried, among others, the following connector section that connects with a wire the center of mass of both rigid bodies along the y-y global direction:

Cartesian connector with two behaviour options:
a) Friction:

Direction u1 (along global x-x parallel to each surface in conta ct) was specified as the slip direction and a value of the friction coefficient was implemented, e.g., 0.65.

A contact Force is also needed. I have defined that the contact Force is specified as F2, i.e., perpendicular to the slip surface and a value equivalent to the weigth of the upper block was implemented. Is this the right procedure? What happens in case of a more complex geometry? How we define this contact Force? The contact Force is also defined in the following option, also.  

b) Elasticity: A non-linear Law for the contact Force along the U2 direction was applied to model hard contact as follows:
F              U
-10000     -0.00001
0              0
0.00001      10000

The above formulation suggests that the stiffness is infinite when contact occurs (I suppose that negative value is compression) and stifness becomes approximately zero at detachment.  

A seismic excitation is applied along the global x-x direction (parallel to the contact surface) so as to provoke an acceleration greater than 0.65g in order to provoke slip, however the two blocks remain unseparable without slip.

Please provide your comm ents or any advice regarding contact between rigid bodies.

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Re: Definition of CPRESS in Abaqus/explicit

 

hello everyone.. im working on calculating hertz contact stress on surface of plate.. pls suggest me some books or materials for hand calculation... 

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Regards
Tamilanban

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chradodjo@yahoo.fr [Abaqus] | 24 May 04:19 2016
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how to make Load-displacement graph decrease?

 

Hi, I’m beginner in abaqus. I’m doing a pull-out modelling. I have done a test experiment I laboratory and got some results, now I want to compare those results with FE result but my curve(load-displacement) doesn’t decrease. Any help will be greatly appreciated 


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Rotation tensor not accurate

 

Hello,

I am trying to calculate the deformation gradient using ABAQUS for a case i am studying, as follows:
1. Firstly i extract the rotation tensor R from ABAQUS (I assigned "local material orientation" to all elements so ABAQUS outputs the localCoordSystem).
2. Then i extract the nominal strain from ABAQUS and calculate the left stretch tensor (in the local coordinates): v_local=NE+I (after dividing the shear components by 2).
3. I rotate the left stretch tensor from local coordinates to global coordinates using the rotation tensor.
4. F=v_global.R

I tested this on a very simple case: homogeneous simple shear deformation of a homogeneous cube of neo-Hookean material.

The global left stretch tensor has the exact values i expected (compared to analytical calculation)  but the rotation tensor values have an error of about 3-4%, so the deformation gradient i calculate is not accurate.
For a more complicated case i expect a larger error..

Am i doing something wrong?
Is there anything i can do to fix this problem?

Thanks


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Help with large strain viscoelasticity

 

Hi there,

I am having problems with large strain viscoelasticity, where I am using Prony series to model the visco part. There is no default for the parameter CETOL, nevertheless, by reducing this tolerance or reducing the time step I am getting results that make no sense.

In my understanding, I solve the problem. Then I want to check that my results are correct, so I do convergence analysis. I refine the time step, I refine the mesh and I reduce the tolerances. Then if everything is defined properly, my solu tion should be better with these refinements. But the case with large strain viscoelasticity is not improving with these refinements, results are getting worse (I can compare simple cases to analytical solution). Thus my question is, how should I select CETOL and why my results are not better for tighter tolerance.

Someone remembers if this problem was ever discussed, I am new in this forum, can I somehow cheque some archives?

Thank you

Zuzana

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Obtaining the Stress and sdistribution from abaqus

 

Hello. I am a beginner in abaqus and I am modelling a composite and non composite solid beam. I have to obtain stress and strain distributions. I also have to find the relative displacement. This was given as an assignment and I am not sure how to obtain it. Any help will be greatly appreciated

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Modeling of novel friction welding process

 

Hello !


I'm trying to model friction welding process between a tool (steel) and workpiece (Aluminium). I'm facing difficulty in the meshing of the model. I want to focus just on the interaction region between the tool and workpiece. I am an attaching an image of the model with the mesh generated.http://tinypic.com/r/2yxgktk/9 I've specified the following parameters:


step: dynamic,explicit, temp-disp. : I am unable to define the remeshing rules for this step. Abaqus shows an error message saying "error indicators cannot be specified for this step type".  My process in completed in two st eps: initial and then next step in which rotation and feed rate is given to the tool. 

Loads: i've specified pressure on the tool so as to insert the tool into the workpiece.

mesh: i've used tetrahedra elements with fine mesh in the interaction region. I've also specified ALE adaptive mesh domain for the interaction region. 


I need help in giving the remeshing rules and also need advice on whether the mesh should be allowed to follow the material or it should be independent of the material in the ALE mesh constraint control ? Another aspect on which help is required is in achieving uniform mesh which can withstand high deformation during the process.


Any suggestions/advice/solution is welcome.


Thanks in advance.

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