Abaqus Damaged Plasticity- problem with Strain Rate

Margi's picture

Hi All,

I am using Abaqus explicit to simulate a simple compression test on a concrete cube. The cube's bottom face is fixed, and the compression is given by giving a displacement to the top face. In order to simulate concrete material I'm using the damaged plasticity model.

From what I understand you can choose if you want the model to be strain dependent or not.  My problem is that when choosing  non dependent on strain rate I get different results for different speeds of loading. If on the other hand I do choose to make the model strain dependent then I get the same results (for a specific speed loads), even though the strain rates I choose are considerably different.

Does anyone have any suggestions? Any comments would be greatly appreciated.

Thanks,

Margi


strain rate , inertia

strain rate , inertia effect, loading speed are different if your model parameters are right. I am a newer, just as a reference.:)

Become a good engineer!


Margi's picture

Re: strain rate , inertia

I do not think that you fully understood the question, and therefore will
lay it out again: whilst using the aforementioned model I use the same speed of
loading, but with different strain rates which can be defined in the damaged plasticity
material model. I get the same results, even though I expected them to be
different due to the dependency on strain rate. Inertia effects may well be the
reason for different results whilst using different loading speeds, but this
still doesn't explain why there is no difference when using differently
pre-defined strain rates.


vikas sharma's picture

Request

hii

 my research  is based on damage of composite material during drilling. as per your research  i need your help, because i am using ABAQUS 6.8 and using HASHIN damage criteia. i thought you aware about this topic. 


many strain rate points you inputed is just general conditions

Become a good engineer!


Margi's picture

In the abaqus manual in the

In the abaqus manual in the part about damaged plasticity it states : model includes the option for "rate sensitivity, especially an increase in the peak strength with strain rate" meaning that when using different strain rates there should be a difference in peak strengths.

If you do not know about this model I suggest you refrain from commenting.


mohanraj1987's picture

hi madam you are looking

hi madam you are looking beautifull... can you please help me to do my project usin abaqus/explicit.... please reply to this mail address.. i'll send complete description of my model please madam.... my e-mail id is  l.mohanraj1987@gmail.com


regarding johnson cook model in abaqus

kindly please tell me the steps to implement johnson cook model in abaqus. i have material constants for johnson cook model. please help me regarding this.


Hutchinson's paper might help

Margi,

 I read one of Hutchinson's paper in predicting sheet forming limit, but I could not remember the name of the paper.

In the paper, he found that the predicted limit strain is insensitive to the real loading speed, but only is related to the material parameter of strain rate sensivity (m value).  The velocity appears in both side of the equal and is cancled.

I hope Hutchinson's finding might help you.

 

Good luck 


Margi's picture

Sounds interesting!!

Sounds interesting- I'll have a look into that.

Thanks,

Margi


Measure of plasticity

Hi Margi,

Sorry for the interruption.I'm not here to answer your doubt,but would like to ask one,if you don't mind.As you seem to have a hang of plasticity,i'd appreciate if you could enlighten me with what you know on the following.While performing fatigue analysis of materials with notches and cracks,it is well known that,the damage accumulation and final fracture,everything happens within elastic limit ,globally.At the local level,near the crack tip,the stress level are above yield,because of which there are plastic deformations.My doubt is,what could be the useful parameter during modeling that would give a measure of plasticity?Hope you understand the question!


mounir_frija's picture

CORDIALEMENT MR MOUNIR FRIJA

CORDIALEMENT MR MOUNIR FRIJA CHERCHEUR EN DOCTORAT GENIE MECANIQUE LABORATOIRE DE GENIE MECANIQUE DE MONASTIR (SERST – LAB – MA – 05) ECOLE NATIONALE D'INGENIEURS DE MONASTIR AVENUE IBN ELJAZZAR 5019 MONASTIR TUNISIE Téléphone : (+216) 73 505 866 Mobil


strain rate control vs displacement control

Hi Margi

In real displacement control testing, to get the stress-strain curve for a particular material means your system strain rate should be less than 1x10^-4 s^-1. Below that material is assumed to be insensitive to the strain rate.

But at higher strain rate, one can get different stress-strain behavior, for example with higher strain rate loading one can achieve higher yield strength etc. Also, these properties varies with temperature also, with increasing temperature nornally these properties decreases, due to the sofetning of the material at higher temperature.

Hence, before performing finite element simulation it is very much important to know these things (strain rate dependent and temperature dependent materials properties) well in advance. And now the problem with the varification of results. If you are using strain rate higher than the above mentioned value than you should get different results. But you have to be careful while defining the materials properties in FEM, because you have to give the strain rate dependent properties otherwise you ll not be able to capture the realistic behavior.

Hope this ll help you.

regardS

Vijay Kumar Sutrakar


CDP model

Hi margi & everyone,

I am modeling a rc beam using abaqus. I have reached the ultimate load but my numerical sumulation curve doesnt matches with the experimental curve in the initial portion. I have attached an image of my load deflection curve. I have used concrete damaged plasticity model (using viscosity parameter 0.001, and also without viscosity parameter).if i usee viscosity parameter the ultimate load becomes almost double then if i dont use. can you suggest me anything regarding this problem?i used viscosity parameter blindly. concret properties used in this model are: f'c=37.655Mpa, E=27272Mpa e'c=.0022,

 i used compression damage and tension damage data also.

  

thanking you

SAJIB


load deflection curve link

http://imechanica.org/files/images/image%20L-D.preview.JPG


strain rate dependent

Hello everybody!!!!!!

I try to model the softening  of the masonry resistance in time.
For that I have tested the Cowper-Symonds law that exists in Abaqus. but I can not understand until now the effect of this law sometimes seems to me that it reduces déformations. sometimes affects the constraints (decrease or increase). how this law affect stress?????

thank you 


eng.femiran's picture

masonry modeling with shotcrete in abaqus