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Re: [lammps-users] How to calculate: J-integral, strain energy release rate, and crack size?
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Re: [lammps-users] How to calculate: J-integral, strain energy release rate, and crack size?


From: Steve Plimpton <sjplimp@...24...>
Date: Thu, 6 Jul 2017 08:11:48 -0600

The LAMMPS potential energy is simply
whatever the pair style you define computes for
the interactions of all the atoms with each other.

The crack length is something that it is easy
to look at a visual snapshot (at least in 2d) and
say, there's the crack, it's this long.  But automating
that to have LAMMPS compute it for you is non-trivial.
How would you compute it, if all you had was a dump
snapshot of atom coords?

Steve

On Wed, Jul 5, 2017 at 1:33 PM, Mohammad Reza Zamani Kouhpanji <mrzamani@...5933...> wrote:

Thanks Steve and Luis for the response.


Let me please rephrase my question. The strain energy release rate (SER) is differential of total energy (U+K-W) with respect to the crack length (SER=d(U+K-W)/dl). Where, U is the total strain energy due to mechanical deformations (also named potential energy); K is the total kinetic energy; W is the total work of the external work; and l is the crack length. I'm somehow familiar how to calculate the U and K but I don't know how to calculate the W as well as the crack length. Furthermore, I am not what is the potential energy that the LAMMPS calculates by 'compute all pe' command. Is it the potential due to the mechanical deformations or the potential due to the charges?


Luis,

Thanks for the file. Now J-integral calculation makes sense to me. Thanks.


Thanks everyone.


Sincerely,

Zamani.

-----------------------------------------------------------------

Graduate Student

Electrical Engineering Department,

And Mechanical Engineering Department,

Research Assistant in

Center for High Technology Materials (CHTM), Albuquerque, USA.

Nanomanufacturing Systems for mobile Computing and Energy Technologies (NASCENT), Austin, USA.

University of New Mexico (UNM), Albuquerque, USA.

Tel.: (618)-305-9636

Skype: mrzk86

Email: mrzamani@...5933...


From: Steve Plimpton <sjplimp@...24...>
Sent: Tuesday, July 4, 2017 5:32:53 PM
To: Axel Kohlmeyer
Cc: Mohammad Reza Zamani Kouhpanji; lammps-users@...396...sourceforge.net
Subject: Re: [lammps-users] How to calculate: J-integral, strain energy release rate, and crack size?
 
All of the quantities you are asking about
are complicated values, depending on things
like surface area of a crack, etc.  LAMMPS
will dump snapshots as often as you wish.
If you can figure out how to compute the
values you want from a snapshot of atom
positions, that is the first step.  Then
you might figure out how to get LAMMPS
to do portions of the calculation for you,
but likely you would have to add new options
to LAMMPS to compute the values you
are asking about.

Steve

On Tue, Jul 4, 2017 at 9:52 AM, Axel Kohlmeyer <akohlmey@...29....> wrote:
On Tue, Jul 4, 2017 at 12:13 AM, Mohammad Reza Zamani Kouhpanji
<mrzamani@...5926...33...> wrote:
> Hello Everyone,
>
>
> I am a beginner using the LAMMPS for modeling crack propagation in 2D
> materials. In my simulation, I would like to calculate the J-integral, the
> crack size, and the strain energy release rate at each time step. I
> developed an input file which is mainly similar to the crack example of the
> LAMMPS. I will be so thankful if someone help me with the following
> questions:
>
>
> 1- How can I calculate the j-integral at each time step using the LAMMPS?
>
> 2- How can I calculate the strain energy release rate at each step using the
> LAMMPS?
>
> Note, as you may know, the strain energy release rate is the amount of
> energy dissipated during fracture per unit of newly created fracture surface
> area.
>
> 3- What is the best technique to accurately find the crack size? Does the
> LAMMPS calculate it (if yes, please let me know the command)? or Do I need
> to visualize the simulation results in a visualization software and then
> find the crack size?
>
>
> I looked in the LAMMPS' manual and some web searches. I saw some partial
> answers for my questions which are not clear for me at all. Unfortunately,
> because I am a new user, I cannot implement them as well. I really
> appreciate it if someone, please, writes and explains the command lines that
> I need to add into my input file for calculating those three parameters.

as a new user, you should not start with your research problem, but
need to learn how to perform basic simulations with LAMMPS first.
nobody is likely to do what you are asking for, as that is essentially
doing *your* work for *and* giving you a customized personal tutorial.
if you are unsure about how to do your research, please discuss with
your adviser, as that is the job of your adviser to advise you on
doing your research.

if you have specific questions to specific commands or how they are
implemented and so on, people are happy to help.
the fact that you are new to LAMMPS is no reason why you should be
entitled to get your work done by somebody else. you need to learn the
tools of the trade just like everybody else has. this doesn't happen
over night and this only works in steps.

axel.

>
>
> Thank you so much in advance.
>
>
> Sincerely,
>
> Zamani.
>
> -----------------------------------------------------------------
>
> Graduate Student
>
> Electrical Engineering Department,
>
> And Mechanical Engineering Department,
>
> Research Assistant in
>
> Center for High Technology Materials (CHTM), Albuquerque, USA.
>
> Nanomanufacturing Systems for mobile Computing and Energy Technologies
> (NASCENT), Austin, USA.
>
> University of New Mexico (UNM), Albuquerque, USA.
>
> Tel.: (618)-305-9636
>
> Skype: mrzk86
>
> Email: mrzamani@...5933...
>
>
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> lammps-users mailing list
> lammps-users@...655....net
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>



--
Dr. Axel Kohlmeyer  akohlmey@...24...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.

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