Machine precision error 1

[Mechanicslearner]

Hello,

I am trying to do tensile test using abaqus implicit analysis with time period 2. I need time increment less than 2 e-16 but abaqus keep on saying MACHINE PRECISION REQUIRES A TIME STEP GREATER THAN 2.22000E-16 how can I overcome this problem . Can anyone help? I even seen that when I delete the plastic strain values it works fine but when I enter it , it shows this error.

My yield stress Plastic strain
350 0
775 0.5
1200 1

I could not find palstic strain values in internet so just took this from example

 

[TGS4]

Why do you need a time step that small?

 

[Mechanicslearner]

Because it shows in the error that time increment needed is less than the minimum specified so I reduced and Am here now. I think it has something to do with plastic strain values

 

[Dave442]

Plot your results at the point where the analysis terminate. Do they make sense? Also, check the .msg file and figure out why the solver is cutting back and look at the problematic nodes. The error you mention can be indicative of any number of problems with your model.

Maybe post more details of your analysis?

 

[Mechanicslearner]

Hello,

I have attached the image for detail. my aim is to break the aluminium by tensile force where I put the lastic values in image too

 

[Mechanicslearner]

Sorry this is the error file

 

[Dave442]

(1) The model wont "break" unless you specify a damage model and associated parameters
(2) Double check your material constants.
(3) You have zero pivot warnings which suggest your model may not be adequately constrained.
(4) Your strain increment is so large at certain stages in the analysis that the solver has not attempted plasticity calculations.

I would review your material properties, boundary conditions and solution controls.

 

[IceBreakerSours]

To be honest, you need supervision. If you do not have expert supervision, then you should talk to your manager and start slow.

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[Mechanicslearner]

Dave thank you so much for replying a detail way of doing it.

 

[TGS4]

So, your analysis is stopping converging. Most typical analysts would set a limit of 1e-5 or 1e-6 and call it a day. Do you actually understand the physical processes that are being simulated numerically? Do you understand what's going on in the numerical simulation? Nobody EVER needs a time step that small for your toe of problem. Do you even fathom that 1e-16s is the time that it takes LIGHT to travel 3e-8m (300 Angstroms)? I second IceBreakerSours - you need some mentorship and adequate supervision.

 

[Dave442]

There are some good examples of how to set up quasi-static and dynamic analyses with ductile failure in the documentation:

Abaqus Example Problems Guide
Section 2.1.16 "Progressive failure analysis of thin-wall aluminium extrusion under quasi-static and dynamic loads"

As suggested above, get some help/supervision if you can. When a static analysis fails to converge, the solver will often suggest that the increment required is lower than the minimum specified. In most cases, this is indicative of problems elsewhere and simply dropping the increment size will not improve convergence.

 

[Mechanicslearner]

Hello,

I learned how to make it. Now the model works. Thanks for the help. Am still a student trying to learn abaqus for my research on my own, where my supervisor knows that and this website taught me a lot.

 

[IceBreakerSours]

a) Student postings are not allowed in these forums; check the FAQs.
b) One comes across way too many folks (in these forums) trying to swim across Nile when they barely know how to swim.
c) You should begin with the Getting Started Guide (Interactive) and Abaqus/CAE User's Guide. Take your time (two weeks or more, if that is what it takes). Learn the basics of linear analyses with linear elastic materials, small strains/rotations, and no contact - in a static analysis.

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