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Creep Data Generation...

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Creep Data Generation...

chidu.G
 Hi all,
 
 I have a problem on creep which has to be solved in ABAQUS. The input we have for the analysis is a graph of creep strain Vs time.
 
 As I have seen, for the creep analysis in abaqus we need to pass
the parameter like "A","m" and "n". in LAW=STRAIN.
 
i would like to know how to generate these material parameters from the creep starin v/s time curve.
  looking for help.
 

  thanks in advance

   Regards
 Chidu.G


       
---------------------------------
 Bollywood, fun, friendship, sports and more. You name it,  we have it.

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Re: Creep Data Generation...

Dave Lindeman
Integrate the creep strain rate equations so that you have an expression
for creep strain vs. time.  Program these equations into Excel and plot
the calculate creep strain curves vs. the experimental curves.  Play
with the constants until you get reasonable agreement.

Regards,

Dave

-------------------------
Dave Lindeman
Lead Research Specialist
3M Company
3M Center 235-3F-08
St. Paul, MN 55144
651-733-6383


chidu.G wrote:

>
>
> Hi all,
>
> I have a problem on creep which has to be solved in ABAQUS. The input we
> have for the analysis is a graph of creep strain Vs time.
>
> As I have seen, for the creep analysis in abaqus we need to pass
> the parameter like "A","m" and "n". in LAW=STRAIN.
>
> i would like to know how to generate these material parameters from the
> creep starin v/s time curve.
> looking for help.
>
>
> thanks in advance
>
> Regards
> Chidu.G
>
> ---------------------------------
> Bollywood, fun, friendship, sports and more. You name it, we have it.
>
> [Non-text portions of this message have been removed]
>
>
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Re: Creep Data Generation...

Merdan Basaran
i find it very bad too. With excel sheet it is not easy to fit these curves.
At least i could not do it before excatly with excel.
Merdan


2007/7/30, Dave Lindeman <[hidden email]>:

>
>   Integrate the creep strain rate equations so that you have an expression
>
> for creep strain vs. time. Program these equations into Excel and plot
> the calculate creep strain curves vs. the experimental curves. Play
> with the constants until you get reasonable agreement.
>
> Regards,
>
> Dave
>
> -------------------------
> Dave Lindeman
> Lead Research Specialist
> 3M Company
> 3M Center 235-3F-08
> St. Paul, MN 55144
> 651-733-6383
>
> chidu.G wrote:
> >
> >
> > Hi all,
> >
> > I have a problem on creep which has to be solved in ABAQUS. The input we
>
> > have for the analysis is a graph of creep strain Vs time.
> >
> > As I have seen, for the creep analysis in abaqus we need to pass
> > the parameter like "A","m" and "n". in LAW=STRAIN.
> >
> > i would like to know how to generate these material parameters from the
> > creep starin v/s time curve.
> > looking for help.
> >
> >
> > thanks in advance
> >
> > Regards
> > Chidu.G
> >
> > ---------------------------------
> > Bollywood, fun, friendship, sports and more. You name it, we have it.
> >
> > [Non-text portions of this message have been removed]
> >
> >
>
>


[Non-text portions of this message have been removed]

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Re: Creep Data Generation...

Dave Lindeman
You'll almost never get an exact fit because real materials don't behave
in exactly the way the creep rate equations imply they should.  You can
always use the CREEP subroutine if you're not happy with available
models.  Also, you can use an optimization code (e.g., DAKOTA or MATLAB)
to derive the best-fit constants (more work than it's worth I usually
find).  Finally, you'll likely see plenty of variation in the measured
creep curves if you perform multiple tests or tests on multiple
specimens.  There's no use fretting over curve fitting errors when the
intrinsic material properties show variation (but remember to err on the
conservative side).

Regards,

Dave

-------------------------
Dave Lindeman
Lead Research Specialist
3M Company
3M Center 235-3F-08
St. Paul, MN 55144
651-733-6383


Merdan Basaran wrote:

>
>
> i find it very bad too. With excel sheet it is not easy to fit these curves.
> At least i could not do it before excatly with excel.
> Merdan
>
> 2007/7/30, Dave Lindeman <[hidden email] <mailto:ddlindeman%40mmm.com>>:
>  >
>  > Integrate the creep strain rate equations so that you have an expression
>  >
>  > for creep strain vs. time. Program these equations into Excel and plot
>  > the calculate creep strain curves vs. the experimental curves. Play
>  > with the constants until you get reasonable agreement.
>  >
>  > Regards,
>  >
>  > Dave
>  >
>  > -------------------------
>  > Dave Lindeman
>  > Lead Research Specialist
>  > 3M Company
>  > 3M Center 235-3F-08
>  > St. Paul, MN 55144
>  > 651-733-6383
>  >
>  > chidu.G wrote:
>  > >
>  > >
>  > > Hi all,
>  > >
>  > > I have a problem on creep which has to be solved in ABAQUS. The
> input we
>  >
>  > > have for the analysis is a graph of creep strain Vs time.
>  > >
>  > > As I have seen, for the creep analysis in abaqus we need to pass
>  > > the parameter like "A","m" and "n". in LAW=STRAIN.
>  > >
>  > > i would like to know how to generate these material parameters from the
>  > > creep starin v/s time curve.
>  > > looking for help.
>  > >
>  > >
>  > > thanks in advance
>  > >
>  > > Regards
>  > > Chidu.G
>  > >
>  > > ---------------------------------
>  > > Bollywood, fun, friendship, sports and more. You name it, we have it.
>  > >
>  > > [Non-text portions of this message have been removed]
>  > >
>  > >
>  >
>  >
>
> [Non-text portions of this message have been removed]
>
>
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Re: Creep Data Generation...

EricL
This post has NOT been accepted by the mailing list yet.
I have a similar problem: I have experimental data (engineering strain vs. time) for uniaxial creep test that I have used for fitting. Then I want to do a validation in Abaqus by modeling the same geometry and load, using the fitted parameters. Even though I get the same initial stress (uniaxial --> principal stress = eq. stress), the strain vs. time curve is much steeper.

Even when using the true stress-corrected curve for model fitting (assumed that transverse strain ratio is 0.5, no clue if that is applicable in any case) I donĀ“t get the same result from my simulation than from my model fitting equation.

I should say that I use a strain rate equation for fitting, as Abaqus uses the strain rate as basis for calculation ("DECRA").
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