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] |
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] > > |
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] |
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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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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In reply to this post by chidu.G
Hello Chidu,
Have you found the solution to this problem? |
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