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Simufact material database for Inconel 718 powder

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I have few questions about the Simufact material database for Inconel 718 powder, when looking into the flow curves all I could see is the data for the plastic region, I would like to know why the Simufact didn't consider the elastic region. Also in the mechanical properties what is the input for elastic modulus for this material because am not able to find it, did you consider infinite elastic modulus? if yes, could you please explain.
 
Kindly look in to the below plot I got from a simple compression test showing true stress and true strain for IN718 powder at 20C .
In718
Could you please explain why the Simufact database doesn't have any elastic region data.
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    Flow cures do not include the elastic region. Flow curves describe the stress needed to transition from the elastic to the plastic deformation: Once the stress reaches the flow stress, the elastic deformation stops and the plastic deformation starts. That is the theory about the math we are using.
     
    Thus, if you have experimental data, you need to remove the elastic part to get a flow curve out of it.
     
    The mechanical properties in the Simufact Material database include the Youngs moduls = elastic modulus for the elastic behavior. Generally we consider elastic-plastic material behavior, but you can simplify and use rigid-plastic, too, thus an infinite elastic modulus. But typically you do not win much with this.
     
    In the simulation result (of a compression test) you should get a force-deflection curve (from the THS plot) containing both, elastic and plastic deformation, like the experiment.
     
    Regarding "powder" materials in our database, please consider: The category Powder doesn’tmean that the data are powder properties,but the properties of the bulk material that is the result of the additive PBF manufacturing. See the relevant section of the Simufact Additive Tutorial.
     
    Sintering properties for MBJ are different again. This is not plasticity any more.
     
  • 0
    Okay, thankyou. The formula you gave in the other post to maintain constant strain seems like its not working. could you please verify what should be the velocity of the hydraulic press for a sample of height 25.4mm to maintain a strain rate 0.01 through out the compression test. I tried 0.229829 but looks like its not working am not getting a uniform flow stress when looking in to the contour plots with this value. what should be the time we need to consider in this formula? velocity= initial_height*phip*exp(-phip*time) with phip being the desired strain rate.
     
  • 0
     
    The formula is correct. It is used to define a table driven press using a time velocity profile. Thus time is not constant but starts at 0 and ranges until the end of the process, in your example after may be 60 sec and a stroke of roughly 11.5 mm. The initial velocity will be 0.254 mm/s decreasing non-linearly to 0.1394 mm/s after 60 sec.
     
    Use the formula in a spreadsheet program of your choice, calculate a time series and export it into a cvs file. Import it into the press in Simufact Forming. I am attaching an example cvs file valid only for 25.4 mm initial height. After the import, the press will look like this:
    grafik
    In the simulation result, the effective plastic strain will be uniform over the workpiece, but increasing with time. The effective plastic strain rate will be uniform and constant.
    Attached Files (1)
  • 0
    Hello Christian,
     
    I was doing the test based on table driven press and I still see my contour plots are not uniform. could you please help me if am doing something wrong? is there something to do with the stroke since we are using the velocity/time based press how to decide the stroke length?
     
     
  • 0
    Hi,
    the result should look like in the attached video (it is axial symmetric, not expanded, but showing just the "half plane" used for the simulation).
     
    Is your shape (cross section) staying rectangular? If you get a round shape at the OD, there is an issue in the friction, and the theory of the test model does not work. Compare with the model I provided in the forum and per e-mail.
     
    Check the scale used for the result display. It needs to have a reasonable range. There will always be some small numerical spread in the result. Some times the automated scale of the legend takes this as range. You see some thing non-uniform, but all values are between 0.0099999999 and 0.0100000001.
     
    If a time velocity press is defined, the stroke will follow from this definition. The stroke = the moving distance is the integral of the velocity. If the velocity is not linear the only trick is to find the correct end time of the press.
     
    I hope this helps, if not you may want to send your model to support@simufact.de mentioning this chat and my name and I will check what causes the non-uniformity in your results.
    Attached Files (1)
  • 0
    Note: The model is a theoretical test model to check the relation between strain, equivalent stress, flow curve, strain rate and (fixed) temperature. The objective is to have a uniform one-directional stress-strain state. Because of this it is friction free. Thus it is not the simulation of a real compression test.
  • 0
    Hello Christian,
     
    I did try to check your model which you have send me via email but I couldn't open it even after installing 2023.4 Simufact version. I have emailed my model as mentioned please verify and let me know what mistakes am making.
     
    Thanks.
  • 0
    Hello Christian,
     
    I have sent you the model through the link you provided. Please have a look into it and let me know what's wrong.
     
    Thanks.
  • 0
    Hello,
    you need to deactivate the thermal effects in the Forming Control \↨ Advanced \ Miscellaneous. Even with the part changing the temperature only by 7°C, this is enough to lead to an uneven distribution. Rerun the simulation with different temperatures if needed.
     
    The plastic deformation generates heat while heat flows from the workpiece to the environment and into the dies.
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