Hello STKO Team,
I am trying to model this IMK curve for joint spring rotations:
(I apologize in advance, I am working in US Units)
I have been able to use the Pinching4 model, but would really prefer to use one of the IMK options in STKO, however I am uncertain of which one to use, and in turn, each one has different notation associated as well, which is giving me results that vary vastly.
Could you help me determine which IMK model is the most suitable, and also show exactly how I would add the inputs? I want to make sure I fully understand how to make this exact same curve in STKO.
Thank you so much, this is something I have been feeling very confused on, and I greatly appreciate your help!
IMK Model
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Kate_Rhoades
- Posts: 29
- Joined: Mon Mar 06, 2023 4:04 pm
IMK Model
- Attachments
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- IMK Curve.JPG (85.48 KiB) Viewed 3041 times
Re: IMK Model
There are so many variations of this material... check this blog post by prof Scott:
https://portwooddigital.com/2019/12/08/ ... mk-models/
I think you should go with the "Mod" version. Even though he suggests the new ones IMKBilin, etc.. (but they don't have the documentation).
Try the "Mod" version for which you have a documentation. And let's see if you can fit your data. (ask here if you have doubts). Later you can try to move to the newest ones
https://portwooddigital.com/2019/12/08/ ... mk-models/
I think you should go with the "Mod" version. Even though he suggests the new ones IMKBilin, etc.. (but they don't have the documentation).
Try the "Mod" version for which you have a documentation. And let's see if you can fit your data. (ask here if you have doubts). Later you can try to move to the newest ones
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Kate_Rhoades
- Posts: 29
- Joined: Mon Mar 06, 2023 4:04 pm
Re: IMK Model
Thank you for the quick response!
I decided to go with the Mod IMK Peak Oriented model, and I have a lot of doubts about my inputs. I think there is something wrong with my stiffness, it should be very stiff at the beginning, and there should be a flat slope between My and Mcr, Mcr is 1.13*My. I'm just finding it to be very strange that in my model, the stresses are very high, and there is a sharp point instead of a flat curve like how I have in my original plot.
If you can provide and explain the proper inputs so my model matches my desired curve, I would be very grateful,
Many thanks
I decided to go with the Mod IMK Peak Oriented model, and I have a lot of doubts about my inputs. I think there is something wrong with my stiffness, it should be very stiff at the beginning, and there should be a flat slope between My and Mcr, Mcr is 1.13*My. I'm just finding it to be very strange that in my model, the stresses are very high, and there is a sharp point instead of a flat curve like how I have in my original plot.
If you can provide and explain the proper inputs so my model matches my desired curve, I would be very grateful,
Many thanks
- Attachments
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- ModIMK_Parameters.PNG (99.08 KiB) Viewed 3019 times
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- ModIMK.PNG (59.44 KiB) Viewed 3019 times
Re: IMK Model
- My_Neg should be negative
- The strain-hardening ratios are wrong (as_plus and as_Neg).
They are the ratio of the post-yield stiffness to the initial stiffness, not the ratio of My/Mcr = 1.13.
Knowing that the strength ratio (call it alpha) = 1.13- Mcr = alpha*My
- Kpost = (Mcr-My)/theta_p_Plus
- as_Plus = Kpost/K = My*(alpha-1)/(K*theta_p_Plus). In your case it is 0.004875
- imk.png (121.5 KiB) Viewed 3011 times
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Kate_Rhoades
- Posts: 29
- Joined: Mon Mar 06, 2023 4:04 pm
Re: IMK Model
Ohhh! This makes so much sense! Thank you so much for all of your help!