I'm trying to simulate a hollow tube compression. i followed your video on unpopular mechanics. however, for the Define Curve, you set for the Boundary Prescribed Motion Set 'VAD' = 2, which is for the displacement. in my case, im given a quasistatic case and my A1 and O1 input will be (0,0) and (280000,47.5), because 47.5/280000 will give me the predetermined velocity 0.00017m/s right? I'm compressing 50% of the length (total length=95mm) and I use material no. 24 picewise linear plasticity. i'm new to LS DYNA so i'm not sure what keyword to define for this kind of situation.
Question is, since my time taken to compress half the length is pretty huge (280000ms), what should i put as my d3plot and termination time as? if you need further details, i'll attach part of the question below and the result that i wish to achieve. Thank you for your time. My project report is due in 3 weeks really appreciate your help!
i attach the result that i wish to achieve here because i cant attach 2 files at once. have a good day thank you again kind sir!
First off, make sure your unit system is consistent. This is a bit of a hard concept to grasp as there are not settings to just define the unit system. You need to pick a unit system and then apply your boundary conditions using that system. Here's an example of a bunch of unit systems which are defined along the rows:
https://www.dynasupport.com/howtos/general/consistent-units
It's really important to check this because you can really mess up your results and they won't make sense. Regarding your first question though, yes, you should always use a time-displacement curve when simulating a controlled compression so that you can give a final compression value and then calculate how much time is required to get the desired deformation rate. Your curves look correct and yes your termination time is 280000ms. Your d3plot frequency is only the frame-rate of the animation so you don't need too many. Maybe say that you want 100 frames: 280000ms/100=2800ms which would be your d3plot frequency.
LS-Dyna has two forms of analysis: explicit and implicit. Explicit is the standard form and is meant for crash analysis and simulation under 1-2 seconds (1000-2000ms), where as implicit is meant for much longer simulations like your case. That's what the problem in the picture is meaning when it says Implicit is required for this problem. There are some specific control cards that you will need to run implicit, which will depend on the simulation. Is there a contact that you defined between the plate and the tube? Or are you prescribing motion to the top of the tube? Contacts within implicit are much more unstable so there are some precautions to take if you have any. I would start with this link below and you can ask questions as you go. General rule is to start with the minimum required cards and get more complicated if it isn't working for you. Good luck!
https://www.dynasupport.com/howtos/implicit/implicit-checklist
I appreciate your fast and informative response. im okay with the unit system already. i think i got that covered after few days with LS DYNA and few youtube videos. But im just wondering if termination time of 280000ms is normal for implicit quasistatic case? or is that a lot? Okay i'll try putting my d3plot as 2800ms. But as for the ASCII options that i ticked, in your video (hollow cylinder compression video), you set the value that you ticked to 0.5. In my case, should i set it to 2800 as well? I'll attach below the simulation ive done so far for a square hollow tube crushed by a rigid wall. However, i set my displacement curve value to (0,0) and (47.5,47.5) instead of (0,0) (280000, 47.5) because i wanted to see if my simulation works within only few mins of waiting.
can i have your email address? to send you my k file for the square hollow tube compression. i cant attach that kind of file here. btw, Thank you again i really appreciate all this! i only have 2 weeks before submission r.i.p