Obtaining ultimate load using Riks method

[Dzonni]

Hello, everybody. I am using the Riks method in order to obtain the bending moment resistance of a beam. My material is aluminium, modeled as a continuous stress-strain curve (elastic and plastic properties). If i set a load value which is large enough, do i get a proportionality factor after the analysis, which i can use to multiply the load and to obtain the ultimate bending moment? If not, how can i, otherwise, go about this?

 

[StefCon]

Hi,
While running (and afterwards of course), you can open the .odb and check "LPF" in history output.

LPF
Load proportionality factor in a static Riks analysis.

.dat: no .fil: automatic .odb Field: no .odb History: automatic


Cheers!

 

[Dzonni]

Thank you for your answer, StefCon. I am wondering what if i assume the arc length wrong? For example, i did a buckling analysis, got the critical load factor, imported the imperfection into the next model, proceeded with Riks method (i have assumed arc length 1), but i get the LPF which is extremely low, and arc length is 2,7. Could that be the problem?

 

[StefCon]

I haven't read it myself but I do believe that arc length can be too large. A large arc length could "miss" your highest LPF if you dont sample enough.

Are you applying the full (or maximum) load in the riks step? If so, the arc length should be smaller (like 0.01), right?