Hi!,
I am modeling a dent in a pipe using a compressive force distributed over a region of the external surface of the pipe. I use an elasto-plastic model with geometric nonlinearity, static analysis and C3D20R elements. I note that the value of the equivalent plastic strain PEEQ does not agree with the Von Mises stress value in the stress-strain curve of the material. That is, for the SVM stress shown in the figure (~90000 Psi), a PEEQ value of 0.26 must be showed, according to the stress-strain curve of the material. However, a value of 0.0357 appears. Is this correct? Could it be a convergence problem?
Thatās the full stress-strain curve but in CalculiX you have to input stress vs plastic strain data. Also, keep in mind that the values might be different due to extrapolation. To avoid that, you should check the integration point values in the .dat file (request them using *EL PRINT).
Figure 1. True stressāstrain curve for API 5L X52, X65, and X80 steel pipe [5,7,20].
Lo, M.; Karuppanan, S.; Ovinis, M. Failure Pressure Prediction of a Corroded Pipeline with Longitudinally Interacting Corrosion
Defects Subjected to Combined Loadings Using FEM and ANN. J. Mater. Sci. Eng. 2021, 9, 281. [CrossRef]
Belachew, C.T.; Ismail, M.C.; Karuppanan, S. Burst strength analysis of corroded pipelines by ļ¬nite element method. J. Appl. Sci.
2011, 11, 1845ā1850. [CrossRef]
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Thanks for your answer.
Yes. Indeed, plastic yield iniciated at stress values above of Sy witn peeq values not according with strain-stress curve value.
Yes I reviewed *dat file, but Indeed, plastic yield iniciated at stress values above of Sy witn peeq values not according with strain-stress curve value.
Second-order full integration elements are not recommended for problems involving large plastic strains (due to volumetric locking). You should use reduced integration elements instead.
Seems too much deviation to me. Do you ramp the load Āæright?
Could you post the full inp.?
Regarding geometry :
I always prefer to start with coarse parabolic elements with nodes on geometry, specially for circular shapes. In case I need to refine or move to linear nodes remain on top of geometry.
Iām thinking there is another option to consider.
Even if the model is a unique component all made of API 5L X52, one doesnāt necessarily need to define plasticity everywhere Āæisnāt it?.
Not sure if this may boost the analysis as NLGEOM will be activated anyway. ĀæWhat do you think?.
At least one would be freer to choose different element formulations far from yielding areas.
Thanks for your answers,
I managed to control the high stress levels quite a bit by using a complete model of the pipe instead of using symmetry conditions. I noticed that the high SVM values āānot related to PEEQ occurred in the symmetry plane (see figure in my first post) where the bending effects are most pronounced. However, Iām still not entirely convinced of the results.
Please tell me, how to attach the *INP file of the model (I donāt see options for this here).
If itās rather short, you can paste it here using the āPreformatted textā option. If itās not so short, upload it to some hosting website like Google Drive, Dropbox or WeTransfer and paste the link here.
