# Von Mises vs PEEQ **URL:** \ **Category:** Uncategorized\ **Created:** [October 4, 2023, 3:04am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855 "2023-10-04T03:04:57Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 3:04am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/1 "2023-10-04T03:04:57Z")
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? Thanks in advance, Jack ![Captura desde 2023-10-03 22-04-21](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/7/71b884a12b42d81f23cb1fd65eb6c3cf66b74cfc.jpeg) ---
**Author:** ![rsmith](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/rsmith/32/1684_2.png) [@rsmith](https://calculix.discourse.group/u/rsmith)\ **Post date:** [October 4, 2023, 6:12am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/2 "2023-10-04T06:12:37Z")
> [@Juseche](#): > > Is this correct? Loooking at the manual, it says: > PEEQ [PE]: equivalent **plastic** strain. That suggests it does not include the elastic strain. Try looking at ME instead. ---
**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\ **Post date:** [October 4, 2023, 7:02am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/3 "2023-10-04T07:02:15Z")
That’s 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). ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [October 4, 2023, 10:25am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/4 "2023-10-04T10:25:02Z")
Hi Juseche, ¿ Would you mind sharing the source of those stress-strain values shown on your curve for API 5L X52 ? This is why I ask. there are different sources out there. ![screenshot.6](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/d/dcdb516e4679c663daa9e6cfa69c28f3992e70cc.jpeg) Figure 1. True stress–strain curve for API 5L X52, X65, and X80 steel pipe [5,7,20]. 1. 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] 2. Belachew, C.T.; Ismail, M.C.; Karuppanan, S. Burst strength analysis of corroded pipelines by finite element method. J. Appl. Sci. 2011, 11, 1845–1850. [CrossRef] 3. de Andrade, E.Q.; Benjamin, A.C.; Machado, P.R., Jr.; Pereira, L.C.; Jacob, B.P.; Carneiro, E.G.; Guerreiro, J.N.; Silva, R.C.; Noronha, D.B., Jr. Finite element modeling of the failure behavior of pipelines containing interacting corrosion defects. In Proceedings of the 25th International Conference on Offshore Mechanics and Arctic Engineering—OMAE, Hamburg, Germany, 4–9 June 2006; pp. 315–325. [CrossRef] Thanks ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 2:49pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/7 "2023-10-04T14:49:33Z")
MPC model of API-579-2021. Here (I’m using ccx2.13): \*\* material definition \*MATERIAL, name=mat \*ELASTIC 2.940000e+07,0.260000,0 \*PLASTIC,HARDENING=ISOTROPIC 52000,0.000,0 54876,0.018,0 57751,0.036,0 60627,0.053,0 63502,0.071,0 66378,0.089,0 69253,0.107,0 72129,0.124,0 75004,0.142,0 77880,0.160,0 \*SOLID SECTION, ELSET=Eall, MATERIAL=mat \*\* Thanks Jack. ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 2:52pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/8 "2023-10-04T14:52:24Z")
in this table real stress (PSI) and real strain (in/in). \*STEP, NLGEOM,INC=10000 \*STATIC 0.000010,2.000000,1.000000e-08,0.010000 Jack. ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 3:20pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/9 "2023-10-04T15:20:59Z")
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. Jairo ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 3:22pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/10 "2023-10-04T15:22:56Z")
Thanks for your answer. 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. Jack ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 3:23pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/11 "2023-10-04T15:23:35Z")
Yes. Indeed, plastic yield iniciated at stress values above of Sy with peeq values not according with strain-stress curve value. Jairo ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [October 4, 2023, 4:52pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/12 "2023-10-04T16:52:00Z")
It works fine to me. Have you tried with ccx v2.21? ¿Could you temporarily remove the temperature dependency from the curve?. ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/1/1686faa9988b39d0a483b105e064f0001f9d6832.png) ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 4, 2023, 11:49pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/13 "2023-10-04T23:49:36Z")
I see. Could be a problem related with time step? Which element, among c3d20 and c3d20 with full o reduced integration, works better for finite plasticity with large displacement problems? Any recomendation about meshing with c3d20 and c3d20? I’m have a problem installing ccx 2.21 in Ubuntu \>20.04, because libgfortran4.so is not available. What can I do? Thanks for your help! ---
**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\ **Post date:** [October 5, 2023, 7:02am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/14 "2023-10-05T07:02:40Z")
> [@Juseche](#): > > Which element, among c3d20 and c3d20 with full o reduced integration, works better for finite plasticity with large displacement problems? 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. ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [October 5, 2023, 7:14am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/15 "2023-10-05T07:14:10Z")
> [@Juseche](#): > > Could be a problem related with time step? Seems too much deviation to me. Do you ramp the load ¿right? Could you post the full inp.? > [@Juseche](#): > > Any recomendation about meshing 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. Regarding element performance > [@Elasto-plastic bending - elements, accuracy](https://calculix.discourse.group/t/elasto-plastic-bending-elements-accuracy/700/12): > > hi, beam & shell element are expanding to solid element in CalculiX during calculation. bellow are an explanation i extracted from official documents, may apply to beam element also. Shell element S4 expanded to solid C3D8I: cannot be used in \*DYNAMIC calculations, has controlled hourglassing, (ed. still questionable for one layers only) Shell element S4R expanded to solid C3D8R: small elements are required to capture a stress concentration at the boundary of a structure,. massive hourglassi… ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [October 5, 2023, 11:42am UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/16 "2023-10-05T11:42:26Z")
I’m thinking there is another option to consider. Even if the model is a unique component all made of API 5L X52, one doesn’t necessarily need to define plasticity everywhere ¿isn’t it?. Not sure if this may boost the analysis as NLGEOM will be activated anyway. ¿What do you think?. At least one would be freer to choose different element formulations far from yielding areas. ---
**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\ **Post date:** [October 5, 2023, 12:14pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/17 "2023-10-05T12:14:02Z")
I think that I wouldn’t risk this approach since, apart from local yielding, there’s also global stress redistribution due to plasticity. ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [October 5, 2023, 12:42pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/18 "2023-10-05T12:42:49Z")
But there is no plasticity below the yield point. Outside the yield area (being conservative when defining it) material could be defined as linear elastic. ¿isn’t it?. With one final check on VM to see if the assumption was correct. I’m considering the paper [JMSE | Free Full-Text | Empirical Failure Pressure Prediction Equations for Pipelines with Longitudinal Interacting Corrosion Defects Based on Artificial Neural Network](https://www.mdpi.com/2077-1312/10/6/764) as example .It might be similar to Juseche problem. ![imagen](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/2/26c2534480a1ac0aa2441101b9776852cbdbdc7e.png) In that case there is no need to define plasticity everywhere. The yield area is well defined arround the defect. ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 5, 2023, 4:15pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/19 "2023-10-05T16:15:26Z")
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 ​​not related to PEEQ occurred in the symmetry plane (see figure in my first post) where the bending effects are most pronounced. However, I’m still not entirely convinced of the results. Please tell me, how to attach the \*INP file of the model (I don’t see options for this here). Regards Jack ---
**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\ **Post date:** [October 5, 2023, 4:36pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/20 "2023-10-05T16:36:33Z")
> [@Juseche](#): > > Please tell me, how to attach the \*INP file of the model (I don’t see options for this here). If it’s rather short, you can paste it here using the “Preformatted text” option. If it’s not so short, upload it to some hosting website like Google Drive, Dropbox or WeTransfer and paste the link here. ---
**Author:** ![Juseche](https://avatars.discourse-cdn.com/v4/letter/j/258eb7/32.png) [@Juseche](https://calculix.discourse.group/u/Juseche)\ **Post date:** [October 5, 2023, 5:05pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/22 "2023-10-05T17:05:39Z")
Here: > **[Google Drive: Sign-in](https://accounts.google.com/v3/signin/identifier?continue=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F1ISGmnm63i-pTVsGhoH_46k_A0UZEcm-i%2Fview%3Fusp%3Ddrive_link&followup=https%3A%2F%2Fdrive.google.com%2Ffile%2Fd%2F1ISGmnm63i-pTVsGhoH_46k_A0UZEcm-i%2Fview%3Fusp%3Ddrive_link&ifkv=AYZoVhfh4Z_Xmd8j37_ImwR7hIprAL8gtS3FSdRBCniIPbvOZ6Pb2KuxrVpKeEPBGB9iJD1pEYIlFw&osid=1&passive=1209600&service=wise&flowName=GlifWebSignIn&flowEntry=ServiceLogin&dsh=S-184215126%3A1696525515392191&theme=glif)** > > Access Google Drive with a Google account (for personal use) or Google Workspace account (for business use). Thanks Jack ---
**Author:** ![Disla](https://yyz2.discourse-cdn.com/free1/user_avatar/calculix.discourse.group/disla/32/3548_2.png) [@Disla](https://calculix.discourse.group/u/Disla)\ **Post date:** [October 5, 2023, 5:15pm UTC](https://calculix.discourse.group/t/von-mises-vs-peeq/1855/23 "2023-10-05T17:15:02Z")
I don’t use google drive. Could you post it via we-transfer [Next page](https://calculix.discourse.group/t/von-mises-vs-peeq/1855.md?page=2)