TABLES1 limited number of stress/strain entries for SOL 401 Using FEMAP 24.06

[EKCP]

Is there a firm number of allowable entries for a Stress-Strain curve when defining a material for plasticity?

I created a function with 10 entries and my model continues to fail giving the FATAL message below. A review of the QRG and everything looks OK so I experimented by deleting entries from the function. At 6 entries on the stress-strain curve the model runs just fine. I experimented with the magnitudes of the entries as well and, in all cases, the model solved provided I have no more than 6 entries.

This is just a simplified test model without consequence, but what if I needed more stress strain entries that 6? Am I simply missing the obvious?

Thank you!



*** USER FATAL MESSAGE 316 (IFPDRV)
ILLEGAL DATA ON BULK DATA ENTRY TABLES1
User information:
See Bulk Data entry description in Section 5 of the NASTRAN
Quick Reference Guide. If you are using the large field format make
sure the number of entries is even.
TABLES1 1 +0000004
+0000004 0. 0. .0033 28950. .0055 30400. .00606 31000.+0000005
+0000005 .02 33950. .03 35100. .03 35100. .04 36710.+0000006
+0000006 .05 37600. .06 38300.ENDT



$COM 0 24.2 5052-H36 AMS-QQ-A-250/8 0.006" - 0.162" Plasticicty Updated
-1
420
2,13,
5052-H36 AMS-QQ-A-250/8 0.006" - 0.162" Plasticicty
1,0.,0.,
2,0.0033,28950.,
3,0.0055,30400.,
4,0.00606,31000.,
5,0.02,33950.,
6,0.03,35100.,
7,0.03,35100.,
8,0.04,36710.,
9,0.05,37600.,
10,0.06,38300.,
-1,0.,0.,
-1

 

[sdm919]

I am not aware of limitation of number of points in the table.

Your points 6 and 7 seem to be the same point: 0.03 strain, 35100 stress. That may be the problem.

 

[EKCP]

Good catch! That was it. I guess I looked at it so long I just couldn't see it. Thank you!

 

[sdm919]

No problem.

By the way, the when I plot the data in Excel, it looks a little "bumpy" to me. I don't think anything is technically wrong, but jobs might behave better if the curve is smoother. I assume the slope for aluminum alloys would be decreasing all the time, whereas this curve has a slope increase between points 3 & 4 and a smaller bump between 7 & 8. Not necessarily a problem, just an observation. Generally speaking, the slope be never be zero or negative.

Good luck!

 

[rb1957]

maybe plot slope along with the data ? and keep slope values monotonic decreasing.

 

[EKCP]

A few observations from this exercise:

1. If you are doing "quick n' dirty" don't use SOL401
2. I initially missed the magnified portion of the stress-strain curve and re-plotted points accordingly. Much better and more smooth curve
3. Had to modify my table in the linear portion of the curve to delete some points. Looks like my 0.7mm lead and strained eyes caused enough variation to confuse NASTRAN (see below). FEMAP window shows the final version deleting some of the points.

Good comments and observations. Thank you for the help!


*** USER FATAL MESSAGE 23231 (SAMDB)
INTERNAL ERROR IN SAMDB WHEN CALLING ROUTINE utnasmatc
RETURN CODE 906
FURTHER INFORMATION MAY BE FOUND IN .DBG FILE.


DBG file showed the following:


%%%E03-OVCAU7: the input hardening curve shows a decreasing value of strain
when converted to PLSTRN. Please check that the provided curve
is correctly defined.
Error occurred for point: 2
Try removing or modifying this data point.
(The points might be too close to each other)

Original curve: Converted curve:
STRAIN STRESS STRAIN STRESS
0.00000000 0.000000 0.00000000E+00 22417.433280
0.00221000 22368.000000 -0.29513896E-04 24135.585650
0.00235000 24079.000000 0.23472431E-02 24135.585650

 

[rb1957]

1) It's complaining about plane strain work hardening. Have you plotted your curve as plain strain ?

2) it notes "maybe points too close to each other" ... reduce the number of points, just to get it to run ?

3) between 0.02 and 0.03 delta stress = 1150, between 0.03 and 0.04 = 1610, between 0.04 and 0.05 = 890 ... is that an issue ? plot slope and check monotonic decreasing.
between 0.003 and 0.004 delta stress = 1908, between 0.004 and 0.005 = 921 ... ?