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Thermal non-linear behavior – Nastran SOL106

Thermal non-linear behavior – Nastran SOL106

Thermal non-linear behavior – Nastran SOL106

(OP)
I am trying to run a non-linear static analysis of a Titanium structure which is joined to an Inconel part. The main load contribution is the temperature increment from 20ºC to more than 600ºC.

I am using Nastran SOL 106 to take into account the non-linear behaviour of the materials with the temperature (MATT1) and I have also simulated contacts through CGAP elements, although their influence in the results is very small. Large displacements are turned off (LGDISP=-1).

The model converges and the FINAL results, with the 100% of the load, make sense. The problem is that in the intermediate steps the results have no sense, for example with the 5% of the load applied the stresses are much higher than with the total load applied. In fact, the stresses grow until the 45-60% and then they decrease…

When I leave only the thermal load, only temperature increment applied, the results are still more surprising for me: the maximum stress (absurdly high) appears in the first step and then they decrease linearly to a reasonable value with the 100% of the load.

Could anyone explain me this estrange behaviour? Am I doing something wrong? I would like to evaluate the results in the intermediate steps, now I have to create intermediate SUBCASEs to evaluate them in intermediate points.

See main parameters of the analysis below:

SOL 106
TIME 10000
CEND
$
DISPLACEMENT(SORT1,PLOT,REAL) = ALL
SPCFORCES(SORT1,PLOT,PRINT,REAL) = ALL
STRESS(SORT1,PLOT,REAL,VONMISES,CENTER) = ALL
FORCE(SORT1) = ALL
OLOAD(SORT1,PLOT,PRINT,REAL) = ALL
GPFORCE(PLOT) = ALL
$
NLPARM = 100
SPC = 3670101
TEMPERATURE(INITIAL)=110000
TEMPERATURE(LOAD)=100000
SUBCASE 1
SUBTITLE = Ultimate
LOAD = 10
$
$============================================================$
$ BULK DATA ENTRY $
$============================================================$
BEGIN BULK
$
TEMPD 110000 20.
TEMPD 100000 612.
$
INCLUDE 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXX.bdf'
$
$ LOADS
$
$ NON LINEAR PARAMETERS
$------><------><------><------><------><------><------><------><------>
NLPARM 100 20 ITER 1 20 PW YES
1.-3 1.-5 20
$
$Parameters
PARAM,AUTOSPC,NO
PARAM,BAILOUT,0
PARAM,GRDPNT,0
PARAM,MAXRATIO,1.E7
PARAM,K6ROT,1.
PARAM,SNORM,20.
PARAM,COUPMASS,1
PARAM,POST,-1
PARAM,NOCOMPS,-1
PARAM,PRTMAXIM,YES
$
ENDDATA


Thank you in advance

RE: Thermal non-linear behavior – Nastran SOL106

Try setting PARAM,LGDISP,1 to switch on geometric nonlinear effects. By default, LGDISP is set to -1 in SOL 106.

DG

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