Thermoelastic check problem 1

[pedrodmar]

Hi everybody,

I´m performing a thermoelastic check to a FEM with Patran/Nastran, that is formed just by shells, beams and MPCs. I have followed the rules to perform the analysis as are; same CTE, poisson´s coef. and Elastic modulus, as well as RBE2 with 0 length and no offsets, the structure is isostatically constrained as well.

The problem is that I have been asked for a stress lower than 100 Pa and I get 8Mpa, the stress spots are located in all the corners of the structure.

I don´t know what is going on, can anyone help me?

Thankyou very much in advance.
Pedro.

 

[StressFEA]

Hi Pedro,
Please ensure that FE model is with minimum possible constraints for thermal analysis.

Also what temperature load case you used? (Initial and Final temp.)

In case control section how initial temperature is specified?
ie Temperature (Initial) = 1 ... $(Suppose 1 is Initial temp load case Id)

 

[pedrodmar]

Hi StressFEA, nice kick

I have performed the analyisis constrained and unconstrained, and I get the same results, therefore I think that is not a constrain issue. Anyway the model is constrained just in one node which is joined to the structure by means of a MPC.

initial temperature: 20ºC
temperature: 120ºC

Regarding the definition for the loadcases, initial temp. is 5 and temp is 3. I copy the .bdf header heredown:

$ Direct Text Input for Nastran System Cell Section
$ Linear Static Analysis, Database
SOL 101
CEND
TITLE = THIS IS A DEFAULT SUBCASE.
ECHO = NONE
RIGID = LAGR
TEMPERATURE(INITIAL) = 5
SUBCASE 1
TITLE=THIS IS A DEFAULT SUBCASE.
SPC = 2
TEMPERATURE(LOAD) = 3
DISPLACEMENT(SORT1,REAL)=ALL
SPCFORCES(SORT1,REAL)=ALL
STRESS(SORT1,REAL,VONMISES,BILIN)=ALL
$ Direct Text Input for this Subcase
BEGIN BULK
PARAM POST 0
PARAM AUTOSPC NO
PARAM PRTMAXIM YES


thankyou very much for answering.

Pedro.