CTRIA3 engineering force for thermal stress is wrong

[victorkemp]

The square has uniform positive temperature change and is constrained in y but free in x. Displacement is qualitatively correct with expansion in x.

Element 2 should have compressive (negative) force in the element y direction (also basic y) and zero in the x direction, but it's positive in both of them. Happens in 15.1.1 and 15.2 and for CTRIA3 and CTRIA3K.

Output

                 Element         N o r m a l   F o r c e s                       M o m e n t s                   T r a n s v e r s e
                    ID                                                                                         S h e a r   F o r c e s
                              Nxx           Nyy           Nxy           Mxx           Myy           Mxy            Qx           Qy
                       1  7.500000E+05  3.750000E+06 -1.734723E-10  0.000000E+00  0.000000E+00  0.000000E+00  0.000000E+00  0.000000E+00
                       2  3.750000E+06  7.500000E+05  0.000000E+00  0.000000E+00  0.000000E+00  0.000000E+00  0.000000E+00  0.000000E+00

Input

SOL 101
CEND
DISPLACEMENT = ALL
FORCE = ALL
SPC = 1
TEMPERATURE = 1
BEGIN BULK
GRID*                  1               0              0.              0.*       
*                     0.               0
GRID*                  2               0             0.1             0.1*       
*                     0.               0
GRID*                  3               0             0.1              0.*       
*                     0.               0
GRID*                  4               0              0.             0.1*       
*                     0.               0
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Material $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
MAT1*                  1           5.+10                              0.*       
*                     0.          0.0006            400.
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
SPC*                   1               1               1              0.*       
*                                                                       
SPC*                   1               1               2              0.*       
*                                                                       
SPC*                   1               1               3              0.*       
*                                                                       
SPC*                   1               2               3              0.*       
*                                                                       
SPC*                   1               2               2              0.*       
*                                                                       
SPC*                   1               3               3              0.*       
*                                                                       
SPC*                   1               3               2              0.*       
*                                                                       
SPC*                   1               4               3              0.*       
*                                                                       
SPC*                   1               4               2              0.*       
*                                                                       
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ Default $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
PSHELL*                1               1           0.001               1*       
*                                      1                              0.
CTRIA3*                1               1               3               2*       
*                      4              0.              0.
CTRIA3*                2               1               1               3*       
*                      4              0.              0.
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ temperature $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
TEMP*                  1               3            500.                *       
*                                                                       
TEMP*                  1               2            500.                *       
*                                                                       
TEMP*                  1               4            500.                *       
*                                                                       
TEMP*                  1               1            500.                *       
*                                                                       
TEMP*                  1               3            500.                *       
*                                                                       
TEMP*                  1               4            500.                *       
*                                                                       
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
TEMPD*                 1            400.                                *       
*                                                                       
$--1---><------2-------><------3-------><------4-------><------5-------><--6--->
ENDDATA