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Queries regarding post buckling analysis in ANSYS 13

Queries regarding post buckling analysis in ANSYS 13

Queries regarding post buckling analysis in ANSYS 13

(OP)
Right now i have been using ansys to study the post buckling behavior of a composite plate. I have been facing problems while studying the post buckling behavior.
These are the following steps that I had followed to study the behavior;
1. I am using Shell181 element for the analysis.Predicted Eigen values and Eigen mode shapes using Linear Eigen buckling Analysis  ( Block Lanczos method).
2. The Geometry had been updated by imposing a imperfection using a scaling factor of 0.2% of the first mode shape.( Main Menu/Preprocessor/Modeling/Update Geom)
3. As the linear analysis predicted the Buckling load to be at 30000N/m, I decided to perform Non-linear analysis in 2 load steps.
4. The first load step with lesser number of substeps and limited the load to 28000N/m and the second load step is run upto 80000N/m.
5. I have been using Arc length method to perform non-linear analysis and the results are good enough till the buckling load but the load drops suddenly after the buckling load showing that the plate doesn't have any post buckling strength, which in contrast the plate do have post buckling strength.
6. I even had run the non-linear analysis using the earlier options with only 1 load step till 90000N/m, but the behavior remained the same.
7. I performed the analysis, one with Prestress on and the other analysis with stress stiffness ON( which is default if NLGEOM is ON), but the results are the same.

I am attaching the log file and the load displacement graph obtained using the graph.

For the load displacement graph, Node 716 is chosen which is the mid-node of the plate and Node 136 is chosen for the load reaction. In the graph, X-axis is UZ displacement and Y-axis is FX displacement.

Please do reply so that i would know what went wrong with my analysis.
 

RE: Queries regarding post buckling analysis in ANSYS 13

(OP)
/COM,  Structural   
/PREP7  
ET,1,SHELL181   
KEYOPT,1,1,0
KEYOPT,1,3,0
KEYOPT,1,8,0
KEYOPT,1,9,0
! SECTION DATA OF THE COMPOSITE
sect,1,shell,,  
secdata, 0.15e-3,1,90,3
secdata, 0.15e-3,1,-45,3
secdata, 0.15e-3,1,0,3  
secdata, 0.15e-3,1,90,3
secdata, 0.15e-3,1,0,3  
secdata, 0.15e-3,1,-45,3
secdata, 0.15e-3,1,0,3  
secdata, 0.15e-3,1,45,3
secdata, 0.15e-3,1,45,3
secdata, 0.15e-3,1,0,3  
secdata, 0.15e-3,1,-45,3
secdata, 0.15e-3,1,0,3  
secdata, 0.15e-3,1,90,3
secdata, 0.15e-3,1,0,3  
secdata, 0.15e-3,1,-45,3
secdata, 0.15e-3,1,90,3
secoffset,MID   
seccontrol,,,, , , ,
! MATERIAL MODELLING
MPTEMP,,,,,,,,  
MPTEMP,1,0  
MPDATA,EX,1,,130e9  
MPDATA,EY,1,,10e9   
MPDATA,EZ,1,,10e9   
MPDATA,PRXY,1,,0.35
MPDATA,PRYZ,1,,0.44
MPDATA,PRXZ,1,,0.35
MPDATA,GXY,1,,5e9   
MPDATA,GYZ,1,,4.1e9
MPDATA,GXZ,1,,5e9  
 
! MODEL
RECTNG,0,.45,0,0.3,
LPLOT   
!*  


FLST,5,1,4,ORDE,1   
FITEM,5,1   
CM,_Y,LINE  
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y   
!*  
LESIZE,_Y1, , ,45, , , , ,1
!*  
FLST,5,1,4,ORDE,1   
FITEM,5,3   
CM,_Y,LINE  
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y   
!*  
LESIZE,_Y1, , ,45, , , , ,1
!*  
FLST,5,2,4,ORDE,2   
FITEM,5,2   
FITEM,5,4   
CM,_Y,LINE  
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y   
!*  
LESIZE,_Y1, , ,30, , , , ,1
!*  
MSHAPE,0,2D
MSHKEY,0
!*  
CM,_Y,AREA  
ASEL, , , ,       1
CM,_Y1,AREA
CHKMSH,'AREA'   
CMSEL,S,_Y  
!*  
AMESH,_Y1   
!*  
CMDELE,_Y   
CMDELE,_Y1  
CMDELE,_Y2  

! LINEAR ANALYSIS PART-BUCKLING LOADS AND MODE SHAPES   

ANTYPE,0
!*  
!*  
NLGEOM,0
NROPT,AUTO, ,   
STAOPT,DEFA
LUMPM,0
EQSLV,SPAR, ,0, ,DELE   
MSAVE,0
PCGOPT,0, ,AUTO, , ,AUTO
PIVCHECK,1  
PSTRES,ON   
TOFFST,0,   
!*  
! BOUNDARY CONDITIONS< LOADING<
FLST,2,4,4,ORDE,2   
FITEM,2,1   
FITEM,2,-4  
!*  
/GO
DL,P51X, ,UZ,   
FLST,2,4,4,ORDE,2   
FITEM,2,1   
FITEM,2,-4  
!*  
/GO
DL,P51X, ,ROTZ,
FLST,2,1,4,ORDE,1   
FITEM,2,4   
!*  
/GO
DL,P51X, ,UX,   
FLST,2,2,4,ORDE,2   
FITEM,2,1   
FITEM,2,3   
!*  
/GO
DL,P51X, ,ROTY,
FLST,2,2,4,ORDE,2   
FITEM,2,2   
FITEM,2,4   
!*  
/GO
DL,P51X, ,ROTX,
klist,all,,,coord   
NPLOT   
FLST,2,2,1,ORDE,2   
FITEM,2,2   
FITEM,2,77  
!*  
/GO
D,P51X, , , , , ,UY, , , , ,
LPLOT   
FLST,2,1,4,ORDE,1   
FITEM,2,2   
/GO
!*  
SFL,P51X,PRES,1e5,  
FINISH  
/SOL
!*  
!*  
NLGEOM,0
NROPT,AUTO, ,   
STAOPT,DEFA
LUMPM,0
EQSLV,SPAR, ,0, ,DELE   
MSAVE,0
PCGOPT,0, ,AUTO, , ,AUTO
PIVCHECK,1  
PSTRES,ON   
TOFFST,0,   
!*  
/STATUS,SOLU
SOLVE   
FINISH  

/SOLU   
!*  
ANTYPE,1
!*  
BUCOPT,LANB,10,0,0,
MXPAND,10,0,0,1,0.001,  


/STATUS,SOLU
SOLVE   

FINISH  
/POST1  
SET,LIST

FINISH  
/PREP7  

! UPDATING THE GEOMETRY

UPGEOM,0.002,1,1,'simply-supported','rst',' '   
!*  
FINISH  

/SOL
!*  
ANTYPE,0
!*  
!*  
NLGEOM,1
NROPT,AUTO, ,OFF
STAOPT,DEFA
LUMPM,0
EQSLV, , ,0, ,DELE  
MSAVE,0
PCGOPT,0, ,AUTO, , ,AUTO
PIVCHECK,1  
SSTIF   
PSTRES  
TOFFST,0,   
!*  
!*  
ARCLEN,1,0,0
ARCTRM,U,1,716,UZ   
AUTOTS,-1.0
NCNV,2,0,0,0,0  
PSTRES,1
!*  
NLGEOM,1
NROPT,AUTO, ,OFF
STAOPT,DEFA
LUMPM,0
EQSLV, , ,0, ,DELE  
MSAVE,0
PCGOPT,0, ,AUTO, , ,AUTO
PIVCHECK,1  
PSTRES,ON   
TOFFST,0,   
!*  
AUTOTS,-1.0
PSTRES,0
!*  
NLGEOM,1
NROPT,AUTO, ,OFF
STAOPT,DEFA
LUMPM,0
EQSLV, , ,0, ,DELE  
MSAVE,0
PCGOPT,0, ,AUTO, , ,AUTO
PIVCHECK,1  
PSTRES,ON   
TOFFST,0,   
!*  
AUTOTS,-1.0
ARCLEN,1,0,0,   
ARCTRM,U,1,716,UZ   
!*  
!*  
OUTRES,ALL,ALL,
SFLLI, ALL  
/DIST,1,1.08222638492,1
/REP,FAST   
APLOT   
/AUTO,1
/REP,FAST   
/REPLOT,RESIZE  
SAVE
FINISH  
/SOLU   
SFLDELE,       2,PRES   
FLST,2,1,4,ORDE,1   
FITEM,2,2   
/GO
!*  
SFL,P51X,PRES,28000,
!*  
TIME,1  
AUTOTS,-1   
NSUBST,25, , ,1
KBC,0   
!*  
TSRES,ERASE
LSWRITE,1,  
LSWRITE,1,  
SFLLI, ALL  
FLST,2,1,4,ORDE,1   
FITEM,2,2   
/GO
SFLDELE,       2,PRES   
FLST,2,1,4,ORDE,1   
FITEM,2,2   
/GO
!*  
SFL,P51X,PRES,80000,
!*  
TIME,2  
AUTOTS,-1   
NSUBST,50, , ,1
KBC,0   
!*  
TSRES,ERASE
LSWRITE,2,  
LSWRITE,2,  
!*  
ANTYPE,0
LSSOLVE,1,2,1,  
FINISH  
/POST1  
SET,LIST
FINISH  
/POST26
FILE,'simply-supported','rst','.'   
/UI,COLL,1  
NUMVAR,200  
SOLU,191,NCMIT  
STORE,MERGE
FILLDATA,191,,,,1,1
REALVAR,191,191
!*  
!*  
!*  
NSOL,2,716,U,Z,middef   
!*  
!*  
!*  
RFORCE,3,136,F,X,   
!*  
VARNAM, ,   
!*  
PLTIME,0,0  
XVAR,2  
SPREAD,0
PLCPLX,0
!*  
PLVAR,3, , , , , , , , , ,  
PRVAR,2,3, , , , ,  
/REPLOT,RESIZE  
FINISH  
/PREP7  
 

RE: Queries regarding post buckling analysis in ANSYS 13

Try using RIKS method to get better post buckling behavior.

Gurmeet
Time is an illusion. Now is the only thing there is.

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