Learning Forum

[Shahrukh Ahmed]

Hi everyone,

I am trying to perform non linear buckling analysis in ANSYS Mechanical APDL 2021 R1.

But the bending stress capacity i am getting (product of reduction factor and yield stress) theoretically is nowhere matching with the numerical results.

fbd(reduction factor x yield stress(250MPa) = 201.2 MPa
fbd(as per model) = 21MPa


Here is my code 

blen=10.0

depth=0.55

fwidth=0.210

 

fthk=17.2/1000

wthk=11.1/1000

 

 

 

TAREA,0,0,0,depth/2.0,0,blen,1

TAREA,0,0,depth/2.0,depth,0,blen,1

TAREA,-fwidth/2.0,0.0,0,0,0,blen,2

TAREA,-fwidth/2.,0,depth,depth,0,blen,2

TAREA,0,fwidth/2.0,0,0,0,blen,2

TAREA,0,fwidth/2.0,depth,depth,0,blen,2

!TACUT,0,0,0,depth,0,blen,0.3

 

poi=0.3

 

damp1=0.02

!Material Number 1

ex,  1,      2e5*1000

ey,  1,      2e5*1000

nuxy,1,      poi

gxy, 1,      2e5*1000/(2*(1+poi))

dens,1,      2.5

alpx,1,      9.50E-06

alpy,1,      9.50E-06

damp,1,      damp1

 

ET,  11,  shell181 !Wall

 

SECTYPE,111,SHELL

SECDATA,fthk,

 

SECTYPE,112,SHELL

SECDATA,wthk,

 

TASEL,0,0,0,depth,0,blen,1

AATT,1,,11,,112

 

 

TASEL,-fwidth/2.0,fwidth/2.0,0,0,0,blen,2

AATT,1,,11,,111

 

TASEL,-fwidth/2.,fwidth/2.0,depth,depth,0,blen,2

AATT,1,,11,,111

 

allsel,all

 

aclear,all

esize,0.1

amesh,all,all

 

 

ddele,all,all

tnsel,0,0,depth/2,depth/2,0,0,

d,all,uy,0

d,all,rotz,0

 

tnsel,0,0,depth/2,depth/2,blen,blen,

d,all,uy,0

d,all,uz,0

d,all,rotz,0

 

 

tnsel,0,0,0,depth,0,0,0,

d,all,ux,0

 

tnsel,0,0,0,depth,blen,blen,

d,all,ux,0

 

!LeftSides

 

fdele,all,all

logforce=1/(0.5328*2)

 

tnsel,-fwidth/2,-fwidth/2,0,0,0,0,0,

f,all,fz,-logforce

 

tnsel,-fwidth/2,-fwidth/2,depth,depth,0,0,0,

f,all,fz,logforce

 

tnsel,fwidth/2,fwidth/2,0,0,0,0,0,

f,all,fz,-logforce

 

tnsel,fwidth/2,fwidth/2,depth,depth,0,0,0,

f,all,fz,logforce

 

 

tnsel,-fwidth/2,-fwidth/2,0,0,blen,blen

f,all,fz,logforce

 

tnsel,-fwidth/2,-fwidth/2,depth,depth,blen,blen

f,all,fz,-logforce

 

tnsel,fwidth/2,fwidth/2,0,0,blen,blen

f,all,fz,logforce

 

tnsel,fwidth/2,fwidth/2,depth,depth,blen,blen

f,all,fz,-logforce

 

 

allsel,all  

eplot   

 

!*change material

 

/VIEW,1,1,1,1   

/ANG,1  

/REP,FAST   

/DIST, 1 ,1.082226,1

/REP,FAST   

/DIST, 1 ,1.082226,1

/REP,FAST   

/DIST, 1 ,1.082226,1

/REP,FAST   

/DIST, 1 ,1.082226,1

/REP,FAST   

/DIST, 1 ,1.082226,1

/REP,FAST   

FINISH  

/SOL

FINISH  

/PREP7  

!*  

TB,BISO,1,1,2,  

TBTEMP,0

TBDATA,,250000,0,,,,

 

 

 

 

!*static anlaysis 

 

 

/VIEW,1,1,1,1   

/ANG,1  

/REP,FAST   

FINISH  

/SOL

PSTRES,1

!*  

ANTYPE,0

solve   

!*  

!*  

!*  

!*  

!*  

!*  

FINISH  

 

!* eigenvalue buckling analysis

/SOLUTION   

ANTYPE,1

!*  

FINISH  

/POST1  

FINISH  

/PREP7  

FINISH  

/SOL

!*  

BUCOPT,LANB,10,0,0,CENTER   

solve   

FINISH  

/POST1  

!*  

/EFACET,1   

PLNSOL, U,SUM, 0,1.0

SET,LIST,999

)/GOP     

 

!*********************************************UPGEOM

allsel,all

eplot

/PREP7  

UPGEOM,10/350,1,6,'test','rst',' '  

FINISH  

/SOL

 

eplot

 

!*change force

fdele,all,all

logforce=1000/(0.5328*2)

 

tnsel,-fwidth/2,-fwidth/2,0,0,0,0,0,

f,all,fz,-logforce

 

tnsel,-fwidth/2,-fwidth/2,depth,depth,0,0,0,

f,all,fz,logforce

 

tnsel,fwidth/2,fwidth/2,0,0,0,0,0,

f,all,fz,-logforce

 

tnsel,fwidth/2,fwidth/2,depth,depth,0,0,0,

f,all,fz,logforce

 

 

tnsel,-fwidth/2,-fwidth/2,0,0,blen,blen

f,all,fz,logforce

 

tnsel,-fwidth/2,-fwidth/2,depth,depth,blen,blen

f,all,fz,-logforce

 

tnsel,fwidth/2,fwidth/2,0,0,blen,blen

f,all,fz,logforce

 

tnsel,fwidth/2,fwidth/2,depth,depth,blen,blen

f,all,fz,-logforce

 

allsel,all

eplot

 

!*NLGEOM

 

!*  

ANTYPE,0

ANTYPE,0

NLGEOM,1

NSUBST,100,100,1

OUTRES,ERASE

OUTRES,ALL,ALL  

RESCONTRL,DEFINE,ALL,ALL,-1 

TIME,1  

FINISH  

/POST1  

FINISH  

/SOL

!*  

!*  

NLGEOM,1

NROPT,AUTO, ,OFF

LUMPM,0 

EQSLV, , ,0, ,DELE  

MSAVE,0 

PCGOPT,0, ,AUTO, , ,AUTO

PIVCHECK,0  

PSTRESS,0   

TOFFST,0,   

!*  

solve   

 

eplot

What is wrong with my analysis ??

[dlooman]

The APDL Materials Reference gives the example input below for temp-dependent bilinear isotropic hardening.  You appear to have only specified the yield stress.  Perhaps a shell element isn't the best choice for a plasticity analysis.  Perhaps a thin solid with several elements through the thickness would be more accurate.   

/prep7
MPTEMP,1,0,500            ! Define temperatures for Young's modulus
MPDATA,EX,1,,14E6,12e6           
MPDATA,PRXY,1,,0.3,0.3
TB,PLAS,1,2,,BISO         ! Activate a data table
TBTEMP,0.0                ! Temperature = 0.0
TBDATA,1,44E3,1.2E6       ! Yield = 44,000; Plastic Tangent modulus = 1.2E6
TBTEMP,500                ! Temperature = 500
TBDATA,1,29.33E3,0.8E6    ! Yield = 29,330; Plastic Tangent modulus = 0.8E6