有关ANSYS不锈钢压弯构件屈曲分析的问题

各位好：
我在做两端简支的工字型和箱型压弯构件屈曲分析，看一阶模态应该是对的，但非线性屈曲有问题，收敛图TIME总是从0.1跳到0.09然后才从小开始增大，最后画出来的荷载-挠度（柱中截面）曲线形状也很奇怪。以下是箱型构件的命令流，麻烦大家帮忙看看，实在找不出原因了，谢谢！
FILE_NAME='XX' !!DEFINE FILE NAME
/CONFIG,NRES,10000
!单位，N，mm
WEB_HEIGHT=130
WEB_THICKNESS=16

/prep7
ET,1,SHELL181
MPTEMP,,,,,,,,
MPTEMP,1,0
MPDATA,EX,1,,200000
MPDATA,PRXY,1,,0.3
TB,KINH,1,,,0
TBTEMP,0,
TBPT,DEFI, 0 , 0
TBPT,DEFI, 0.000100000 , 20
TBPT,DEFI, 0.000200096 , 40
TBPT,DEFI, 0.000301088 , 60
TBPT,DEFI, 0.000406113 , 80
TBPT,DEFI, 0.000523319 , 100
TBPT,DEFI, 0.000669631 , 120
TBPT,DEFI, 0.000875583 , 140
TBPT,DEFI, 0.001191232 , 160
TBPT,DEFI, 0.001693139 , 180
TBPT,DEFI, 0.002492431 , 200
TBPT,DEFI, 0.003821343 , 220
TBPT,DEFI, 0.007039374 , 240
TBPT,DEFI, 0.013448509 , 260
TBPT,DEFI, 0.023824378 , 280
TBPT,DEFI, 0.058778644 , 320
TBPT,DEFI, 0.133771012 , 370
TBPT,DEFI, 0.248920426 , 420
TBPT,DEFI, 0.409044081 , 470
TBPT,DEFI, 0.618314286 , 520
TBPLOT,KINH
sect,1,shell
secdata,16,1,0.0,3


k,1,,57,-57
k,2,,57,57
k,3,,-57,57
k,4,,-57,-57
kgen,2,1,4,1,4000,0,0,4


a,1,2,6,5
a,1,4,8,5
a,3,4,8,7
a,6,7,3,2
a,1,2,3,4
a,5,6,7,8

mshape,0,2d
mshkey,1
esize,30

amesh,1,6,1
ALLSEL,ALL
/ESHAPE,1.0
EPLOT

NSEL,S,LOC,X,0
NSEL,R,LOC,Y,57
NSEL,R,LOC,Z,0
D,ALL,UX
D,ALL,UY
D,ALL,UZ
NSEL,S,LOC,X,0
NSEL,R,LOC,Y,-57
NSEL,R,LOC,Z,0
D,ALL,UX
D,ALL,UY
D,ALL,UZ
NSEL,S,LOC,X,4000
NSEL,R,LOC,Y,57
NSEL,R,LOC,Z,0
D,ALL,UY
D,ALL,UZ


NSEL,S,LOC,X,4000
NSEL,R,LOC,Y,-57
NSEL,R,LOC,Z,0
D,ALL,UY
D,ALL,UZ

NSEL,S,LOC,X,0
NSEL,R,LOC,Y,0
NSEL,R,LOC,Z,0
!F,ALL,FX,-1
F,ALL,MY,5
NSEL,S,LOC,X,4000
NSEL,R,LOC,Y,0
NSEL,R,LOC,Z,0
F,ALL,FX,-1
F,ALL,MY,-5


/SOLU
PSTRES,ON
ANTYPE,STATIC
SOLVE
FINISH

/SOLU
ANTYPE,BUCKLE,
!BUCOPT,SUBSP,1
BUCOPT,LANB,1
MXPAND,,,,YES
OUTPR,NSOL,ALL
SOLVE
FINISH !
!
/post1 !
set,first !
pldisp,1

/SOLU
*GET,LOAD_FACTOR,MODE,1,FREQ
!COL_AXIAL_FORCE=COL_AXIAL_FORCE*LOAD_FACTOR
!
/solu !
antype,0
NLGEOM,ON !
nsubst,10,0,0
outres,all,all !
ARCLEN,1,10,0.01
ARCTRM,U,100,73,UZ
!CNVTOL,F,100,0.001,2 !
NSEL,S,LOC,X,0
NSEL,R,LOC,Y,0
NSEL,R,LOC,Z,0
F,ALL,MY,5*LOAD_FACTOR
NSEL,S,LOC,X,4000
NSEL,R,LOC,Y,0
NSEL,R,LOC,Z,0
F,ALL,FX,-1*LOAD_FACTOR
F,ALL,MY,-5*LOAD_FACTOR
solve !
finish

/post26
nsol,2,73,u,Z,p1-uy
rforce,3,140,f,x,reactionf
prod,4,2,,,DISPLACEMENT,,,1
prod,5,1,,,LOAD,,,20000000
/AXLAB,X,DISPLACEMENT(MM)
/AXLAB,Y,LOAD(N)
xvar,4
plvar,5