azimuthal shear of incompressible hyperelastic rubber

[jenny]

hello,everyone:
i am doing a analysis in Ansys about azimuthal shear of a hollow circular cylindrical rubber tube. this represents a model for a rubber bushing, a device widely used in vehicle suspension systems. i select incompressible neohookean material and use plane strain analysis . i do four analyse for different boundary condition: the inner cylindrical surface is fixed, while the outer cylindrical surface is subjected a uniformly distributed circular shear or a angular displacement; the outer cylindrical surface is fixed, while the inner surface is subjected a uniformly distributed circular shear or a angular displacement.
i am mainly interested in the normal stress at the inner and outer surface.
According C. O. Horgan's papers the normal stress at the inner surface is always negative, but i get the positive normal stress at inner surface for the two boundary conditon when the outer surface is fixed and get the negative normal stress at inner surface for the two boundary condition when the inner surface is fixed. i don't know why.
another question is the normal stress should be zero at the surface which is subjected circular shear,but the fea results are not.
Anyone has idea what mistake I am doing in analysis then let me know.
thanks

jenny

[Jorgen]

Hello Jenny,

Two ideas:
:arrow: Try to represent the material with slight compressibility. No material is completely incompressible.
:arrow: Try a full 3D model. Plane strain can be too restrictive.

Best of luck,
Jorgen

[jenny]

Thank you, Dr. Bergstrom
i do this problem again with hyperelastic comressible materials an 3D model, but the result is not good. my biggest problem is why the normal stress at outer surface is not zero when inner surface is fixed while the outer surface is subjected to shear stress. the shear stress apply to the outer surface effect elements, the shear stress will change direction, "following" the elements as they undergo large rotations.
please help me!

thanks a lot

jenny

[Jorgen]

Hello Jenny,

I assume that the outer surface is a "free surface" on which you have applied a shear stress and not constrained the displacement. In that case you cannot have any normal stress on the outer surface.

I have the following recommendations:
:arrow: Check that you applied shear stress only on the outer surface
:arrow: Check that you did not constain the displacements of the outer surface
:arrow: Check how you determined that the simulation give normal stresses on the outer surface

One of these 3 steps is likely incorrect.

- Jorgen

[dt]

Hello Jenny,
I have a question for you. I am new to ANSYS and so am not able to figure out how to do angular displacement. I am trying to do something similar to what you are doing. I have a vane put into a cup with a viscoelastic material. I have created the vane and the material in the form of a solid cylinder. Now, I have two questions:
(1) How to rotate the vane? i.e., how to create an angular displacement or an angular velocity in the vane
(2) How to input viscoelastic properties into the material (I think I can figure this out, but if you know I will be glad if you can share it with me)
Please let me whats the procedure to induce an angular displacement, I will be very greatful. Thanks very much,
Regards,
DT

[jenny]

Dear Dr. Bergstrom
i have not yet solved the problem about azimuthal shear of a hollow circular cylindrical rubber tube. the following is the command input.
Could you run the input in ANSYS and check what mistakes i made if you have time. thanks in advance.


PREP7
ET,1,PLANE183
KEYOPT,1,3,2
KEYOPT,1,6,0
KEYOPT,1,10,0
TB,HYPE,1,1,2,NEO
TBTEMP,0
TBDATA,,1.379,,,,,
CYL4, , ,10, ,20
LSTR, 5, 4
LSTR, 6, 1
LSTR, 8, 2
LSTR, 7, 3
FLST,3,4,4,ORDE,2
FITEM,3,9
FITEM,3,-12
ASBL, 1,P51X
FLST,5,8,4,ORDE,2
FITEM,5,1
FITEM,5,-8
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1, , ,10, , , , ,1
!*
FLST,5,4,4,ORDE,2
FITEM,5,9
FITEM,5,-12
CM,_Y,LINE
LSEL, , , ,P51X
CM,_Y1,LINE
CMSEL,,_Y
!*
LESIZE,_Y1, , ,8, , , , ,1
!*
FLST,5,4,5,ORDE,2
FITEM,5,2
FITEM,5,-5
CM,_Y,AREA
ASEL, , , ,P51X
CM,_Y1,AREA
CHKMSH,'AREA'
CMSEL,S,_Y
!*
MSHKEY,1
AMESH,_Y1
MSHKEY,0
!*
CMDELE,_Y
CMDELE,_Y1
CMDELE,_Y2
!*
CSWPLA,11,1,1,1,
CSYS,11,
FLST,2,1040,1,ORDE,2
FITEM,2,1
FITEM,2,-1040
NROTAT,P51X
CSYS,0
NSEL,S,LOC,X,10
! NPLOT
ALLSEL,ALL
! NPLOT
CSYS,1
NSEL,S,LOC,X,10
! NPLOT
FLST,2,80,1,ORDE,10
FITEM,2,22
FITEM,2,38
FITEM,2,-57
FITEM,2,298
FITEM,2,314
FITEM,2,-332
FITEM,2,538
FITEM,2,-557
FITEM,2,798
FITEM,2,-816
!*
/GO
D,P51X, , , , , ,ALL, , , , ,
ALLSEL,ALL
NSEL,S,LOC,X,20
! NPLOT
!*
ET,2,SURF153
!*
TYPE, 2
MAT, 1
REAL,
ESYS, 0
SECNUM,
TSHAP,LINE
!*
FLST,5,80,1,ORDE,8
FITEM,5,1
FITEM,5,-21
FITEM,5,278
FITEM,5,-297
FITEM,5,558
FITEM,5,-577
FITEM,5,817
FITEM,5,-835
CM,_Y,node
NSEL, , , ,P51X
CM,_Y1,node
CMSEL,,_Y
!*
CMSEL,,_Y1
ESURF,0
CMSEL,,_Y
CMDELE,_Y
CMDELE,_Y1
!*
ESEL,S,TYPE,,2
FLST,5,40,2,ORDE,2
FITEM,5,321
FITEM,5,-360
CM,_Y,ELEM
ESEL, , , ,P51X
CM,_Y1,ELEM
CMSEL,S,_Y
CMSEL,ALL
CMDELE,_Y
!*
/GO
!*
SFE,_Y1,2,PRES, ,0.5, , ,
ALLSEL,ALL
! EPLOT
FINISH
/SOL
ANTYPE,0
NLGEOM,1
NSUBST,8,0,0
TIME,1
!*
!*
NLGEOM,1
NROPT,FULL, ,
LUMPM,0
EQSLV, , ,0,
PRECISION,0
MSAVE,0
PIVCHECK,1
SSTIF
PSTRES
TOFFST,0,
solve


Jenny

[Jorgen]

Hi Jenny,

Unfortunately, I do not have access to Ansys at the moment :|

Best of luck,
Jorgen