Ansys Shell 63 elementAnsys Shell 63 elementAnsys Shell 63 element

SHELL63 http://www.et.byu.edu/docs/ansys/ansys8.0/Hlp_E_SHELL63.html

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SHELL63Elastic Shell

MP ME ST <> <> PR <> <> <> PP ED

SHELL63 Element Description

SHELL63 has both bending and membrane capabilities. Both in-plane and normal loads arepermitted. The element has six degrees of freedom at each node: translations in the nodal x, y, andz directions and rotations about the nodal x, y, and z-axes. Stress stiffening and large deflectioncapabilities are included. A consistent tangent stiffness matrix option is available for use in largedeflection (finite rotation) analyses. See SHELL63 in the ANSYS, Inc. Theory Reference for moredetails about this element. Similar elements are SHELL43 and SHELL181 (plastic capability), andSHELL93 (midside node capability). The ETCHG command converts SHELL57 and SHELL157 elementsto SHELL63.

Figure 63.1 SHELL63 Geometry

xIJ = Element x-axis if ESYS is not supplied.

x = Element x-axis if ESYS is supplied.

SHELL63 Input Data

The geometry, node locations, and the coordinate system for this element are shown in Figure 63.1: "SHELL63 Geometry". The element is defined by four nodes, four thicknesses, an elastic foundationstiffness, and the orthotropic material properties. Orthotropic material directions correspond to theelement coordinate directions. The element coordinate system orientation is as described inCoordinate Systems. The element x-axis may be rotated by an angle THETA (in degrees).

SHELL63Element Reference> Part I. Element Library>


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The thickness is assumed to vary smoothly over the area of the element, with the thickness input atthe four nodes. If the element has a constant thickness, only TK(I) need be input. If the thickness isnot constant, all four thicknesses must be input.

The elastic foundation stiffness (EFS) is defined as the pressure required to produce a unit normaldeflection of the foundation. The elastic foundation capability is bypassed if EFS is less than, orequal to, zero.

For certain nonhomogeneous or sandwich shell applications, the following real constants areprovided: RMI is the ratio of the bending moment of inertia to be used to that calculated from theinput thicknesses. RMI defaults to 1.0. CTOP and CBOT are the distances from the middle surface tothe extreme fibers to be used for stress evaluations. Both CTOP and CBOT are positive, assumingthat the middle surface is between the fibers used for stress evaluation. If not input, stresses arebased on the input thicknesses. ADMSUA is the added mass per unit area.

Element loads are described in Node and Element Loads. Pressures may be input as surface loads onthe element faces as shown by the circled numbers on Figure 63.1: "SHELL63 Geometry". Positivepressures act into the element. Edge pressures are input as force per unit length. The lateralpressure loading may be an equivalent (lumped) element load applied at the nodes (KEYOPT(6) = 0)or distributed over the face of the element (KEYOPT(6) = 2). The equivalent element load producesmore accurate stress results with flat elements representing a curved surface or elementssupported on an elastic foundation since certain fictitious bending stresses are eliminated.

Temperatures may be input as element body loads at the "corner" locations (1-8) shown in Figure 63.1: "SHELL63 Geometry". The first corner temperature T1 defaults to TUNIF. If all othertemperatures are unspecified, they default to T1. If only T1 and T2 are input, T1 is used for T1, T2,T3, and T4, while T2 (as input) is used for T5, T6, T7, and T8. For any other input pattern, unspecifiedtemperatures default to TUNIF.

KEYOPT(1) is available for neglecting the membrane stiffness or the bending stiffness, if desired. Areduced out-of-plane mass matrix is also used when the bending stiffness is neglected.

KEYOPT(2) is used to activate the consistent tangent stiffness matrix (that is, a matrix composed ofthe main tangent stiffness matrix plus the consistent stress stiffness matrix) in large deflectionanalyses [NLGEOM,ON]. You can often obtain more rapid convergence in a geometrically nonlinearanalysis, such as a nonlinear buckling or postbuckling analysis, by activating this option. However,you should not use this option if you are using the element to simulate a rigid link or a group ofcoupled nodes. The resulting abrupt changes in stiffness within the structure make the consistenttangent stiffness matrix unsuitable for such applications.

KEYOPT(3) allows you to include (KEYOPT(3) = 0 or 2) or suppress (KEYOPT(3) = 1) extra displacementshapes. It also allows you to choose the type of in-plane rotational stiffness used:

KEYOPT(3) = 0 or 1 activates a spring-type in-plane rotational stiffness about the elementz-axis

KEYOPT(3) = 2 activates a more realistic in-plane rotational stiffness (Allman rotationalstiffness - the program uses default penalty parameter values of d1 = 1.0E-6 and d2 = 1.0E-3).

Using the Allman stiffness will often enhance convergence behavior in large deflection (finiterotation) analyses of planar shell structures (that is, flat shells or flat regions of shells).

KEYOPT(7) allows a reduced mass matrix formulation (rotational degrees of freedom terms deleted).This option is useful for improved bending stresses in thin members under mass loading.


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KEYOPT(8) allows a reduced stress stiffness matrix (rotational degrees of freedom deleted). Thisoption can be useful for calculating improved mode shapes and a more accurate load factor in linearbuckling analyses of certain curved shell structures.

KEYOPT(11) = 2 is used to store midsurface results in the results file for single or multi-layer shellelements. If you use SHELL,MID, you will see these calculated values, rather than the average of theTOP and BOTTOM results. You should use this option to access these correct midsurface results(membrane results) for those analyses where averaging TOP and BOTTOM results is inappropriate;examples include midsurface stresses and strains with nonlinear material behavior, and midsurfaceresults after mode combinations that involve squaring operations such as in spectrum analyses.

A summary of the element input is given in "SHELL63 Input Summary". A general description ofelement input is given in Element Input.

SHELL63 Input Summary

Nodes

I, J, K, L

Degrees of Freedom

UX, UY, UZ, ROTX, ROTY, ROTZ

Real Constants

TK(I), TK(J), TK(K), TK(L), EFS, THETA,

RMI, CTOP, CBOT, (Blank), (Blank), (Blank),

(Blank), (Blank), (Blank), (Blank), (Blank), (Blank),

ADMSUA

See Table 63.1: "SHELL63 Real Constants" for a description of the real constants

Material Properties

EX, EY, EZ, (PRXY, PRYZ, PRXZ or NUXY, NUYZ, NUXZ), ALPX, ALPY, ALPZ (or CTEX, CTEY, CTEZ orTHSX, THSY, THSZ), DENS, GXY, DAMP

Surface LoadsPressures --

face 1 (I-J-K-L) (bottom, in +Z direction), face 2 (I-J-K-L) (top, in -Z direction),

face 3 (J-I), face 4 (K-J), face 5 (L-K), face 6 (I-L)

Body LoadsTemperatures --

T1, T2, T3, T4, T5, T6, T7, T8

Special FeaturesStress stiffening

Large deflection

Birth and death

KEYOPT(1)

Element stiffness:


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0 --

Bending and membrane stiffness

1 --

Membrane stiffness only

2 --

Bending stiffness only

KEYOPT(2)

Stress stiffening option:

0 --

Use only the main tangent stiffness matrix when NLGEOM is ON. (Stress stiffeningeffects used in linear buckling or other linear prestressed analyses must be activatedseparately with PSTRES,ON.)

1 --

Use the consistent tangent stiffness matrix (that is, a matrix composed of the maintangent stiffness matrix plus the consistent stress stiffness matrix) when NLGEOM isON and when KEYOPT(1) = 0. (SSTIF,ON will be ignored for this element whenKEYOPT(2) = 1 is activated.) Note that if SOLCONTROL is ON and NLGEOM is ON, KEYOPT(2) is automatically set to 1; that is, the consistent tangent will be used.

2 --

Use to turn off consistent tangent stiffness matrix (i.e., a matrix composed of themain tangent stiffness matrix plus the consistent stress stiffness matrix) whenSOLCONTROL is ON. Sometimes it is necessary to turn off the consistent tangentstiffness matrix if the element is used to simulate rigid bodies by using a very largereal constant number . KEYOPT(2) = 2 is the same as KEYOPT(2) = 0, however,KEYOPT(2) = 0 is controlled by SOLCONTROL, ON or OFF, while KEYOPT(2) = 2 isindependent of SOLCONTROL.

KEYOPT(3)

Extra displacement shapes:

0 --

Include extra displacement shapes, and use spring-type in-plane rotational stiffnessabout the element z-axis (the program automatically adds a small stiffness to preventnumerical instability for non-warped elements if KEYOPT(1) = 0).

Note

For models with large rotation about the in-plane direction, KEYOPT(3) =0 results in some transfer of moment directly to ground.

1 --


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Suppress extra displacement shapes, and use spring-type in-plane rotational stiffnessabout the element z-axis (the program automatically adds a small stiffness to preventnumerical instability for non-warped elements if KEYOPT(1) = 0).

2 --

Include extra displacement shapes, and use the Allman in-plane rotational stiffnessabout the element z-axis). See the ANSYS, Inc. Theory Reference.

KEYOPT(5)

Extra stress output:

0 --

Basic element printout

2 --

Nodal stress printout

KEYOPT(6)

Pressure loading:

0 --

Reduced pressure loading (must be used if KEYOPT(1) = 1)

2 --

Consistent pressure loading

KEYOPT(7)

Mass matrix:

0 --

Consistent mass matrix

1 --

Reduced mass matrix

KEYOPT(8)

Stress stiffness matrix:

0 --

“Nearly” consistent stress stiffness matrix (default)

1 --

Reduced stress stiffness matrix

KEYOPT(9)


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Element coordinate system defined:

0 --

No user subroutine to define element coordinate system

4 --

Element x-axis located by user subroutine USERAN

Note

See the Guide to ANSYS User Programmable Features for user written subroutines

KEYOPT(11)

Specify data storage:

0 --

Store data for TOP and BOTTOM surfaces only

2 --

Store data for TOP, BOTTOM, and MID surfaces

Table 63.1 SHELL63 Real Constants

No. Name Description

1 TK(I) Shell thickness at node I

2 TK(J) Shell thickness at node J

3 TK(K) Shell thickness at node K

4 TK(L) Shell thickness at node L

5 EFS Elastic foundation stiffness

6 THETA Element X-axis rotation

7 RMI Bending moment of inertia ratio

8 CTOP Distance from mid surface to top

9 CBOT Distance from mid surface to bottom

10, ..., 18 (Blank) - -

19 ADMSUA Added mass/unit area

SHELL63 Output Data

The solution output associated with the element is in two forms:

Nodal displacements included in the overall nodal solution


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Additional element output as shown in Table 63.2: "SHELL63 Element Output Definitions"

Several items are illustrated in Figure 63.2: "SHELL63 Stress Output". Printout includes the momentsabout the x face (MX), the moments about the y face (MY), and the twisting moment (MXY). Themoments are calculated per unit length in the element coordinate system. The element stressdirections are parallel to the element coordinate system. A general description of solution output isgiven in Solution Output. See the ANSYS Basic Analysis Guide for ways to view results.

Figure 63.2 SHELL63 Stress Output

xIJ = Element x-axis if ESYS is not supplied.

x = Element x-axis if ESYS is supplied.

The Element Output Definitions table uses the following notation:

A colon (:) in the Name column indicates the item can be accessed by the Component Name method[ETABLE, ESOL]. The O column indicates the availability of the items in the file Jobname.OUT. The Rcolumn indicates the availability of the items in the results file.

In either the O or R columns, Y indicates that the item is always available, a number refers to a table footnote that describes when the item is conditionally available, and a - indicates that the item isnot available.

Table 63.2 SHELL63 Element Output Definitions

Name Definition O R

EL Element Number Y Y

NODES Nodes - I, J, K, L Y Y

MAT Material number Y Y


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Name Definition O R

AREA AREA Y Y

XC, YC, ZC Location where results are reported Y 1

PRES Pressures P1 at nodes I, J, K, L; P2 at I, J, K, L; P3 at J, I;P4 at K, J; P5 at L, K; P6 at I, L

Y Y

TEMP Temperatures T1, T2, T3, T4, T5, T6, T7, T8 Y Y

T(X, Y, XY) In-plane element X, Y, and XY forces Y Y

M(X, Y, XY) Element X, Y, and XY moments Y Y

FOUND.PRESS Foundation pressure (if nonzero) Y -

LOC Top, middle, or bottom Y Y

S:X, Y, Z, XY Combined membrane and bending stresses Y Y

S:1, 2, 3 Principal stress Y Y

S:INT Stress intensity Y Y

S:EQV Equivalent stress Y Y

EPEL:X, Y, Z, XY Average elastic strain Y Y

EPEL:EQV Equivalent elastic strain [2] - Y

EPTH:X, Y, Z, XY Average thermal strain Y Y

EPTH:EQV Equivalent thermal strain [2] - Y

Available only at centroid as a *GET item.1.

The equivalent strains use an effective Poisson's ratio: for elastic and thermal this value isset by the user (MP,PRXY).

2.

Table 63.3 SHELL63 Miscellaneous Element Output

Description Names of Items Output O R

Nodal Stress Solution TEMP, S(X, Y, Z, XY), SINT, SEQV 1 -

Output at each node, if KEYOPT(5) = 2, repeats each location1.

Table 63.4: "SHELL63 Item and Sequence Numbers" lists output available through the ETABLEcommand using the Sequence Number method. See The General Postprocessor (POST1) in the ANSYS Basic Analysis Guide and The Item and Sequence Number Table in this manual for more information.The following notation is used in Table 63.4: "SHELL63 Item and Sequence Numbers":

Name

output quantity as defined in the Table 63.2: "SHELL63 Element Output Definitions"

Item

predetermined Item label for ETABLE command


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E

sequence number for single-valued or constant element data

I,J,K,L

sequence number for data at nodes I,J,K,L

Table 63.4 SHELL63 Item and Sequence Numbers

Output Quantity Name

ETABLE and ESOL Command Input

Item E I J K L

TX SMISC 1 - - - -

TY SMISC 2 - - - -

TXY SMISC 3 - - - -

MX SMISC 4 - - - -

MY SMISC 5 - - - -

MXY SMISC 6 - - - -

P1 SMISC - 9 10 11 12

P2 SMISC - 13 14 15 16

P3 SMISC - 18 17 - -

P4 SMISC - - 20 19 -

P5 SMISC - - - 22 21

P6 SMISC - 23 - - 24

Top

S:1 NMISC - 1 6 11 16

S:2 NMISC - 2 7 12 17

S:3 NMISC - 3 8 13 18

S:INT NMISC - 4 9 14 19

S:EQV NMISC - 5 10 15 20

Bot

S:1 NMISC - 21 26 31 36

S:2 NMISC - 22 27 32 37

S:3 NMISC - 23 28 33 38

S:INT NMISC - 24 29 34 39

S:EQV NMISC - 25 30 35 40

SHELL63 Assumptions and Restrictions


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Zero area elements are not allowed. This occurs most often whenever the elements are notnumbered properly.

Zero thickness elements or elements tapering down to a zero thickness at any corner are notallowed.

The applied transverse thermal gradient is assumed to vary linearly through the thicknessand vary bilinearly over the shell surface.

An assemblage of flat shell elements can produce a good approximation of a curved shellsurface provided that each flat element does not extend over more than a 15° arc. If anelastic foundation stiffness is input, one-fourth of the total is applied at each node. Sheardeflection is not included in this thin-shell element.

A triangular element may be formed by defining duplicate K and L node numbers asdescribed in Triangle, Prism and Tetrahedral Elements. The extra shapes are automaticallydeleted for triangular elements so that the membrane stiffness reduces to a constant strainformulation. For large deflection analyses, if KEYOPT(1) = 1 (membrane stiffness only), theelement must be triangular.

For KEYOPT(1) = 0 or 2, the four nodes defining the element should lie as close as possible toa flat plane (for maximum accuracy), but a moderate amount of warping is permitted. ForKEYOPT(1) = 1, the warping limit is very restrictive. In either case, an excessively warpedelement may produce a warning or error message. In the case of warping errors, triangularelements should be used (see Triangle, Prism and Tetrahedral Elements). Shell elementwarping tests are described in detail in tables of Applicability of Warping Tests and Warping Factor Limits in the ANSYS, Inc. Theory Reference.

If the lumped mass matrix formulation is specified [LUMPM,ON], the effect of the impliedoffsets on the mass matrix is ignored for warped SHELL63 elements.

SHELL63 Product Restrictions

When used in the product(s) listed below, the stated product-specific restrictions apply to thiselement in addition to the general assumptions and restrictions given in the previous section.

ANSYS Professional.

The DAMP material property is not allowed.

The only special features allowed are stress stiffening and large deflection.

KEYOPT(2) can only be set to 0 (default).

KEYOPT(9) can only be set to 0 (default).

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