4.18
PLATE NO.18 WITH 6 NODES
This is a curvilinear
Serendipity Reissner- Mindlin plate element with square shape functions.
The transformation is isoparametric. The integration is carried out numerically
in both axises according to Gauss- Legendre. Consequently, the integration
order can be selected in Z88I1.TXT in the material information lines. The order
3 (= 3 points) is mostly sufficient (reduced integration). This element
calculates both displacements and stresses quite good. The integration order
can be chosen again for the stress calculation. The stresses are calculated in
the corner nodes (good for an overview) or calculated in the Gauss points
(substantially more exactly). Area loads are defined in the appropriate
material lines, file Z88I1.TXT, instead of Second moment of inertia RIYY. For
this element you need to set the plate flag IPFLAG to 1. Attention: In contrary
to the usual rules of the classic mechanics Z88 defines ThetaX the rotation
around the X- axis and ThetaY the rotation around the Y- axis.
This element type is
implemented for use with automeshers e.g. Pro/MECHANICA for the 3D CAD system Pro/ENGINEER by
Parametric Technology. Thus, a mesh generation with Z88N is not possible,
because this will make no sense. Use plates No.20 for the mesher Z88N.
Because plates No.20
compute both the deflections and the stresses more exactly than the curvilinear
triangle plates No.18, you should prefer always plates No.20.
CAD : 1-4-2-5-3-6-1 , ref. chap. 2.7.2
> KFLAG for cartesian (0) or cylindrical coordinates (1)
> set plate flag IPFLAG to 1 (or 2, if you want to reduce the shear
influence)
> set surface and pressure loads flag IQFLAG to 0 for your convenience. Then
the entry of the pressure is done via the "Second moment of inertia
RIYY", see below. If IQFLAG is set to 1, then the entry of the pressure is
done via the surface and pressure loads file Z88I5.TXT
> 3 degrees of freedom for each
node (w, ThetaX, ThetaY )
> Element type is 18
> 6 nodes per element
> Cross-section parameter QPARA is the element thickness
> "Second moment of inertia RIYY" is the area load
> Integration order INTORD per each mat info line. 3 is usually good.
Possible is: 3 for 3 Gauss points, 7 for 7 Gauss points and 13 for 13
Gausspoints. For easy use with plate element No.20 (e.g. with Pro/ENGINEER),
function SPLA88 of Z88 uses internally these values:
integration order 1 or 2 in Z88I1.TXT: 3 Gauss points
integration order 4 in Z88I1.TXT: 7 Gauss points
Example: Z88I1.TXT uses an entry of 2 for INTORD: Thus, plate elements No.20
use 2*2 = 4 Gauss points and plate elements No.18 use 3 Gauss points for
integration.
Z88I3.TXT
> Integration order INTORD: Basically, it is a good idea to use the
same value as chosen in Z88I1.TXT , but different values are permitted
0 = Calculation of the stresses in the corner nodes
1, 7, 13 = Calculation of the stresses in the Gauss points (e.g. 7 Gauss
points) See note for Z88I1.TXT.
> KFLAG has no meaning
> Reduced stress flag
ISFLAG:
0 = no calculation of reduced stresses
1 = von Mises stresses computed for the Gauss points (INTORD not 0 ! )
This file is optional and normally
not used here because it is much more convenient to enter the pressure data for
the plate elements into Z88I1.TXT in the section
material informations. However, the possibility for entering the pressure loads
by the surface and pressure loads file Z88I5.TXT, too, is implemented for
universal use of this file. Then set IQFLAG to 1 and proceed as follows:
> Element number with pressure load
> Pressure, positive if poiting towards the
edge
Results:
Displacements in Z (i.e. w) and rotations ThetaX
around X- axis and ThetaY around the Y- axis.
Stresses: The stresses are calculated in the corner nodes or Gauss
points and printed along with their locations. The following results will be
presented:
Optional von Mises
stresses
Nodal forces in X and Y for each element and each node.