4

4.14 PLANE STRESS ELEMENT NO.14 WITH 6 NODES

This is a curvilinear Serendipity plane stress element with square shape functions. The transformation is isoparametric. The integration is carried out numerically according to Gauss- Legendre. Consequently, the integration order can be selected in Z88I1.TXT in the material information lines. The order 7 (=7 Gauss points) is mostly sufficient. This element calculates both displacements and stresses very exactly. 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). Pay attention to edge loads, cf. chapter 3.4.

This element type is implemented for use with automeshers e.g. Pro/MESH for the 3D CAD system Pro/ENGINEER by Parametric Technology. Thus, a net generation with Z88N is not possible. Use plane stress elements No.7 for Z88N.

Use plane stress element No.7 whenever possible. It is substantially more precise than this isoparametric triangle.

Input:

CAD (see chapter 2.7.2): 1-4-2-5-3-6-1

Z88I1.TXT

> KFLAG for cartesian (0) or polar coordinates (1)

> 2 degrees of freedom for each node

> Element type is 14

> 6 nodes per element

> Cross-section parameter QPARA is the element thickness

> Integration order INTORD per each mat info line. 7 is usually good. Possible is: 3 for 3 Gauss points, 7 for 7 Gauss points and 13 for 13 Gausspoints. For easy use with plane stress element No.7 (e.g. with Pro/ENGINEER), function ISOD88 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, plane stress elements No.7 use 2*2 = 4 Gauss points and plane stress elements No.14 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 = 0: Calculation of SIGXX, SIGYY and TAUXY

> KFLAG = 1: Additional calculation of SIGRR, SIGTT and TAURT

> Reduced stress flag ISFLAG:

0 = no calculation of reduced stresses

1 = von Mises stresses computed for the Gauss points (INTORD not 0 ! )

Results:

Displacements ino X and Y.

Stresses: The stresses are calculated in the corner nodes or Gauss points and printed along with their locations. For KFLAG = 1 the radial stresses SIGRR, the tangential stresses SIGTT and the accompanying shear stresses SIGRT are computed additionally (makes only sense if a rotational-symmetric structure is available). For easier orientation the respective radiuses and angles of the nodes/points are printed. Optional von Mises stresses

Nodal forces in X and Y for each element and each node.