Mechanical APDL Structural Analysis Guide

system which you can change using the ESYS element attribute (ESYS) .You may also write your own

subroutines to define the element and layer coordinate systems (USERAN and USANLY ); for more inform-

ation, see the Guide to User-Programmable Features.

• Layer Thickness -- If the layer thickness is constant, you only need to specify TK(I), the thickness at node
  I. Otherwise, the thicknesses at the four corner nodes must be input. Dropped layers may be represented
  with zero thickness.


• Number of integration points per layer -- Allows you to determine in how much detail the program should
  compute the results. For very thin layers, when used with many other layers, one point would be appro-
  priate. But for laminates with few layers, more would be needed. The default is three points. This feature
  applies only to sections defined via the SECxxxxx section commands.

13.1.2.2. Sandwich and Multiple-Layered Structures

Sandwich structures have two thin faceplates and a thick, but relatively weak, core.Figure 13.2: Sandwich
Construction (p. 412) illustrat es sandwich construction.

Figure 13.2: Sandwich Construction

Fac eplate

Fac eplate

Core(atleas t1/2

oftotalthic k nes s)

You can model sandwich structures with SHELL181 or SHELL281; however, both elements model the
transverse-shear deflection using an energy-equivalence method that makes the need for a sandwich
option unnecessary.

13.1.2.3. Node Offset

For SHELL181 and SHELL281 using sections defined via the section commands (SECxxxxx), nodes can
be offset during the definition of the section via the SECOFFSET command.

The figures below illustrat e how you can conveniently model ply drop-off in shell elements that are
adjacent to each other. In Figure 13.3: Layered Shell With Nodes at Midplane (p. 412), the nodes are
located at the middle surfaces and these surfaces are aligned. In Figure 13.4: Layered Shell With Nodes
at Bottom Surface (p. 413), the nodes are located at the bottom surfaces and these surfaces are aligned.

Figure 13.3: Layered Shell With Nodes at Midplane

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