Mechanical APDL Structural Analysis Guide

13.1.2.1. Specifying Individual Layer Properties

With this method, the layer configuration is defined layer-by-layer from bottom to top. The bottom
layer is designated as layer 1, and additional layers are stacked from bottom to top in the positive Z
(normal) direction of the element coordinate system. You need to define only half of the layers if
stacking symmetry exists.

At times, a physical layer will ext end over only part of the model. In order to model continuous layers,
these dropped layers may be modeled with zero thickness.Figure 13.1: Layered Model Showing Dropped
Layer (p. 411) shows a model with four layers, the second of which is dropped over part of the model.

Figure 13.1: Layered Model Showing Dropped Layer

1 1

2

3

4
4
3

Layer 2

isdr opped

For each layer, the following properties are specified in the element real constant table (R,RMORE,
RMODIF) accessed with REAL attributes:

• Material properties (via a material reference number MAT )


• Layer orientation angle commands (THETA)


• Layer thickness (TK)

You can also define layered sections via the Section Tool (Prep>Sections>Shell - Add/edit). For each
layer, the following are specified in the section definition via the section commands (SECTYPE,SECDATA)
or the Section Tool accessed with the SECNUM attributes.

• Material properties (via a material reference number MAT )


• Layer orientation angle commands (THETA)


• Layer thickness (TK)


• Number of integration points per layer (NUMPT)

Layer Property Descriptions

Following is more information about each of the layer properties:

• Material Properties -- As with any other element, the MP command defines the linear material properties,
  and the TB command is used to define the nonlinear material data tables. The only difference is that the
  material attribute number for each layer of an element is specified in the element's real constant table.
  For the layered elements, the MAT command attribute is used only for the BETD, ALPD, DMPR, and REFT
  arguments of the MP command. The linear material properties for each layer may be either isotropic or
  orthotropic. Typical fiber-reinforced composites contain orthotropic materials and these properties are
  most often supplied in the major Poisson's ratio form. Material property directions are parallel to the layer
  coordinate system, defined by the element coordinate system and the layer orientation angle.


• Layer Orientation Angle -- Defines the orientation of the layer coordinate system with respect to the element
  coordinate system. It is the angle (in degrees) between X-axes of the two systems. By default, the layer
  coordinate system is parallel to the element coordinate system. All elements have a default coordinate

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Modeling Composites