Lay-up Definition

@LAYUP_DEFINITION {
@LAYUP_NAME {LayUpName} {
@MATERIAL_PROPERTY_NAME {DefaultMatPropName}
@LAYER_THICKNESS {tdefault}
@LAYER_DEFINITION {
@MATERIAL_PROPERTY_NAME {MatPropNamei}
@LAYER_THICKNESS {ti}
@LAYER_STATIONS (ηI(i), ηF(i))
@ORIENTATION_ANGLES {βi, γi}
}
@LAYER_DEFINITION {
...
}
@COMMENTS {CommentText}
}
}

Introduction

Figure 1. Configuration of a lay-up.

The physical properties of beam cross-sections made of possibly heterogeneous anisotropic material are described by solid properties, which rely the definition of a lay-up as illustrated in fig. 1. It consists of N layers of possibly anisotropic material stacked on top of each other. The first layer, layer 1, is at the bottom of the stacking sequence and the last layer, layer N, is at the top.

The depiction of the lay-up presented in fig. 1 is too simplified. Indeed, the various layers might not extend over the entire length of the mold line. The upper portion of fig. 2 shows the sequence of layers that compose the lay-up: it consists of N layers of possibly anisotropic material stacked on top of each other. The first layer of the lay-up, layer 1, espouses the shape of the mold line and the last layer, layer N, is at the top.

Figure 2. Configuration of a lay-up.

Lay-ups are used to define the structural properties of walls and shapes. The geometry of the mold line of the lay-up, see fig. 2, is defined by the NURBS curve inherited from its parent wall or shape. In fig. 2, layers 1, 2, and N, extend over the entire length of the mold line, i.e., the initial and final stations of those layers are ηI = 0 and ηF = 1. Layers 3 and 4 cover a portion of the mold line only. For layer 3, ηI = η2 and ηF = η3 whereas for layer 4, ηI = η1 and ηF = η4. Note the following requirements: 0 ≤ ηI ≤ 1, 0 ≤ ηF ≤ 1, and ηI ηF.

During the curing process, pressure is applied on the top layer and all layers are pressed against the mold line, as illustrated in the bottom portion of fig. 2. At the locations where layer are added or dropped, upper layers undergo a transition that puts them in contact with lower layers. This transition takes place over a finite zone called the “add-drop zone”, as indicated in the fig. 2. The initial configuration of the draping illustrates the draping sequence, as the layer are draped one at a time on the mold. The configuration of the draping after cure is similar to the final, cured configuration.

In summary, the physical characteristics of a generic Layer i are defined by the following parameters: (1) its thickness ti; (2) its material properties; (3) its orientation angles βi and γi; (4) the location of its initial station ηI(i); (5) the location of its final station ηF(i).

Notes

  1. It is not uncommon for lay-ups to be made of a single material but the various layers have different orientation angle. In such case, it is convenient to define an optional default material properties, DefaultMatPropName, and an optional default layer thickness, tdefault.
  2. Each layer of the lay-up is defined in its own subsection starting with the keyword @LAYER_DEFINITION. The first subsection defines Layer 1, which lies onto the mold first; the last Layer N. The order in which the subsections appear defines the stacking sequence of the lay-up. The following conventions apply.
    • The layer thickness is ti. (Default: ti = tdefault).
    • The layer material properties are MatPropNamei. (Default: MatPropName = DefaultMatPropName).
    • The layer orientation angles are βi and γi. These must be defined as no default values are provided. These angles bring the cross-section basis to the material basis, see sign conventions.
    • The location of the layer initial station is ηI. (Default: ηI = 0).
    • The location of the layer final station is ηF. (Default: ηF = 1).
  3. Because materials can present anisotropic stiffness and strength properties, the orientation of each layer must be specified precisely. Material properties are defined with respect to a material basis. Orientation angles βi and γi determine the orientation of this material basis with respect to the global reference basis. If the lay-up is used to define the sectional properties of beams via solid element properties, the procedure to determine the relative orientation of the material basis with respect to the global basis is presented here.
  4. It is possible to attach comments to the definition of the object; these comments have no effect on its definition.
  5. Examples

    Example 1.

    The first example creates a four-ply lay-up. Because the material properties and layer thickness are omitted for the first three layers, the default material properties, MatPropT500-4208, and default thickness, t = 0.0625 will be used. The last layer defines its own material properties and thickness.

    @LAY_UP_DEFINITION {
    @LAY_UP_NAME {LayUp} {
    @MATERIAL_PROPERTY_NAME {MatPropT500-4208}
    @LAYER_THICKNESS { 0.0625}
    @LAYER_DEFINITION {
    @ORIENTATION_ANGLES {0.0, 30.0}
    }
    @LAYER_DEFINITION {
    @ORIENTATION_ANGLES {0.0, -30.0}
    }
    @LAYER_DEFINITION {
    @ORIENTATION_ANGLES {0.0, -30.0}
    }
    @LAYER_DEFINITION {
    @MATERIAL_PROPERTY_NAME {MatPropT300-5208}
    @LAYER_THICKNESS { 0.0525}
    @ORIENTATION_ANGLES {0.0, 30.0}
    }
    }
    }