Question:

I have a problem using PROP16 for fabric shell. THICK is defined in global thickness as 0.93, then three layers are set each 0.31 mm thickness.

What is the meaning of the following error?

ERROR ID : 28

** ERROR IN LAYERED SHELL SET

FOR LAYERED SHELL PID 15 :

NUMBER OF LAYERS MUST BE LOWER OR EQUAL TO 1

WARNING ID : 29

** WARNING WITH COMPOSITE SHELL THICKNESS

SHELL THICKNESS DISCREPENCY WITH

SUM OF LAYER THICKNESSES IS 67 PERCENT

     LAYER   1

           ANGLE (DIR 1,PROJ(VECT / SHELL) .= 0.000000000000

           ANGLE (DIR 1,DIR 2) . . . . . . .= 90.00000000000

           THICKNESS . . . . . . . . . . . .= 0.9300000000000

           POSITION. . . . . . . . . . . . .= 0.000000000000

           MATERIAL NUMBER . . . . . . . . .= 2

Answer:

This error means the number of layers in your model is higher than 1. As mentioned, you defined three layers which is not allowed for /PROP/TYPE16.

The following input parameters are available in /PROP/TYPE16:

Thick: Shell thickness

N: Number of layers, with 1 < N < 100, Default set to 1 (Integer)

Ti: Thickness of layer i (currently only one is allowed)

Since this property is currently compatible with Elastic Anisotropic Fabric (/MAT/LAW58 - FABR_A), only one layer is allowed. It is recommended:

Thick = 1*T1

/PROP/TYPE16 + /MAT/LAW58 will consider only membrane stress, no bending stress, since fabric cannot resist bending.

/PROP/CONNECT is used only for /MAT/LAW59. This element formulation is based on relative elongation of element in normal and shear direction. This allows avoiding the dependence of element time step from element height. Element height can be even equal to 0. Note that material stiffness is specified in normal and in shear direction. Material has no stiffness in lateral direction. Therefore, it is always advised to couple nodes of LAW59 elements to some Lagrange components either directly or through a tied contact.

The parameter Ismstr in /PROP/CONNECT specifies how the nodal forces are calculated from stresses.

For Ismstr=4 use the actual middle area of the element and for Ismstr=1 use initial middle area. This is implemented in order to avoid time step drop, when LAW59 element separates from master surface (due to the failure of master surface elements) and it starts to expand laterally.

In these two properties, options “Thick”, “ti” and Ipos will affect the layer thickness and layer position.

Ipos = 0

Layer positions Zi are automatically calculated with regard to layer thicknesses.

If the sum of the layer thickness is different from the input value “Thick”, a warning message is displayed. Then RADIOSS adjusts the layer thickness and layer position.

Example 1

Shell thickness “Thick” (1.8) is not equal to the sum of layer thickness (0.5+0.6+0.5=1.6) in input.

During the computation, RADIOSS takes the sum of input layer thickness (1.6) to adjust each layer thickness with . So that the adjusted sum of layer thickness is in respect to shell thickness “Thick” (1.8).

The position of each layer is also adjusted regarding to the new layer thickness.

The Adjusted layer thickness is calculated, as shown below:

Ipos = 1

All layer positions Zi in the element thickness MUST be user-defined.

Example 2

If Ipos=1 but layer position Zi leave as default (set to 0). In this case, layers are all in the same position and overlap each other.

During the computation, RADIOSS takes the thickness of the thickest layer (0.6) to adjust each layer thickness with .

The position of each layer will not be adjusted.

The Adjusted layer thickness is calculated, as shown below:

Example 3

If Ipos=1 but layers have a small overlap, due to the user-defined Zi. In this case, layers thickness and layer position will be adjusted.

During the computation RADIOSS calculates the distance between upper and lower surfaces of layers:

And takes this distance to adjust each layer thickness with .

The Adjusted layer thickness is calculated, as shown below:

Note: The local Z-axis defines the position of middle of the thickness shell. Since the Zi is user-defined, the layers are stacked according to the user definition.