Bending-twisting coupling in effective laminates

[mraedel]

This question is related to the picture in the "In-Plane" section of http://hypersizer.com/help_7.3/#Materials/EffLam/el-properties-stiffness.php.

From my understanding you get bending-twisting coupling, so populated D16 & D26 terms, in the laminate stiffness matrix and therefore non-orthotropic stiffness behavior in bending as soon as you have non 0° or 90° layers in your discrete stacking sequence, e.g. by +45° and -45° layers. The reason is that, even if the stacking sequence is symmetric and balanced, +45° and -45° layers may not be located at the same offset from the middle-plane.

However, this information, the stacking order and therefore distance from the laminae middle-plane to the stacking sequence middle plane gets lost in the effective laminate approach. The approach for the calculation of the bending stiffness is described here: http://hypersizer.com/forum/index.php/topic,535.0.html

So how can it be that the ABD-matrix shown in the mentioned figure has D16 & D26 populated?

[James]

The ABD shown in the help topic is for a discrete laminate with the same ply percentages. This is not the effective laminate ABD. You're correct that the D16 and D26 bending coupling terms are ignored for effective laminate sizing.

-James