To [[Composite laminate models|model a composite laminate]] there are a few options, the most important are the equivalent single layer and the [[Layerwise Theories|layerwise]].

Those theories works by computing the homogenized material properties, and solving only at the mid plane. They are useful for global response for thin laminates and are computationnally inexpensive.

*They have issue with layers of different properties.*

#### Classical Laminate Theory (CLT), hypothesis :
The normal line to the median plane of the plate before deformation stays normal to the plane after deformation.
-> lack of transverse shear

#### First-order Shear Deformation Theory (FSDT), hypothesis :
The normal line to the median plane of the plate stays straight after deformation but it is not normal to the middle plane, the shear constraint stays constant along the thickness of the plate.

#### High-order Shear Deformation theory (HSDT) :
More complex variation of the shear constraint along the thickness of the plate, but more computationally expensive.