Composite sandwich panel is not a thick laminate !
Nevertheless many engineers believe that a composite sandwich panel is a laminate with a thick and light middle layer, the mechanical behaviors and damage models of sandwich panel prove that a composite sandwich panel is not a thick laminate.
A sandwich beam is like a I-beam which means that it has a high bending ratio to weight so it is a advance optimized structural composite.
in the sandwich panel with light core the shear shress of the core is constant through thickness and tensile stress is approximately zero and the compression of the core is considerable. On the contrary a composite laminate has a tensile stress and in the classical laminate deformation theory the shear stress of the core is neglected.
core fracture and indentation is a major failure of a sandwich panel that they are generated by shear and normal stress of the core respectively.
CLDT (classical laminate deformation theory) or FOSDT (first order shear deformation theory) cannot predict the core fracture and core indentation of a composite sandwich panel correctly.
in conclusion, the behaviors of sandwich beams or panels shall be determined by sandwich panel relation . below reference help to understand the sandwich panel better.