A composite sandwich panel offers particular mechanical advantages : the facings absorb traction and compression forces , while the core material resists shear and thrust forces .
Each component of a sandwich panel plays a particular role :
FACES : The faces carry the tensile and compressive stresses in the sandwich . Local flexural rigidity is so small it can often be ignored .
CORE : The core ’ s function is to support the thin skins so that they do not buckle , and to keep them in relative position to each other . To accomplish this , the core must have several important characteristics . It has to be stiff enough to keep the distance between the faces constant . It must also be so rigid in shear strength that the faces do not ‘ slide over each other ’. The shear rigidity forces the faces to ‘ cooperate ’ with each other . If the core is weak in shear strength , the faces will not cooperate and the sandwich will lose its stiffness .
It is the sandwich structure as a whole that makes this type of panel so beneficial . However , the core has to fulfil the most complex demands . Strength in different directions is not the only property that the core has to have . Often there are special demands for buckling , insulation , absorption of moisture , resistance to ageing , etc .
ADHESIVE ( bonding layer ): To keep the faces and the core cooperating with each other , the adhesive between the faces and the core must be able to withstand and transfer the shear forces between them . The adhesive must be able to carry both shear and tensile stresses .
It is hard to specify what kind of demands an adhesive needs to meet . A simple rule is that the adhesive should be able to withstand the same shear stress as the core .