Dynamic wrinkling in sandwich beams

Facings of sandwich structures employed in typical applications are often subject to parametric periodic loading. Such loading can cause local dynamic instability of the facings, i.e. large-amplitude small wavelength lateral vibrations. This phenomenon, called in the paper dynamic wrinkling, may result in fatigue damage or immediate failure. The problem of dynamic wrinkling of the facings is analyzed in the present paper for sandwich beams and for large aspect ratio wide panels that vibrate forming a cylindrical surface. The solution is obtained for the case of a relatively thick or compliant core where the Winkler elastic foundation model of the core is applicable. In addition, the problem is formulated as an extension of the Plantema core model that may be preferable for thinner and stiffer cores. In addition, a new simplified elasticity model is introduced in the paper that is based on the assumption that both facings experience simultaneous and interactive dynamic wrinkling instability. Numerical results shown for the elastic foundation model include the criterion for the onset of dynamic wrinkling and the critical value of the damping coefficient of the facing that is sufficient to prevent such wrinkling. As follows from these results, dynamic wrinkling is unlikely in most engineering applications, except for the case in which the maximum stresses in the facing approach the static wrinkling value.