Stresses and failure patterns in the bending of sandwich beams with transversely flexible cores and laminated composite skins

The stresses and failure maps in a sandwich beam that consists of a transversely flexible compressible core between two laminated composite skins, are presented. The stresses and the failure maps are determined using a general, systematic rigorous, and high-order analysis that is based on variational principles, and includes the flexibility effects of the core on the global and local bending behavior of the beam. The analysis uses closed form solutions for any type of skin construction, symmetric or unsymmetric laminated composite layups, any type of core, compressible or incompressible, any type of loading, concentrated or distributed, and any types of boundary and continuity conditions that may differ from one skin to the other, even in the same section. Failure patterns are determined with the aid of the analytical description of the longitudinal stresses in the skins and the principal stresses through the thickness of the core. The stresses in the core and the skins, along with an appropriate failure criteria, for a specified three point bending beam, are demonstrated in the form of principal stresses, failure and failure load maps, that indicate possible failure patterns and locations.