Design of sandwich structures under contact loading

The problem of contact loading of sandwich beams is considered, in which the load is applied by means of an indentor. Examples of loading of this type are the common three-point bend test used to determine the strength properties and failure modes, as well as accidental impact problems. It is known that the stress and strain distributions in sandwich beams under relatively concentrated loading are complex, with significant stress concentrations adjacent to the loading not predicted by simpler structural theories. The approach taken here is to use the elasticity solution of Pagano and Srinivas and Rao for surface traction loading of a layered, orthotropic simply supported body, and to vary the pressure distribution iteratively to achieve the best fit between the calculated surface displacements and the indentor profile. Results are given for an orthotropic half-space, where the exact solution is known, as well as for typical sandwich beams with carbon/epoxy faces and foam cores. Comparisons with strains obtained experimentally using embedded strain gages show excellent agreement.