Buckling of laser-welded sandwich panels. Part 2 : Elastic buckling normal to the webs

This is the second of three companion papers that examine the elastic buckling andcollapse of laser-welded sandwich panels with an adhesively bonded core and uni-directionalvertical webs. In the first paper, it has been shown that the critical load in compression parallelto the webs can be accurately predicted by using a Pasternak foundation to model the coreand by using a simple clamping factor to describe the boundary conditions at the laser weld.In this paper, the same model is adapted to predict the critical load in compression normal tothe webs. As the face plate is now short and wide, rather than long and narrow as before, a‘constrained wrinkling’ approach is outlined that recognises that the face plate is limited in itsability to wrinkle naturally and can only deform in certain mode shapes. The clamping factorand the effective wave length are derived for different buckling mode shapes and boundaryconditions at the laser weld, and the constrained wrinkling load is determined by evaluatingthe buckling load for successive modes and simply picking the smallest value. It is shown that,for low modulus core materials, the constrained wrinkling load is equal to the bare platebuckling load and, for high modulus materials, the solution converges toward anti-symmetricalwrinkling, as has been found for the case of compression parallel to webs. The constrainedwrinkling load agrees well with finite element results but as before the proportional limit ofthe face plate material is usually reached well before elastic buckling occurs.
QC 20111220