Buckling of Disbonds in Honeycomb-core Sandwich Beams

ABSTRACT: The buckling behavior of a disbond in a sandwich beam is analyzed by modeling the sandwich as a beam on a Winkler foundation. The foundation stiffness is derived through a stress function approach, modeling the core as a two-dimensional, orthotropic material in plane strain. When the resulting stiffness term is used in the Winkler foundation model, the predicted buckling loads vary from the specimen test results by only 1.7 % (with a standard deviation of 2.3%). This is the most accurate published prediction of disbond buckling and is discussed in terms of previous studies. An extensive specimen test program is described, the results of which are used to validate the Winkler foundation model. The buckling load, as a function of core thickness, is found to have a minimum when the core thickness is approximately equal to the natural wrinkling half-wavelength of the sandwich. Further, a characteristic curve is found using the wrinkling wavelength and the Euler buckling load as normalizing values. A semi-empirical formula for the buckling load is developed from a non-dimensional analysis and predicts the specimen test results to within 2.8 % (standard deviation of 3.6%). KEY WORDS: honeycomb core, disbond buckling, 4-point bending, delamination, sandwich beam