The sandwich principle is a highly weight efficient construction method. Sandwich structures are fairly susceptible to flaws in the face-to-core interface. Face-to-core debonds are one common form of flaws in sandwich structures. The aim of this work was to study the effect of debonds on the strength of sandwich panels. Experiments with laterally loaded panels were conducted. Finite element modelling on corresponding panel configurations was performed. The tested panels had glass fibre facesheets and PVC foam core. The panel load was lateral uniform pressure. Three different debond locations were investigated. The locations were inside the supports and only single, circular
debonds were studied. All studied debonds were between the pressure face and the core. A parametric FE model of a debond flawed sandwich panel was successfully developed. The debonds were modelled as circular cracks. The FE analysis results were used for fracture mechanical calculations. The fracture
mechanical calculations used relative nodal displacements of the crack flanks as input data. Energy release rates and stress intensities were calculated. Also mode mix, which measures the ratio between the opening and sliding modes of crack loading, was calculated. Based on other work critical values for the Griffith energy and stress intensities were established. The critical Griffith energy was used for strength estimation of the modelled debonded panels. The results from the fracture mechanical calculations were compared with test results. The panel experiments showed that debonds near the supports effects the residual strength considerably. This is due to high transverse core shear stresses in the areas near the supports. A central debond did not effect the panel strength in the tests. The results from the calculations show good agreement with the test
results. Debond criticality evaluation using fairly simple modelling techniques seems to produce good results.