Fatigue of Undamaged and Damaged Honeycomb Sandwich Beams

In this paper, the fatigue characteristics of shear loaded honeycomb sandwich beams are experimentally investigated through constant load amplitude tests. Two honeycomb sandwich configurations are test differentiated only by the orientation of the honeycomb core. The fatigue test results are presented in standard S-N diagrams with a best curve fit to the experimental data. Furthermore, the effect of sub-surface damages, such as flawed butt-joints and interface disbonds is investigated. Two loading ratios are applied for all fatigue test series. On the basis of the difference in these test results, the effect of crack opening and closing is discussed. An empirical prediction model for the fatigue life of damaged beams is proposed based on the results from both the fatigue tests of undamaged beams and the static strength of the damaged specimens. The prediction model is verified against the fatigue test results of the damaged beams. The fatigue fracture initiation and propagation for undamaged and damaged honeycomb core sandwich beams are also discussed.