Influence of face sheet thickness on flexural strength characteristics of carbon/epoxy/Nomex honeycomb sandwich panels

This study presents the findings of an investigation into the effect of varying the thickness of a carbon/epoxy face sheet of a Nomex honeycomb sandwich panel on its the flexural properties. The thickness (h_s) of the face sheet was varied by increasing the number of plies from one 0.25 mm thick layer to eight such layers, giving a total nominal thickness of 2.0 mm, whilst maintaining a constant thickness of the core. The flexural properties of the sandwich panels were investigated through a series of three- and four-point bending tests. A particular focus was on identifying changes in the failure mode with increasing face sheet thickness. The flexural properties of the sandwich panels were predicted using sandwich beam theory, where the deviation from the experimental values was shown to be less than 13%. A two parameter Weibull distribution model was used to predict the maximum flexural load using an analysis of variance (ANOVA) tool and an excellent level of correlation was observed with the experimental values. The difference between the predicted maximum load values and the experimental results was below 5% in all cases. A brittle mode of failure was observed in the thickest panel. The sandwich panel based on 1.5 mm thick face sheet was identified as being the most appropriate design, both in terms of strength and stiffness.