Effect of Processing Conditions and Material Properties on the Debond Fracture Toughness of Foam-Core Sandwich Composites: Experimental Optimization

Abstract

The structural performance and reliability of the foam-core sandwich composites are known to be dependent on the strength of the core-skin bonding. Mechanical tests have repeatedly demonstrated that the failure modes for the sandwich during flexural, compression, and tension loading are first triggered by the failure of the interface or the sub-interface zones between the core and the skin. Once this failure mode sets in, core shear and delamination progress rapidly, leading to the final failure of the sandwich construction. The strength of the core-skin bonding depends on the chemical reactions taking place during the cure process. The effect of processing parameters and material properties on the core-skin bonding strength were investigated experimentally. The skincore debond fracture toughness was measured using Tilted Sandwich Debond specimens. Verifying the heuristics developed in the previous part of this paper [1], we achieved a 78% increase in debond fracture toughness with elevated temperature processing, and observed reduced variability with higher suction pressures. We also saw increase in debond fracture toughness with foam density, validating the assumption that interfacial bonding controls the debond fracture toughness. An increase in resin uptake with foam density was an interesting observation from these experiments.