The influence of water immersion on skin-core debonding in GFRP-balsa sandwich structures

A new test technique has been developed in order to characterise the skin-core interfacial properties of a series of fibre reinforced sandwich structures similar to those presently being used in the marine industry. The technique involves peeling the lower surface skin away from the core in a controlled fashion. Four different glass fibre reinforced epoxy/balsa structures have been tested and the effect of incorporating various skin-core interlayers assessed. Tests were also undertaken on specimens that had been immersed in seawater for a period of forty-five days. The results indicate that the fracture energies associated with skin-core debonding are relatively high, typically 1000 J/m². It has also been shown that neither a pre-treatment of the balsa core nor the incorporation of a layer of CSM fibres resulted in an improvement in the fracture energy of the interfacial region. Immersion in seawater for forty-five days resulted in a significant increase in the fracture toughness of this region. A subsequent examination of the fracture surfaces showed that fibre bridging between the GFRP skin and the balsa core was more extensive in the soaked samples.