Experimental study of the effect of pre-bond contamination with de-icing fluid and ageing on the fracture toughness of composite bonded joints

The scope of the present work is to experimentally investigate the effect of pre-bond contamination with de-icing (DI) fluid and the combined effect of DI fluid and hygrothermal ageing on the fracture toughness of carbon fibre reinforced plastic bonded joints. These scenarios could occur in the implementation of an adhesively bonded patch repair in a composite aircraft structural part. To this end, mode I and mode II fracture toughness tests were conducted on contaminated specimens and mode II fracture toughness tests on contaminated/aged specimens. Three levels of contamination with a de-icer were considered. The hygrothermal ageing conditions applied until saturation are 70 degrees C/85% relative humidity. The experimental results reveal a detrimental effect of DI fluid on both mode I and mode II fracture toughness of the bonded joints. With increasing the contamination level, the mode I and mode II critical energy release rates decrease. Under mode I loading, the specimens failed mainly in light-fibre-tear mode, while under mode II loading, in adhesive failure mode. Hygrothermal ageing decreased further the mode II fracture toughness of the specimens and increased the adhesive failure mode. The present study reveals that the pre-bond DI contamination and after-bond ageing could critically degrade the strength of adhesively bonded patch repairs.