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

Abstract

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°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.

Determination of adhesion strength of pre-bond contaminated composite-to-metal bonded joints by centrifuge tests

“…Runway de-icing fluid is one of the most commonly encountered fluids that aircraft structures may be exposed to, as it can be swirled from the runway to outer parts of the aircraft [2]. During patch-repairing of composite parts, inadequate cleaning can result to de-icing fluid remains.…”

“…In aerostructures, adhesive bonding is applied in metal-to-metal joints, composite-to-composite joints and composite-to-metal joints both for assembling parts and for patch-repairing. However, application of adhesive bonding in aerostructures is limited for the moment to secondary structural parts that are not load-critical [1,2] due to certification reasons. In the certification requirements for primary composite aircraft structures, it is stated that for bonded joints repeatable and reliable non-destructive inspection techniques (NDI) must be established that ensure the strength of each joint [3].…”

“…In a series of works published by the authors [1,2,16,17], it has been found by means of Mode-I and Mode-II fracture toughness tests, that kissing bonds created by production-and repair-related contamination scenarios, might degrade significantly the fracture toughness of composite bonded joints. Additionally, the joint strength of contaminated adhesively bonded joints has been studied with conventional testing methods indicating the detrimental effect of the contaminant [18][19][20].…”

Development of the symmetrical laser shock test for weak bond inspection

“…For example, release agent specimens were created by deep-coating of one of the composite plate. In addition, GIC and GIIC tests have been performed by University of Patras, and show that various bonding strength have been obtained [9]- [11].…”

Study of CFRP adhesive bonds influenced by factors encountered during aircraft operations

“…As far as the de-icing fluid is considered it was shown that it has a negative effect on both mode I and mode II fracture toughness of the bonded joints. The increasing level of contamination results in decrease of the mode I and mode II critical energy release rates [3]. In this paper we report results of five techniques employed for assessment of the bonds.…”