The Effect Of Pre-Bond Contamination With Fingerprint And Ageing On The Fracture Toughness Of Composite Bonded Joints

Abstract

The effect of the pre-bond contamination with fingerprint, both during the production and the application of adhesively bonded patch repairs on composite aircraft parts, and the combined effect of fingerprint and hygrothermal ageing on the fracture toughness of carbon fiber reinforced plastic (CFRP) bonded joints are experimentally investigated. To this end, mode I and mode II fracture toughness tests were conducted on fingerprint contamination coupons and mode II fracture toughness tests on contaminated/aged coupons. The artificial fingerprint was applied in the middle of the adherent’s surface in the size of a human fingerprint. The fingerprints consisted of an artificial hand perspiration solution, for the production scenario, and of Skydrol hydraulic-oil, for the repair scenario. Three levels of contamination with fingerprint were considered for each scenario. The hygrothermal ageing conditions applied until saturation were 70oC/85% RH. For the production scenario, the negative effect of the fingerprint contamination on the fracture toughness was designated. The reduction was even greater for the contaminated/aged samples compared to the uncontaminated joints. For the repair scenario, the results were contradictory since GIC fracture toughness increased with increasing the level of contamination, while GIIC fracture toughness deteriorated as a result of the increasing level of contamination. The combined fingerprint contamination and hygrothermal ageing for the repair scenario led to even greater reduction of the GIIC fracture toughness compared to the reference joints.