The use of acoustic emission and composite peel tests to detect weak adhesion in composite structures

Abstract

Adhesive bonding is one of the most promising joining technologies for composite aircraft. However, to comply with current aircraft certification rules, current safety-critical bonded joints, in which at least one of the interfaces requires additional surface preparation, are always used in combination with redundant mechanical fasteners, such as rivets and bolts. This lack of trust in bonded structures is mostly linked to the fear of lack of adhesion or a "weak bond".The aim of this paper is to tackle this challenge by assessing the ability to use composite peel tests and acoustic emission (AE) technique to assess adhesion quality and distinguish a good bond quality from a "weak bond".Composite Bell Peel (CBP) tests and Double-CantileverBeam (DCB) tests were performed on contaminated and noncontaminated CFRP bonded specimens. The results show that peel strength drops significantly at the location of the contaminated interface that has led to weak adhesion, as a result from adhesive failure. The AE signals obtained during DCB tests show different features for cracks growing at the interface ("weak bonds") and inside the adhesive layer (cohesive failure). In addition to this, scattering of the AE signals were observed in the contaminated specimens with "weak bonds". ARTICLE HISTORY

A statistical optimization of a green laser‐assisted ablation process towards automatic bonded repairs of CFRP composites

“…Combined with the previous observation on the higher number of AE hits in the cohesive failure case, this suggests that AE events generated during adhesive failure have higher energies compared to the corresponding ones during cohesive failure. It is worth to be mentioned that Teixeira de Freitas et al observed the exact opposite (i.e., higher energy content in AE from cohesive failure) in DCB and peel tests, both dominated by normal stresses rather than shear stresses as in the stepped lap shear test case. This is verified by (Fig.…”

Enhanced Interface Adhesion by Novel Eco-Epoxy Adhesives Based on the Modified Tannic Acid on Al and CFRP Adherends

“…Besides the contaminant removal, UV/ozone treatment is employed for the oxidation of the CFRP surface and the introduction of hydroxyl and carboxylic groups that would improve the interfacial adhesion [ 31 ]. Exposure times higher than 5 min were found to be successful in the introduction of a significant amount of oxygen containing functional groups in cured epoxy in printed circuit boards [ 32 , 33 , 34 , 35 ]. In addition, a significant increase in surface roughness was found due to the etching effect of UV/ozone treatment of epoxides [ 32 ].…”

Condition monitoring of crack extension in the reinforcement adhesive joints by carbon nanotubes

“…Croccolo et al [4] use acoustic emission as condition monitoring technique for the evaluation of defect densities in adhesive bonding to predict the actual failure load of the adhesive joint. Some of these techniques, like acoustic emission are online methods for determining the damage progression in bonded joints and composites as reported by Cawley [5] and De Freitas [6] respectively. Such online methods enable to predict the onset and progression of damage under the mechanical load.…”