Test method to assess interface adhesion in composite bonding

Abstract

This paper introduces a new type of peel tests dedicated to composite bonding: Composite Peel Tests. This test is inspired on the standard floating roller peel test widely used for metal bonding. The aim of this study is to investigate the potential of the Composite Peel Test to assess interface adhesion in composite bonded structures. To this end, peel tests were performed with nine different types of adhesives and at two environmental temperatures, room temperature and +80°C. The results were compared with the standard floating roller peel tests with Aluminium adherends. The results show that when using the Composite Peel Test good interface adhesion results either in cohesive failure of the adhesive or intra-laminar failure of the composite, while bad adhesion results in adhesive failure. In most cases of good interface adhesion, increasing the temperature favors cohesive failure of the adhesive in detriment of intra-laminar failure of the composite. Peel strengths can be used as a quality indicator of interface adhesion only if using exactly the same type of flexible adherend (peeling-off member). Nevertheless, if cohesive failure is the dominant failure mode, the comparison between adhesives' peel strength is consistent disregarding of the type of peel-off adherend. Composite Peel Tests are suitable to assess interface adhesion of composite bonded structures.

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

“…This has been observed in previous research, not only on CBP tests but also in other bonded joint geometries. [35,39,49] This is the reason why the peel load for UV/Ozone specimens is lower than for the non-contaminated area of the UV/Ozone contaminated specimens. The predominant failure mode is ILFC in the former and cohesive failure inside the adhesive in the later.…”

“…CBP test set up. [39] diameter, scanned every 1 mm, 10 dB damping, no filters). As it can be observed, the contamination area cannot be detected by the C-scan, which proves the existence of a "weak bond" or a "kissing bonds" in the specimens.…”

“…In both cases the tested bonded joint is metal-to-composite and not composite-to-composite. Recently Teixeira de Freitas [39] has studied a Composite Bell Peel (CBP) test in which both flexibleand rigid adherend are composite laminates. Results show that the suggested test method is able to screen and compare the adhesion quality of different adhesives to composite adherends.…”

Failure analysis of adhesively-bonded skin-to-stiffener joints: Metal–metal vs. composite–metal

“…Both are epoxy film adhesives with a curing temperature of 120 C for 90 min in the autoclave. The adhesives were chosen after performing screening tests on ten adhesives [15]. These two adhesives scored the best results in terms of good adhesion to metals and to composites, and in terms of apparent average shear strength (higher than 20 MPa).…”

Effect of the structural reinforcement of composite adherends on the mechanical strength of adhesive joints

“…In a single lap joint, the peel stress concentrations are generally produced at the end of the overlap and the spew fillet enables a reduction in the stress concentration [12]. The adhesion properties of composite bonded to aluminum adherends and adhesive joint configurations subjected to peel loads were investigated [13]. Adhesive joint fracture is produced by a crack propagation from the free edges.…”