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The development of new adhesives has allowed to expand the application of bonding into the most diverse industrial fields. This review article presents the commonly used experimental methods for the investigation of mechanical performance of adhesively bonded joints in the aerospace, wind energy, automotive and civil engineering sectors. In these sectors, due to their excellent intrinsic properties, composite materials are often used along with conventional materials such as steel, concrete and aluminium. In this context, and due to the limitations that the traditional joining techniques present, adhesive joints are an excellent alternative. However, standardized experimental procedures are not always applicable for testing representative adhesive joints in these industries. Lack of relevant regulations across the different fields is often overcome by the academia and companies' own regulations and standards. Additional costs are thus mitigated to the industrial sectors in relation with the certification process which effectively can deprive even the biggest companies from promoting adhesive bonding. To ensure continuous growth of the adhesive bonding field the new international standards, focusing on actual adhesive joints' performance rather than on specific application of adhesive joints are necessary. [ABSTRACT FROM AUTHOR]

Double Cantilever Beam (DCB) specimens were made from aluminium plates bonded with Hysol®EA9321 epoxy adhesive. These were tested both under monotonic and cyclic loading conditions. Experimental testing data were obtained from classic force and displacement measurements, as well as from backface strain recordings. Apart from the usual crack propagation monitoring, evolution of the process zone at the crack tip was studied during the experiment. Results of fatigue were compared with those of standard loading. Despite the viscoelastic nature of the adhesive, an elastic treatment of the results proved most satisfactory. In addition, good agreement was found between experimental and theoretical results obtained with a Timoshenko beam on Winkler elastic foundation model. [ABSTRACT FROM PUBLISHER]

We have studied the effect of interface heterogeneity on fracture, at both local and global scales. The single cantilever beam adhesion test was used to investigate interfacial fracture between polycarbonate plates and an elastic/fragile epoxy adhesive. Two surface treatments were applied to a (given) polycarbonate plate giving zones of strong and weak adhesion parallel to the crack direction. Calculated fracture energies differed from those expected from a simple rule-of-mixtures. A perturbation method, proposed by Rice, was used and results compared with crack fronts observedin situ. The technique was applied successfully but the difference in values of stress intensity factor between the zones was found substantially different from the experimental value. In an attempt to explain discrepancies, specimens with discontinuous crack fronts (adhesive and/or plates severed along the strong/weak adhesion frontier) were tested. Good agreement was found with the rule-of-mixtures predictions raising questions about the role of crack front continuity in load transfer. [ABSTRACT FROM AUTHOR]

The effects of heterogeneities (weak zones in particular) in adhesive joints and their importance on overall fracture properties are relatively unknown, but doubtlessly they may be crucial in many applications. Using a model heterogeneous adhesive bond, represented by a given mixture of regions of strong and weak adhesion, we have studied the influence of interface variability on overall fracture energy (global energy release rate). Adopting the original Griffith-Irwin arguments, we have employed a simple, fracture scaling law. By varying relative proportions of the weak and strong interfaces, a nonlinear evolution of fracture energy was observed. This was contrary to expectations, cf. rules of mixtures. Inspired by rheological models (Maxwell, Voigt/Kelvin, etc.), an appropriate model was found empirically. [ABSTRACT FROM PUBLISHER]