Strength Improvement of Adhesively-Bonded Joints Using a Reverse-Bent Geometry

Abstract

Adhesive bonding of components has become more efficient in recent years due to the developments in adhesive technology, which has resulted in higher peel and shear strengths, and also in allowable ductility up to failure. As a result, fastening and riveting methods are being progressively replaced by adhesive bonding, allowing a big step towards stronger and lighter unions. However, single-lap bonded joints still generate substantial peel and shear stress concentrations at the overlap edges that can be harmful to the structure, especially when using brittle adhesives that do not allow plasticization in these regions. In this work, a numerical and experimental study is performed to evaluate the feasibility of bending the adherends at the ends of the overlap for the strength improvement of single-lap aluminium joints bonded with a brittle and a ductile adhesive. Different combinations of joint eccentricity were tested, including absence of eccentricity, allowing the optimization of the joint. A Finite Element stress and failure analysis in ABAQUS ® was also carried out to provide a better understanding of the bent configuration. Results showed a major advantage of using the proposed modification for the brittle adhesive, but the joints with the ductile adhesive were not much affected by the bending technique.

Modelling adhesive joints with cohesive zone models: effect of the cohesive law shape of the adhesive layer

“…The TAST characterisation of the adhesive was carried out according to the 11003-2:1999 ISO standard, considering DIN Ck 45 steel adherends. More details about the fabrication and testing procedures can be found in reference [31]. Characterisation of the adhesives regarding the elastic constants, strengths and strains in tension and shear, was previously conducted in the work of da Silva et al [32] (Araldite s AV138) and by the authors in a previous work [33] (Araldite s 2015).…”

Fracture toughness determination of adhesive and co-cured joints in natural fibre composites

“…A large amount of studies is available for the mechanical, thermal, rheological and impact characterization of jute fibres and their composites [8,16]. Typical properties of jute are as follows: density of 1.3-1.4 g/cm 3 , elongation at failure of 1.5-1.8%, tensile strength of 400-800 MPa and Young's modulus (E) of 15-30 GPa. Epoxy was chosen for the matrix material on account of the good mechanical (strength and stiffness) and toughness properties, and also because of the superior wetting characteristics of epoxy on natural fibres and improved chemical stability to allow protection of the fibres against external agents [9].…”

“…However, stress concentrations exist in bonded joints along the bond length owing to the gradual transfer of load between adherends and also the adherends rotation in the presence of asymmetric loads [2]. A large amount of works addresses the critical factors affecting the integrity of adhesive joints, such as the parent structure thickness, adhesive thickness, bonding length and geometric modifications that reduce stress concentrations [3][4][5]. On the other hand, natural fibre matrix materials are polypropylene, polyester, polyurethane and epoxy.…”

Comparative study of adhesive joint designs for composite trusses based on numerical models

“…The material used for the adhesive layer in the numerical models is a rubber-toughened epoxy adhesive, Araldite 2015 [27]. The mechanical properties of this adhesive were determined in a study by Campilho et al [28], along with another brittle adhesive of the same brand. The choice of a rubber-toughened ductile adhesive instead of a brittle one is based on the ductile adhesives' increased toughness due to particle cavitation, which increases their strength and makes them a preferred choice for aerospace applications [29].…”