Modelling of bonded joints with flexible adhesives

Despite the significant technical/scientific progress achieved in the lasts years, design and modelling of adhesive joints is still an active research area. Among different approaches, the finite element method (FEM) constitutes one of the most useful, precise and powerful calculation tools for the analysis and design of bonded joints. Through a proper definition of the models, the FEM allows the determination of accurate fields of stresses and strains in the adhesive and in the adherents even for complex joint geometries or load histories. Moreover, the influence of geometrical parameters (joint configuration, thicknesses, fillets, etc) on the stress and strain levels in critical regions of the adhesive can be easily evaluated. In this way, different designs can be analysed to optimize the performance and reliability of the joints. The definition of the material models clearly constitutes one of the most relevant aspects of these numerical methodologies. The prediction capability of the FE simulations and the precision of the results will strongly depend on the material definition and the accuracy level of the material models to reproduce the mechanical behaviour of the adhesive. This is especially critical for adhesives that present markedly non linear behaviour. This work presents a study of the application of FE models for the analysis of joints with flexible adhesives. The work is focused on the characterization of elastomeric-like adhesives and the definition of proper material models to correctly reproduce their mechanical response. The operation of the models is checked through a numerical/experimental study of different bonded joints configurations. As result, it has been evidenced that a proper selection/adjustment of hyperelastic models can lead to accurate FE predictions for different joints configurations. In addition, special care must be taken when assuming incompressible hyperelastic adhesive behaviours since in some cases this hypothesis could lead to erroneous results.