Mechanical characterization of adhesive joints under shear using the Asymmetric Four-Point Bending test

: Developing experimental procedures to minimise parasitic effects (such as peel stresses and bending moments) remains a major challenge in characterising shear behaviour of adhesive joints. This paper investigates the Asymmetric Four-Point Bending (AFPB) test as an alternative configuration. Analytical modelling confirms zero bending moment along the adhesive layer centreline. However, Finite Element (FE) simulations show low-magnitude peel stresses and local stress singularities at the adhesive extremities, particularly at substrate interfaces. Utilising stiffer substrates enhances shear stress uniformity, while chamfered edges effectively reduce stress concentrations. Experiments on a structural adhesive using Digital Image Correlation (DIC) demonstrate high repeatability for shear stress-strain analysis. Although minor parasitic peel stresses persist and stress singularities are present at the edges, especially at the interface with the substrates, these results establish AFPB as a promising and robust protocol for shear characterisation of adhesive joints.