In-situ SEM mechanical testing of miniature bonded joints

A novel experimental regime is undertaken to investigate the peel and shear failure behaviour of adhesive joints with composite adherends. Identical single-lap joint specimens were manufactured using an aircraft grade carbon fibre composite material with a high strength, high toughness adhesive used to bond the specimens. Peel dominant conditions are produced through a three-point bend test, and shear conditions were achieved using a compressive lap shear test. A brief finite element study was carried out to verify the presence of peel dominant and shear conditions. The experiments were carried out under an SEM beam, allowing a novel in-situ analysis of the tests to be carried out, and has been used to identify damage progression during failure of the bonds. Post failure SEM analysis has been used to identify the wide range of failure processes under peel and shear conditions. Under peel conditions, a range of failure modes are produced, including; adhesive failure, thin layer cohesive failure, fibre tear and light fibre tear failure and importantly, mixed failure. Under shear failure conditions, only interface failure was observed, with cusps being the dominant visible feature on the failure surface.