A tension/compression–torsion test suited to analyze the mechanical behaviour of adhesives under non-proportional loadings

Structural adhesives are nowadays recognized to be an efficient alternative to traditional fastening methods, such as riveting or welding. However, their behaviour is complex, slowing down their spreading in the industry which requires reliable numerical models to predict their behaviour. Indeed, it is also well known that the dependency to the hydrostatic stress should be taken into account and the non-associated formalism should be considered. The identification of such models therefore requires a large experimental database under multi-axial loadings. To this end, a modified Arcan device was developed in a previous study. It enables the solicitation of an especially designed bonded sample under a wide range of proportional loadings between tension and compression–shear. A logical improvement is the development of a test that can complete the modified Arcan test by allowing loadings between compression–shear and compression as well as non-proportional loadings. This work focuses on the development of such a test: a tension/compression–torsion test. A finite element study of a specimen geometry well suited for the test was carried out. A great attention was paid to edge effects classical from adhesively bonded structures. As was done with the modified Arcan device, a geometry with beaks was proposed. The bonding device and the manufactured testing device are presented along with the first experimental campaign results which validate the test design.