Shear property measurement of additively manufactured continuous fibre reinforced plastics by in-plane torsion testing

In-plane shear properties are essential for calculating the plane stress state of composites. Test results for in-plane shear properties of fibre-reinforced polymers (FRPs) are generally obtained with methods that generate multiaxial stress states, and no simple shear response is measured. In this paper, the in plane torsion test method is applied to additively manufactured (AM) continuous FRPs. With this method, planar simple shear loading is achieved for a dedicated, spiral lay-up of the AM specimen. Using digital image correlation, surface strains were obtained for an observed section of the specimen, and shear stress–strain curves were extracted for fibre bundles, co-extruded thermoplastic material, and the composite of both. Shear stiffness and shear strength values are yielded for representative surface areas. Furthermore, the fracture behaviour in shear is discussed. The co-extruded thermoplastic filler material is shown to be the phase where cracks progress is most likely, however as some fibre bundles are split, these can be bridged by the crack. In conclusion, the method is well suited for determination of shear properties of AM continuous FRP material, giving consistent results for the test sample.