Strength of single-lap-joint assemblies of continuous unidirectional carbon fibre reinforced thermoplastic matrix tapes under tensile loading

Unidirectional tape placement technologies appeared as a promising alternative due to their potential in large-scale component production. While the optimization strategies used to define the tape lay-out can be of different nature, the utilization of tape-to-tape joints is inevitable. Whereas several studies have focussed their efforts on the process and design stages, no study has yet addressed the influence of the manufacturing process on the mechanics of unidirectional tape joints. In this study, the strength of single-lap-joint assemblies of carbon fibre reinforced thermoplastic tapes under tensile loading was analysed. The dependence of the strength on the overlap geometry and the manufacturing pressure was of main focus. Single-lap-joint assemblies with rectangular and rounded overlaps of the same overlap area were prepared employing a pre-heating stage at 250°C and forming pressures from 3 to 100bar. Failure of the assemblies was not observed on the overlap itself but instead on the zone near the overlap end on the adherend. Traditional determination of strength of single-lap-joint assemblies is not applicable in this case. Consequently, a typical Hashin failure criterion was used to model the failure of the assemblies. The study showed that although cohesive failure is not likely within the analysed pressure range, overlap geometry and forming-pressure affect the strength of single-lap-joint assemblies under tensile loading.