Experimental Characterisation of In-plane Shear Behaviour of Uncured Thermoset Prepregs

The generation of defects (such as wrinkles and tow pull off) in the course of the steering process of automated fibre placement (AFP) is one of the critical limitations of this technique for the manufacturing of composite laminates. The in-and out-of-plane properties of the prepreg materials used have a strong influence on the final quality. In this paper, the in-plane shear behaviour of uncured thermoset prepreg was characterised to analyse the limits of steering and derive material parameters for the model predicting defects. An off-axis tensile test was applied to unidirectional uncured prepregs subjected to different testing rates consistent with the AFP processes. Innitial tests on the influence of temperature were also performed. Test parameters were optimized to minimise earlier buckling of thin samples, non-uniformity of strain distribution. The results show expected strain-rate and less-expected strain dependency of apparent viscosity, as well as common trends in material response at range of temperaures as determinded previously for compaction behaviour of the same material. The data presented in this paper opens the way towards a new material model for predicting the quality of the steering of prepreg tapes in automated deposition processes.