Anisotropic rheology of continuous fibre thermoplastic composites

Insights into complex rheological behaviour of carbon fibre/PEEK from a novel numerical methodology incorporating fibre friction and melt viscosity

“…When compared to previous results (see Fig. 1), it was interesting to note that the low pressure data matched the results in [4] and [5], for which loading conditions approximated simple shear, while the high pressure data was closer to that of [6] and [7], for which combined shear-compression was applied. Other surprising results were that viscosity also increased substantially during constant-frequency oscillatory tests over just a few minutes, and increased with increasing temperature.…”

“…For example, as can be seen in Fig. 1, the data of Groves et al [5] differs from that of O'Bradaigh et al [6] by two orders of magnitude at a strain rate of 1 s -1 . This lack of clarity makes choosing values for ATP process models of CF/PEEK very problematic.…”

“…This represents the normal force arising from twisting and entanglement, together with the additional normal force from applied pressure (which should be small at low pressure). [8], and data from Stanley and Mallon [4] and Groves et al [5], for which the loading was close to simple shear. It can be seen that, with the chosen N F value (and f   0.05), the viscosity from this purely frictional process (i.e.…”

“…Fig. 8(a) shows viscosity, RVE  , versus shear rate, RVE  , overlaid with data from experiments in which a low pressure was applied to the sample by the rheometer plates (52 kPa), [8], and data from Groves et al [5].…”

“…Although CF/PEEK has been extensively characterised, the literature reveals large variations in reported values of transverse-shear viscosity [4][5][6][7], with no satisfactory explanation for why this is. For example, as can be seen in Fig.…”