Effects of the chip size on flow resistance, structural development and mechanical properties in the direct extrusion of twill woven carbon-fibre reinforced thermoplastic composite chips

Direct extrusion is a potential route for re-forming chipped carbon-fibre-reinforced thermoplastic composites (CFRTPs), but the influence of feedstock size on processing and final properties remains unclear. Unused commercial 2/2 twill-woven CFRTP sheets were cut into 4-, 8- and 12-mm square chips and used as a controlled model feedstock rather than as manufacturing scrap or end-of-life material. The chips were compression-moulded into 30-mm-diameter, 30-mm-long billets, reheated and directly extruded into 10-mm-diameter rods. As chip size increased from 4 to 12 mm, ram speed increased from 2.238 ± 0.091 to 2.713 ± 0.063 mm/s, whereas the pressure–ram-stroke slope decreased from 21.32 ± 1.40 to 16.43 ± 0.63 MPa/mm. Apparent flexural strength increased from 52.9 ± 10.9 to 108.4 ± 6.8 MPa and apparent flexural modulus from 2.02 ± 0.27 to 3.65 ± 0.35 GPa. Apparent shear strength varied only from 20.7 to 21.6 MPa. Structure tensor analysis of one longitudinal section per condition yielded global a 11 values of 0.976, 0.951 and 0.963 for the 4-, 8- and 12-mm conditions, respectively. The analysed 8-mm section showed the largest standard deviation of local a 11 and the largest misalignment. Under the present material, geometry and thermal conditions, chip size was associated with extrusion resistance, cross-sectional morphology, local orientation heterogeneity and apparent flexural performance. These results are condition-specific and require validation using practical recycled feedstock and independently sampled cross-sections.