Damage mechanisms and fracture-process-zone evolution during Mode I delamination of autoclave- and vacuum-assisted oven-cured flax/epoxy composites

Natural fibre-reinforced composites are promising alternatives to synthetic composites, yet the relationship between manufacturing quality, damage development and delamination resistance remains unclear. This study examines this relationship in unidirectional flax/epoxy laminates manufactured by autoclave and vacuum-assisted oven curing. Double cantilever beam testing, digital image correlation, acoustic emission (AE), video observations and X-ray computed tomography were used to relate apparent fracture resistance to microstructure and detected damage activity. The sampled regions exhibited segmented void fractions of approximately 1%–2% in the autoclave-cured material and 21%–22% in the oven-cured material, with large inter-fibre/inter-bundle pores accounting for most of the latter. Mean propagation resistance was 848 ± 45 J/m 2 for oven-cured specimens and 793 ± 58 J/m 2 for autoclave-cured specimens (mean ± standard deviation). The oven-cured laminates were approximately 21% thicker, while the fitted DCB-arm bending stiffnesses were similar. The AE clustering identified three populations with distinct acoustic descriptors, providing complementary information on the recorded fracture activity. These findings relate contrasting consolidation states to apparent propagation resistance and crack-wake activity in the two tested laminate systems. The accompanying differences in thickness and constituent fractions limit attribution of the response to curing route alone.