PSI - Issue 82

Jet Best et al. / Procedia Structural Integrity 82 (2026) 98–106 J. Best et al. / Structural Integrity Procedia 00 (2026) 000–000

104

7

(a)

(b)

Fig. 5. (a) G IC of reference and PES interleaved samples; (b) R-Curve of G IC over total crack length.

(a)

(b)

Fig. 6. Force vs crosshead extension for (a) reference and (b) PES interleaved samples.

The load-displacement curves of the reference and PES samples show a jag-shaped pattern, signifying unstable crack propagation, a key characteristic observed in unidirectional CFRP composites subjected to Mode-I delamination (Beylergil et al., 2018). Average final crosshead displacement values for the reference composites are 24 mm, while PES interleaved samples achieved an average value of 30 mm, showing their greater resistance to fracture before ultimate failure. 3.5. Mode I fracture mechanism & SEM images Fig. 7 depicts SEM images of the delaminated fracture surfaces of the reference and PES interleaved composite samples studied for Mode I interlaminar fracture toughness. SEM images of the reference (Fig. 7 (a) & (b)) show a damaged carbon fibre surface at the delaminated region with large voids and missing fibre bundles, indicating the propagation of the crack to the interfacial region and fibre-pullout being a main contributor to the reference samples’ fracture performance (Quan et al., 2019). For PES interleaved samples (Fig. 7 (c) & (d)), the delaminated region is characterised by a relatively smoother, epoxy-rich appearance, with more intact fibre bundles. This indicates failure was better constrained to the interlaminar matrix region (Zheng et al., 2017). The smooth surface and presence of some hackle markings indicate the matrix underwent a relatively brittle failure, however, the influence of the tough, ductile PES within the matrix, along with the constraint of crack propagation to this region, was still enough to see improved Mode I ILFT over reference samples.