PSI - Issue 82

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

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J. Best et al. / Structural Integrity Procedia 00 (2026) 000–000

Fig. 3. 0.05 mm PES film cured in EC IN2 resin viewed under 40x magnification.

(a)

(b)

(c)

Fig. 4. Results for flexural testing: (a) force vs. displacement; (b) strength & modulus; (c) interlaminar shear strength.

3.3. Mechanical Properties The flexural properties of the reference and PES interleaved composites were compared to observe the effect of the interleaving polymer films (Fig. 4) The peak force sustained, and modulus of the PES interleaved samples appears to be higher in Fig. 4 (a), however, considering the slightly increased thickness of the PES samples over the control, the flexural strength of the PES interleaved composites actually decreased by 9.6% and the modulus was unchanged. The flexural strength of the composite in the longitudinal direction is a fibre dependent property (Beylergil et al., 2018). Thus, the interleaving of the PES veils couldn’t contribute to enhancing this remarkably. Fig. 4 (c) presents the ILSS values of the reference and PES interleaved composite samples. The ILSS value of the reference composite was obtained as 49.7 ± 1.0 MPa. The ILSS value of the PES interleaved composites increased to 55.8 ± 3.3 MPa, an improvement of 12.4 %. The presence of the PES veils resulted in a tougher interlaminar region, allowing more load to be transferred to the carbon plies and leading to increased shear strength. 3.4. Mode I ILFT Fig. 5(a) displays the average Mode I ILFT values, G IC, for reference and PES interleaved composite samples, Fig. 5 (b) shows the R-Curve, or variance in G IC over varying crack lengths, and Fig. 6 (a) & (b) shows the typical force displacement curves for reference and PES interleaved composite samples. The Mode I ILFT, G IC value for the reference sample was obtained as 820.0 J/m 2 . The PES interleaved composite showed an increase in Mode I ILFT of 24.7%, to 1023 J/m 2 . The R-Curve in Fig. 5 (b) shows the reference composite displaying a relatively flat curve, with Mode I resistance increasing slightly and linearly with crack length. The R-Curve for PES interleaved samples shows an increase in Mode I fracture resistance across all crack lengths compared to the reference, with a more rapid, non linear increase at shorter crack lengths. This is likely due to the interlaminar region benefitting from the enhanced strength and ductility of the interleaving PES, with the presence of the PES possibly offering crack growth inhibiting or diverting effects.