PSI - Issue 77

Magdalena Mieloszyk et al. / Procedia Structural Integrity 77 (2026) 256–263 M.Mieloszyk & S.Bhadra / Structural Integrity Procedia 00 (2026) 000–000

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GFRP components are often susceptible to complex environmental and mechanical loads during their long service life. Embedded fibre optic (FO) sensors, such as the fibre Bragg grating (FBG) and distributed sensors, provide real time strain, temperature, and vibration measurements with minimal intrusion due to their small diameter, multiplexing capability, and immunity to electromagnetic interference Gonza´lez-Gallego et al. (2024). Investigating how these interact with GFRP structures and how manufacturing methods such as additive manufacturing (AM) and infusion techniques a ff ect structural integrity is critical to designing durable and high-performance smart composites. Vacuum infusion manufacturing and autoclave curing can produce GFRP laminates with low porosity and high fibre volume fraction, resulting in high tensile strength and wear performance Lee and Chung (2003). FBG sensors can be embedded in GFRP structures during manufacturing by placing them between the plies. When embedded, the small-diameter sensor ( < 200 µ m) is situated within the fibre layers. This protects it from shear and environmental factors, ensuring that strain transfers directly from the composite to the sensor Zhang et al. (2025). The inclusion of single-mode fibres optics (FO) does not compromise tensile strength. Strain level up to ∼ 7500 microstrain and de tected non-homogeneous strain distributions, enabling early detection of delamination and cracks Maldonado-Hurtado et al. (2021). Distributed fibre optic sensing (DFOS) technologies, encompassing both Rayleigh- and Brillouin-based approaches, enable the continuous monitoring of strain, temperature, and vibration along the full length of a structure, therebyo ff ering a viable alternative to the deployment of thousands of discrete strain gauges. Embroidering fibres into textiles simplifies placement and integrates sensors directly into composite lay-ups Biondi et al. (2022). AM enables complex geometries and customised reinforcement placement but faces challenges related to fibre impregnation and voids. Continuous fibre co-extrusion (CFC) 3D-printing impregnates dry fibres with polymer melt in situ, producing continuous fibre-reinforced parts with improved strength and reduced post-processing Struzziero et al. (2021). Thermoplastic matrices such as Polylactic Acid (PLA) and polyamide (PA) are preferred due to their low melt viscosity and recyclability Liampas et al. (2024). 3D-printed GFRP composites benefit from low material cost, greater fracture strain and improved toughness compared with carbon fibre reinforced polymers (CFRP) Zheng et al. (2025); Yu et al. (2021); Popan et al. (2021). Optimising and improvising polymer impregnation and fibre surface treatment enhances fibre-matrix adhesion and flexural strength. Vacuum-assisted resin infusion (VARI) and related processes, such as the vacuum-assisted process (VAP), are techniques employed in the manufacturing of GFRP components, whereby dry fibre mats are impregnated with resin under vacuum, producing high-quality laminates with minimal void content Grisin et al. (2024). In infusion, resin flows through the dry stack under negative pressure, eliminating air and ensuring uniform wet-out. Studies on ther moplastic ELIUM resin show that high vacuum pressures (0.8 bar) produce defect-free GFRP laminates with elastic moduli of ∼ 20 GPa and tensile strengths of ∼ 305 MPa Ciardiello et al. (2023). Degassing pressure has little e ff ect, but a higher vacuum improves fibre wetting and reduces voids. Autoclave-based vacuum bag curing further consolidates laminates; a typical cycle uses approximately 0.9 bar vacuum with heating from 80–120 ◦ C under 4 bar pressure, producing a fibre weight fraction of ∼ 69 % Birleanu et al. (2023). This infusion technique also supports embedding FBG sensors by grooving and placing them between fabric layers. Sensors remain protected and detect strain along the laminate Zhang et al. (2025). Despite manufacturing advances, structural integrity issues remain in GFRP structures and components. In AM, void formation due to the incomplete impregnation, poor bonding between printed beads and fibres, and the limited fibre volume fraction can reduce strength and fatigue life. Also, poor adhesion is a common issue in AM-printed structures. Temperature gradients during polymer extrusion may introduce residual stresses in the fibre-matrix inter face. In the infusion technique, regulating the resin flow and vacuum pressure is important. Very low vacuum pressure leads to the creation of voids, while very high pressure may cause fibre misalignments Peng et al. (2024); Wang et al. (2023). Embedding FO sensors can also make the fabrication and processing more complex. Grooves and paths for the placement of fibres can act as stress concentration areas. The minimal (local) mechanical properties reduction is observed Zhang et al. (2025). However, di ff erences in the thermal expansion coe ffi cient between the sensor coatings and the matrix material may induce micro-cracks and debonding. Under mechanical loading, GFRPs fail through several interacting mechanisms: matrix cracking, fibre–matrix interface debonding, delamination and fibre fracture. Mode-1 fatigue delamination is a dominant failure mode in composites during their service life. Interlaminar cracks initiate between the plies under cyclic loading and propa gate, thus resulting in catastrophic failure Gao et al. (2022). Fatigue crack growth involves micro-cracking, which is undetectable externally, and should be properly investigated. The fibre–matrix interface quality strongly influences