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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fatigue resistance; inadequate bonding allows fibres to pull out, reducing load transfer capacity and causing delam ination Thomason and Xypolias (2023). Fibre pull-out scenarios have also been observed in aged GFRP, indicating interface degradation and poor adhesion between the glass fibre and matrix Namrata et al. (2024). In addition to mechanical loading, various environmental conditions also contribute to degradation phenomena in GFRP samples. Exposure to moisture, temperature fluctuations, ultraviolet radiation and chemicals leads to environ mental ageing. Accelerated ageing at elevated temperature or humidity is often used to simulate long-term exposure, but results must be investigated cautiously. Although thermomechanical loading or sometimes temporary thermal con ditioning may lead to a reduction in the residual stresses, which can improve the mechanical strength by crack closure or improved adhesion, prolonged exposure can lead to a reduction in fatigue life and sti ff ness.

2. Manufacturing Methods and Samples

The analyses were performed on GFRP samples manufactured using the infusion method and AM. In the first set, the reinforcement was in the form of glass fibre textile and epoxy resin as the matrix material. While in the second, continuous glass fibre and Polylactic Acid (PLA) were applied. The dimensions of the samples prepared using AM and the infusion method are given in Table 2. During both processes, FBG sensors were embedded at specific locations.

Table 1. Dimensions for AM and Infusion specimens. Dimension (mm)

Additive Manufacturing (AM)

Infusion Method

Length Width Height

150

200

15

70

2

1 4

Number of layers

2or 4

2.1. Additive Manufacturing- mFDM

The AM techniques are generally chosen based on the type of material used. In this study, the 3D-printed specimens were created using the modified Fused Deposition Modelling (mFDM) method. Composite samples were produced on a MeCreator 2 platform equipped with an improvised double-feed printing head developed at Kaunas University of Technology (Lithuania) Rimasˇauskas et al. (2019). The manufacturing process combines co-extrusion with tow preg processing. The printhead features two independent inlets- one supplying the PLA thermoplastic matrix and the other delivering pre-impregnated glass fibre. The process then involved merging these in the heated output nozzle for co-deposition. The fibre tow was pre-impregnated using a solution-based impregnation technique. These processing conditions significantly influenced consolidation and the final quality of the printed part. The modification to the AM process was specifically aimed at enhancing fibre-matrix adhesion within the printed architecture Rimasˇauskas et al. (2019). Vacuum infusion is a closed-mould composite fabrication technique that utilises vacuum pressure to impregnate a dry fibre with resin Lehmann et al. (2020). In a typical vacuum infusion process, dry fibre reinforcements are laid onto a mould prepared with a releasing agent. For the preparation of the samples in the present study, the sample stacking sequence was built on a Polytetrafluoroethylene (PTFE) plate. During the process, a porous flow distribution ply was added on top of the sample to allow resin to spread evenly. The prepared layup was then sealed under a flexible vacuum bag with ports for a resin inlet and vacuum outlet. After evacuating the bag to near-full vacuum ( 0.9 bar), resin (epoxy) was introduced and drawn through the fibres by the pressure di ff erential until the reinforcement is fully saturated. Finally, the inlet was closed, and the part was kept under vacuum for the curing process. The component was left under vacuum for approximately 24 hours to ensure the resin fully cures and the composite is able to achieve its final properties. 2.2. Infusion Method