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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Fig. 1. Schema of 4-layer sample manufacturing using: (a) infusion, (b) AM method; P – polymer, CF – continuous fibre (CF).

A comparison of the GFRP samples structure manufactured using the infusion and the mFDM methods is presented in Figure 1. Adding pressure to the infusion process results in parallel layers of glass reinforcement separated by a thin layer of polymer. On the contrary, fibre reinforcement in the AM sample is separated by the polymer from the neighbours in both directions. Each two fibre layers are separated by a polymer layer.

3. Non-destructive methods

Structural analyses of samples were performed using two non-destructive techniques (NDT): THz spectroscopy and scanning electron microscopy (SEM). The first method was applied for both GFRP sample types to present the internal structures and indicate the di ff erences among them. SEM was applied to AM structures to determine the damage types that occur in the samples.

3.1. THz spectroscopy

THz spectroscopy is an NDT method based on electromagnetic radiation that can be applied to inspect the internal structure of non-conductive materials. Imaging process using THz radiation based on changes in THz wave param eters: refractive index, absorption coe ffi cient, or wave scattering. The THz technique can be used for inspection of internal structures of GFRP to detect delaminations Ryu et al. (2016), embedded FBG sensors Mieloszyk et al. (2019) or porosity Lu et al. (2022).

Fig. 2. THz images of 4-layer GFRP structure: (a) B-scan, (b) C-scan of FO-plane; FO – fibre optic .

The used THz spectrometer device was TPS Spectra 300 THz Pulsed Imaging and Spectroscopy from TeraView. The scanning heads were arranged in a reflection mode. During the measurements, the samples were placed on a metal table. The measurement step was equal to 0.2 mm in both directions in the xy plane, and the THz signals were recorded with 10 times averaging. The time di ff erence in each measured signal was equal to 0.0632 ps. An example of the internal structure of the GFRP sample manufactured using the infusion method is shown in Fig ure 2. As it was presented in the scheme (Figure 1(a)), all layers in the laminate can be easily determined. Embedded