Issue 73

A. Masmoudi et alii, Fracture and Structural Integrity, 73 (2025) 41-58; DOI: 10.3221/IGF-ESIS.73.04

strand mat glass fiber; four layers of mat, outer layer of 300 gr/m2 glass fiber and three layers of 600 gr/m2 glass fiber. Tab. 1 presents the mechanical properties of the used resin obtained through tensile test according to ASTM D638-14 [16]. The fiber weight fraction was determined by following the standard ISO 1172 [17] and it is estimated to be 36.55%. A CNC machine was used to cut the specimens from a 45x45 cm 2 plate into the desired shapes, 5 cm were removed from all the edges of the plates to avoid discrepancy in thickness (Fig.1a). The core is made of open-cell polyurethane foam with a density of 50 kg/m 3 . To prevent the cutting effect, the skin and core of each specimen were cut separately and then assembled under cold pressure using epoxy resin as an adhesive (Fig.1b). All the materials used were commercially available. To create a random speckle pattern for DIC analysis, the specimens were coated with white paint and subsequently sprinkled with black paint.

Tensile properties

σ max (MPa)

ε max (mm/mm)

E (MPa) 3620.02

Unsaturated polyester resin

29.88

0.0132

Table 1: Mechanical properties of resin used.

Plate of glass 50x50 cm²

b

a

GFRP skin

PU foam

GFRP plates of 45x45

Figure 1: a) Molded GFRP plate, b) Manufactured sandwich structure.

Mechanical testing: GFRP skin In order to investigate the mechanical performance of GFRP skin, experimental studies were carried out using an Instron 5659 Universal testing machine. The mechanical properties of GFRP skin were investigated through compressive and tensile tests, in accordance with ASTM D695-15 [18] and ASTM D638-14 [16] respectively. Fig.2 displays the specimens studied and their dimensions. Compression test methods for the skin require application of a compressive load with preventing buckling of the material [19]. Fig.3 shows the fixture for the test. Because the interface of the specimen is covered by the compressive fixture, the speckle pattern for DIC is painted on the side of the specimen. Mechanical testing: PU core Three specimens of 50x50x20 mm 2 were used to acquire the mechanical properties of the used foam. Flatwise compression test was carried out according to ASTM C265 [20]. The load was applied on using cylindrical loading blocks with displacement rate of crosshead of 1 mm/min. Mechanical testing: Sandwich structure To study the mechanical behavior of the sandwich structure, flatwise compression test was carried out in accordance with ASTM C365 [20]. The load was applied on the specimens using cylindrical loading blocks (Fig.4a and Fig.4d). The edgewise compression test was performed according to ASTM D364 [21]. The compression load was applied on the specimens using an edgewise fixture and cylindrical loading blocks (Fig.4b, Fig.4c and Fig.4e). Two different geometries of samples were studied under edgewise compression load: w=L (S-60) and w

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