PSI - Issue 54

Norman Osa-uwagboe et al. / Procedia Structural Integrity 54 (2024) 44–51 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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and foam cores, whose performances could also be affected by moisture ingress. This study examines and compares the effects of seawater degradation on the energy absorption properties of FRPSS with CFRP and GFRP facesheets under an out-of-plane loading regime after prolonged seawater exposure.

Nomenclature CFRP Carbon fibre-reinforced plastic CS Carbon sandwich FRPSS Fibre-reinforced plastic sandwich structures GFRP Glass fibre-reinforced plastic GS Glass sandwich PVC Polyvinylchloride QSI Quais-static indentation SEA specific energy absorption SEM Scanning electron microscopy

2. Materials and Experimental set up Composite sandwich structures were fabricated using aerospace-grade E-glass plain weave fabric from Samson Composites Ltd (China) and T300 plain weave carbon fabric from EASY Composites (UK) while polyvinylchloride (PVC) foam served as the core [6]. Epoxy resin with a C-1 catalyst hardener from EPOCHEM Ltd (Nigeria) in a volumetric ratio of 2:1 was used as the matrix. Details of the constituents’ parameters are described in Table 1. GFRP sandwich (GS) and CFRP sandwich (CS) samples with a configuration of 4 layers/PVC foam/4 layers and thickness of 4 mm and 4.5 mm, respectively, were fabricated using a hand lay-up and a vacuum bagging technique with a curing time of 18 hours. The samples were subjected to seawater degradation in a salt bath with artificial seawater with 3.5% salinity made from potassium chloride void of micro-organisms for 16 weeks. It is worth noting that while the material properties might be influenced by time-dependent chemical changes, in this work, the dominant factors causing the degradation of material properties are limited only to time-dependent physical changes. This approach was ensured by periodic measurement of the PH levels throughout the degradation period. A gravimetric analysis was conducted throughout exposure and the moisture uptake was calculated as: = ( − 0 )×100% (1) where is the percentage of moisture gained, and and are the weights of the wet and dry samples at a specific time respectively. A quasi-static indentation (QSI) test was performed on unexposed and exposed samples using a hemispherical indenter with a diameter of 13 mm until complete perforation on a minimum of 5 samples per configuration. The experiment was carried out in line with an ASTM D6264/D6264M-17 standard test method with a displacement control of 1 mm/min while the vertical displacement was measured using a linear variable differential transformer (LVDT) as described in Fig 1 [7]. Table 1. Mechanical Properties of Constituents Materials [8 – 10] Material Young modulus (GPa) Shear modulus (GPa) Tensile strength (MPa) Poisson ratio Density (g/cm 3 )

12 0.26 0.3

E

G 12 8.27

E-glass fabric

72.39

3100 - 3800 1860 - 3530

2.25 1.76 0.075 1.16

T300

135

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PVC Foam Epoxy matrix

0.075

0.028

1.89 70-80

-

3.2 – 3.5

-

0.29