PSI - Issue 52

Wouter De Corte et al. / Procedia Structural Integrity 52 (2024) 99–104 W. De Corte, J. Uyttersprot & W. Van Paepegem/ Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Geometric properties of perforated steel plates Steel A and Steel B Steel A Steel B Thickness, t [mm] 2.0 1.5 Permeability, P [%] 22.30% 9.60% Perforation shape Round (Ø 3.2 mm) Round (Ø 4.2 mm) Perforation pattern Square (6.0 mm) Square (12.1 mm)

Besides the perforated steel plates, a steel wire mesh with a steel wire diameter of 1mm is also incorporated into the composite plate. The mesh size of the steel wire mesh is 1.6 mm and the permeability is significantly higher than for the perforated steel plates with a value of 38.0%. Although the main purpose of this research is to make the composite stiffer, the steel wire mesh has a low stiffness compared to the other two types, but the resin can better cover the woven threads and thus improve the bonding between the steel and the composite plate. The perforated steel plates Steel A and Steel B together with de steel wire mesh are shown in Fig. 1.

Fig. 1. Perforated steel plate Steel A (left) and Steel B (middle) and the steel wire mesh (right) used in the hybrid composite The fibre volume percentage for the different GFRP plates was between 35% and 45% and was determined after production based on the difference in weight between the dry fibre fabrics and steel and the infused composite. The infused hybrid GFRP plates were saw cut using a water jet and tested shortly afterwards to prevent any corrosion of the internal steel plate. In accordance with the ASTM D3039 standard, the test specimen have a width of 25 mm, a length of 250 mm and a thickness between 5.5 and 6.0 mm for the GFRP reference and hybrid composites. Cardboard tabs were adhesively bonded on both sides of the specimens to prevent the claws of the tensile machine from biting into the specimens and consequently lead to premature failure. All tests were performed using a displacement controlled Instron 5800R tensile machine with a 100 kN load cell and a loading speed of 2 mm/min. The full 3D displacement field of the specimen is captured using an AVT digital image correlation (DIC) setup with speckle pattern. 3. Results To enable a good estimation of the influence of the steel plates in the composite, various reference measurements were performed on the individual steel and GFRP plates. The results of these reference measurements can be found in the first part of this section. The second part then discusses the results related to the hybrid steel/GFRP composites. 3.1. Reference measurements Fig. 2 shows the stress-strain graphs for the individual perforated steel plates Steel A and Steel B. Here, the strain is retrieved from a virtual extensometer in the DIC images located between the perforations of the steel plate. The stress was calculated as a weighted average of the stress at a gross cross-section (i.e. cross-section without perforations equal to 50 mm² and 37.5 mm² for Steel A and Steel B respectively) and the stress at the perforations with a reduced cross-section of 24.4 mm² and 24.9 mm² for Steel A and Steel B respectively. The weighted average is determined on the basis of the percentage of open area of the steel sample. The relationship between the stress and the strain from the graphs in Fig. 2 gives an idea of the global stiffness of the entire plates including the perforations. The average maximum stress and strain will occur at the perforations and ar equal to 465 MPa and 3.2% for Steel A and 329 MPa and 13.9% for Steel B respectively. From Fig. 2 it can also be found that Steel B has a larger elongation at failure with a slight strain hardening, while for Steel A the elongation is smaller. In both cases, yielding will occur at a similar strain of approximately 0.2%. The weighted average stiffnesses for Steel A and Steel B are approximately 154 GPa and 190 GPA, respectively.