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

102 4

120 150 180 210 240 270 300 330 360

120 150 180 210 240 270 300 330 360

Test 2 Test 5 Test 10 Test 11 Test 13

Test 1 Test 2 Test 3

0 30 60 90

0 30 60 90

Stress [MPa]

Stress [MPa]

0.0% 0.5% 1.0% 1.5% 2.0% 2.5% 3.0% 3.5% 4.0% 4.5%

0.0% 3.0% 6.0% 9.0% 12.0% 15.0% 18.0%

Strain [-]

Strain [-]

Fig. 2. Weighted average of stress in function of the strain for the perforated steel plates Steel A (left) and Steel B (right) Fig. 3 (left) shows the stress-strain graph for the steel wire mesh. Here, the strain is retrieved from the relative displacement between two adhesive markers on the steel wire mesh, which is registered using DIC. The markers will act as a virtual extensiometer and from their relative displacements the general strain is calculated. The stress was calculated as the ratio between the force exerted by the tensile machine and the transverse section of the mesh, which is equal to 7.85 mm².

0 100 200 300 400 500 0.0% 0.5% 1.0% 1.5% 2.0% 2.5% Stress [MPa] Strain [-] Test 1 Test 2 Test 3

0 100 200 300 400 500 600 700 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0% Stress [MPa] Strain [-] Test 1 Test 2 Test 3 Test 4

Fig. 3. Stress in function of strain for steel wire mesh (left) and for the reference GFRP [[0/90/±45/0] S ] S (right) Given the relatively small transverse section of the steel wire mesh, the calculated stresses before failure in the steel wires of the mesh will be higher compared to these in the perforated steel plates of Fig. 2. The average maximum stress and strain for the steel wire mesh are 585 MPa and 11.4% respectively. The weighted average l stiffness of the plate amounts to 44.6 GPa, which is significantly lower than the perforated steel plates. Finally, the stress-strain curve of the reference GFRP is presented as a benchmark for the comparison of the hybrid composites in the next part of this section in Fig. 3 (right). The strains are determined using a virtual extensometer and the stress is calculated as the ratio between the measured force and the cross-section of the composite, equal to 100 mm². Compared to the graphs for the steel plates and mesh, there will be a larger spread due to possible inaccuracies inherent in the production of composite elements. The mean maximum stress, strain and initial stiffness for the quasi-isotropic GFRP laminate build-up are 407 MPa, 2.3% and 22.1 GPa, respectively. As can be seen from Fig. 2 and Fig. 3, the GFRP will fail in a much more brittle way compared to the ductile behaviour of steel. However, in a hybrid composite the steel will be well past its yield point before the GFRP will fail, which means that the stiffness increase of the hybrid composites will only be

noticeable in the first initial phase. 3.2. Hybrid steel / GFRP composites

Fig. 4 (left) shows the stress-strain graph for a hybrid composite with a combination of GFRP and perforated steel A. As already mentioned in the previous section, two clear parts in the graph can be distinguished, a first part up to a strain of about 0.2% and a second part from 0.2% strain until failure.