PSI - Issue 28

Anurag Singh et al. / Procedia Structural Integrity 28 (2020) 2206–2217 Anurag Singh/ Structural Integrity Procedia 00 (2019) 000 – 000

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4. Conclusions In this work, two unique 0° layup carbon fibre reinforced epoxy composite specimens were tested and compared for tensile, flexural and fracture toughness properties in a quasi-static condition. One of the specimens is electrically modified and uses functionalised interlayer technology for their production; this distinct specimen houses a nylon veil functionalised by the nanoparticles in between the carbon fibre prepregs. Graph and tables of the experimental results show the consistency in all three mechanical tests through standard deviation values in tables and visually in graphs. Tensile tests show that ec specimens are less stiff compared to the ref specimen, which indicates the use of interlayered veil has led to the decrease of the stiffness. However, the maximum tensile stress remains the same, but a slight increase in the maximum strain is noticed with the ec specimen when compared with the ref specimen. In both cases, matrix failure is the cause of rupture of the specimens, and there is nothing to keep the fibrils together. Therefore, the use of functionalised veil affects the stiffness of the material; stiffness is the property from the elastic domain. However, from the matrix failure, the strength properties get limited to the strength of the matrix. Therefore, the use of electrical conductive veil showed no effect on the tensile properties. For the flexural tests, image processing from the MATLAB calculates the strain field from the series of images taken during the tests. Results obtained from the MATLAB are coherent with the displacement results obtained from the MTS machine. In this case of flexural, ec specimens showed higher flexural stress and higher values of tangent modulus. This particular case shows that in this situation, the use of functionalised interlayer veil for ec specimen has increased the modulus and maximum stress. However, in bending ec specimens suffered a significant decrease in the maximum strain values compared to the ref specimens. In the case of the fracture tests, all calculations use the modified beam theory. The value of the fracture initiation toughness for ec specimen is almost double than the ref specimens. Electrically conductive composite specimens were able to absorb more energy before the crack jump immediately after the first unloading ascertaining that ec specimen absorbs higher energy as seen from the higher plateau at the end of the first unloading. In this case, it shows the nanoparticle coated interlayered veil has helped to absorb more energy for the ec specimens. R curve shows the consistency in the experiment from the load vs crack propagation graph. Energy release rate after the initiation of the crack showed higher value to initiate the crack in case of ec specimen but as the crack propagates through the specimen, the energy release rate decreases compared to the ref specimen. Functionalised interlayer veil increased the threshold of initial fracture toughness, but as the crack propagates, the veil has resulted in quicker delamination between the plates. Overall results establish that manufacturing of the composite specimens using FIT is a step in the right direction, concerning inducing the multifunctionality to the composite specimens.

Figure 10: Modulus values from the ref and ec specimens