PSI - Issue 82

Sana Ullah et al. / Procedia Structural Integrity 82 (2026) 138–145 S. Ullah et al. / Structural Integrity Procedia 00 (2026) 000–000

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3.3. Flexural test results for CFRP and C/C pyrolyzed To evaluate the flexural properties of CFRP, using the configuration of a three-point bending setup, bending tests on 6 samples on each layup of [B0°] and [B45°] were conducted. Fig. 6 (a, b) represents the bending stress-strain relationship for both types of specimens having layup 0° and 45°. The bending stress and strain are calculated using Euler-Bernoulli beam theory according to the standards ASTM C1341-00 (2000). The scatter of curves for both types of specimens is in close agreement, showing a good repeatability. The flexural modulus, failure stress, and strain are represented in Table 4. The elastic modulus calculated using flexural tests is slightly lower than that of tensile and compression tests for 0° layups. This difference is mainly due to non-uniform axial stress, as 3PB also includes shear deformation and interlaminar effects, whereas in tensile and compression tests, the axial stress across the gauge section is uniform. In bending, maximum stress is experienced by the outer layer, and the middle layers experience lower stress. However, flexural strength is quite close to that of tensile strength calculated in the tensile test.

Fig 6. (a) CFRP flexural stress-strain; (b) Pyrolyzed C/C flexural stress-strain.

Table 4. Three point bending properties of CFRP and C/C samples with different layups. Specimens Elastic modulus (GPa) Failure strength (MPa) Failure strain (%) CFRP [B0°] 50.4 ± 1.1 511.9 ± 51 1.43 ± 0.10 CFRP [B45°] 12.3 ± 0.03 200.8 ± 11 3.09 ± 0.42 C/C [B0°] 50.7 ± 2.7 121.9 ± 6 0.62 ± 0.38 C/C [B45°] 10.6 ± 0.04 37.8 ± 2 0.81 ± 0.06

4. Conclusion From this comprehensive experimental campaign, it can be concluded that each manufacturing stage is crucial and essential to accurately characterize the final manufacturing of CMC. Starting from CFRP showing high stiffness and structural properties, pyrolysis process greatly influences stiffness as removal of phenolic resin lowers the structural properties causing a weaker carbon-carbon matrix. Comparable and close values of Young’s modulus for both CFRP and C/C stage calculated using different static test indicates a good fibre architecture and integrity even after the pyrolysis. Finally, failure strength is greatly affected by pyrolysis process, as it significantly reduces the fibre bonding and matrix cohesion.