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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1. Introduction In recent years, Ceramic Matrix Composites (CMC) have found numerous applications in aerospace, automobiles, space structures, due to their extraordinary thermo-mechanical properties like high temperature strength retention, damage tolerance, low density and light weight being reported by Binner et al. (2020), Bansal & Lamon (2014) and Novembre et al. (2024). Continuous carbon fibre reinforced with silicon carbide C-C/SiC manufactured using Liquid Silicon Infiltration (LSI) have emerged as a key player in re-entry vehicle thermal protection systems, brake disk, rocket nozzles and combustor liners. Starting from pyrolysis of phenolic matrix-based Carbon Fiber Reinforced Polymer (CFRP) to make amorphous carbon-carbon porous composite, molten liquid silicon is infiltrated, which reacts with carbon to make SiC matrix and finally produces a C-C/SiC composite has been reported by Shi et al. (2021), Liu & Xia (2021) and Krenkel (2004). In this work, according to manufacturing stages of CMC produced using Liquid Silicon Infiltration (LSI) methodology, three manufacturing stage samples identified as CFRP, C/C, and CMC are being investigated to characterize the mechanical properties at each manufacturing stage. The objective of the research is to thoroughly characterize the manufacturing induced mechanical properties at each stage to improve the reproducibility of the manufacturing process and to analyse the changes in mechanical properties at each stage. This paper focuses on the experimental campaign to characterize the mechanical properties using static tests involving tensile, compression and flexural test at each manufacturing stage samples. Further fracture tests on final ceramic matrix composite and numerical validation will be performed at later stage of this on-going research activity. 2. Experimental methodology 2.1. Materials and method The objective of this study is to develop a framework for the initial design criteria for C-C/SiC CMC by mechanically characterizing all 3 manufacturing stages i-e CFRP, C/C, and C-C/SiC CMC under in-plane static loading and failure at room temperature. This objective has been achieved carrying out Tensile, Compressive, and 3 point bending static tests on the first two stages of CFRP, and C/C. Two different layups have been considered identified in the following as [0°] and [45°]. Finally, the mechanical characterization of the final CMC material obtained at the end of the three stages will be achieved not only by tensile, compressive and 3-point bending tests but also by two different fracture tests (SENB and DCB) that have been planned on specimens having the same layups of static tests. As stated earlier, experiments were performed on the first two phases of CMC manufacturing process by Liquid Silicon Infiltration (LSI). Initially, twill 6k 2×2 layers of carbon fibres pre-impregnated with phenolic resin were moulded. Compaction in autoclaving is carried out at a specific pressure and temperature. After the manufacturing of CFRP, pyrolysis is carried out at high temperature. During pyrolysis, due to heat treatment, a porous and amorphous carbon matrix is developed from the phenolic resin matrix of CFRP. This carbon matrix has very thin and small micro cracks and pores due to the shrinking of the matrix in the pyrolysis process. Molten liquid silicon is infiltrated into the porous and amorphous carbon matrix at high temperature to densify the matrix. During LSI, a silicon carbide matrix is developed due to the reaction of carbon with silicon being introduced due to capillary reaction studied by Krenkel (2001) However, some of the silicon remains unreactive and is still present in the final C-C/SiC CMC after the infiltration. 2.2. Static tests on CFRP and C/C pyrolyzed A monotonic tensile test was carried out on two different layups of CFRP and pyrolyzed samples, which are [T0°] and [T45°]. The ASTM standard C1275 was used as a standard guideline for specimen geometry and test set-up configuration, as it is an obligatory requirement to follow for materials being used in high-end applications. Tensile test according to ASTM C1275-00 (2000) were performed on 6 specimens of dog-bone shape having a total length of 200mm, a gauge length of 45mm, and an average thickness of 4.74 ± 0.03mm. The average gauge width of the specimen was 7.89 ± 0.09, while the total width of the broad part was 10mm. The sketch of the geometry of the