PSI - Issue 82

Mr. Parthasarathy Iyengar et al. / Procedia Structural Integrity 82 (2026) 309–316 P. Iyengar, J. Mardaras, S. Kyle-Henney / Structural Integrity Procedia 00 (2026) 000–000

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• Interface – It denotes meeting of the fibre and matrix seen as result of the processing used. It is a discontinuity across the bounding surface between the two and occurs in parameters such as chemical composition, elastic modulus, CTE and properties such as chemical potential and imparts the characteristics seen in service. Crystallographic nature, wettability, chemical bonding and mechanical bonding are not discussed. • Interfacial bonding – Bonding is a combination of chemical and mechanical phenomena. Mechanical bonding is by keying of the matrix into the pores and fibre’s surface roughness. For a liquid matrix, the fibre’s surface must be wet and asperities penetrated. Else voids will form. It involves atomic transport by diffusion, includes solid solution and/or interfacial compound formation. May result in formation of an interfacial zone containing a solid solution and/or a fibre to matrix interfacial reaction zone with a certain thickness. Most MMC systems are non equilibrium systems in the thermodynamic sense; i.e., there exists a chemical potential gradient across the interface. Prolonged contact between liquid metal and reinforcement can lead to a significant chemical reaction, which may adversely affect composite behavior (Chawla and Chawla, 2013). Fig. 1(a) below depicts a cross-sectional micrographic view of uni-directional GD111. When liquid drops on a solid substrate, it replaces a portion of the solid–vapour interface by a liquid–solid and a liquid–vapour interface. Spreading will occur if this results in a fall in the system‘s free energy. Also, the lower the contact angle θ, the better the wettability. A good interfacial wetting of fibres at 16μm semi-major axis is shown in 1(b). Most interfaces are incoherent and high-energy interfaces and can act as efficient vacancy sinks and provide rapid diffusion paths, segregation sites, heterogeneous precipitation sites, as well as sites for precipitate-free zones (Chawla and Chawla, 2013). 1.2. Potential of benefit to aircraft application AMMCs asset lies in their high specific strength, which is comparable with Titanium and Polymer matrix composites, as depicted in Fig. 1(b). Those applicable here are observed to have strength comparable with Titanium, endurance comparable with steel and density and therefore mass which is close to that of aluminium. The density of Al2O3 fibres used was declared to be 3.9 g/cc and the matrix is generically assumed to be 2.7 g/cc based upon MMPDS-14 (2019). Representatively assuming 55% fibre-volume, 3.40 g/cc is the estimated density of the AMMC, which is less than Ti. The possibility of tailoring for application at higher temperatures than commonly used aircraft Aluminium Alloys products such as 2024-T351 are amenable to is foreseen. Its sustainability is being studied, and compared to Ti6Al4v. a b

Fig. 1. (a) Cross-sectional micrograph of GD111; (b) Specific-strength vs temperature depiction (Gardiner, 2017).