PSI - Issue 60

Chinnam Sivateja et al. / Procedia Structural Integrity 60 (2024) 245–255 Sivateja et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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at the outer regions of the thumbnail regions, distinctive clamp shell marks become apparent, which are then followed by an overload-induced failure mechanism characterized by the formation of dimples around precipitate sites, as seen in Fig. 8(d).

Fig. 8. Fractography of CMAS-AA depicting regular features as CAA specimens (a) Crack initiation site (within the closure), arrows showing the direction of crack growth (b) striations (c) Striations and lateral cracks forming bands in CMAS tested at higher stress values, indicating a higher rate of crack growth (d) overload failure region. 6. Conclusions A comparative study was conducted to evaluate the static and high cycle fatigue properties of Chemically milled, anodized, and sealed (CMAS-AA) material, aiming for corrosion protection against commercially available Cladded Al alloy (CAA) material, with a focus on weight reduction applications in typical aircraft design usage. The following observations were made:  The static strength properties of both materials were similar, falling within the range of the coefficient of variation (COV) typically observed in similar materials.  The fatigue test results indicated that the 95% confidence bounds for the mean life of the two materials overlap.  Residual stress measurements on the two materials showed insignificant differences. However, it was noted that CAA exhibited compressive stress, while CMAS showed tensile stress, which warrants further study and understanding.  The S-N life curves for both materials (CAA and CMAS) coincidentally showed similar fatigue life but with 3-5 times lower fatigue life compared to unprotected electro-polished samples (Mirror polished bare Al 2024 T3).  The surface roughness of CMAS specimens was seven times higher than that of CAA specimens, demanding closer examination in future studies. As many factors influence material fatigue life, careful experimental design and observations are required to understand the effects of individual factors and the collective impact of all parameters.  These findings suggest that CMAS material can potentially replace CAA material in weight reduction applications without significant design changes or compromising structural integrity.