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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Fig. 2. Surface micrographs of (a) CA surface (b) CMAS showing the micropores

Fatigue cracks typically initiate from the surface, making surface roughness a crucial and highly surface-sensitive property (often denoted as S-Nature) with potential implications on the material's fatigue behaviour. However, pits developed during the chemical milling, and their depth is much more influential in deciding the static and fatigue life (Sesana et al., 2019). Despite efforts in production and finishing techniques, it is practically impossible to eliminate surface roughness.

Fig. 3. Roughness (R a ) – With Normal distribution with Probability bounds

Qualitative and quantitative assessments are necessary to understand surface roughness's effects comprehensively. The CAA specimens have roughness (measured from 30 measurements) of 0.148 microns which is 7 times lower than the CMAS samples of average roughness 1.142 microns. Sesana et al. (2019) reported that such an increment in surface roughness is around 5 times after chemical milling. However, here anodizing layer adds the roughness further. Statistical analysis of the roughness values using the normal distribution has been conducted. The cumulative distribution function (CDF) of the roughness is presented in Fig. 3. This graph serves as a reference to understand the expected range of surface roughness and aids in making informed decisions during material production and surface finishing processes to establish reliable methods for material selection and selecting the chemical milling parameters. 5.2. Tension Test The tension test results, as presented in Table 1, demonstrate the impact of the CMAS procedure on the material properties. The CMAS specimens have shown slight increase in (around 10%) both Yield and Ultimate Strength and a marginal improvement in Young's Modulus compared to the CAA specimens. However, as seen in Fig. 4, there was a minor decrease in the average elongation percentage. It is worth noting that the differences between the properties of the CMAS-AA and CAA specimens are insignificant from an engineering standpoint (With the COV of similar