# Effectiveness of Nanotechnology Treatments in Composite Aircraft Applications
## 3 Corrosion and Fatigue Test
### Fatigue Test  
The INTROM 8801 machine (Figure 4), available at Politecnico di Torino-DIMEAS structural laboratories, was used to carry out the fatigue tests. In addition to the 9 specimens subjected to corrosive treatment, the other 4 specimens were added, bringing the total of those mechanically tested to 13 in order to have a direct comparison between the same types of surface coatings with the only discriminating factor being the corrosive process undergone. All the samples reported in Table 2 were subjected to the fatigue test, highlighting those that underwent the corrosive process. Table 2 also shows the three selected load levels, the maximum and minimum force of the applied cycle, and the frequency of load application. The need to conduct fatigue tests, operating with three different load levels, arises from the need, albeit with the limitation of the reduced number of specimens, to approach the definition of the S-N curves [10; 16]. Figure 3: Specimens: (**A1**–**A3**) before corrosion; (**B1**–**B3**) after corrosion. “Raw 2024-T3”: aluminum without corrosion protection; “Primer”: aluminum treated with a standard primer; “Nanotech”: aluminum treated with nanotechnology. Figure 5 presents the number of cycles to failure of the specimens subjected to load type 1 corresponding to \(F_{max}=11\) kN, \(F_{min}=0\) kN, and a frequency of \(f=5\) Hz. The specimens subjected to corrosion are also indicated. For this load, we note a significant reduction in fatigue life for the untreated MCF001 specimen and also for the Al-Primer specimen (MCF04) compared to the uncorroded case MF000, demonstrating the evident reduction in fatigue life due to the corrosion effect. The specimen treated with nanotechnologies (MCF007) in this case had a very similar behavior to that of the specimen of the same category not subjected to the corrosion process (MCS10), demonstrating an increased protective property against corrosion with an increase in fatigue life of +48% compared to raw Al, of +44% with respect to Al-Primer, and a small reduction of \(-1.44\%\) when considering the uncorroded Nanotech specimen. The results relating to the intermediate load level indicated with type 2 and corresponding to \(F_{max}=9\) KN, \(F_{min}=0\) N, and a frequency of \(f=5\) Hz are shown in Figure 6. Also in this case, an excellent behavior of the specimens treated with nanotechnologies and subjected to the corrosion process can be noted. In particular, the MCF008 specimen had an increase in life of +48% compared to raw aluminum (MCF002), +35% compared to the specimen treated with primer (MCF05), and a reduction of \(-29\%\) compared to the specimen treated with nanotechnology but not corroded (MCS11). Finally, considering the lowest load level indicated in Figure 7 with type 3 and corresponding to a cycle defined by \(F_{max}=6\) KN, \(F_{min}=0\) N, and a frequency of \(f=5\) Hz, we still noticed a better behavior of the specimen treated with nanotechnologies albeit reduced compared to the previous case. In this case the MCF009 specimen had an increased fatigue life compared to raw aluminum (MCF003) of +39%, while compared to the primer (MCF006), the life increase was 33%, and the reduction compared to the uncorroded case (MCS012) increased to \(-66\%\). In order to get closer to the definition of the S-N curves and associate the effect of corrosion as well as the protective effect of the primer and the innovative nanotechnological treatment to a variation in the stress concentration factor \(k_{t}\), a modified Basquin equation was introduced [10; 16]:  
\[logN=A-Blog\left(k_{t}^{E}S\left(2-\frac{2S_{m}}{S}\right)^{C}-D\right) \tag{1}\]  
where \(A,B,C,D,E\) are specific constants which in the particular case of Al2023-T3 assume the values: \(A=12.81;B=3.36;C=0.68;D=158.96;E=0.75\)[16; 17]. Figure 4: Specim installed in the fatigue test machine.