# Study of Drilled Holes after a Cryogenic Machining in Glass Fiber-Reinforced Composites
## 3 Results
### Statistical Results in Cryogenic Environments
#### 3.2.1. Thrust Forces  
The results of an analysis of variance for the data shown in Table 3, allows us to observe the detailed statistical results (Tables 4 and 5) and standardized Pareto charts (see Figure 2a,b). The results were similar in both materials, and this was expected due to their similar mechanical properties (see Table 1). The cutting conditions were statistically significant at a 95% confidence level, and had a very high percentage of contribution to the results (46.97% for f and 49.30% for N in PEEK-GF30 and 48.87% for f and 48.74% for N in PA66-GF30). Besides \(f^{2}\) and f \(\times\) N are significant for reinforced PEEK and f \(\times\) N for reinforced PA66. These results could be expected due to the similar mechanical proprieties of these composites. Note that the percentage of contribution assigned to total residual was very low (0.27 and 0.33%). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **Df** & **Mean Square** & **F-Ratio** & \(p\)**-Value** & **Contribution (\%)** \\ \hline f & 0.3313 & 1 & 0.3313 & 9.21 & 0.0561 & 67.05 \\ N & 0.011 & 1 & 0.011 & 0.31 & 0.6191 & 2.23 \\ f\({}^{2}\) & 0.00094 & 1 & 0.00094 & 0.03 & 0.8819 & 0.19 \\ f \(\times\) N & 0.00467 & 1 & 0.00467 & 0.13 & 0.7425 & 0.94 \\ N\({}^{2}\) & 0.0382 & 1 & 0.0382 & 1.06 & 0.3782 & 7.73 \\ Total residual & 0.1079 & 3 & 0.036 & & 21.84 \\ Total & 0.4941 & 8 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Analysis of variance for Ra_PEEK-GF30. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **Df** & **Mean Square** & **F-Ratio** & \(p\)**-Value** & **Contribution (\%)** \\ \hline f & 0.01964 & 1 & 0.01964 & 5.69 & 0.0971 & 50.37 \\ N & 0.0067 & 1 & 0.0067 & 1.93 & 0.2588 & 17.18 \\ f & 0.00022 & 1 & 0.00022 & 0.06 & 0.8159 & 0.56 \\ f \(\times\) N & 0.000025 & 1 & 0.00025 & 0.01 & 0.9371 & 0.06 \\ N\({}^{2}\) & 0.0021 & 1 & 0.0021 & 0.60 & 0.4945 & 5.39 \\ Total residual & 0.0103 & 3 & 0.0034 & & & 26.42 \\ Total & 0.03899 & 8 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Analysis of variance for Ra_PA66-GF30. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **Df** & **Mean Square** & **F-Ratio** & \(p\)**-Value** & **Contribution (\%)** \\ \hline f & 14,933.4 & 1 & 14,933.4 & 511.41 & 0.0002 & 46.97 \\ N & 15,674.1 & 1 & 15,674.1 & 536.77 & 0.0002 & 49.30 \\ f & 320.89 & 1 & 320.89 & 10.99 & 0.0452 & 1.01 \\ f \(\times\) N & 774.69 & 1 & 774.69 & 26.53 & 0.0142 & 2.44 \\ N\({}^{2}\) & 5.56 & 1 & 5.56 & 0.19 & 0.6922 & 0.017 \\ Total residual & 87.6 & 3 & 29.2 & & & 0.27 \\ Total & 31,793.2 & 8 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Analysis of variance for Fz_PEEK-GF30. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Sum of Squares** & **Df** & **Mean Square** & **F-Ratio** & \(p\)**-Value** & **Contribution (\%)** \\ \hline f & 10,809.2 & 1 & 10,809.2 & 438.52 & 0.0002 & 48.87 \\ N & 10,780.9 & 1 & 10,780.9 & 437.37 & 0.0002 & 48.74 \\ f \(\geq\) 2 & 47.8 & 1 & 47.8 & 1.94 & 0.2580 & 0.22 \\ f \(\times\) N & 393.36 & 1 & 393.36 & 15.96 & 0.0281 & 1.78 \\ N\({}^{2}\) & 13.63 & 1 & 13.63 & 0.55 & 0.5110 & 0.062 \\ Total residual & 73.95 & 3 & 24.65 & & & 0.33 \\ Total & 22,118.8 & 8 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Analysis of variance for Fz_PA66-GF30. An analysis of the RSM means showed the relationship between variable and parameter, represented by Equations (2) and (3), and predicting the values of these variables. The second-order model may be valid because the coefficient of determination, R\({}^{2}\), had values of 99.73 and 99.67% for PEEK-GF30 and PA66-GF30, respectively. Moreover, these relationships are shown in Figure 3a,b, where very similar behavior of the two compounds is observed.