# Random Vibration Fatigue Life Analysis of Airborne Electrical Control Box
## 6 Random Vibration Test  
### Experimental Procedures  
The vibration test fixture in X, Y and Z directions of the electrical control box were de-signed and manufactured based on GJB150.16 A-2009 standard before the test, and in-stalled on the vibration test bench, as shown in Figure 14.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Direction**} & \multirow{2}{*}{\begin{tabular}{c} **Maximum Stress** \\ **Point Location** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Stress/MPa** \\ **Stress/MPa** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Fatigue Life/Cycle** \\ **Fatique Life/Cycle** \\ \end{tabular} } & \multicolumn{2}{c}{**Cumulative**} & \multirow{2}{*}{
\begin{tabular}{c} **Total** \\ **Different** \\ **Directions** \\ \end{tabular} } \\ \cline{5-8}  & & 1\(\sigma\) & 2\(\sigma\) & 3\(\sigma\) & \(N_{1\sigma}\) & \(N_{2\sigma}\) & \(N_{2\sigma}\) & \(D\) \\ \hline \multirow{4}{*}{X} & Lower part of right & \multirow{4}{*}{14.787} & \multirow{2}{*}{29.573} & \multirow{2}{*}{44.36} & \multirow{2}{*}{\(2.004\times 10^{12}\)} & \multirow{2}{*}{\(1.452\times 10^{10}\)} & \multirow{2}{*}{\(8.128\times 10^{8}\)} & \multirow{2}{*}{\(2.3418\times 10^{-5}\)} \\  & bottom plate of & & & & & & & 0.10197 \\ \cline{1-1} \cline{5-8}  & electric control box & & & & & & & & 0.10197 \\ \hline \multirow{4}{*}{Y} & Upper part of left & \multirow{4}{*}{48.039} & \multirow{2}{*}{96.078} & \multirow{2}{*}{144.12} & \multirow{2}{*}{\(4.613\times 10^{8}\)} & \multirow{2}{*}{\(3.342\times 10^{6}\)} & \multirow{2}{*}{\(1.866\times 10^{5}\)} & \multirow{2}{*}{\(0.1019\)} \\  & bottom plate of & & & & & & & & \\ \cline{1-1} \cline{5-8}  & electric control box & & & & & & & & \\ \hline \multirow{4}{*}{Z} & Upper part of right & \multirow{4}{*}{16.413} & \multirow{2}{*}{32.826} & \multirow{2}{*}{49.239} & \multirow{2}{*}{\(9.55\times 10^{11}\)} & \multirow{2}{*}{\(6.918\times 10^{9}\)} & \multirow{2}{*}{\(3.873\times 10^{8}\)} & \multirow{2}{*}{\(4.9147\times 10^{-5}\)} \\  & & & & & & & & & \\ \cline{1-1} \cline{5-8}  & electric control box & & & & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 7: Fatigue analysis of electrical control box.  
Figure 14: Installation direction of the electrical control box on the test bench: (**a**) X direction; (**b**) Y direction; (**c**) Z direction.  
1. The random vibration function of the vibration table was debugged, and the electrical control box was fixed on the surface of the vibration table according to the installation requirements.
2. Two calibrated acceleration sensors were attached to the fixture, as close as possible to the diagonal position of the fixed bolt of the electrical control box, for accurate two-point average random vibration control. The frequency response under each axis excitation is illustrated in Figure 15.
3. Durability vibration tests in the X, Y, and Z directions of the electrical control box were performed.
4. The electrical control box was examined after the functional vibration tests.  
Figure 15: Different direction random vibration test control. (**a**) X direction; (**b**) Y direction; (**c**) Z direction.  
In the Figure 15, the green line is the target spectrum, and the blue line is the actual vibration spectrum. When the vibration is between the two orange lines, the random vibration is within the control error range, and the red line is the interrupt mark, indicating that, when the vibration PSD value reaches or exceeds the red line, the vibration is too large. In order to protect the specimen and equipment, the vibration control system sends out instructions and the random vibration stops.