# Mechanical Structure Design and Experimental Study of Gamma-ray Monitor for Small Satellite Payload
## 4 Simulation and Experimental Results  
### Static Analysis  
In order to verify the static characteristics of the product under overload conditions, its strength is evaluated on the basis of transportation conditions of the identification level:  
Figure 4: Vibration testing site: (**a**) \(X\)-axis direction. (**b**) \(Y\)-axis direction. (**c**) \(Z\)-axis direction.  
Figure 5: Finite element analysis boundary conditions.  
Figure 6: Layout of mechanical measurement points.  
(1) maximum axial (X-direction) overload of the satellite: 12 g; and (2) maximum lateral (Z-direction and Y-direction) overload of the satellite: 9 g.  
According to the detailed design requirements of the satellite payload system, the safety factor corresponding to the yield strength of the structure is 1.5. Since it is difficult to predict the overload conditions in all directions during transportation, under the combined action of the above maximum overload conditions, the overload environment estimated by the model is more serious than the actual situation, and the calculation results are relatively safe. In this overload analysis, the stress and displacement results of the structural adhesive, photoconductive glass and beryllium sheet are focused on, as shown in Figure 7.  
Figure 7: Cont.  
In order to obtain the shear stress of the structural adhesive conveniently, a mathematical model was established according to its distribution and shape characteristics, as shown in Figure 8. The \(r\)-axis and \(z\)-axis respectively correspond to the \(Y\)-axis and \(X\)-axis of the original coordinate system, and the positive direction of the \(\theta\)-axis is determined according to the right-handed rule. The shear stress \(\tau_{\theta}\), \(\tau_{\theta z}\) and \(\tau_{\tau z}\) of the structural adhesive correspond to \(\mathrm{S_{12}}\), \(\mathrm{S_{23}}\) and \(\mathrm{S_{13}}\) in the ABAQUS coordinate system, respectively. The maximum von Mises stress and safety margin of key parts are shown in Table 5.  
The calculated minimum safety margin of the structural adhesive is 4.07, which is greater than the minimum bearing strength requirement of non-metallic materials of 0.25. The distance between the beryllium sheet and the sodium iodide crystal is 1.3 mm, and the maximum displacement of the beryllium sheet is 15.48 \(\upmu\)m, which will not interfere with the sodium iodide crystal. Therefore, the structural strength and stiffness meet the design requirements under overload conditions.  
Figure 8: Mathematical model of structural adhesive shear stress: (**a**) column coordinate system; and (**b**) schematic diagram of shear stress in column coordinate system.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline \multirow{2}{*}{**Name**} & \multirow{2}{*}{**Materials**} & \multicolumn{2}{c}{**Maximum Stress**} \\  & & **(MPa)** & **Safety Margin (MS)** \\ \hline Structural adhesive & GN522 & 0.263 & 4.07 \\ Photoconductive & K9 & 0.94 & \textgreater{}10 \\ glass & Be & 7.88 & \textgreater{}10 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Overload analysis results.  
Figure 7: Stress and strain cloud diagram of the novel GRM parts: (**a**) Overall stress and strain cloud diagram of the novel GRM. (**b**) Stress and strain cloud diagram of the beryllium sheet. (**c**) Stress and strain cloud diagram of the quartz. (**d**) Stress and strain cloud diagram of the structural adhesive.