## 3 Durability Tests
\begin{table}
\begin{tabular}{l l l} \hline \hline
1 & \multicolumn{2}{l}{Preparing the Vehicle for Testing:} \\ \hline  & 1. & Installation of sensors recording the vehicle’s behavior on the road; \\  & 2. & Defining the routes along which reference data will be collected. \\ \hline
2 & \multicolumn{2}{l}{Collecting reference data from the road:} \\ \hline  & 1. & Driving on different types of roads and recording data; \\  & 2. & Reference drive of approximately 500 km with a loaded vehicle up to full GVM; \\  & 3. & Reference drive of approximately 500 km with an unloaded vehicle. \\ \hline
3 & \multicolumn{2}{l}{Installation of the vehicle on the MTS 320 durability test stand:} \\ \hline  & 1. & Configuration of the stand for the tested vehicle; \\  & 2. & Configuration and connection of sensors located on the vehicle to the station; \\  & 3. & Generating control profiles reflecting the vehicle’s behavior as in real conditions. \\ \hline
4 & \multicolumn{2}{l}{Calculations of test duration on the simulator:} \\ \hline  & 1. & Determining the damage accumulation coefficient according to Palmgren and Miner [30; 31]; \\  & 2. & Calculation of the test duration based on the determined damage accumulation coefficient. \\ \hline
5 & \multicolumn{2}{l}{Carrying out the test:} \\ \hline  & 1. & Test for a loaded vehicle; \\  & 2. & Test for an unloaded vehicle. \\ \hline
6 & \multicolumn{2}{l}{Vehicle inspection during the test:} \\ \hline  & 1. & Checking the places defined as checkpoints. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The process of carrying out vehicle fatigue tests. The next stage is to build a system model. The purpose of building a system model is to define the relationship between input and output signals:  
* The input signals are signals controlling the station actuators, referred to as DRV (Drive);
* The output signals are signals from sensors installed in the vehicle, called RSP (Response);
* The system model is the frequency response function FRF (Frequency Response Function). This is the relationship of outputs to inputs over the entire frequency band. MTS RPC Pro software enables the creation of a system model in the form of transmittance. The sensors installed on the vehicle are used in the same configuration as on the road to determine the FRF for each frequency. FRF binds the output of the vibration system to the input, as described and confirmed by [PERSON] [32]. To generate matrix (H) Equation (1), the inputs are the displacement of the platform actuators and the outputs are the responses of the transducers, as shown in Figure 8.  
\[H(f)=\frac{G_{yx}(f)}{G_{xx}(f)}=\frac{CSD}{ASD} \tag{1}\]  
where:  
_CSD_--Cross Spectral Density, which is the power spectral density at each frequency proportional to the power between the input and output signals. _ASD_--Auto Spectral Density, which is the spectral density at each frequency, proportional to the input signal. Figure 8: Preparation of the system model: (**A**) schematic; (**B**) visualization. Figure 7: An example of an edition of the reference signal collected during the test run. After creating the system model, it is possible to generate a signal controlling the station actuators (DRV). The displacement of hydraulic actuators and the force generated on them are analyzed as signals controlling the operation of the station. As for the signals coming from the sensors, this was indicated in the article in the earlier fragment regarding the description of the sensors used. The DRV signal, as the displacement of the actuators, was determined by multiplying the signals collected from the road using the inverse of the matrix \(H\) Equation (2):  
\[ \begin{bmatrix}x_{1}\\ \vdots\\ x_{8}\end{bmatrix} =\left[H\right]^{-1} \begin{bmatrix}y_{1}\\ \vdots\\ y_{19}\end{bmatrix}  \tag{2}\]  
where:  
\(x_{1-8}\)--represents the input signals controlling the station actuators under each wheel (DRV); \(y_{1-19}\)--represents the output signals from sensors installed in the vehicle (RSP).