# Measurement and Analysis of Vibration Levels for Truck Transport Environment in Korea
## 3 Results and Discussion  
### Transport Vibration Levels in the Pre-Planned Test Route  
Figure 4 shows each PSD profiles for the tri-axial vibration records measured in three target trucks on the test route. As expected, the vibration levels were significantly higher in the vertical axis than in the lateral and longitudinal axes for all target tracks, and the change in the value of the longitudinal vibration level was smaller than that of the other two directions. In particular, the differences in directional vibration levels were more pronounced in the low-frequency range of 110 Hz. The vehicle's overall rms G value at that frequency range was the largest in the vertical direction, followed by the lateral direction and the longitudinal direction (Table 3). For the overall frequency range of this study, 1-250 Hz, the values of the vertical overall rms G were approximately 2.6 and 3.0 times higher than those of the lateral and longitudinal directions, respectively, and the highest level of vibration in the vertical direction was the same as that of other countries. The vibration level transmitted to products during truck transport is very large in the vertical direction; thus, the design of the cushioning packaging of the product depends on the vertical vibration level [24; 25; 26; 34]. Figure 5 shows only the PSD profiles for the vertical direction. The overall rms G values of the leaf-spring truck in the low-frequency range of 1-10 Hz were about 1.5 times greater than those of the air-ride truck. Figure 4: PSD plots for triaxial vibration levels in truck transport. (**a**) leaf-spring 5-ton truck (**b**) air-ride 5-ton truck. (**c**) leaf-spring 11-ton truck. \begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline \multirow{2}{*}{**Kinds of Truck**} & \multicolumn{2}{c}{**1–250 Hz**} & \multicolumn{3}{c}{**Under 10 Hz**} & \multicolumn{3}{c}{**Peak PD Level (1)**} \\ \cline{2-9}  & \(x\) **(G)** & \(y\) **(G)** & \(z\) **(G)** & \(x\) **(G)** & \(y\) **(G)** & \(z\) **(G)** & **Frequency (Hz)** & **PD Level (G\({}^{2}\)/Hz)** \\ \hline Leaf-spring 5-ton truck & 0.1078 & 0.0583 & 0.2119 & 0.0377 & 0.0188 & 0.1632 & 3.0 & 0.0116 \\ Air-ride 5-ton truck & 0.0472 & 0.0477 & 0.1075 & 0.0234 & 0.0110 & 0.0901 & 1.5 & 0.0052 \\ Leaf-spring 11-ton truck & 0.0740 & 0.0885 & 0.2385 & 0.0393 & 0.0152 & 0.1305 & 3.0 & 0.0062 \\ \hline \hline \end{tabular} Note: \({}^{(1)}\) in the vertical direction (\(x\): lateral, \(y\): longitudinal, \(z\): vertical).  
\end{table} 
Table 3: Overall rms G values for triaxial PSD profiles and vertical peak PD level. However, the value of the first PSD peak, which occurred as suspension's response to external forces at the low-frequency region, was about two times smaller in the air-ride truck than in the leaf-spring truck, and its frequency was approximately 1.5 Hz and 3 Hz, respectively. The low frequency of the first PSD peak in the air-ride truck is considered as an effect of damping of the air-ride suspension (damped natural frequency \(\omega_{d}=\omega_{n}\sqrt{1-\zeta^{2}}\), where \(\omega_{n}\) is the natural frequency, and \(\zeta\) is the damping ratio). The results of this study for the two suspension trucks agree well with the research results by [PERSON] and [PERSON] [15] and [PERSON] et al. [21]. Therefore, package designers should preferentially avoid designing 'product + cushioning material' system with natural frequencies between these ranges to avoid resonance during transport [21]. Figure 5 also shows the analysis results of PSD from time-domain rms G data for the following three cases: (1) high-level PSD representing the top 30% of the recorded data, (2) low-level PSD representing the lower 70% of the data recorded, and (3) PSD representing all data recorded. The overall rms G value for each of the three classifications is shown in Table 4.  
Figure 5: PSD plots for the vertical vibration levels in truck transport and the existing standardized test protocols. (**a**) leaf-spring 5-ton truck (**b**) air-ride 5-ton truck (**c**) leaf-spring 11-ton truck.