# Measurement and Analysis of Vibration Levels for Truck Transport Environment in Korea
## 3 Results and Discussion
### Composite PSD Profiles for the Measured Vibration Level in Truck Transport  
In this study, the composite PSD profile for Korea's truck transport environment was divided into four categories based on the transport vibration characteristics revealed through this study and the research results published by other researchers [7; 10; 11; 12]: (1) high-level composite PSD profile representing the top 30% of the data recorded for leaf-spring trucks, (2) low-level composite PSD profile representing the lower 70% of the data recorded for leaf-spring trucks, (3) high-level composite PSD profile representing the top 30% of the data recorded for air-ride trucks, and (4) low-level composite PSD profile representing the lower 70% of the data recorded for air-ride trucks. The method applied here to develop the composite PSD profile was previously presented by researchers [32] of this study. This method divides each PSD profile into pre-planned groups. Each PSD profiles in each group are represented on a graph, and the breakpoints with relatively high-energy are connected to obtain a single comprehensive PSD profile. In the simplification process, the slope between breakpoints was suppressed by less than +25 dB/OCT or greater than \(-\)25 dB/OCT [42; 43], ensuring the reproducibility of the developed composite PSD profile during the in-lab simulation. To meet this requirement, sharp peaks or deep valleys at about one-half their height (\(-\)3 dB) were selected [42]. Figures 11 and 12 show the resultant high-level and low-level composite PSD profiles, respectively, for the top 30% and lower 70% of the data recorded in Korea's truck transport environmental. The characteristics of these composite PSD profiles are shown in Tables 8 and 9. The overall rms G of the developed high- and low-level composite PSD profiles were 0.47 and 0.32 for leaf-spring trucks, and 0.30 and 0.14 for air-ride trucks, respectively. Figure 11: Recommended high-level composite PSD profile representing the top 30% of the data recorded in truck transport (**a**) leaf-spring truck (**b**) air-ride truck. In Korea, vibration test machines are used a lot to simulate the vibration of truck-carrying products, and packaging engineers from each company are investing many time and money in proper cushion packaging of products to reduce costs. Until now, to simulate vibrations in transport environments, only the international standard (ASTM: West Conshohocken, USA, ISO: Geneva, Switzerland) transport environment has been used to analyze product damage and vibration behavior. Testing transport vibration simulation in Korea by applying foreign standards makes it difficult to achieve optimal cushion-packaging design of products. Previously, there was no research related to PSD development by transport routes of truck in Korea, but if PSD profiles measured in this paper are applied, proper cushion-packaging of products will be possible through vibration simulation tests on domestic distribution products. Compared to the results of measurement of transport environment presented by existing researchers, parameters affecting vibration levels of domestic and foreign transport trucks (such as truck speed and road type) were similar results in low frequency bands below 15 Hz, but differed in  
Figure 12: Recommended low-level composite PSD profile representing the lower 70% of the data recorded in truck transport (**a**) leaf-spring truck (**b**) air-ride truck.