# Failure Life Prediction of Hub Bearing in Composite Tooling
## 2 Derivation of Loads on the Hub Bearing
### Field Test Workload Measurement of the Composite Working Implement  
The specifications of the tractor selected to derive the workload of the composite working implement are as shown in Table 1. A GPS speedometer was used to measure the actual driving speed,  
Figure 1: Structure of composite working implements.  
considering the slip of the tractor wheel. A six-component load cell was installed at the three-point hitch connection between the tractor and the composite working implement. Strain gauges were attached to the disk narrow assemblies of the composite working implement to measure the loads acting on the composite working implement.  
Finite element analysis determined select positions at the disk narrow arm for attachment of strain gauges. Four locations (S1, S2, S3, S4) where large strains were shown were selected and attached with strain gauges, as shown in Figure 3. An accurate measurement system was configured with the data acquisition system (DAQ) model Quantum X (MX840B, MX1615B) of HBM Co. We also used an industrial PC model UNO-2483G of ADVANTECH Co. that is robust against tractor vibrations. An inverter converted the tractor 12 V direct current into the alternating current required by DAQ and PC, and an uninterrupted power supply for stable data acquisition, since the tractor is turned off during the measurement. The measurement equipment was installed inside the tractor cabin.  
The experimental field for the field tests is a rectangular pavement located in Baeksan-myeon, Gimje-si, Jeonbuk, Korea. The soil strength and moisture content were measured using the soil cone penetrometer model DIK-5530 ((DAIKI Co.), which measures strength according to soil penetration depths, and the soil moisture sensor model WT1000B (Mirae Sensor Co.), which measures moisture contents in soil. The measured soil strength and penetration depths were 1939 kPa and 18 cm, respectively, and the determined moisture content was 8.6%.  
The field test condition for the composite working implement was set to 15 km/h, which is the maximum speed. A travel distance was selected to allow an acceleration of 15 s after the tractor starts, a deceleration of 15 s before the tractor stops, and the maximum speed lasted for 24 s.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Model** & **PS100N** \\ \hline Company & LS Miron \\ \hline Engine power, PS & 95 \\ \hline Rated speed, rpm & 2300 \\ \hline Dimensions, mm & \(4342(\text{L})\times 1965(\text{W})\times 2650(\text{H})\) \\ \hline Weight, kg & 3340 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of farm tractor.  
Figure 2: Structure of disk narrow assembly.  
A total of five field tests were conducted. The representative workload was determined to calculate the equivalent load for fatigue life prediction of the hub bearing, as shown in Figure 4. Stain data were taken only when the traveling speed was in a range of 14-16 km/h, and the plowing depth varied from 20 to 30 cm, which helped to minimize changes in the workload according to travelling speed and plowing depth of the tractor. The traveling rate was measured using a tractor-attached GPS speedometer, and the plowing depth of the disk narrow was identified by analyzing the images of the tractor-attached CCD camera. Although the strain data obtained in these methods are judged to be severer than actual working conditions, they are worthy of bringing about somewhat conservative results in the prediction of the fatigue life of the hub bearing. Figure 4 shows the results of field tests(1 st-5 th test) of the disk narrow assembly at the traveling speeds of 14-16 km/h. The data are measured during 224.3 s in total (results of five trials).