# Failure Life Prediction of Hub Bearing in Composite Tooling
## 1 Introduction  
A farm tractor is a machine for various farm jobs by installing attachments such as a rotary and a plow in the vehicle's power take-off (PTO) or a three-point hitch system. Attachments must be replaced according to the different jobs, which lowers efficiency. Composite work tools have been found to perform two or more concurrent operations [1; 2]. A composite tool can concurrently perform tillage operation and hilling work. It consists of the mainframe, disk narrow assemblies, chisel plows, and a hiller. A disk narrow assembly includes a disk narrow arm, a hub bearing, and a disk narrow. The part durability of composite tooling is much more critical compared to general working tools such as rotaries and plows because composite working implements have many components and diverse shapes of working implements and are subject to relatively large load fluctuations according to soil environments. Field loads should be measured considering field environments and working conditions and reflected based on the design [3] to ensure the durability of composite work tools. In the case of the hub bearing used for smooth rotation of the disk narrow in composite working implements, severe misalignment occurs because of combined loads acting on the disk narrow, and there are difficulties in lubrication because of poor working environments. This misalignment dramatically affects the accuracy of the fatigue life of the bearing predicted through the ISO standard. Moreover, the most crucial factor in predicting the fatigue life through the ISO standard is the load acting on the bearing, and it is not easy to derive the reliable load level considering working environments. [PERSON] and [PERSON] installed torque meters on the axle to measure the load acting on the tractor transmission [4; 5]. This method is very easy to measure when the torque meters are installed on the tractor's wheels, but it is necessary to reduce the measurement error of wheel speed in order to measure the transmitted output power exactly. It also may differ slightly from the actual load since it is assumed that the measured load is the same as the tractor's tractive force and this load is applied equally to all components of the working implement. [PERSON] and [PERSON] installed a six-component load cell on the three-point hitch system of the tractor to measure the tractive force required for the working implements [6; 7]. A six-component load cell is installed between the three-point hitch system of the tractor and the composite working implement, and the tractive force was calculated by converting the force and moment components measured by 3-axis load cells. The load acting on a disk narrow was modeled as the resistance of soil crushing force, shear force and soil weight [8], and calculated using the equation of motion. However, there is an advantage in measuring the load acting on all of the working implements, but it is impossible to measure the load of the component itself since the six-component load cell is installed as an integrated measuring device. [PERSON] measured and analyzed the loads measured by a torque meter installed on the PTO shaft of a tractor during the rotary work and a six-component load cell installed on the three-point hitch system during the plow work [9]. However, the loads acting on the transmission input shaft, the steering and the three-point hitch system could not be measured, so the load on the component itself could not be measured accurately. [PERSON] and [PERSON] analyzed the effects of rotational speed, radial load and misalignment on the bearing fatigue life [10; 11]. Bearing fatigue life decreased as the radial load increased in the low speed region. Whereas since the contact force caused by the centrifugal force acting on rolling elements became relatively larger than it caused by the radial load in the high speed region, the effect of the radial load decreased.