One, bearing the basic structure and stress analysis
TB aircraft wheel bearings Timken (Timken) the company produced conical bearings, which consists of four parts: the inner race, outer race, tapered roller and cage bars. Under normal circumstances, the inner race, outer race and roll bar load bearing, and roll bar cage so evenly spaced from one another, in order to avoid collision and friction with each other and make each roll bar evenly and alternately subjected to equal loads. Inner raceway, roll bar and kept rolling rack assembly called together. Usually it is separable and outer race (outer race fixed on the decomposable hub), the mounting bearing more convenient.
Bearing low-carbon steel, the surface carburizing treatment, which makes bearings for hardness, fatigue, Ren Xing overall performance. Under normal circumstances, bearing the maximum temperature in the range 120-150 ℃, short-term temperature up to 175 ℃, the maximum contact stress cycle in 2100 ~ 3100MPa, and the holder is typically made of mild steel.
Since the geometric characteristics of tapered bearings and design features, it can withstand combined loads and axial warp. The angle between the centerline of the outer race of the bearing, the greater the ratio can withstand axial thrust and thrust through to the longer roll bar and the contact wire raceway, then the load bearing capacity of the stronger. Aircraft in different working conditions, different bearing stress situation:
1. The aircraft is stationary, still bear the main load bearing. Down load generated by gravity aircraft -P roll bar passed through to the outer bearing raceway, namely wheels. P can be decomposed in the axial direction of the axial force N and perpendicular to the outer raceway force F. As shown, the pressure of foreign raceway generated much greater than P P on the wheel of the force, to put a lot of pressure roller.
2. aircraft taxiing on the ground, mainly also withstand the vertical loads. Because they do not absolutely flat ground, up and down motion of the aircraft is greater than the magnitude of the gravity of the aircraft.
3. When landing, instant wheel grounded first and foremost be a huge shock stationary vertical load, then the wheel with high acceleration rate reaches the same speed and the aircraft taxiing on the ground. If the aircraft had a hard landing, the bearing is not running in the state to withstand the shock loads harm is great. If the airplane with a sliding ground, such as crosswind larger when the wheel but also by a large lateral load, wheel subjected to lateral friction, due to inertia, aircraft tilt to one side of the trend. Therefore, acting on the outboard bearing vertical load and lateral load large than the inside.
Second, bearing common failure mode
l. rolling contact fatigue
Rolling contact fatigue failure caused by bearing means during operation due to the alternating stress leads to fatigue cracks in the sub-surface of the contact surface or contact surface is formed and cause failure. When cracks began to form, the surface damage is minimal or not apparent until the final stage of the process, cracking and peeling it were apparent.
When subjected to a load bearing, pressed against each other between the rolling elements and raceway, deformation and stress in the contact area near the area, since the contact surface is small, even if the load is not too large, contact stress may be quite large. Typically, within the rolling bearing contact stress between 2000-4000MPa. Contact stress determines the static load bearing capacity, static load carrying capacity of the bearing main stress distribution between the contact surfaces, in particular the effect of shear stress distribution. If the rolling bodies rolling across the contact surface, a lower surface parallel to the rolling direction of shear stress will be alternating stress. At a depth of maximum amplitude, called the maximum dynamic shear stress. The maximum dynamic shear stress on the contact fatigue cracks occur and extended play a major role, while the maximum dynamic shear stress on the plastic deformation of the contact surface of the lower play a major role. When the cylindrical roll bar through the raceway surface, the impact of sub-surface shear stress field in graphical form from right to left as shown in the figure below.
