## 4 Results and Discussions
### Contact Load Distribution of DACBB  
Contact load distribution is very important to analyze the characteristic of rolling bearings. The study of fatigue life, contact stress, frictional torque and energy loss of rolling bearings greatly depends on the contact load distribution. Therefore, in this section, contact load distribution of DACBB is evaluated under different working conditions. Figure 10 shows the effect of axial preload on the contact load distribution of the left and the right rows of DACBB under combined external loads. The misaligned angle of inner ring is 0.2 mrad. The external radial and axial loads are 550 N and 500 N, respectively. From Figure 10, it can be seen that contact load distribution of DACBB is closely related to the axial preload. With the increase of axial preload, the contact load of the left and the right rows of DACBB increase. Meanwhile, the contact region of the left and the right rows also tends to be increased. This means that more of rolling balls are in contact with the inner ring and participate in the load transfer. It is also found that the situation of the contact load of the left row is opposite to that of the right row. In the upper half part of the left row (at the azimuth angle \(\varphi=0^{\circ}\sim 90^{\circ}\) and \(\varphi=270^{\circ}\sim 360^{\circ}\)), contact load between ball and  
Figure 8: Variation of maximum contact load under various radial loads and angular misalignments:  
(a) the left row of DACBB; (b) the right row of DACBB. Figure 9: Variation of maximum contact load under various axial preloads and angular misalignments:  
(a) the left row of DACBB; (b) the right row of DACBB. raceway is significantly higher than that of the lower half part (at the azimuth angle \(\varphi=90^{\circ}\sim 270^{\circ}\)). As for the right row of DACBB, contact load of lower half part is greater than that of the upper half part. This difference is because that the inner ring of DACBB is subjected to the angular misalignment. In addition, as shown in Figure 10, owing to the symmetrical structure of DACBB, the contact load of each row of DACBB distributes symmetrically with respect to the azimuth position of 180 degrees. Figures 11 and 12 illustrate the relationship between angular misalignment and the contact load distribution of each row of DACBB. It is assumed that the direction of angular misalignment shown in Figure 2 is positive, and the opposite misalignment direction is negative. In this section, the positive and negative angular misalignment are both considered. As shown in Figure 11, the effect of positive angular misalignment is described. The axial preload is 800 N, and the external radial and axial loads are 1500 N and 500 N, respectively. It is found that angular misalignment has a great influence on the contact load distribution of DACBB. Angular misalignment of inner ring causes uneven contact load distribution in each row of DACBB. This leads to the fluctuation of contact load distribution of each row along the azimuth angle of ball. Meanwhile, the fluctuation is symmetric with respect to the position of 180 degrees due to the symmetric structure of DACBB. Furthermore, angular misalignment has a limited influence on the contact loads of rolling balls near 90 and 270 degrees. This is because that these two positions are the boundary between the upper and lower half part of DACBB. Meanwhile, as demonstrated in Figure 11a, for the left row of DACBB, under lower misalignment angle, all the rolling balls are in contact with inner ring and participate in the load transfer, while under higher angular misalignment, some rolling balls do not participate in the load transfer because they are no longer constrained by the inner ring. This means that the inactive number of rolling balls is closely related to the magnitude of angular misalignment. Moreover, the load zone is the upper half part, and the contact load obviously increases with the increase of angular misalignment. For the right row of DACBB, the main load zone is the lower half part.