# Study on Lubrication Performance of Journal Bearing with Multiple Texture Distributions
## 5 Concave-Convex Composite Spherical Texture
### Effect of Area Density  
With a fixed texture depth \(h_{p}\) of \(2\times 10^{-6}\) m, the load capacity \(W\) and the friction coefficient \(\mu\) of different textured bearings are simulated under various of area densities \(\lambda\) from 0.03 to 0.8. From Figure 8, it can be observed that the area density \(\lambda\) of the composite textured not only has a great effect on the load capacity \(W\), but also significantly affects the friction coefficient \(\mu\) of the bearing. Both the pure convex and the convex-concave composite textures are able to enhance the bearing load capacity when the texture depth is increased. In addition, the improvements of both sorts of texture in the load capacity are nearly the same. For \(\lambda=0.8\), the load capacity of the composite textured bearing increases  
Figure 7: Effect of texture depth on (**a**) the load capacity and (**b**) the friction coefficient.  
by 8.2% from 1085 N (plain bearing) to 1174 N and that of the convex one increases to 1173 N as well. Compared with the pure texture (convex or concave), the composite texture has a significant effect on the friction coefficient. As seen in Figure 8b, the friction coefficients of the bearing with both texture types decrease with increasing area density. It should be noted that the decrement of the composite textured bearing caused by the increase of area density is much greater than that of the pure convex textured bearing. At \(\lambda=0.8\), the maximum reduction in friction coefficient of the composite bearing is 6.6%, based on the plain bearing. In the same case, the biggest decrement of the convex textured bearing is only 0.97%, which is far smaller than the composite textured bearing.  
That is to say, the convex-concave composite texture has considerable potential for improving lubrication performance in terms of increasing load capacity and decreasing friction coefficient.  
Based on the above studies, a combination of texture depth and area density is used for both the convex and the composite cases, which are \(h_{p}=3\times 10^{-6}\) m and \(\lambda=0.8\). The oil film pressure distributions of the plain, the convex and the composite textured bearings are calculated and compared in Figure 9. Taking the plain bearing as a reference, the load capacity and the friction coefficient of the convex and the composite textured bearings are calculated with the optimal texture depth and area density and listed in Table 1. With the optimal texture parameters, both the pure convex and the composite textures can improve the lubrication performance of bearing. The improvements in load capacity are the same for both texture types. The reductions of the friction coefficient are significantly different between the two cases; the composite texture has a much greater reduction than the convex texture.  
Figure 9 shows the circumferential oil film pressure distributions of the plain bearing, the convex textured bearing and the concave-convex composite textured bearing. The circumferential length with  
Figure 8: Effect of texture area density on (**a**) the load capacity and (**b**) the friction coefficient.  
oil film of the convex textured bearing is the same as that of the plain bearing. However, the oil film pressure in the convex texture in the main load region is much higher than that of the plain bearing. For the composite texture, the oil film is still higher than the plain bearing, but lower than the convex texture at peak, and higher than the convex texture at other locations. Additionally, the pressurized area of the composite textured bearing is wider than those of the plain and the convex textured bearings by 10 degrees. A wider pressurized area indicates a wider load region and a higher oil film pressure throughout the whole departure half of the contact area.