*4.1. The E*ff*ect of Texture Depth (Td)*

In order to study the influence of the effect of texturing in starved lubricated contact with respect to the texture depth, several simulations were carried out, based on groove and chevron texturing patterns. In these calculations, the texturing parameters other than the texture depth are constant. The coefficient of friction is calculated based on three different values of texture depth, and ranges from 5 to 10 μm. In Figures 11 and 12, the simulation results show the effect of different values for the texture depth based on starved and non-starved lubrication for grooves and chevrons. In Figure 11a, it can be seen from the results that a depth of 10 μm gives the lowest coefficient of friction. In Figure 11b, a limited input film thickness is applied in order to simulate the starvation. The results in Figure 11b show that the calculated coefficient of friction for different values of texture depth tend to the same values, therefore the Stribeck curves are merging together. In the calculations shown, the input film thickness (*hoil*) is set to 10 μm. The texturing properties of following calculations are given in Table 2.

**Table 2.** Texturing properties.


**Figure 11.** Stribeck curves as a function of texture depth for grooves when the lubrication is: (**a**) Non-starved, (**b**) starved, and *hoil* = 10 μm.

In Figure 12a, in case of chevron patterns similar to the groove pattern, the lowest coefficient of friction in the case of non-starved lubrication is achievable when the depth is around to 10 μm. In Figure 12b in the case of the starved lubrication, results show that the calculated coefficient of friction for different values of texture depth are tending to the same values, therefore the Stribeck curves are merging. By comparing the curves in Figure 12, and based on the results from the study on film thickness [57], (which showed that a higher film thickness is achievable for grooves and chevrons when the depth is around 10 μm), it is possible to conclude that the lowest coefficient of friction is achievable when the film thickness has the highest value. This is because in the case of mixed lubrication an increasing film thickness separates the surfaces and reduces contact. Although the growth in the depth of cavities to the optimum values leads to the higher film thicknesses, in the case of starved lubrication, this growth in lubricant film thickness is limited due to the limit in oil supply; this will result in a limitation in effect of this parameter on the coefficient of friction as shown in Figure 12.

**Figure 12.** Stribeck curves as a function of texture depth for chevrons when the lubrication is: (**a**) Non-starved, (**b**) starved, and *hoil* = 10 μm.
