The misalignment of the roller rotation axis relative to the actual direction of rolling motion is an important  parameter influencing the wear rates. In this work the VRR was operated with misalignment angle of 0.9 degree as such misalignment had produced relevant wear phenomena in previous work [3,4]. The sliding distance that promotes wear of slightly misaligned rollers may be approximated as proportional to the product of misalignment angle and the width of the contact region. This approximate sliding distance concept is depicted in Figure 5. The approximate sliding distance per contact pass was 3.1 micrometer  for the VRR. If operating at the same misalignment angle of 0.9 degree the approximate sliding distance  per contact pass for the mechanism would be 1.9 micrometer. The speed of the test rig was 20  revolutions per minute. The speed was selected to provide a contact passing time of same order as the mechanism but the test was operated with a slightly faster rate to obtain the desired number of contact  passes in practical calendar time. The contact passing times were 0.009 second for the mechanism and  0.005 second for the VRR tests.  There was no single VRR test duration that could mimic the duration needed for the mechanism. The  VRR makes use of equally sized rollers and so VRR roller surfaces experience equal number of contactpass cycles per unit of time. For the mechanism, the steel rollers and titanium-alloy planes have differing  numbers of contact cycles. Using 48,000 actuations of the mechanism as the needed life, with each actuation requiring a forward and reverse traverse, the duration for some points on the mechanism’stitanium-alloy plate is 96,000 contact cycles. Other points of the mechanism’s plate are passed over by two rollers for each traverse, requiring 192,000 contact cycles. The mechanism steel roller surfaces experience up to three contact cycles per traverse, requiring 288,000 contact cycles. Further complicating selection of the VRR test duration, the lifetime of a solid lubricating film is not reliably calculated for all situations by simple proportionality to contact cycles.  For mild wear, the wear rate is often modeled, to a first approximation, using the Archard wear model [12] as proportional to the product of contact pressure  and sliding distance. The VRR test duration was selected as 90,000 contact cycles. This selection enabled a desired testing pace of two tests per week and was considered to provide a reasonable match of both total contact cycles and a simple wear index (product of sliding distance and contact pressure) in  comparing the VRR to the mechanism. Table 2 summarizes some of the key engineering parameters one  might use to compare VRR to the mechanism in terms of contact conditions and durability concepts. The VRR can be considered as an accelerated wear test in terms of higher contact pressures and faster  speeds. In this way the alternative materials were evaluated on a relative basis with good relevance to the application. The VRR tests were intended to complement but not substitute for qualification testing.  Table 1. Hertz Contact Conditions mechanism test rig pressure, max. (MPa) 330 460 pressure, mean (MPa) 220 310 a (mm) 1.77 2.30 b (mm) 0.124 0.200 aspect ratio, a/b 14.3 11.3 (a)          (b) Figure 5.  Approximate model of sliding distance of a misaligned roller contact.  (a) Elliptical  contact ellipse of width R, misalignment angle t,  and actual rolling path R’.  (b) Approximate  /g86/g79/g76/g71/g76/g81/g74/g3/g71/g76/g86/g87/g68/g81/g70/g72/g3/g54/g3/g167/g53/g194/g87/g68/g81/g11 /g87/g87/g12/g3/g167/g3/g53/g194/g87/g87/g17 91