The term Stribeck curve is used to describe a plot showing the frictional characteristics of a liquid lubricant over conditions usually spanning the Boundary, Mixed and Hydrodynamic regimes. Each regime is defined by the ratio of the film thickness to the surface roughness, or the λ ratio (Figure 1). Such curves are often used to evaluate the effect of changes to the lubricant’s viscosity or to the lubricant’s additive package, or the effect of surface roughness. The primary requirement for generating a Stribeck curve is a fluid that can be drawn into a converging gap, thus creating a pressure increase to support the load (Figure 2).
While there is currently no standard published test method for generating a Stribeck curve, either in reciprocating or unidirectional motion, a number of other lubricant performance-related tests can be conducted with the same reciprocating motion for the lower sample. By exchanging the cylinder-on-side upper sample for either a ball or a flat-pin, and adjusting the frequency and/or stroke-length, the same setup can be used to run the following standard ASTM-, DIN- or ISO-issued reciprocating tests:
ASTM D5706-11: Standard test method for determining extreme pressure properties of lubricating greases using a high-frequency, linear-oscillation (SRV) test machine
ASTM D5707-11: Standard test method for measuring friction and wear properties of lubricating grease using a high-frequency, linear-oscillation (SRV) test machine
ASTM D6425: Standard test method for measuring friction and wear properties of extreme pressure lubricating oil
ASTM D6079-11: Standard test method for evaluating lubricity of diesel fuels by the high-frequency reciprocating rig (HFRR)
ASTM D7688-11: Standard test method for evaluating lubricity of diesel fuels by the high-frequency reciprocating rig (HFRR) by visual observation
ASTM D7594-11: Standard test method for determining fretting wear resistance of lubricating greases under high Hertzian contact pressures using a high-frequency, linear- oscillation (SRV) test machine
ASTM D7755-11: Standard practice for determining
the wear volume on standard test pieces used by high- frequency, linear-oscillation (SRV) test machine
ASTM G133-10: Standard test method for linearly reciprocating ball-on flat sliding wear
ASTM G203-10: Standard guide for determining friction energy dissipation in reciprocating tribosystems
ASTM G206-11: Standard guide for measuring the wear volumes of piston ring segments run against flat coupons in reciprocating wear tests
DIN 51834: Determination of friction and wear data of lubricating oils
ISO 12156-1:2006: Diesel fuel — assessment of lubricity using the high-frequency reciprocating rig (HFRR),
Part 1: Test
Bruker Senior Applications Scientist