High Pressure Torsion tests on two types of rail sand under wet contact conditions

This data set contains the data of sanded High Pressure Torsion (HPT) tests under wet contact conditions.
Tested were two types of rail sand, which are used to increase friction in wheel-rail contacts.
Please see the following paper for a detailed description of experiments:
"B. Suhr, W. A. Skipper, R. Lewis, and K. Six, “Mechanisms of Adhesion Increase in Wet Sanded Wheel–Rail Contacts—A DEM-Based Analysis,” Lubricants, vol. 13, no. 7, 2025, doi: 10.3390/lubricants13070314."

The material tested was two types of sand used in railways, called AT sand (used in Austria) and GB sand (used in the UK).
The sand grains used in the tests nearly had the same size, passed through a 1.2mm sieve but did not pass a 1.18mm sieve.
The HPT top and bottom specimen were made of R260 grade rail. 
To ensure repeatability and a realistic state of both top and bottom specimen, 
they are run together to fully condition (shakedown) the surfaces. 
In each test, roughly the same weight of sand grains was used, which resulted in placing ten sand grains manually.
After placing the grains, water is added and a normal stress of 900MPa is applied, followed by a shearing of 0.4mm keeping the normal stress constant.
The folder HPT_measurements contains the measurement results in txt format.
Tests number 2,3,4 are conducted with GB sand, and tests number 5,6,7 are conducted with AT sand.
In each file, column 1 is the time [s], column 2 is the shear displacement [mm] and column 3 is the adhesion coefficient [-].

After conducting the tests, a non-contacting imaging and measuring tool named Alicona InfiniteFocusSL was used to take 3d scans of the surfaces. Both top and bottom specimen were scanned. First scans were taken directly after the test, with sand clusters still attached to the steel surface. Second scans were taken after cleaning the surfaces showing indents caused by the sand clusters.
The images obtained can be found in the folder AliconaImages.
File names are build using the test number, T (top) or B (bottom) and _Cleaned for cleaned surfaces.
Thus: 
2_B.jpg: GB sand, Bottom specimen, first scan with sand clusters on the the surface
2_B_Clean.jpg: GB sand, Bottom specimen, secon scan after cleaning the surface

Please see the referenced paper for further details on the conducted experiments.