Fig. 3.

Procedures for sliding tests: the first five phaseswere identical to those in indentation tests (Fig. 2), establishing equilibriumbetween the probe and the sample prior to sliding. During sliding (phase 6), the horizontal stage reciprocated over the probe with a 1500 μm track, resulting in fluid pressurization in the sample and increased normal force until reaching a steady state. The penetration depth, normal and friction forces were collected and analyzed at the center of the sliding track during the steady state.