2:30 PM - 2:45 PM
[SCG63-14] Contribution of brucite nanoparticles to velocity-weakening
Keywords:Sheet-structure nanoparticle, Friction experiments, Velocity-weakening
Friction experiments were conducted with chemically synthesized brucite nanoparticles (purchased from WAKO; purity: 99.9%; grain size: 70 nm & 600 nm). Biaxial testing machine in Hiroshima University was used and two gouges of brucite were formed with three gabbro blocks which surfaces contacted to gouges were roughened with abrasive.
Experimental results showed that friction coefficients are 0.44 (stable slip) and 0.34 (small stick-slip) for grain sizes of 70 nm and 600 nm, respectively. Velocity stepping test showed that both brucite nanoparticles were velocity weakening. Although the amplitude of roughened surfaces of gabbro blocks was >10 μm, optical observation showed brucite nanoparticle filled up those roughness and there were clear straight boundary shears on both sides of gouge. In the near region of these boundary shears, orientation of particles was observed within ~1μm.
Shear localization to boundary shear or Y-plane parallel to shear direction is thought to be one of the reasons of velocity-weakening (Scruggs & Tullis, 1998). On the other hand, sheet-structure minerals were observed to be oriented mainly along P-shear (e.g. Haines et al., 2013). Considering the grain size we used in this study, shear localization can be generated only with some scores of nanoparticle. Therefore, it is implied that velocity-weakening is caused by the shear localization with the orientation of nanoparticles along boundary shear other than macro particles.
In this presentation, we will discuss the effects of gouge thickness and the displacement-dependent formation of smooth shear planes.