2:00 PM - 2:15 PM
[SSS06-12] Friction and wear properties of siliceous sandstone associated with input work rate
★Invited Papers
The friction of fault rock is one of the key factors to describe the slip instability and thereby is important to understand the mechanisms of earthquake nucleation. The wear property also plays a role in estimating the seismic histories inferred from the wear accumulation of the fault core. Numerous studies have been conducted to clarify the friction and wear properties for various types of rocks and gauges (e.g., Di Toro et al., 2011; Hirose et al., 2012; Boneh et al., 2013). However, the quartz-rich sandstone has not been fully explored even though the quartz is an abundant mineral and the sandstone is a major component of the crust in Japan. Therefore, we conducted the rotary shear experiments and analyzed the microstructure of the fault surface on siliceous sandstone to investigate the mechanisms of lubrication on the simulated fault, and its effect on the friction and wear properties.
We used a rotary-shear friction apparatus installed in National Research Institute for Earth Science and Disaster Resilience (Mizoguchi and Fukuyama, 2010; Yamashita et al., 2014). The sandstones of arenite were collected at Karauli, Rajasthan in India. We conducted the experiments with the slip rates between 1.2×10-3 and 1.7×10-1 m/s under the normal stress between 0.5 and 1.5 MPa. We kept a combination of normal stress and slip rates constant during the slip up to 200–300m to evaluate the friction and total wear on the simulated fault. We recorded normal stress, shear stress, slip velocity, and the weight of wear products collected after the experiments. We also measured the temperature at the outer rim of the sliding surface using a radiation thermometer (Keyence, IT2-02, IT2-50). Our previous study showed the friction and wear properties are classified into four phases based on the state of the sliding fault surface observed after the experiments as follows: Phase I) generation of the fault mirror structure, Phase II) initiation of the destruction of fault mirror structure, Phase III) destruction of the entire fault mirror structure, and Phase IV) regeneration of the fault mirror structure partially on the fault surface (Maeda et al., 2021, SSJ). The transition of phases can be associated with the input work rate, which is a metric of rotary shear experiments obtained by a product of slip rate and normal stress (Maeda et al., 2022, SSJ). Phase I showed the average friction is weakened with the increase in the input work rate, while it is re-strengthened after Phase II. The wear rate positively correlates with the input work rate after Phase II, but almost no wear materials were produced in Phase I.
In the present study, we investigated the microstructure of the surface using the scanning electron microscope (SEM) installed in Osaka Metropolitan University. We found the microstructure of the shear surface evolved with the phase transition; in Phase I, the nanograins filled the voids of the surface and its agglomeration formed the smooth planes. The angular grains then emerged due to the failure of smooth plane after Phase Ⅱ, and melt patches were observed after Phase Ⅳ. The maximum and average temperatures at the boundaries between Phases I and II were 100°C and 80°C, respectively.
We interpret the observed fault mirror structure in Phase I with a relatively low temperature indicates the lubrication due to wear materials of hydrated amorphous silica or silica gel. Then, the destruction of the fault mirror structure with the average temperature of >80°C after Phase Ⅱ (input work rate > ~0.06MW/m2), and the traces of melt patches (Phase Ⅳ) can contribute to the mechanisms of a frictional strengthening with a crack formation caused by thermal expansion of quartz, and the formation of initial melt patches. When friction and wear phenomena such as those in this experiment occur on natural faults in quartz-rich sandstone may exhibit different slip behaviors depending on normal stress and slip velocity. In addition, fault core growth is expected to be significantly lower at low slip velocities.
We used a rotary-shear friction apparatus installed in National Research Institute for Earth Science and Disaster Resilience (Mizoguchi and Fukuyama, 2010; Yamashita et al., 2014). The sandstones of arenite were collected at Karauli, Rajasthan in India. We conducted the experiments with the slip rates between 1.2×10-3 and 1.7×10-1 m/s under the normal stress between 0.5 and 1.5 MPa. We kept a combination of normal stress and slip rates constant during the slip up to 200–300m to evaluate the friction and total wear on the simulated fault. We recorded normal stress, shear stress, slip velocity, and the weight of wear products collected after the experiments. We also measured the temperature at the outer rim of the sliding surface using a radiation thermometer (Keyence, IT2-02, IT2-50). Our previous study showed the friction and wear properties are classified into four phases based on the state of the sliding fault surface observed after the experiments as follows: Phase I) generation of the fault mirror structure, Phase II) initiation of the destruction of fault mirror structure, Phase III) destruction of the entire fault mirror structure, and Phase IV) regeneration of the fault mirror structure partially on the fault surface (Maeda et al., 2021, SSJ). The transition of phases can be associated with the input work rate, which is a metric of rotary shear experiments obtained by a product of slip rate and normal stress (Maeda et al., 2022, SSJ). Phase I showed the average friction is weakened with the increase in the input work rate, while it is re-strengthened after Phase II. The wear rate positively correlates with the input work rate after Phase II, but almost no wear materials were produced in Phase I.
In the present study, we investigated the microstructure of the surface using the scanning electron microscope (SEM) installed in Osaka Metropolitan University. We found the microstructure of the shear surface evolved with the phase transition; in Phase I, the nanograins filled the voids of the surface and its agglomeration formed the smooth planes. The angular grains then emerged due to the failure of smooth plane after Phase Ⅱ, and melt patches were observed after Phase Ⅳ. The maximum and average temperatures at the boundaries between Phases I and II were 100°C and 80°C, respectively.
We interpret the observed fault mirror structure in Phase I with a relatively low temperature indicates the lubrication due to wear materials of hydrated amorphous silica or silica gel. Then, the destruction of the fault mirror structure with the average temperature of >80°C after Phase Ⅱ (input work rate > ~0.06MW/m2), and the traces of melt patches (Phase Ⅳ) can contribute to the mechanisms of a frictional strengthening with a crack formation caused by thermal expansion of quartz, and the formation of initial melt patches. When friction and wear phenomena such as those in this experiment occur on natural faults in quartz-rich sandstone may exhibit different slip behaviors depending on normal stress and slip velocity. In addition, fault core growth is expected to be significantly lower at low slip velocities.