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a A schematic diagram showing the structures of the shaking table and the large biaxial friction apparatus. Reinforced concrete is used as the basement of the shaking table. b A schematic diagram showing machine elements (springs) and specimens. k m1 , k m2, and k st are the stiffness values of the reaction force unit, specimen-holding part of the main frame, and shaking table, respectively. Displacement was measured at the end of the specimens which correspond to the (d 2 -d 1 ). Numbers in a denote machine elements and foundation (see text). Sheet pile (22) and added concrete mass (23) were installed for the reinforcement of the foundation during the renovation of the shaking table in 1989
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This paper reports stick–slip behaviors of Indian gabbro as studied using a new large-scale biaxial friction apparatus, built in the National Research Institute for Earth Science and Disaster Prevention (NIED), Tsukuba, Japan. The apparatus consists of the existing shaking table as the shear-loading device up to 3,600 kN, the main frame for holding...
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... use the Large Scale Earthquake Simulator of NIED, Tsukuba on which a large biaxial apparatus is placed (17 in Fig. 3a), as the loading device. This simulator was built by Mitsubishi Heavy Industries, Ltd. and was installed in 1970 at the National Research Center for Disaster Prevention (NRCDP), the former organization of NIED (National Re- search Center for Disaster Prevention 1983). It was used extensively in earthquake resistance tests on wooden ...
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... of NIED (National Re- search Center for Disaster Prevention 1983). It was used extensively in earthquake resistance tests on wooden houses, oil tanks, and various structures, and was renovated in the late 1980s to extend the servocontrol and stroke capabilities ( Minowa et al. 1989). The shaking table of 14.5 m 9 15 m in horizontal sizes (6 in Fig. 3a) is driven with four servo- controlled hydraulic actuators (18 in Fig. 3a) which can produce a horizontal force up to 3,600 kN in total, a horizontal velocity up to 1.0 m/s, and an acceleration up to 9.4 m/s 2 . Two actuators are set on both sides of the shaking table, and a leftward motion for loading in our experiments is produced by ...
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... used extensively in earthquake resistance tests on wooden houses, oil tanks, and various structures, and was renovated in the late 1980s to extend the servocontrol and stroke capabilities ( Minowa et al. 1989). The shaking table of 14.5 m 9 15 m in horizontal sizes (6 in Fig. 3a) is driven with four servo- controlled hydraulic actuators (18 in Fig. 3a) which can produce a horizontal force up to 3,600 kN in total, a horizontal velocity up to 1.0 m/s, and an acceleration up to 9.4 m/s 2 . Two actuators are set on both sides of the shaking table, and a leftward motion for loading in our experiments is produced by compressive push with the actuators on the right and by tensile pull with ...
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... whole system is built in Quaternary sediments (23). Figure 3b exhibits a simplified constitution of our ex- perimental system using springs, masses (heavy parts only), and frictional interface between specimens. Stiffness is defined here as a ratio of a force exerted to an elastic object to a change in its length (e.g., Jaeger and Cook 1979;Ohnaka 1973Ohnaka , 1978Shimamoto et al. 1980). ...
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... consider that k m2 is an effective stiffness re- lating shear force acting in the system and the displacement of the left end of the lower specimen where displacement is measured, without going into the complexity of the real be- haviors. The shear force is measured within the reaction force unit, very close to the upper specimen (location FG in Fig. ...
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... displacement measurement, we take the position on the foundation where the reaction force base is fixed as a reference point with zero displacement (filled circle on the upper left side of Fig. 3b). We denote displacements of the left ends of the upper and lower specimens by d 1 and d 2 , respectively (Fig. 3b). All displacements are taken positive leftward. Difference in displacements between the left ends of the specimens d is measured in our ...
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... displacement measurement, we take the position on the foundation where the reaction force base is fixed as a reference point with zero displacement (filled circle on the upper left side of Fig. 3b). We denote displacements of the left ends of the upper and lower specimens by d 1 and d 2 , respectively (Fig. 3b). All displacements are taken positive leftward. Difference in displacements between the left ends of the specimens d is measured in our ...
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... and 100 in the left diagrams of Fig. 6 which exhibit shear stress-time records (solid curves) and displacement-time records (dashed curves). The shear stress-time records are slightly smoother than the dis- placement-time records as can be seen in the figures be- cause the shear stress represents a force in the stationary column (spring k m1 in Fig. 3b) that is separated from the shaking table by frictional interface. On the other hand, the displacement d is the relative motion between the two specimen blocks and is affected directly by the movements of the specimens on both sides. We thus define the onset and stop of a slip event as points of the maximum and the minimum shear ...
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... (time = 0 corresponds to 299 s in the dia- gram), with vertical axis showing shear force F (black curve), relative displacement u 2 -u 1 (pink curve), and displacement of the shaking table l (green curve). The displacement u 2 -u 1 is the same as the displacement d = d 2 -d 1 as measured by a laser-displacement trans- ducer in the X direction (Figs. 2, 3b), but we use different symbols because u 1 and u 2 were measured differently. Figure 12b shows temporal changes in F, d, l, -u 1, u 2 , and u 2 -u 1 with different colors as shown in the diagram, for the sixth stick-slip event marked with a dashed rectangle in the inset diagram. Note that (u 2 -u 1 ) shown by a pink curve coincides with ...
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... of parts n is 8. We renumbered those parts and gave stiffness k i and mass m i of part i in Table 1, and the stiffness values give the bulk stiffness of the stationary side k m1 of 0.159 GN/m. Shortening or elongation of part i is given by (k m1 /k i )d 1 assuming uniform force distribution, where d 1 is the displacement of the stationary side (Fig. 3b). Then the effective mass of part i during its dynamic deformation is given by (m i / 3)(k m1 /k i ) 2 (the first term in Eq. (3); Table 1, sixth column). We did not include the dynamic deformation of the upper specimen, and its stiffness is set to infinite in Table 1. On the other hand, displacement of each part has to be evaluated to ...
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... an important question on the meaning of the data on DF/Dd in Fig. 10a. Our interpretations in Sect. 4 were that the slope of DF versus Dd relationship gives the stiffness of the whole system k and that this k and k m1 values, used above, give the stiffness of 4.16 9 10 8 N/m (555 MPa/ m) for the lower part (k m2 and k st connected in series; Fig. 3b). However, if the shaking table did not move much before the fault motion stopped at around the minimum shear force (Fig. 12b), the stiffness given by DF/Dd does not in- clude the stiffness of the shaking table k st (Fig. 3b). Then the stiffness k m2 (4.16 9 10 8 N/m) is more likely to give a stiffness of k m2 . The mass of the lower ...
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... used above, give the stiffness of 4.16 9 10 8 N/m (555 MPa/ m) for the lower part (k m2 and k st connected in series; Fig. 3b). However, if the shaking table did not move much before the fault motion stopped at around the minimum shear force (Fig. 12b), the stiffness given by DF/Dd does not in- clude the stiffness of the shaking table k st (Fig. 3b). Then the stiffness k m2 (4.16 9 10 8 N/m) is more likely to give a stiffness of k m2 . The mass of the lower specimen (1.6 9 10 3 kg) and this stiffness give a rise time of 6 ms. The displacement of the lower specimen u 2 exhibits a small peak at 4.4 ms after the onset of shear-force drop (blue curve and vertical dashed blue line in ...
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... during dynamic rupture propagation, it is essential to measure the shear stress directly along the sliding surface as conducted by Dieterich (1981b), Dieterich (1981, 1984), Lockner and Okubo (1983), Ohnaka et al. (1987), and Beeler et al. (2012). The shear force gauge between the reaction force bar and the upper specimen (12 in Fig. 1c, FG in Fig. 3b) cannot separate the axial forces due to the friction along the sliding surface and dynamic forces to accelerate or decelerate machine elements and the upper specimen. The situation is similar to a spring-slider block system in Fig. 13a. The shear stress as calculated from the restoring force in the spring divided by the fault area is ...
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... side affects the fault motion, and the loading side cannot be separated from the analysis. The behavior of this side is more complex because of the huge mass of the shaking table as revealed by the slip histories of the lower moving specimen and the shaking table (Fig. 12b). We conventionally separated two springs k m2 and k st for this side in Fig. 3b, but we could not fully model the behavior of the moving side yet in this paper. Full understanding of the elastic and inertial properties of the loading side will be a key to restore the frictional properties accurately from the observed ...
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Japan is one of the disaster-prone countries. Then, various disaster education is conducted in schools and local communities for alleviating the damage caused by disasters. However, according to various surveys, disaster prevention awareness among young people is known to be lower than in other age groups in Japan. Therefore, we worked with Kanagaw...
Citations
... Some laboratory experiments and theoretical investigations showed that a higher loading rate contributes to a transition from stick-slip to stable slip [20,22,[29][30][31]. On the contrary, some experimental results suggested that a higher loading rate may promote unstable slip [3,6,32] or favor ruptures with higher speed [33]. It was also suggested that the impact of loading rates on fault slip behaviors hinges on the fault's proximity to a steady state. ...
The loading rate of tectonic stress is not constant during long-term geotectonic activity and significantly affects the earthquake nucleation and fault rupture process. However, the mechanism underlying the loading rate effect is still unclear. In this study, we conducted a series of experiments to explore the effect of the loading rate on earthquake nucleation and stick–slip characteristics. Through lab experiments, faults were biaxially loaded at varying rates to produce a series of earthquakes (stick–slip events). Both shear strain and fault displacement were monitored during these events. The findings indicate a substantial effect of the loading rate on the recurrence interval and the shear stress drop of these stick–slip events, with the recurrence interval inversely proportional to the loading rate. The peak friction of the fault also decreases with the increasing loading rate. Notably, prior to the dynamic rupture of earthquakes, there exists a stable nucleation phase where slip occurs in a quasi-static manner. The critical nucleation length, or the distance required before the dynamic rupture, diminishes with both the loading rate and normal stress. A theoretical model is introduced to rationalize these observations. However, the rupture velocity of these lab-simulated earthquakes showed no significant correlation with the loading rate. Overall, this study enhanced our comprehension of earthquake nucleation and rupture dynamics in diverse tectonic settings.
... Stick-slip FIV is a typical non-smooth vibration, which has two motion regimes in a single period: the stick phase when two bodies in contact stick together with no relative motion and the slip phase when relative motion happens [14]. The creep groan noise of brake systems [15], earthquakes [16], the beautiful music produced by violin strings [17], are all the results of stick-slip vibration. Stick-slip vibration is generally caused by the velocity weakening relation between the friction force and the relative motion, the declining friction has a negative damping effect which compensates the energy dissipation in the friction system to maintain a stable limit cycle vibration without relying on external excitations [18]. ...
A bistable energy harvester incorporated in a friction system is modelled and numerically investigated, aiming to realize an improved power extraction from stick–slip vibration. Kinetic energy is converted into electricity through piezoelectric patches, and bistability is achieved via two magnets. The theoretical results indicate that large-amplitude periodic motion of the nonlinear energy harvester can be triggered by the stick–slip limit cycle excitations. However, under the influence of the loading force and the belt velocity, the vibration pattern of the energy harvester can be very complicated, which exhibits abundant bifurcation behaviour. Quasi-periodic and chaotic oscillations can happen when the loading force gets large. Small-amplitude intrawell oscillation happens at low sliding velocities, while large-amplitude periodic oscillation occurs when the belt velocity increases to a level at which the stick–slip excitation is strong enough to provide sufficient energy to make the tip magnet escape the potential barrier. In addition, coexistence solutions of periodic and chaotic oscillations can be observed at some sliding velocities due to the nonlinear effects of the energy harvester and the negative gradient of friction versus the relative velocity. To fully understand the vibration behaviour of the energy harvester, a solution map is plotted in terms of loading force and belt velocity according to numerical simulation results. In the end, an experimental work is performed to prove the theoretical investigation.
... Considering the time dependent healing, larger stress drops in faster loading experiments might be counterintuiti ve. Howe ver, this feature w as already reported in previous studies (Togo et al. 2015 ;Xu et al. 2018 ). Since the loading is relati vel y fast, one possible interpretation is that there might not be enough time to relax stress and dissipate strain before the stress reached the threshold value (Xu et al. 2018 ). ...
... After 22 s from the beginning of the experiment LB01-113, the amount of stress drop and the recurrence interval of stick-slip events became larger than those observed at the beginning of the experiment, and the amount of slip rate was from 5 to 10 times higher. Artificial oscillations in the displacement of the specimens were reported in case of large stick-slip events and interpreted to be induced by an oscillation of the displacement sensor, not by dynamic sliding (Togo et al. 2015 ). Thus, we estimated the RSF friction parameters for events up to 22 s for LB01-113. ...
The laboratory-derived Rate- and State-dependent Friction (RSF) law governs rock friction Although a number of studies have investigated the RSF friction parameters, they are not fully understood yet within a physical framework. In this study, we estimated the variation of RSF parameters during stick-slip cycles, in order to have insights into the temporal variation of fault conditions during slipping, which may help understand the relation between the change in friction parameters and the generation of gouge particles. To get a more refined understanding of the evolution of RSF parameters, we estimated these parameters for each of the hundreds of stick-slip events that occurred on laboratory faults during an experiment. We used experiment data for which the gouge particles were removed from the laboratory faults at the beginning of each experiment; this procedure made possible to evaluate the influence of the gouge layer evolution on the variation of the RSF parameters. Since the amount of data was very large, we adopted a Random Forest (RF) machine learning approach for data analysis. The RF model was trained on simulated friction data and then applied to the experiment stick-slip event data to estimate the RSF parameters. To generate simulated friction data of stick-slip events, a one-degree-of-freedom spring-slider model governed by the RSF law was assumed. From plots of friction change as a function of displacement, some representative features were extracted to account for the RSF parameters and were used as input to the RF algorithm. Using the RF approach, we captured the variation of the RSF parameters a, $b - a$ and ${D}_c\ $defined in the RSF law. The results show that during a first transient phase, the parameter a becomes smaller, while parameters $b - a$ and ${D}_c$ become larger, as the gouge layer becomes thicker. The variation of the RSF parameters becomes less pronounced during the following steady-state phase. These results suggest that the variation of RSF friction parameters may be related with the evolution of the gouge layer.
... In other cases, it has to be reduced or suppressed because it can induce noise [12]. The stick-slip vibration of earth plate may case devastating earthquake [13]. Therefore, it is very important to understand and control stick-slip vibration. ...
In this work, a comparative study is performed to investigate the influence of time-varying normal forces on the friction properties and friction-induced stick-slip vibration by experimental and theoretical methods. In the experiments, constant and harmonic-varying normal forces are applied, respectively. The measured vibration signals under two loading forms are compared in both time and frequency domains. In addition, mathematical tools such as phase space reconstruction and Fourier spectra are used to reveal the science behind the complicated dynamic behaviour. It can be found that the friction system shows steady stick-slip vibration, and the main frequency does not vary with the magnitude of the constant normal force, but the size of limit cycle increases with the magnitude of the constant normal force. In contrast, the friction system harmonic normal force shows complicated behaviour, for example, higher-frequency larger-amplitude vibration occurs as the frequency of the normal force increases. The interesting findings offer a new way for controlling friction-induced stick-slip vibration in engineering applications.
... Light colored fault gouge was distributed in a thin layer (a few microns thick) all over the fault surfaces; however, gouge was observed to coat and spill out from the grooves (Figure 3), consistent with previous laboratory observations Togo et al., 2015;Yamashita et al., 2015). There was a heavy coating of gouge (~100 μm thick) at the higher stressed fault ends. ...
... Normal stress increases do not appear to change the groove width, unlike groove density. Many grooves were narrower on one side, which we refer to as the head, and appear to widen and deteriorate with continued fault slip, as gouge is transported in the z direction (perpendicular to the slip direction), similar to previous observations (Doblas, 1998;Togo et al., 2015;Yamashita et al., 2015). For example, the groove shown in Figures 3b and 3d on the moving block is narrower on the right side (+x direction), and has a wider tail with gouge smeared out in the z direction on the left side of the photo. ...
... As described schematically in Figure 8, we infer that a weak grain is plucked from the wall rock and crushed into finely comminuted wear product (gouge) that is then dragged by the dislocating fault surfaces to extend the grooves (Bhushan, 2002;Renard et al., 2012;Togo et al., 2015;Wang & Scholz, 1994;Yamashita et al., 2015). Groove widths were 0.1 to 2 mm, which is similar to the grain size of the granite (Observation 5). ...
Faults are the products of wear processes acting at a range of scales from nanometers to kilometers. Grooves produced by wear are a first‐order observable feature of preserved surfaces. However, their interpretation is limited by the complex geological histories ofnatural faults. Here we explore wear processes on faults by forensically examining a large‐scale controlled, laboratory fault which has a maximum offset between the sides of 42 mm and has been reset multiple times for a cumulative slip of approximately 140 mm. We find that on both sides of the fault scratches are formed with lengths that are longer than the maximum offset but less than the cumulative slip. The grooves are explained as a result of interaction with detached gouge rather than as toolmarks produced by an intact protrusion on one side of the fault. The density of grooves increases with normal stress. The experiment has a range of stress of 1–20 MPa and shows a density of 10 grooves/m/MPa in this range. This value is consistent with recent inferences of stress‐dependent earthquake fracture energy of 0.2 J/m2/MPa. At normal stresses above 20 MPa, the grooves are likely to coalesce into a corrugated surface that more closely resembles mature faults. Groove density therefore appears to be an attractive target for field studies aiming to determine the distribution of normal stress on faults. At low stresses the groove spacing can be measured and contrasted with areas where high stresses produce a corrugated surface.
... Stick-slip vibration is very common and sometimes it is unwanted because it leads to noise, such as the creaking of dry door hinges, the creep groan noise of a brake system [19,20]. On a grand scale, an earthquake is attributed to stick-slip motion of the Earth plates [21]. In other cases, it is desired, for example, the stick-slip vibration of the strings of a violin can produce beautiful music [22,23] or can help reduce vibration (as in a friction damper [24]). ...
Friction is known to cause vibration in many situations and one particular kind of friction-induced vibration is in the form of stick-slip vibration, which is of fundamental significance in science due to its ubiquitous nature. In this paper, an experimental and theoretical study is performed to investigate friction-induced stick-slip vibration. An experimental setup with a sophisticated dual-pin-on-disc configuration is produced. A detailed solid model is constructed and modal tests are conducted to establish a novel, simplified 2-degree-of-freedom (DoF) theoretical model for the test rig. A series of stick-slip oscillation tests at several levels of normal load and disc velocity are performed and interesting vibration behaviour is discovered. A non-smooth Coulomb’s law of friction is adopted and identified for the 2-DoF model and the method of the Switch Model is used to deal with the non-smooth transitions from stick to slip and from slip to stick. The theoretical results predicted by the 2-DoF model agree qualitatively quite well with the experimental results. The differences between the two sets of results also suggest that there are challenges in realising regular stick-slip vibration in real machines/structures and capturing it theoretically. The main contributions of this work are the new designed test rig, the experimental findings, and the established theoretical model that can be used to reveal interesting dynamic behaviour of stick-slip vibration.
... Young's modulus, density, P-wave velocity and S-wave velocity are 64 GPa, 2650 kg.m −3 , 5800 m.s −1 and 3500 m.s −1 respectively.Indian Gabbro :Indian Gabbro is a metagabbro coming from Tamil Nadu in India. This rock was notably used for meter-scale rock friction experiments(Togo et al., 2015;Xu et al., 2018;Yamashita et al., 2018;Fukuyama et al., 2018). Major minerals are clinopyroxene (∼FIGURE 2.1: Sample preparation. ...
Au cours de cette thèse, nous avons reproduit expérimentalement des séismes à l’échelle centimétrique dans des conditions de pression proches de la réalité. Les expériences réalisées nous ont permis d’explorer deux grandes thématiques : (i) l’origine du rayonnement haute-fréquence pendant la rupture dynamique et (ii) les signaux précurseurs pendant la phase de nucléation de la rupture dynamique. Nos résultats montrent que le rayonnement haute-fréquence est concomitant à la propagation du front de rupture et que deux paramètres induisent une augmentation du rayonnement haute-fréquence : l’état de contrainte initial et la vitesse de rupture. Les analyses microstructurales des échantillons de roches suggèrent que la production d’endommagement cosismique ou de particules de gouge contribue au rayonnement haute fréquence. L’étude des signaux précurseurs (i.e., précurseurs acoustiques) montre que la nucléation est un processus en très large majorité asismique. Ce très faible couplage pourrait expliquer le peu d’observations de séismes précurseurs à l’échelle des failles crustales. L’analyse temporelle des émissions acoustiques suggère que leur dynamique est principalement contrôlée par l’accélération du glissement pendant la phase de nucléation. La microtopographie et la microstructure des échantillons de roches montrent que le couplage est directement relié à la rugosité du plan de faille. Une augmentation des conditions de pression favorise l’occurrence de processus de déformation plastique ou de fusion partielle au cours de la rupture sismique, ce qui diminue la rugosité et donc le couplage.
... Complete rupture events ( Figure 4d) propagate across the entire fault surface and are similar to stick-slip instabilities observed previously (Brace & Byerlee, 1966;Dieterich, 1981;Johnson & Scholz, 1976;Togo et al., 2015). D(x) is approximately uniform across the fault, while the aforementioned edge effect causes an increase in _ D max x ð Þ at the two sample ends ( Figure 4d). ...
Loading a 3‐m granite slab containing a saw‐cut simulated fault, we generated slip events that spontaneously nucleate, propagate, and arrest before reaching the ends of the sample. This work shows that slow (0.07 mm/s slip speeds) and fast (100 mm/s) contained slip events can occur on the same fault patch. We also present the systematic changes in radiated seismic waves both in time and frequency domain. The slow earthquakes are 100 ms in duration and radiate tremor‐like signals superposed onto a low‐frequency component of their ground motion. They are often preceded by slow slip (creep) and their seismic radiation has an ω⁻¹ spectral shape, similar to slow earthquakes observed in nature. The fastest events have slip velocity, stress drop, and apparent stress (0.2 m/s, 0.4 MPa, and 1.2 kPa, respectively) similar to those of typical M −2.5 earthquakes, with a single distinct corner frequency and ω⁻² spectral falloff at high frequencies, well fit by the Brune earthquake source model. The gap between slow and fast is filled with intermediate events with source spectra depleted near the corner frequency. This work shows that a fault patch of length p with conditions favorable to rupture can radiate in vastly different ways, based on small changes in ph*, where h* is a critical nucleation length scale. Such a mechanism can help explain atypical scaling observed for low‐frequency earthquakes that compose tectonic tremor.
... [11][12][13][14] For example, stick-slip oscillation of the Earth's plates can cause serious earthquakes, stick-slip vibration in car brakes can result in irritating noise, stick-slip vibration of a drill string can cause tool failure and so on. [15][16][17][18][19][20] As a kind of non-smooth vibration, stickslip oscillation is a complex nonlinear problem. [21][22][23][24] Usually, stick-slip motion is undesirable and thus should be suppressed or reduced. ...
This work presents an experimental and theoretical combined study of the effects of the elastic rubber blocks with different surface modifications on the friction-induced stick–slip oscillation and wear of a brake pad sample in sliding contact with an automobile brake disc. The experiments are conducted on the customized experimental setup in a pad-on-disc configuration. The experimental results show that (1) the friction system with the plain rubber block still exhibits visible stick–slip oscillation, but the intensity of the stick–slip oscillation is reduced to a certain degree compared with the Original friction system (without rubber block); (2) the grooved rubber blocks display a better ability to reduce the stick–slip oscillation compared with the plain rubber block; (3) the rubber blocks with a vertical groove (perpendicular to the relative velocity) or a horizontal groove (parallel to the relative velocity) or a diagonal groove (45° inclined to the relative velocity) on their surfaces can suppress the stick–slip oscillation more effectively with various degrees of success. The experimental results also reveal the varying effects of the different rubber blocks on wear. To explain the experimental phenomenon reasonably, a theoretical analysis is conducted to investigate the effects of different rubber blocks on both stick–slip oscillation and wear using ABAQUS. Furthermore, the analysis of the contact pressure on the pad interfaces and the deformation of the rubber blocks are studied to provide a possible explanation of the experimental results.
... In the context of laboratory experiments, some studies report a transition from stick-slip to stable sliding by increasing the strain rate (or the loading rate for a fixed sample size) (e.g. Ohnaka, 1973;Teufel and Logan, 1978;Wong and Zhao, 1990;Baumberger et al., 1994;Karner and Marone, 2000), whereas other studies observe an opposite trend towards increasingly unstable slip with an increase in strain rate (Kato et al., 1992;Togo et al., 2015;McLaskey and Yamashita, 2017). This raises a need to resolve the strain-rate discrepancy among different experimental studies. ...
... In a later experimental study, McLaskey and Yamashita (2017) found that rapid increase in loading rate or long healing time could give rise to more unstable rupture along a selected fault portion, by shrinking the characteristic length and time scales required for nucleation. By adopting a one-degree-of-freedom spring-slider model governed by a rate-and state-dependent friction law, Urata et al. (2017) inferred the apparent macroscopic source parameters using the data reported by Togo et al. (2015). They found that the indirect parameter b increases while the characteristic slip distance L c decreases with increasing the loading rate. ...
... The experiments were conducted at the National Research Institute for Earth Science and Disaster Resilience (NIED), utilizing a large-scale shaking table that can provide loading over meter-scale rock samples. The general description of the apparatus, including design diagrams and parts assembling, can be found in Fukuyama et al. (2014) and Togo et al. (2015) as an original model. The current apparatus has been modified from the original one as described in Yamashita et al. (2015a). ...
We conduct meter-scale rock friction experiments to study strain rate effect on fault slip and rupture evolution. Two rock samples made of Indian metagabbro, with a nominal contact dimension of 1.5 m long and 0.1 m wide, are juxtaposed and loaded in a direct shear configuration to simulate the fault motion. A series of experimental tests, under constant loading rates ranging from 0.01 mm/s to 1 mm/s and under a fixed normal stress of 6.7 MPa, are performed to simulate conditions with changing strain rates. Load cells and displacement transducers are utilized to examine the macroscopic fault behavior, while high-density arrays of strain gauges close to the fault are used to investigate the local fault behavior. The observations show that the macroscopic peak strength, strength drop, and the rate of strength drop can increase with increasing loading rate. At the local scale, the observations reveal that slow loading rates favor generation of characteristic ruptures that always nucleate in the form of slow slip at about the same location. In contrast, fast loading rates can promote very abrupt rupture nucleation and along-strike scatter of hypocenter locations. At a given propagation distance, rupture speed tends to increase with increasing loading rate. We propose that a strain-rate-dependent fault fragmentation process can enhance the efficiency of fault healing during the stick period, which together with healing time controls the recovery of fault strength. In addition, a strain-rate-dependent weakening mechanism can be activated during the slip period, which together with strain energy selects the modes of fault slip and rupture propagation. The results help to understand the spectrum of fault slip and rock deformation modes in nature, and emphasize the role of heterogeneity in tuning fault behavior under different strain rates.
