High Slip Research Articles

Designing high-performance green tire treads by reinforcing the styrene-butadiene rubber/silica interface with chain difunctionalization

For green tires, monofunctionalization of rubber has been extensively studied to enhance the interface between rubber and silica. However, the effect of chain difunctionalization has not been reported. In this work, the difunctionalized styrene-butadiene rubber (SBR-DF) was first prepared by grafting small molecules with different functional groups (3-mercaptopropionic acid, 3-mercaptoethanol, and mercaptosilane) to end-group functionalized SBR through thiol-ene click reaction. Then, the molecular dynamics simulation was adopted to calculate the interaction energy between SBR-DF and silica. The results showed that the chain difunctionalization can significantly increase the interfacial interaction energy between them, which was further validated by using RPA and SEM. Moreover, the introduced siloxane groups in the rubber chain can greatly improve the interfacial interaction energy by more than 20 %, which can achieve the uniform dispersion of silica. As a result, the SBR-DF/Silica composites showed the excellent dynamic mechanical properties, such as high wet slip resistance (21 % increase), low rolling resistance (23 % reduction) and high wear resistance (20 % reduction). As a result, the energy consumption of SBR-DF/Silica composites was reduced, which endowed green tires with excellent safety. In summary, this work provides a new and effective strategy for manufacturing the energy-saving, green and safe design of “green tires”.

A Cam Clay constitutive relation for semi-analytical elasto-plastic modeling of wheel-soil interaction for fast applications

In this paper, a semi-analytical elasto-plastic (SAEP) model is proposed to simulate wheel motion on soft soil using a Modified Cam Clay (MCC) constitutive model. The focus is on enhancing computational efficiency by integrating the MCC model into the framework. The MCC-based model outperforms the Drucker-Prager with Cap hardening (DPC)-based model in terms of reduced computation time, stability, and convergence. Simulations with a 30% slip ratio show a significant reduction in solution time compared to the DPC-based model. For slip ratios of 50% and 90%, the computation time decreases even further. Overall, the MCC-based model demonstrates over 100 times reduction in the solution time compared to the DPC-based model, particularly with high slip ratios. Indeed, the DPC-based model was found to be highly sensitive to high values of slip ratios, whereas the MCC-based model is not. In comparison with existing methods in the literature, the proposed formulation is superior in terms of significantly reduced solution time and improved numerical stability, making it ideal for advanced applications where fast solutions are crucial.

사비도성 내 수공업 공방의 양상과 외경부

This paper examined the location, structure, and operation of handicraft workshops in Sabi Capital in Baekje, and attempted a poetic review of Oegyeongbu location around the workshops. During the Three Kingdoms period, handicrafts include weaving such as sericulture and weaving, ceramics manufacturing earthenware and tile, mining gold, silver, copper, and iron, metallurgy to refine them, and various manufacturing industries to produce household goods, tools, and weapons. It is known that it was operated as a government-operated crust industry as the scale gradually increased over time. In Sabi Capital, metal workshops and ceramics workshops are mainly identified. It is understood that ceramics workshops are mainly distributed across the Baekma River, which is the western boundary of the capital, while metal or glass workshops are distributed at different times around specific points in the city. It is understood that the workshop in the early stages of Sabi-period was located in the south of Buso-Mountain, centered on the ruins of Gwanbuk-ri, and then moved to the northeast area of the capital. The northeastern area of Sabi Capital is vulnerable to running water because it corresponds to the alluvial land, but it is a place where abundant water sources can be supplied and smooth logistics and distribution is possible as it is close to a transportation route to enter from the outskirts of the capital. It is understood that this movement of the workshop facilities is due to the stabilization of the capital system after the capital city and the gradual development of wetlands inside the capital city. Along with the spatial movement of the workshop, changes in the structure are also confirmed. The initial Gwanbuk-ri workshop is a structure that simultaneously produces various goods within a dense space, while the workshop in the northeast of the capital divides individual ranges into a certain range and shows a structure in which production and accessories are organized within it. Based on underground storage facilities, hierarchical building structures, distribution patterns of various building sites, and high wooden slips in Sabi Capital, it is estimated that there was a space with functions as a part of the Oegyeongbu, as a government office for the operation and management of the workshop system in the west and north areas of the workshop.

Deep CO2 emissions facilitated by localized shear deformation: A case study of the Karakoram fault system, western Tibet

Strike-slip faults play a significant role in creating deeply penetrating fractures with high permeability, thus promoting rapid migration of CO2-rich fluids to the surface. However, there are rare observations regarding how strike-slip movement could affect deep CO2 emissions. Here, we focus on the Karakoram fault system (KKFS), western Tibet, to estimate diffuse soil CO2 fluxes and to unravel potential controlling factors for CO2 emissions. Average CO2 fluxes of geothermal fields range in 22–2475 g m−2 d−1, significantly higher than the across-fault profiles (6–116 g m−2 d−1). A mass balance model based on δ13C-CO2 and CO2 concentration of soil gases reveals that deep carbon constitutes 49.1–91.5 % (average = 73.9 %) and 0.2–40.5 % (average = 25.5 %) of soil-gas carbon released from geothermal fields and across-fault profiles, respectively. Deep carbon could be produced by thermal decomposition of crustal rocks considering CO2-rich fluids with radiogenic helium isotopes. Strikingly, higher CO2 fluxes preferentially occur in geothermal fields along a bending segment of the KKFS, where localized shear deformation is prominent as documented by high slip rates over geological timescales, dense splay faults, clustering of earthquake events, and elevated strain rates. We suggest that high stress acting on the KKFS bend could enhance the deformation and fracturing of fault zone rocks, leading to production of metamorphic CO2 and efficient release of CO2-rich fluids through the highly permeable fault system. Our results could shed new light on CO2 origins and fluxes of strike-slip faults that are characterized by spatially heterogeneous strain partitioning and thus localized enhanced shear deformation.

Optimization control strategy for diesel urea-selective catalytic reduction (SCR) urea injection based on the interior point method (IP) + higher order SCR model

In order to ensure that the NOx and NH3 emissions of diesel engines comply with the Euro VII emission standards, this paper optimizes the urea injection using a SCR model combined with the interior point method. First, the equations of the higher-order SCR model were simplified by the variable substitution method and the line method and solved by the backward difference formula to improve computational accuracy. The Levenberg-Marquardt algorithm was used to calibrate the chemical reaction rate parameters to optimize model performance. Second, an optimization cost function was designed to optimize the upstream NH3 concentration in combination with the interior point method and the higher-order SCR model to meet the requirements of Euro VII emission standards. Third, the model effect was verified by performing WHTC hot-start testing on an engine complying with the National VI emission standard. The results show that the average error between the measured NOx concentration and the calculated is 1.49 ppm, which verifies the high accuracy of the model. Finally, the effects of the interior point method, NSGA-II, and MOPSO algorithms in optimizing the upstream NH3 concentration were compared. The results showed that the interior point method outperformed the other algorithms in terms of optimization time and effect, with an optimization time of 149 s, a NOx conversion rate of 97.36 %, and an average downstream NH3 concentration of 4.65 ppm. This achieved a high NOx conversion rate and low NH3 slip in accordance with the requirements of the Euro VII regulation.

Internal deformation of the North Andean Sliver in Ecuador-southern Colombia observed by InSAR

Summary In the Northern Andes, partitioning of oblique subduction of the Nazca plate beneath the South American continent induces a northeastward motion of the North Andean Sliver. The strain resulting from this motion is absorbed by crustal faults, which have produced magnitude 7 + earthquakes historically in the Andean Cordillera of Ecuador and southern Colombia. In order to quantify the strain in that area, we derive a high-resolution surface velocity map using InSAR time-series processing. We analyzed 6 to 8 years of Sentinel-1 data and combined different satellite line-of-sight directions to produce a reliable velocity map in the East direction. We use interpolated GNSS data to express the velocity map with respect to Stable South America and remove the long-wavelength pattern due to the post-seismic deformation following the 2016 Mw 7.8 Pedernales earthquake. The InSAR velocity map finds high E-W shortening strain rates along N-S trending structures within the Western Cordillera and the Interandean valley, with little deformation taking place east of them. This result strengthens the previous proposition of a ∼350 km long Quito-Latacunga tectonic block, forming a restraining bend in the overall right-lateral strike-slip fault system accommodating the northeastward escape motion of the North Andean Sliver. However, the high spatial resolution provided by InSAR indicates that previously proposed boundaries for this block need to be revised. In particular, InSAR results highlight high strain rate (>300 nstrain/yr) along undescribed active structures, south and west of the proposed limits for the Quito-Latacunga block, respectively in Peltetec and Ibarra regions. Interestingly, the two areas with the largest strain rates spatially correlate with the proposed areas of large historical earthquakes. Modeling of the InSAR and GNSS velocities in these areas suggests shallow coupling and high slip rates on structures which, previously, were not identified as active. We also demonstrate a slow-down of the shallow aseismic slip on the Quito fault after the Pedernales earthquake, suggesting that stress changes following large megathrust events might trigger transient slip behaviors on crustal faults. The high-resolution strain map provided by this work provides a new basis for future tectonic models in the Ecuadorian and southern Colombian Andes, and will contribute to the seismic hazard assessment in this highly populated area of the Andes.

Deformation behavior of PST-TiAl bicrystals at 800 °C

PST (polysynthetic twinned) TiAl crystal exhibits excellent mechanical properties, and thus, it has been regarded as a critical candidate for turbine blades in the aero-engine industry. For the first time, the deformation behavior of PST-TiAl bicrystals with two different α2/γ lamellar orientations was studied in this work. Ti-46Al-6Nb bicrystals were cut from directionally solidified ingots, and three bicrystals of B1 (10°–14°), B2 (10°–19°), B3 (6°–75°) together with a single crystal of S1 (3°) were stretched at 800 °C. Then, the deformation behaviors, including fracture morphology, crack propagation, and deformation mechanism, were analyzed. Interestingly, these bicrystals show good high-temperature tensile performance, and their deformation behaviors seem to be very anisotropic. The findings indicate that the misorientation disparity in bicrystals primarily determines their deformation coordination capacity and corresponding mechanical performance. Subsequently, the difference in deformation orientation between the two lamellae significantly controls fracture behavior and deformation compatibility. High slip potential and abundant variant choices in γ phases are supposed to be beneficial for deformation capacity improvement. Meanwhile, the deformation potential of ordinary dislocation and superlattice dislocation slip systems in the α2 phase was also examined. Results show that the disparity in dislocation motion ability between γ variants gradually amplifies the advantages of the easy-mode phase in deformation through strain coordination, while mitigating the disadvantages associated with the difficult-mode phase. During further deformation, the relatively low bicrystal misorientation and small deformation capacity differences between the two lamellae determine high deformation coordination and improved performance. Overall, our work reveals that bicrystal deformation initiates at the relatively softer lamellae and proceeds to the harder lamellae, and its final comprehensive performance is determined by the deformation coordination capacity between the two lamellae.

Small-scale segmented fault rupture along the East Anatolian fault during the 2023 Kahramanmaraş earthquake

Rupture velocity affects the shaking damage potential of an earthquake, but it is hard to estimate. Here we track the rupture front of the first 25 s of the 2023 Kahramanmaraş earthquake using the P-wave polarization vector vs time as measured by the dense three-component accelerometer network surrounding the slipping fault. We find a coherent increase of the rupture velocity along portions of the fault zone where high coseismic slip has been previously mapped. This is detected in a domain of the Pazarcık segment of the East Anatolian fault at 40 km NE of the mainshock epicenter where the rupture becomes super-shear. This domain spatially matches the part of the Pazarcık segment where most micro-earthquakes nucleate in the inter-seismic phase and edges at north a nearly aseismic domain. We postulate the existence of a velocity-weakening subsegment on the Pazarcık fault sandwiched between velocity-strengthening domains and/or mechanic barriers to the fault slipping.

Thermoplastic Vulcanizates with an Integration of High Wear-Resistant and Anti-Slip Properties Based on Styrene Ethylene Propylene Styrene Block Copolymer/Styrene Ethylene Butylene Styrene Block Copolymer/Solution-Polymerization Styrene-Butadiene Rubber.

Distinguished from traditional vulcanized rubber, which is not reusable, thermoplastic elastomer (TPV) is a material that possesses both the excellent resilience of traditional vulcanized rubber and the recyclability of thermoplastic, and TPVs have been widely studied in both academia and industry because of their outstanding green properties. In this study, new thermoplastic elastomers based on solution polymerized styrene butadiene rubber (SSBR) and thermoplastic elastomers (SEPSs/SEBSs) were prepared by the first dynamic vulcanization process. The high slip resistance and abrasion resistance of SSBR are utilized to improve the poor slip resistance of SEPSs/SEBSs, which provides a direction for the recycling of shoe sole materials. In this paper, the effects of different ratios of the rubber/plastic phase (R/P) on the mechanical properties, rheological properties, micro-morphology, wear resistance, and anti-slip properties of SSBR/TPE TPVs are investigated. The results show that the SSBR/TPE TPVs have good mechanical properties. The tensile strength, tear strength, hardness, and resilience of the TPVs decrease slightly with an increasing R/P ratio. Still, TPVs have a tensile strength of 18.1 MPa when the ratio of R/P is 40/100, and this reaches the performance of the vulcanized rubber sole materials commonly used in the market. In addition, combined with microscopic morphology analysis (SEM), it was found that, with the increase in the R/P ratio, the size of the rubber particles gradually increased, forming a stronger crosslinking network, but the rheological properties of TPVs gradually decreased; crosslinking network enhancement led to the increase in the size of the rubber particles, and the increase in the size of rubber particles made the material in the abrasion of rubber particles fall easily, thus increasing its abrasion volume. Through dynamic mechanical analysis and anti-slip tests, when the R/P ratio was 40/100, the tan δ of TPVs at 0 °C was 0.35, which represents an ordinary vulcanized rubber sole material in the market. The viscoelasticity of TPVs increased with the increase in the R/P ratio, which improved the anti-slip performance of TPVs. SSBR/TPE TPVs are expected to be used in footwear and automotive fields due to their excellent abrasion resistance and anti-slip performance.

Coseismic Slip and Downdip Afterslip Associated with the 2021 Maduo Earthquake Revealed by Sentinel-1 A/B Data

On 22 May 2021, an earthquake (98.3° E and 34.59° N) struck Maduo town in Qinghai province, occurring along a relatively obscure secondary fault within the block. We utilized 105 archived Sentinel-1A/B acquisitions to investigate the coseismic deformation and the evolution of postseismic displacements in both the temporal and spatial domains, as well as the associated dynamic mechanisms of the 2021 Maduo earthquake. The interference fringes and coseismic deformation revealed that the primary feature of this event was the rupture along a left-lateral strike-slip fault. The released seismic moment was close to 1.88 × 1020 N·m, which is equivalent to an Mw 7.45 event. Simultaneously, the maximum coseismic slip reached approximately 4 m along the fault plane. The evolution of postseismic displacements in both the temporal and spatial domains over 450 days following the mainshock was further analyzed to explore the underlying physical mechanisms. Generally, the patterns of coseismic slip and afterslip were similar, although the postseismic displacements decayed rapidly over time. The modeled afterslip downdip of the coseismic rupture (at depths of 15–40 km) effectively explains the postseismic deformation, with a released moment estimated at 4.57 × 1019 N·m (corresponding to Mw 7.04). Additionally, we found that regions with high coseismic slip tend to exhibit weak seismicity, and that afterslip and aftershocks are likely driven by each other. Finally, we estimated the Coulomb Failure Stress changes (ΔCFS) triggered by both coseismic rupture and aseismic slip resulting from this event. The co- and postseismic ΔCFS show similar patterns, but the magnitude of the postseismic ΔCFS is much lower (≤0.01 MPa). We found that ΔCFS notably increased on the Yushu segment of the Garze-Yushu-Xianshuihe Fault (GYXF), as well as the Maqin–Maqu and Tuosuo Lake sections of the East Kunlun Fault (EKF). Therefore, we infer that these fault segments may have a higher potential seismic risk and should be carefully monitored in the future.

EVALUATING THE STRUCTURAL EFFICACY OF ANGLE AND CHANNEL SHEAR CONNECTORS IN BRICK AGGREGATE CONCRETE AND STONE AGGREGATE CONCRETE AND COMPARISON

Composite structure is becoming prominent for its economy, less time consumption, and higher stiffness-mass ratio. Composite action of the steel-concrete composite structure mainly depends on the connector's geometry and materials. Proper choice of shear connector could make steel beam and concrete slab cross-section minimal. This study carries out push-out tests to evaluate the structural efficiency of channel and angle shear connectors in brick aggregate concrete and stone aggregate concrete. It specifically looks at the failure mode, ductility, load-slip behavior, and energy absorption capacity. In brick aggregate concrete, results show that under monotonic loading, channel connectors have been found to have 15.27% more shear capacity & 28.38% more slip than angle connectors. Similarly, in stone aggregate concrete, channel connectors have been found to have 14% more shear capacity & 12.97% higher slip than angle connectors. On average, stone aggregate concrete has been found to have 34.84% higher shear capacity and 6.7% greater slip than brick aggregate concrete. Strain energy and plastic energy were found 78% and 17.6% less in brick aggregate specimens than those in stone aggregate specimens, respectively. Experimental results were slightly lower for both shear connectors than the empirical values.

Computational Fluid Dynamics Analysis of Slip Flow and Heat Transfer at the Entrance Region of a Circular Pipe

In the era of sustainable development goals (SDGs), energy efficient heat transfer systems are a must. Convective heat transfer within circular pipes is an important field of research on a rarely addressed limitation of fluid flows. Vacuum solar tubes is one of many applications that could benefit from the existence of nanoparticles, Al2O3, for example, to enhance the heating of air or water steam. The current research investigates the impacts of the Reynolds number (Re), Prandtl number (Pr), Knudsen number (Kn), aspect ratio (x/Dh), and volume fraction of Al2O3 nanoparticles (ϕ) on the Nusselt number (Nu) under constant wall heat flux conditions. An axisymmetric computational fluid dynamics (CFD) analysis of the nanofluid flowing at the entrance region of a circular pipe was conducted under a slip flow at steady-state developing laminar conditions using the Ansys-Fluent 2018 software package. A mesh sensitivity analysis was conducted, and a proper number of mesh elements was selected. The results showed that an increasing Re and/or ϕ would result in an increasing Nu. The dependance of Nu on Kn was strong due to the high slip values and temperature jump. An increasing x/Dh ratio resulted in reduced Nu values. The major impact was due to Kn, which caused a reduction of up to 40% in the Nu value due to slip conditions. However, there was an enhancement of 2.5% in the heat transfer due to the addition of nanoparticles, which was found at Re = 250, Kn = 0.1, and ϕ = 0.1 (Pr = 0.729). Finally, Nuavg, Nux, U/Um, and ReCf were corelated with Kn, Pr, Re, and x/Dh with proper coefficient of determination (R2) values.

Self-Driven Gas Spreading on Mesh Surfaces for Regeneration of Underwater Superhydrophobicity.

Underwater superhydrophobic surfaces stand as a promising frontier in technological applications such as drag reduction, antifouling, and anticorrosion. Unfortunately, the air film, known as the plastron, on these surfaces tends to be unstable. To address this problem, active approaches have been designed to preserve or restore plastrons. In this work, a self-driven gas spreading superhydrophobic mesh (SHM) surface is designed to facilitate recovery of the plastron. The immersed SHM can be "wetted" by gas, even when the plastron is removed. We demonstrate that the injected gas can spread spontaneously along the SHM over a large area, which greatly simplifies the plastron replenishment process. By incorporating a locally coated gas-producing layer, we achieve rapid in situ plastron recovery and long-term immersion stability, extending the plastron lifespan by at least 48 times. We also provide a framework for designing an SHM with suitable structural dimensions for gas spreading. Furthermore, an SHM with asymmetric structural dimensions enables unidirectional gas transport by the capillary pressure difference. This SHM surface shows excellent drag reduction properties (37.2%) and has a high slip recovery coefficient (73.4%) after plastron loss. This facile and scalable method is expected to broaden the range of potential applications involving nonwetting-related fields.

Exploring torque characteristics of an integrated ultra conducting magnetic coupling incorporating axial magnetic field through magnetic equivalent circuit modelling

Ultra-conductors are a recent class of materials that display superconducting attributes at room temperature and even at higher temperatures. In this paper, we introduce a novel hybrid ultra-conducting coupling (NHUC) where the secondary component includes copper and an ultra-conductor (considered as a room temperature superconductor in much research). We suggest a model based on magnetic equivalent circuit (MEC) to evaluate the distribution of magnetic fields and characteristics related to torque. The 3D model accounts for boundary impacts during mating, and formulation for magnetic flux and torque are derived using Kirchhoff’s and Ampere’s loop laws, respectively. A 3D finite element (FEM) model is constructed, and simulations are performed using iodine-doped double-walled carbon nanotube (IDWCT) as the ultra-conductor for a wider operating range. At a high slip speed of 1200 rpm, a maximum torque of 309 Nm and stable torque of 113 Nm are observed. Adjusting air gap thickness or permanent magnet dimensions results in torque variations. Additionally, due to carbon nanotube (CNT) characteristics, a reduction in losses from the Joule effect is noted. The maximum error between torque results from simulation and the suggested model is 7.68%, confirming accordance. Comparison alongside the slotted eddy current coupling (SEC) reveals that the torque of the NHUC exceeds that of the SEC, diminishing as the air gap widens.

Effect of boundary slips and magnetohydrodynamics on peristaltic mechanism of Jeffrey nanofluid along with microorganisms through a porous medium

The development on entropy generation in fluid flows has applications in many medical equipment such as cryogenic devices and therapeutic heat apparatus. This study looks at how porous medium, multi-slips, and entropy formation affect the pumping of Jeffrey nanofluid flow through an asymmetric channel containing motile microorganims. A lubrication theory is used to neglect the fluctuation effects in the flow. Numerical simulations are utilized to generate data for specific physical features of the problem utilizing the Shooting approach on Mathematica. Following a thorough research, it is appropriate to conclude that the porous medium's permeability reduces flow speed along the walls while increases at the center of the flow region. Graphical representation of the results further reveals that entropy production can be decreased by including high thermal slip and low viscous slip elements. It is also worth noting that the Brinkman number reduces the thermal distribution in the flow while it helps in increasing the flow speed.

Implications of FCC and HCP cobalt phases on wear performance of weld deposited cobalt-based coating

SS316L possesses comparatively low wear and abrasion resistance properties and thus needs proper surface modification to sustain under severe industrial applications. Cobalt-based Stellite 6, a suitable coating for such applications, contains 4–5 % of tungsten that provides solid solution strengthening to the cobalt-based matrix, due to which it shows good wear resistance in abnormal working conditions. Stellite 6 is dominated by face-centered cubic (FCC) and hexagonal close packed (HCP) cobalt along with different carbide phases such as M7C3, M23C6, MC and M6C where M is Cr, W, Mo, Co and Fe. Weld deposited cobalt-based Stellite 6 coating on SS316L substrate, contains FCC structure as primary phases. Pure cobalt contains a stable HCP phase at temperature below 417 °C and FCC phase at and above 417 °C up to melting point of pure cobalt i.e., 1495 °C. Under the frictional stresses caused during wear test, impact more on FCC cobalt than HCP cobalt due to the high slip system of FCC. Because of this, FCC cobalt underwent through high wear losses compared to HCP cobalt in cobalt-based coating. Present study revealed that, high wear losses are seen in samples where FCC cobalt phases are dominant. The observed mechanism by SEM shows abrasive wear in which material removal takes place by ploughing, micro cutting and indentation. The targeted industrial applications where such wear losses are supposed to happen includes slurry transportation applications such as pipes, sea engineering components, submersible pumps, control valves.

A numerical scale-up study of annular fluidized bed reactor with high centrifugal acceleration

A rotating fluidized bed imposes a strong centrifugal force to form the dense annular bed with high interphase slip velocity for significantly enhanced gas-solids contact. The fundamental fluidization behaviors in rotating fluidized beds have been well understood in small-scale systems. The current study focuses on the scale-up of a rotating fluidized bed from lab-scale to commercial-scale through computational fluid dynamics modeling. The computational model was first validated against a lab-scale horizontal rotating fluidized bed for the general flow behavior and pressure drop. The validated computational model with a column diameter of 0.12 m was then scaled up to 0.48 m and 1.92 m to investigate the flow hydrodynamics at larger scales. By comparing the solids distribution and other flow field variables, major limitations in the stable operation of a rotating fluidized bed at large scales were identified. The challenges faced in the scale-up of an annular fluidized bed with centrifugal acceleration are discussed and ways to overcome such challenges are explored.

Numerical modelling of earthquake sequences involving valving and pumping of fluids

SUMMARYFaults in the upper crust are sometimes thought to act as self-sealing valves, episodically releasing highly overpressured fluids trapped at greater depth during earthquakes. They are also often considered to be capable of actively pumping fluids into or out of faults in response to coseismic volumetric strain, thermal pressurization or other mechanisms. In this study, we investigate how these different types of behaviour (i.e. valve versus pump) are manifested in earthquakes. We do this using a 2-D plane strain model where frictional sliding on a thrust fault that is fed by a fluid source at its base is coupled to porous flow, thermal pressurization and strong variations in permeability. Our results show that thermal pressurization leads to dramatic dynamic weakening that produces earthquakes that propagate as slip pulses producing large stress drop, large slip and high slip velocities. On the other hand, valve-type behaviour typically produces smaller, less energetic earthquakes that commonly arrest before rupturing the entire fault. In some valve models, we observe complex compound ruptures and swarm activity, which is linked to the ascent of a propagating fluid pressure pulse driven by a large increase in permeability during sliding. Both pump and valve mechanisms can produce anomalously weak faults, though they are each associated with distinctly different fluid pressure and strength evolution over the seismic cycle and during rupture. Our models highlight the complex way in which fluids may interact with earthquakes, especially if valve and pump models coexist.

Relationship of evolution of slip-surface structure in Indian sandstone to changes in friction coefficient for a wide range of slip rates

Although many experimental studies have investigated the frictional properties of sandstone, few of them have considered the evolution of slip-surface structures with changes of friction coefficient over a wide range of slip rates. Here we report the results of rock-on-rock rotary shear experiments on specimens of Indian sandstone at slip rates from 2 × 10−4 to 1 m s−1. The resultant slip behaviors and microscale surface structures indicate two types of dependency on slip rate. At high slip rates (≥5 × 10−1 m s−1), the friction between the sandstone blocks fluctuated markedly and the surfaces of the blocks were intensively worn. At low slip rates (≤1 × 10−1 m s−1), the friction decreased gradually with increasing slip distance and the slip surfaces became reflective. The high slip-rate experiments produced abundant rock fragments (∼10–100 μm diameter), whereas the slip surfaces after low slip-rate experiments were highly polished fault mirrors accompanied by abundant rounded ultrafine grains (∼100 nm diameter). Such slip-rate-dependent evolution of slip-surface structures in Indian sandstone may arise from the relatively low cohesiveness of that rock. This insight may further our understanding of faulting and sliding mechanisms in sandstone near the ground surface.

Dynamic shear behaviours of granite under coupled static and high-rate loadings

Understanding dynamic shear behaviours of rock under quasi-static confinement and dynamic loads is not only of great importance in underground engineering structures, but also beneficial to reveal earthquake mechanics regarding pre-stressed rocks fracturing from initial intact to rapid shear sliding. Here we propose a dynamic shear test setup and present full-field observations of stressed rock failure at high shear rate (up to γ˙ = 220 s−1) and sliding at high slip velocity over 10 m/s in the order of coseismic slip, with the integration of a novel triaxial Hopkinson bar (Tri-HB) and high-speed three-dimensional Digital Image Correlation (3D-DIC) techniques. Dynamic shear strength and friction coefficient are determined during the dynamic shear test under confinement, with different shear strain rates and pre-stresses. The dynamic shearing process can be divided into three stages, i.e. shear deformation, fracture degradation and dynamic frictional sliding. The high energy density of shear fracture band is observed, the rate and stress state dependences of rock shear strength and dynamic frictional coefficient are revealed. The dynamic shear strength of granite follows the Mohr-Coulomb criteria under varying pre-stresses and strain rates. The gouge materials with size of 1∼10 μm are generated within the high-rate shearing zone, and this appears to control the frictional resistance. The results could help determination of rock shear strength and post-shear failure, as well as explain the shear rupture and the resistance to slip mechanism of rock faults and strong near-surface earthquake events.