Mechanical Weakening Research Articles

Research on the Rule of Explosion Shock Wave Propagation in Multi-Stage Cavity Energy-Absorbing Structures.

The propagation laws of explosion shock waves and flames in various chambers were explored through a self-built large-scale gas explosion experimental system. The propagation process of shock waves inside the cavity was explored through numerical simulation using Ansys Fluent, and an extended study was conducted on the wave attenuation effect of multiple cavities connected in a series. The findings show that the cavity's length and diameter influenced the weakening impact of shock waves and explosive flames. By creating a reverse shock wave through complicated superposition, the cavity's shock wave weakening mechanism worked. By suppressing detonation creation inside the cavity, the explosive flame was weakened by the cavity's design. The multi-stage cavity exhibited sound-weakening effects on both shock waves and explosive flames, and an expression was established for the relationship between the suppression rate of shock force and the number of cavities. Diffusion cavities 35, 55, 58, and 85 successfully suppressed explosive flames. The multi-stage cavity efficiently reduced the explosion shock wave. The flame suppression rate of the 58-35 diffusion cavity explosion was 93.38%, whereas it was 97.31% for the 58-35-55 cavity explosion. In engineering practice, employing the 58-58 cavity is advised due to the construction area, construction cost, and wave attenuation impact.

Evaluation of microstructure and tensile properties of Mg–5Zn-xZr-yCa alloys

In this work, an attempt was made to study the synergetic effects of changes in alloying elements including Zr and Ca, as well as the hot extrusion process on the microstructure, texture, and mechanical properties of Mg–Zn-xZr-yCa (x= 0.2 and 0.8 wt %; and 0<y<2) alloy. To do so, a variety of tests (OM, SEM, EBSD, EDS, TEM, APT, hardness and tensile tests) were performed after sample preparation. It was shown that Ca/Zr ratio plays an essential role in modifying the microstructure and mechanical properties of the alloy. For Ca/Zr<1, the grains size was remarkably refined to 1.2 μm, the wrought texture was moderately weakened, and the mechanical properties were significantly increased to 429 MPa. However, for Ca/Zr>1 grain size was almost unchanged, the texture of hot-extruded alloys became more equiaxed after hot extrusion, and tensile strength decreased compared to with Ca/Zr=1. Microstructural analysis revealed that Zr-bearing phases (Zn22Zr and Zn39Zr5) and solute theory were the dominant mechanisms of grain refinement in the as-cast state. An atom probe tomography technique was utilized to assess the segregation of solute elements into the grain boundaries. It was shown that particle stimulated nucleation is not likely to be the main mechanism of texture weakening of extruded alloys; and the solute segregation into grain boundaries facilitates this phenomenon. Finally, it was seen that values of yield and ultimate tensile strengths of Mg–5Zn-0.8Zr-0.5Ca were 372 and 429 MPa, respectively.

Microstructure and mechanical properties of Mg-Al-Sn-Ca alloy extruded by asymmetric severe shear extrusion with different asymmetric coefficients

Magnesium alloys with grain refinement and texture weakening are long-term targets in the field of light alloys. A new asymmetric severe shear extrusion (ASSE) process is developed in this paper, which is specially designed to refine the grain and weaken the texture of deformed magnesium alloys. The effect of asymmetry coefficient (AC) on microstructure and properties of extruded products was studied. The results show that ASSE can effectively change metal flow. AC-1.5 shows the best mechanical properties, grain refinement (∼8.6 µm) and texture weakening. The yield strength is about 175.9 MPa and elongation is about 19 %. This study provides a theoretical basis for the further development of partial symmetric extrusion.

Estimates of earthquake temperature rise and frictional energy

The development of multiple paleotemperature proxies over the last twenty years has led to an increasing number of coseismic temperature measurements collected across a variety of faults. Here we present the first compilation of coseismic temperature rise measurements and frictional energy estimates to investigate the contribution of frictional heating to the earthquake energy budget and how this varies over different fault and earthquake properties. This compilation demonstrates that there is no clear relationship between coseismic temperature and displacement or thickness of the principal slip zone. Coseismic temperature rise increases with the depth of faulting until ~5 km and below this depth temperature rise remains relatively constant. Frictional energy, similarly, increases with depth until ~5km. However, frictional energy is remarkably similar across all of the faults studied here, with most falling below 45 MJ/m2. Our results suggest that dynamic weakening mechanisms may limit frictional energy during coseismic slip. We also demonstrate a basic difference between small and large earthquakes by comparing frictional energy to other components of the earthquake energy budget. The energy budget for small earthquakes (&lt;1-10 m of displacement) is dominated by frictional energy, while in large events (&gt;1-10 m of displacement), frictional, radiated, and fracture energy contribute somewhat equally to the earthquake energy budget.

Study on mechanism of strength weakening of concrete subjected to microwaves in microwave-assisted concrete recycling

This paper explores the multi-field distribution in concrete by coupling of the electromagnetics, heat transfer and solid mechanics in COMSOL Multiphysics software under microwave irradiation. The numerical model is validated by the temperature data captured from the experiment. The physicochemical reactions in mortar and aggregate during heating and evolution of surface cracks are further investigated by the tests. The results show that when the radiation effect is considered above 100 °C, the simulated temperature profile is in alignment with the experimental one. The hot spots formed by heating exist at surface edges and in aggregate area on the cross section. The maximum tensile stress and compressive stress appear at the boundary on the cross section. Although the stress in aggregate is greater than that in mortar, it maintains in the elastic deformation stage, whereas mortar will undergo the plastic strain with the strain over 0.04%, approximately rheological behavior. In the first 100 s of heating, the migration and evaporation of water and the dehydration of hydration products are the main factors of strength degradation of concrete, which is manifested by the generation and propagation of cracks and the decrease in density. The initial position of visible cracks has a lot to do with the path of moisture migration. The surface cracks have been coalesced over stress relief caused by the increase in open porosity after heating for 150 s. The pore pressure induced by moisture migration and thermal stress caused by temperature gradient initiate more internal cracks. This paper can provide reference and insight for effective strength weakening of concrete exposed to microwaves so as to make its weakened mechanical properties can work to recovery of high-quality aggregate after mechanical crushing.

Nelinearno mikromehaničko ponašanje heterogenog makadama stabiliziranog cementom

This study aims to examine the internal meso-mechanical behaviour of cement-stabilised macadams subjected to loading damage following water immersion. By constructing a numerical analysis model, the mechanism of water-immersion weakening of the cement-stabilised macadam material and the internal micro-mechanical behaviour of the specimen were analysed. The numerical simulation results were compared with laboratory test data. The peak stress error was 2.414%, whereas the maximum error in the strain corresponding to the peak stress of the specimens with different immersion durations was 3.05%. By comparing the direction distributions of the normal and tangential contact forces in each stage, it was found that the tangential forces at approximately 0º, 90º, 180º, and 270º were much smaller than those at other angles. In the peak stress stage, the normal contact angles between 45–135º and 225–285º were higher than those at other angles. For model M (mean factor) less than 20, the peak stress was significantly affected and increased as a function of M. When M was greater than 20, the peak stress fluctuated within a small range as a function of M. This study provides a new research method for the study of the structural mechanical effect of pavement structures based on cement-stabilised macadam materials damaged following water immersion.

Landslides in the Remolinos gypsum escarpment (NE Spain): controls imposed by stratigraphy, fluvial erosion, and interstratal salt dissolution

Dissolution of karst rocks (evaporites and carbonates) can cause significant mechanical weakening, but its preparatory role for landslide development has been scarcely explored. Fluvial valleys carved in gypsum bedrock typically display prominent escarpments with numerous landslides and perched valleys indicative of rapid retreat rate. The stratigraphic and cartographic analysis of the 37-km-long Remolinos gypsum escarpment in the Ebro Valley (NE Spain) reveals that landslide types are controlled by the lithological succession: (1) rotational slides in sections with mudstones and marls at the base; (2) rock-slope collapses (massive rock-falls) where the cliff includes halite packages at the foot; and (3) relatively small rock-falls and topples being the main failures affecting cliffs entirely made by gypsum. Fluvial undercutting by the highly mobile Ebro River is the main process that controls the spatial and temporal distribution of slope instability. Geomorphic and chronological evidence supports that the abandonment in 1574 of the El Castellar village was at least partially motivated by a shift in the river channel toward the escarpment and the consequent landslide activity. Several lines of evidence support the concept whereby interstratal salt dissolution (halite and glauberite), here designated as subsurface solutional undermining, play a significant preparatory role for landslide development: (1) dissolution of salt close to the scarp by the inward advance of dissolution fronts and subsidence of the overlying strata; (2) collapsed fault blocks with no offset across the grabens; and (3) brine seepages and extensive efflorescences and precipitates of Na-sulfates and halite.

Impact of supercritical CO2 exposure time on the porosity and permeability of dry and wet shale: The influence of chemo-mechanical coupling effects

CO2 storage in shale formation is a potential way to reduce CO2 emissions for carbon neutrality. The variation of permeability in shale triggered by CO2-shale interaction plays an important role in CO2 sequestration. The effect of supercritical CO2 (ScCO2) exposure times (0, 10, 20, 30, 40 days) on the porosity and permeability evolution of dry and wet shale samples was investigated herein. Results show that the porosity and permeability of both dry shale and wet shale increased first and then decreased over exposure time, and there is an inflection point. The porosity and permeability evolution of shale is controlled by the chemical-mechanical coupling effects. The dissolution of mineral induced by ScCO2 exposure increases the porosity and permeability of shale. The mechanical weakening induced by ScCO2 exposure enhances the pores compressibility of shale, makes the porosity and permeability decrease at stressed condition. In the early stage, the chemical effect is dominant, after the time of inflection point, the mechanical weakening effect is dominant. The inflection time of wet shale is earlier than that of dry shale, indicating that the chemical effect dominant stage in wet shale is shorter than that in dry shale. This can be attributed to that the water promoted the chemical reaction and enhanced the weakening of mechanical properties, then shortened the chemical corrosion dominated stage. Our findings suggest that ScCO2-shale interaction can contribute to the decrease in porosity and permeability of shale with the increase of ScCO2 exposure time, and hence adversely affecting the shale gas recovery and the continue injectivity of CO2. Thus, the time dependent chemical-mechanical coupling effects should be considered in evaluating the shale gas production and CO2 storage capacity.

Understanding and Mitigating the Spatial Bias of Earthquake Source Imaging With Regional Slowness Enhanced Back‐Projection

AbstractWe investigate characteristics of spatial biases in the Back‐projection method and the effectiveness of the Slowness Enhanced Back‐projection (SEBP). The spatial bias refers to the location error in Back‐projection caused by travel time errors due to 3D Earth structure. SEBP reduces such bias by calibrating the gradient of travel time (slowness) in the source. We first analyze 22 M4–M6 earthquakes in the Commander Island and find that the amplitudes and directions of spatial biases follow distinct regional patterns. In light of this, we propose a regional SEBP approach that introduces spatially variable slowness correction. The regional SEBP in the Commander Island resulted in a ∼50% reduction in the average length of spatial bias from ∼20 to ∼10 km, which is more effective than the uniform SEBP that gives a 25% error reduction. We then analyze 109 M4–M7 earthquakes in the Tohoku region and also find a 50% error reduction by regional SEBP. This indicates that half of the spatial biases are aleatory uncertainties that are caused by regional structural complexity and can be calibrated with SEBP, while the residue errors are epistemic uncertainties that are random and caused by local velocity heterogeneities. With regional SEBP applied to the 2011 Tohoku earthquake, we find that high‐frequency radiators did not reach beyond the down‐dip limit of interplate seismicity, indicating that the coseismic slip unlikely penetrated the down‐dip velocity‐strengthening zone. Such observations suggest that the enhanced dynamic weakening mechanism due to thermal pressurization effects may not be activated during this event.

Structural Relationships Across the Sevier Gravity Slide of Southwest Utah and Implications for Catastrophic Translation and Emplacement Processes of Long Runout Landslides

AbstractThe physical processes that facilitate long‐distance translation of large‐volume gravity slides remain poorly understood. To better understand these processes and the controls on runout distance, we conducted an outcrop and microstructural characterization of the Sevier gravity slide across the former land surface and summarize findings of four key sites. The Sevier gravity slide is the oldest of three mega‐scale (&gt;1,000 km2) collapse events of the Marysvale volcanic field (Utah, USA). Field observations of intense deformation, clastic dikes, pseudotachylyte, and consistency of kinematic indicators support the interpretation of rapid emplacement during a single event. Furthermore, clastic dikes and characteristics of the slip zone suggest emplacement involved mobilization and pressurized injection of basal material. Across the runout distance, we observe evidence for progressive slip delocalization along the slide base. This manifests as centimeter‐ to decimeter‐thick cataclastic basal zones and abundant clastic dikes in the north and tens of meters thick basal zones characterized by widespread deformation of both slide blocks and underlying rock near the southern distal end of the gravity slide. Superimposed on this transition are variations in basal zone characteristics and slide geometry arising from interactions between slide blocks during dynamic wear and deposition processes and pre‐existing topography of the former land surface. These observations are synthesized into a conceptual model in which the presence of highly pressurized fluids reduced the frictional resistance to sliding during the emplacement of the Sevier gravity slide, and basal zone evolution controlled the effectiveness of dynamic weakening mechanisms across the former land surface.

Application of a Three-Dimensional Wind Field from a Phased-Array Weather Radar Network in Severe Convection Weather

In 2019–2020, an array weather radar (AWR) network consisting of seven X-band phased-array radars (PARs), with a detection spatial resolution of 30 m and a temporal resolution of 30 s, was built in the city of Foshan in China’s Guangdong Province. The detection time deviation in the same space is within 5 s. Through variational data assimilation, the three-dimensional wind field inside the storm can be obtained. This study selected instances of hail, thunderstorms, strong winds, and short-duration heavy precipitation in 2020 to conduct a detailed analysis. The results show the following: (1) The fine detection ability enables phased-array radars to detect the complete evolution process of convective storms, including development, strengthening, and weakening, providing a useful reference for judging the future variation trends of convective storms. (2) Through evolutionary analysis of the three-dimensional wind field, the dynamic mechanisms of storm strengthening and weakening could be obtained, which could serve as a reference to predict the development of storms. The gust wind index and convection index calculated based on the three-dimensional wind field could provide advanced warning for nowcasting. When the gust wind index was greater than 263, the probability of gale-force wind (above 17.0 m/s) was determined to be high. Moreover, the warning could be provided 10–20 min in advance. A convection index greater than 35 and the presence of concentrated contour lines were found to be conducive to the strengthening and formation of a convection, and the warning could be provided 20 min in advance. These results show that the application of PAR can provide important technical support for nowcasting severe convective weather.

Mechanical weakening of a mudrock seal by reaction with CO2-charged fluids

Abstract The long-term interaction of CO2-charged fluids with low permeability cap rocks is important for seal integrity assessment. To address this potential risk, we studied long-term geomechanical changes in a reservoir seal due to fluid-rock interactions with CO2-charged fluids, focusing on a natural CO2 analogue near Green River, Utah, USA. The observed chemo-mechanical changes are on the millimeter scale, which required small-scale petrophysical, mineralogical, and micromechanical analyses. Results showed that over the 7 cm thick reaction front, the low permeability cap rock underwent mechanical weakening, as indicated by indentation tests. This weakening is inferred to be due to dissolution of dolomite and hematite, with the former leading to porosity decrease, as shown by small-angle neutron scattering, while the latter likely led to loss of electrostatic forces between the clay particles. This resulted in loss of cohesion, compaction, and formation of bedding-parallel fractures. Microfracturing occurred in situ, as evidenced by fractures infilled with pyrite and gypsum. This study demonstrates that mechanical weakening of cap rocks might occur, but only over time scales of ~100,000 yr and over small distances. Considering the thickness of cap rocks above CO2 storage reservoirs, we do not anticipate a considerable threat of losing containment integrity over time scales of hundreds to thousands of years as a result of these small-scale fluid-rock interactions.

AN INTERACTIVE STUDY ON THE BRITISH AND GERMAN SEMI-COLONIAL STRATEGY AND THE CHANGE OF TRADITIONAL CHINESE SOVEREIGNTY-BASED ON THE COMPARISON BETWEEN SHANGHAI AND QINGDAO

The emergence of “Concessions” is not a simple historical problem. Based on the sovereignty declining theory, this paper attempts to explore the emergence of “Concessions” and the mechanism and process of sovereignty change. Unlike the ceded territory, Chinese “Concessions” in modern times are a special sovereign space. It means China shares its sovereignty with the western states. “Concessions” breaks the “supremacy” and “exclusiveness” of sovereignty. As “Concessions” with different legal statuses, Shanghai and Qingdao are not only part of the global colonial strategy between Britain and Germany, but also the watershed of Chinese sovereignty change. By comparing the changes in Chinese sovereignty in Shanghai and Qingdao, this paper finds out the mechanism and process of Chinese sovereignty weakening in the different Concessions. At the same time, the maintenance of sovereignty is related to whether China can form a centralized system. Before 1949, China could not form a centralized system, which was the main reason for the capacity of the state. The emergence and development of “Concessions” is also a manifestation of the Chinese vulnerable capacity to external interference and loss of sovereignty. This political phenomenon has affected the change of the Chinese state form.

Understanding AMOC stability: the North Atlantic Hosing Model Intercomparison Project

Abstract. The Atlantic meridional overturning circulation (AMOC) is an important part of our climate system. The AMOC is predicted to weaken under climate change; however, theories suggest that it may have a tipping point beyond which recovery is difficult, hence showing quasi-irreversibility (hysteresis). Although hysteresis has been seen in simple models, it has been difficult to demonstrate in comprehensive global climate models. Here, we outline a set of experiments designed to explore AMOC hysteresis and sensitivity to additional freshwater input as part of the North Atlantic Hosing Model Intercomparison Project (NAHosMIP). These experiments include adding additional freshwater (hosing) for a fixed length of time to examine the rate and mechanisms of AMOC weakening and whether the AMOC subsequently recovers once hosing stops. Initial results are shown from eight climate models participating in the Sixth Coupled Model Intercomparison Project (CMIP6). The AMOC weakens in all models as a result of the freshening, but once the freshening ceases, the AMOC recovers in half of the models, and in the other half it stays in a weakened state. The difference in model behaviour cannot be explained by the ocean model resolution or type nor by details of subgrid-scale parameterisations. Likewise, it cannot be explained by previously proposed properties of the mean climate state such as the strength of the salinity advection feedback. Instead, the AMOC recovery is determined by the climate state reached when hosing stops, with those experiments where the AMOC is weakest not experiencing a recovery.

Selective determination of ellagic acid in aqueous solution using blue-green emissive copper nanoclusters

Development of beneficial sensors to analyze ellagic acid concentrations is of great importance for food safety and human health. Herein, a facile and fast fluorescent probe was carried out for the excellently selective and sensitive measurement of ellagic acid in real samples through histidine protected copper nanoclusters (histidine@Cu NCs) as a nanosensor. This as-developed histidine@Cu NCs were performed through UV–vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and fluorescence lifetime analysis. The TEM image revealed that this nanomaterial had spherical features with the average diameter of 2.5 ± 0.05 nm. The blue-green fluorescence of this Cu NCs was found under the UV light. Meanwhile, the maximum excitation and emission wavelength were located at 387 nm and 488 nm. After addition of ellagic acid, the fluorescence of histidine@Cu NCs was slowly weakened with excellent linear range of 0.5–300 μM and detection limit of 0.077 μM. The fluorescence weakening mechanism of this nanosensor were attributed to the inner filter effect (IFE) and static quenching. Finally, this as-established analysis platform was successfully employed to measure ellagic acid in real samples.

Hydrothermally altered deposits of 2014 Askja landslide, Iceland, identified by remote sensing imaging

Volcanic flanks subject to hydrothermal alteration become mechanically weak and gravitationally unstable, which may collapse and develop far-reaching landslides. The dynamics and trajectories of volcanic landslides are hardly preserved and challenging to determine, which is due to the steep slopes and the inherent instability. Here we analyze the proximal deposits of the 21 July 2014, landslide at Askja (Iceland), by combining high-resolution imagery from satellites and Unoccupied Aircraft Systems. We performed a Principal Component Analysis in combination with supervised classification to identify different material classes and altered rocks. We trained a maximum-likelihood classifier and were able to distinguish 7 different material classes and compare these to ground-based hyperspectral measurements that we conducted on different rock types found in the field. Results underline that the Northern part of the landslide source region is a hydrothermally altered material class, which bifurcates halfway downslope and then extends to the lake. We find that a large portion of this material is originating from a lava body at the landslide headwall, which is the persistent site of intense hydrothermal activity. By comparing the classification result to in-situ hyperspectral measurements, we were able to further identify the involved types of rocks and the degree of hydrothermal alteration. We further discuss associated effects of mechanical weakening and the relevance of the heterogeneous materials for the dynamics and processes of the landslide. As the study demonstrates the success of our approach for identification of altered and less altered materials, important implications for hazard assessment in the Askja caldera and elsewhere can be drawn.

Microscale Spatial Variations in Coseismic Temperature Rise on Hematite Fault Mirrors in the Wasatch Fault Damage Zone

AbstractCoseismic temperature rise activates fault dynamic weakening that promotes earthquake rupture propagation. The spatial scales over which peak temperatures vary on slip surfaces are challenging to identify in the rock record. We present microstructural observations and electron backscatter diffraction data from three small‐displacement hematite‐coated fault mirrors (FMs) in the Wasatch fault damage zone, Utah, to evaluate relations between fault properties, strain localization, temperature rise, and weakening mechanisms during FM development. Millimeter‐ to cm‐thick, matrix‐supported, hematite‐cemented breccia is cut by ∼25–200 μm‐thick, texturally heterogeneous veins that form the hematite FM volume (FMV). Grain morphologies and textures vary with FMV thickness over μm to mm lengthscales. Cataclasite grades to ultracataclasite where FMV thickness is greatest. Thinner FMVs and geometric asperities are characterized by particles with subgrains, serrated grain boundaries, and(or) low‐strain polygonal grains that increase in size with proximity to the FM surface. Comparison to prior hematite deformation experiments suggests FM temperatures broadly range from ≥400°C to ≥800–1100°C, compatible with observed coeval brittle and plastic deformation mechanisms, over sub‐mm scales on individual slip surfaces during seismic slip. We present a model of FM development by episodic hematite precipitation, fault reactivation, and strain localization, where the thickness of hematite veins controls the width of the deforming zones during subsequent fault slip, facilitating temperature rise and thermally activated weakening. Our data document intrasample coseismic temperatures, resultant deformation and dynamic weakening mechanisms, and the length scales over which these vary on slip surfaces.

The Effect of the Garnet Content on Deformation Mechanisms and Weakening of Eclogite: Insights From Deformation Experiments and Numerical Simulations

AbstractWe performed deformation experiments on omphacite‐garnet aggregates at a temperature of 1000°C, a confining pressure of 2.5 GPa, and a strain rate of 3 × 10−6 s−1 and complemented them by numerical simulations to gain insight into the role of garnet fraction for the deformation behavior of dry eclogite, with a focus on strain weakening mechanisms. We determined the spatial and temporal evolution of strain and strain rate by basing numerical simulations on experimentally derived microstructures, and thereby identified characteristic deformation mechanisms. Pure omphacite and garnet aggregates deform by two different mechanisms. Internally strained clasts and low‐angle grain boundaries indicate crystal plasticity for omphacitite; the fracture dominated fabric of garnetite documents brittle deformation. Electron channeling contrast imaging, however, revealed low‐angle grain boundaries and free dislocations in garnet crystals, suggesting that minor crystal plasticity accompanies the brittle failure. Eclogitic aggregates show varying deformation behavior between the two end‐members shifting from crystal plastic toward brittle deformation with increasing garnet content. All samples exhibit strain weakening. The intensity of weakening shows a positive correlation with the garnet content. Our combined experimental, numerical, and microstructural investigations suggest that the majority of strain weakening is associated with crystal plastic processes in omphacite. Numerical simulations and experiments show that a garnet content above 25% enhances the activity of crystal plastic processes in omphacite and results in strain localization, which subsequently weakens the eclogite.

Reduction of Pole-Frequency Vibration of Surface-Mounted Permanent Magnet Synchronous Machines With Piecewise Stagger Trapezoidal Poles

An optimization method of the piecewise stagger trapezoidal poles is proposed for the reduction of the pole-frequency vibration of the surface-mounted permanent magnet synchronous machines (SPMSMs) in this article. By offsetting the zero-crossing region of flux density, this method can weaken the pole-frequency force harmonic while ensuring the torque density. First, based on the Maxwell tensor method, the analytical model of concentrated force acting on the teeth is deduced. Taking a 10-pole/12-slot SPMSM as an example, the deep cause of the pole-frequency radial force harmonic is analyzed. Then, the weakening mechanism of the piecewise stagger trapezoidal poles for the pole-frequency radial force harmonic is revealed with the finite-element model (FEM). Based on the multiphysics coupling model, the key electromagnetic properties and vibration spectrum between the common and proposed motors are compared. The results show that the piecewise stagger trapezoidal pole structure has a significant suppression effect on the pole-frequency vibration. Finally, the vibration experiment of the two prototypes is carried out, and the effectiveness of the optimized structure is verified.

Frictional power dissipation in a seismic ancient fault

The frictional power per unit area Q˙ (product of frictional traction τ and slip rate u˙ in MW m−2) dissipated during earthquakes triggers fault dynamic weakening mechanisms that control rupture nucleation, propagation and arrest. Although of great relevance in earthquake mechanics, Q˙ cannot, with rare exceptions, be determined by geophysical methods. Here we exploit theoretical, experimental and geological constraints to estimate Q˙ dissipated on a fault patch exhumed from 7-9 km depth. According to theoretical models, in polymineralic, silicate rocks the amplitude (< 1 mm) of the grain-scale roughness of the boundary between frictional melt (pseudotachylyte) and host rock decreases with increasing Q˙. The dependence of grain-scale roughness with Q˙ is due to differential melt front migration in the host rock minerals. This dependence is confirmed by friction experiments reproducing seismic slip where pseudotachylytes were produced by shearing tonalite at Q˙ ranging from 5 to 25 MW m−2. In natural pseudotachylytes across tonalites, the grain-scale roughness broadly decreases from extensional to compressional fault domains where lower and higher Q˙ are expected, respectively. Analysis of the natural dataset calibrated by experiments yields Q˙ values in the range of 4-60 MW m−2 (16 MW m−2 average value). These values, estimated in small fault patches, are at the lower end of broad estimates of Q˙ (3-300 MW m−2) obtained from frictional tractions (30-300 MPa) and fault slip rates (0.1-1 m/s) assumed as typical of upper crustal earthquakes.