Arc Region Research Articles

Mechanism of plastic deformation in chain die forming of variable cross section

Chain die forming is a new type of sheet metal forming process. The material flow law and characteristics of chain die forming process were studied through simulation. The analysis results show that the maximum principal strain at the corner of the variable section forming part is larger, and the direction is perpendicular to the outside bending surface; the maximum principal strain at the concave arc region in the flange is tensile strain, which decreases along the height direction of flange from high to low; the flange height and forming angle have great influence on the longitudinal strain of the forming part, and increasing the height of the flange and forming angle can increase the longitudinal strain of the flange; the effect of material properties on the longitudinal strain of the forming part is small. The longitudinal strain of the variable cross section was extracted from the simulation model. The results show that the four arc zones in the flange of variable cross section part have larger longitudinal strain, where tensile or compressive deformation occur during forming process, but the equivalent plastic strain mainly concentrates in bending areas of variable cross section part. The simulated results were verified through experiment of chain die forming of variable cross section tests, and the experimental results are in good agreement with the simulation results.

3D modeling and simulation of high-current vacuum arc subjected to real external transverse magnetic field

Vacuum circuit breakers (VCBs) are widely used in power distribution systems. When the VCB in a switchgear interrupts the short circuit current, the U type loop, which consists of a vacuum interrupter, an external busbar and a conductive rod, generates an external transverse magnetic field (ETMF). This field deflects the vacuum arc and affects the interruption performance of the VCB. In this paper, the real magnetic field data of the arc region are obtained by establishing a simulation model of an electrode system, taking into account the real ETMF and real axial magnetic field (AMF). Furthermore, the three dimensional steady magnetohydrodynamic model of the vacuum arc is established by using real magnetic field data as the boundary condition. The vacuum arc characteristics under the combined effect of AMF and the asymmetric transverse magnetic field (TMF) are studied. The simulation results show that the ETMF considerably changes the Bx of the arc column, which demonstrates asymmetry in the positive and negative directions, whereas By demonstrates a weaker asymmetry. Moreover, the asymmetric TMF deflects the distributions of the vacuum arc plasma and increases the partial heat flux density and axial current density. With the increase in the severity of the short circuit, the TMF asymmetry of the arc region is enhanced and the deflection of the vacuum arc plasma is also enhanced.

Ionization features in cathode spot region of vacuum arc

A model of ionization processes in a low-temperature plasma within the cathode region of a vacuum arc is presented. This mathematical model is represented by a system of nonlinear differential equations of drift-diffusion for the electron density and the average energy of second-order electrons. The system of equations was solved by the finite element method in two coordinates in numerical form using the COMSOL Multiphysics software program. It was shown that due to nonequilibrium processes, Langmuir waves appeared at the plasma boundary, which leads to multistage ionization of metal vapor. The arc discharge was presented in the form of a cylindrical plasma column with a length of 200 μm and a diameter of 50 μm. At the interface between the cathode and the plasma column, a double electric layer has appeared which holds hot electrons in the central zone of the discharge. High specific power was focused close to the cathode surface, which provided the continuous supply of metal vapor. The numerical results of the model have appeared to be in good agreement with the experimental data.

Thermophysical Parameters of the Anode Region of Plasma Arc under the Reduction Smelting of Quartz-Leucoxene Concentrate in a Metal-Graphite Reactor

The process of reducing plasma-arc smelting of titanium raw materials from the Yarega deposit aimed at refining it from silicon has been studied. The smelting was performed in a water-cooled metal-graphite reactor, consisting of a copper cylindrical chamber with a diameter of 100 mm and a graphite bottom insert with a thickness of 30 mm serving as the anode of the arc. A hollow graphite cathode through the channel of which a mixture of quartz-leucoxene with graphite was supplied to the region of the anode spot was installed in the upper part of the chamber. In the course of quartz-leucoxene melting, silicon dioxide SiO2 contained therein was reduced to SiO with the evaporation thereof, thus enriching the melt in titanium. The arc power amounted to 13 kW. The experimentally measured parameters of the temperature field and the current density in the anode spot and in the arc column are in good agreement with the results of calculations made under the assumption that the arc occurring on the quartz-leucoxene anode acts as a heat source with approximately uniform heat flux density.

On the source region and orientations of nightside auroral arcs

Using large data base of stable auroral arcs observed at Gillam we identified those passes of POES spacecraft which were magnetically conjugate to these arcs. We studied statistically arc locations with respect to the energetic particle isotropy boundaries (IBs), which are the well-known markers of the magnetotail regions. In the dusk and night sectors we confirm previous finding that arcs tend to appear close to or poleward of the electron isotropy boundary (IBe), indicating the location of the arcs in the small BZ (large magnetic field curvature) region of the tail current sheet. Different from that, in the dawn sector significant fraction of arcs appears deeper in the magnetosphere, between electron and proton IBs, in the transition region between the current sheet and dipole-like magnetosphere. Addressing the orientations of stable arcs we use the empirical magnetospheric models to demonstrate that nearly sun-aligned plasma sheet structures in the tail are significantly rotated toward azimuthal alignment when mapped from the tail equator to the ionosphere. We discuss how the flow braking/rotation can provide (in direct or secondary/way) the E-W aligned arcs. Based on these results we argue that a significant fraction of the highlatitude stable auroral arcs could be formed by the fast flow convection channels (BBFs); particularly the observed dawn-dusk asymmetry in the relative location of arcs and isotropy boundary can be contributed by this mechanism.

The 25 October 2018 Mw = 6.7 Zakynthos earthquake (Ionian Sea, Greece): A low-angle fault model based on GNSS data, relocated seismicity, small tsunami and implications for the seismic hazard in the west Hellenic Arc

We present a joint analysis of seismological and Global Navigation Satellite System (GNSS) data of the seismic sequence that started on October 25, 2018 with a shallow Mw = 6.7 earthquake offshore Zakynthos (Ionian Sea, Greece). The inversion of the GNSS data shows the activation of a N-S striking thrust/oblique-slip fault at the African-Aegean plate interface with a length of ∼26 km, and depth shallower than 15 km. The fault-plane geometry is well constrained by GNSS with a low-dip angle (23°), and dip-direction towards east. This is consistent with the distribution of the relocated aftershocks (1811 events). Our analysis indicates that the October 25, 2018 event ruptured the Hellenic megathrust. This event highlights the high degree of seismic coupling in the western region of the Hellenic Arc. It also highlights the “strong” nature of the subducting slab with the occurrence of “locked” patches under the Ionian seafloor that fail during large, reverse/oblique-slip earthquakes. The latest, shallow seismic events of the western Hellenic arc (1976 Zakynthos, 1997 Strofades, 2018 Zakynthos) point to a sequence of low-angle events along the plate interface with most of co-seismic deformation taken up by the upper (Aegean) plate. The GNSS data also point to a similar pattern between the co-seismic strain release and the long-term (interseismic) strain accumulation along the west Hellenic Arc.

Infestation dynamics between parasitic Antarctic fish leeches (Piscicolidae) and their crocodile icefish hosts (Channichthyidae)

An understanding of host–parasite interactions represents an important, but often overlooked, axis for predicting how polar marine biodiversity may be impacted by continued environmental change over the next century. Here, we survey three species of crocodile icefish (Notothenioidei: Channichthyidae) collected from two island archipelagos in the southern Scotia Arc region for evidence of leech infestations. Specifically, we report on infestation prevalence, intensity, spatial patterns of relative abundances, size distribution of parasitized fish, and patterns of host and attachment site specificity. Our results reveal high levels of attachment area fidelity for each leech species. These results suggest skin thickness and density of the vascular network constrain leech attachment sites and further suggest trophic (i.e., post-cyclic) transmission to be an important axis of parasitization. We also demonstrate that, while leech species appear to be clustered spatially, this clustering does not appear to be correlated with fish biomass. This study illuminates the complex interactions among fish hosts and leech parasites in the Southern Ocean and lays the groundwork for future studies of Antarctic marine leech ecology that can aid in forecasting how host–parasite interactions may shift in the face of ongoing climate change.

Overriding Plate Velocity Control on Surface Topography in 2‐D Models of Subduction Zones

AbstractWe study the dynamically induced flexural topography in subduction numerical mechanical models. We focus on the topographic changes at the overriding plate (OP) surface induced by variations in OP kinematics, particularly when the subducting plate (SP) has a stationary motion after having reached the rigid base of the upper mantle. Our models consist of two viscoelastic plates with free surfaces and an isoviscous mantle. Friction is imposed along the planar subduction interface. We first characterize the main topographic features at a constant OP velocity, using spatial definitions based on geometrical estimations of the volcanic arc position. The models exhibit the formation of a bulge in the forearc area followed landwards by a depression and a smaller second bulge, both bracketing the arc region. The steady‐state distance to the trench of these features increases with OP velocity. Their amplitude is affected by the far‐field OP tectonic regime that depends on kinematics, and plates and subduction interface strength. We next test the effect of sudden changes in OP velocity. An OP acceleration yields a transient topographic tilt, during which the outer forearc quickly subsides whereas the arc region uplifts, and that is followed by reverse slower motions. An OP slowdown induces opposite motions. The rates of elevation change during the tilt are approximately proportional to velocity variations and mainly sensitive to the SP strength. The rates are higher than 0.1 mm/yr for velocity changes higher than 1 cm/yr. We suggest that topographic accommodations of OP velocity changes should be considered when quantifying nonisostatic topography.

Crustal Structure of Andaman Islands using Joint Inversion of Receiver Functions and Surface Wave Dispersion Measurements

We investigate the crustal structure of Andaman Islands, central part of Burma-Sunda-Java subduction complex, through joint inver- sion of receiver functions and surface wave dispersion measurements. For this study, we used teleseismic earthquakes recorded over 13 temporary broadband seismographs operated in two different phases: pre and post 2004 Sumatra earthquake. Beneath the Andaman fore- arc region, the crustal thickness varies between ~24 and 28 km. The uppermost crust consists of ~4 to 7 km thick soft accretionary sed- iments. Average Vp/Vs ratio, between ~1.79 and 1.83, suggests accretionary hydrated oceanic crust with different level of saturation. Combining derived crustal structure with global seismicity and CMT fault plane solutions indicate a complex convergence along the arc, with transitional (continental-oceanic) type in the north to oceanic type in the south Andaman.

Simultaneous Observations of SAR Arc and Its Ionospheric Response at Subauroral Conjugate Points (L ≃ 2.5) During the St. Patrick's Day Storm in 2015

AbstractDuring the St. Patrick's Day storm on 17 March 2015, an all‐sky imager at King Sejong Station (KSS; geo: 62.2°S, 58.8°W; mag: 50.2°S) captured diffuse aurora and a stable auroral red (SAR) arc. Ground‐based Global Positioning System observations were also simultaneously conducted at KSS, but there was no significant increase in the total electron content's rate‐of‐change index or the ionospheric scintillation indices around the SAR arc region. Auroral activities including a SAR arc were also detected by the all‐sky imager at Millstone Hill Station (geo: 42.6°N, 71.4°W; mag: 52.5°N), which is magnetically conjugate to KSS. The total electron content's rate‐of‐change index map around Millstone Hill Station, too, indicates that the ionospheric irregularities occurred only near the diffuse aurora and not in the SAR arc. The northern SAR arc is broader than the southern one and also shows a multiplicity pattern, which may be due to latitude structure within the seasonally dependent midlatitude ionospheric trough. These conjugate observations, despite their hemispheric differences, validate the classical SAR arc mechanism of emission driven by heat conduction from the inner magnetosphere that does not generate small‐scale ionospheric irregularities that can affect Global Positioning System radio signals. Previous studies of SAR arcs and very high frequency radiowave scintillations did show a positive correlation.

Seismicity and geodynamics of western Peloponnese and central Ionian Islands: Insights from a local seismic deployment

The tectonic setting of western Peloponnese and central Ionian Islands, Greece, is characterized by the subduction of the oceanic African plate beneath the Aegean micro-plate. The transition from subduction to continental collision in northwestern Greece is accommodated by the right-lateral Cephalonia transform fault. In this work, we exploit the recordings of a temporary seismic network composed of 15 stations operating from July 2016 until May 2017 to investigate the complex deformation of this region.Our local network fills in a major observational gap in one of the most tectonically active regions of the Hellenic arc. We detected and located more than 1200 local earthquakes and constrained five 1D optimum local velocity models. The relocated seismicity (including the aftershock sequence that followed the October 2018 Mw 6.7 earthquake offshore Zakynthos) and associated focal mechanisms constrained for the major earthquakes point out a complex crustal deformation.We propose a clockwise rotation of the Ionian Akarnania Block accommodated by major marginal strike-slip fault zones that appear segmented along their strike. Additionally, left-lateral motion is observed on the Kyllini-Cephalonia fault along a north-west direction. Finally, the seismicity recorded in north Cephalonia (offshore Myrtos and Fiskardo) suggests that the Cephalonia transform fault is a large deformation zone where secondary WNW-striking sinistral strike-slip faults occur.

Unusual volcanic instability and sector collapse configuration at Chimpa volcano, central Andes

Upper Miocene Chimpa volcano is one of the largest stratovolcanoes of the back–arc region of the central Andes. The gentle–sloped volcano underwent previously unrecognized volcanic instability, consisting of ≈ 2 km3 mass–wasting processes and catastrophic sector collapse, whose characteristics have been identified by means of stratigraphy, geological mapping and structural analysis. The origin of instability at Chimpa can be attributed to tectonic faulting, hydrothermal alteration and overloading. These common promoting and triggering factors have produced an unusual configuration of the volcano gravitational instability, characterized by parallel landslide scars delimiting unstable sectors on eastern and western volcano flanks, with large toreva blocks sliding in opposite directions, perpendicular to the flow direction of a subsequent long–run out debris avalanche. Even if the style of such a complex volcanic instability has never been described before, its identification may be also useful to study volcano sector failures and mass–wasting deposits in other volcanoes worldwide.

Study on die-less spinning of square section cone with fillets

Due to the high flexibility and low cost, die-less spinning has great potential in aviation, aerospace, agricultural machinery, and lighting manufacturing industries. However, forming accuracy will restrict the application of die-less spinning in square section cone with fillets which is often used as the intermediate shape of box parts according to the lack of die support. In view of this, the mathematical analytical method is adopted to design the roller path which contains arc regions and linear regions. The designed roller path is tested and verified through the spinning experiment which was carried out on the PS-CNCSXY 5 spinning machine. The thickness and the radius of the fillets are compared with theoretical values. And the causes of relative errors are analyzed in three different depths. In addition, the stress-strain fields during the spinning process were analyzed by finite element modeling whose creditability was evaluated by using various energy histories. The measurement values of the thickness and fillets radius are basically consistent with the theoretical ones. The feasibility of the die-less spinning method for square section cone with fillets is certificated.

A new perspective on Cenozoic calc-alkaline and shoshonitic volcanic rocks, eastern Saveh (central Iran)

ABSTRACT Late Eocene – Oligocene volcanic rocks in the eastern Saveh region of the Urumieh-Dokhtar magmatic arc (UDMA) are representative of Paleogene magmatic activity in Iran. They show a wide range of silica-undersaturated to silica-oversaturated compositions, from basalt-trachy basalt and tephri-phonolite to trachyte-latite. Whole rock chemical compositions define a continuous assemblage of mafic and felsic rocks in terms of SiO2 (46.3 to 71.1 wt.%), Al2O3 (12.5–19.2 wt.%), K2O (2.06–12.23 wt.%) and TiO2 (0.41–1.75 wt.%) contents, Mg number (6.8–51) and K2O/Na2O ratios (0.53–30.2). Abundances of rare earth elements in the tephri-phonolite group are much higher than in the trachyte-latite and basalt-trachy basalt groups. Elevated contents of large ion lithophile elements such as Ba (191–7311 ppm) and Pb (6.49–118 ppm) as well as depletions in high field strength elements such as Nb (2.43–40.6 ppm), Ta (0.15–2.24 ppm), Zr (40.8–258 ppm) and TiO2 (0.40–1.77 wt.%) characterize these rocks. Initial ratios of 87Sr/86Sr from 0.7046 to 0.7074 and ɛNd(t) from +0.9 to +3.3 show that these were derived from parental magma extracted from partial melting of metasomatized mantle, namely amphibole- and/or phlogopite-bearing peridotite. Fractionation of feldspar, clinopyroxene, amphibole and phlogopite, and minor contamination with upper crust was responsible for the large variation of the rock types observed. We explain contemporaneous late Eocene – Oligocene calc-alkaline and high-K magmatic activity in the UDMA as due to the partial melting of both hot metasomatized asthenospheric and subcontinental lithospheric mantle in an extensional tectonic regime. This extensional regime probably developed due to the rollback of the subducted Neo-Tethys oceanic plate.

Palaeoslab and plume signatures in the mantle transition zone beneath Eastern Himalaya and adjoining regions

SUMMARY A comprehensive data set of 73 876 high quality receiver functions computed using waveforms recorded by 327 broad-band seismic stations is used to investigate the mantle transition zone (MTZ) structure beneath the eastern Himalaya, southern Tibet, Assam valley and the previously unexplored Burmese arc and Bengal basin regions. A highly variable and perturbed mantle transition zone, with depressed 410 and 660 km discontinuities, is observed beneath the Bengal basin and to the east of the eastern Himalayan syntaxis. The 410 is elevated by ∼10 km along the Himalayan collision front, while it deviates in the range of ±5 km beneath most parts of Tibet and the Himalayan Foredeep. In northern Tibet and along the Red River Fault, delayed conversions from the 410 reveal a deepening of more than 10 km. The 410 and 660 km discontinuities are uplifted by nearly 10 km beneath the Arunachal Himalaya, due to the presence of a subducting Indian lithosphere, as evident in the regional tomographic images. We observe a thick (>20 km) transition zone beneath the Burmese Arc and close to the Tengchong volcano. An uplifted 410 together with a depressed 660 km discontinuity requires presence of lithospheric slabs within the MTZ. Delayed P-to-s conversions from the 410 and 660 km discontinuities in the proximity of the Jinsha suture zone seem to be consistent with the earlier results that invoke flow of a hot Tibetan asthenosphere into the mantle transition zone, as an explanation. Interestingly, results from the Bengal basin reveal a deepening (∼10 km) of both the 410 and 660 km discontinuities. Similar results from other plume affected regions prompt us to interpret this as a signature of the Kergulean plume.

Effect of Gas Metal Arc Welding on Magnetic Response of Ferritic Stainless Steel

The variation of magnetic Barkhausen noise (MBN) response of different regions of the gas metal arc welded ferritic stainless steel SS409L plate in terms of number of pulses and root mean square value with the variation of MBN analysis parameters (magnetic field intensity and magnetizing frequency) have been investigated in the present work. Five different values of magnetic field intensity 250, 500, 750, 1000 and 1250 Oe at the constant magnetizing frequency of 25 Hz and four different values of magnetizing frequency 10, 20, 30 and 40 Hz at a constant magnetic field intensity of 800 Oe were used as MBN analysis parameters. It was found that MBN response depends upon the magnetic field intensity and magnetizing frequency as well on grain size and microhardness of different regions.

Numerical study on arc-droplet coupled behavior in magnetic field controlled GMAW process

The metal transfer behavior is one of the most pivotal links of gas metal arc welding (GMAW) for improving the welding quality. Arc impacts the current path and heat input on the droplet surface, in reverse, the metal droplet detachment makes the arc to flicker. It is hard to make the metal transfer process clear with only experimental methods since the limited measuring space and high temperature in the welding region. In this work, with the help of computational fluid dynamics software ANSYS FLUENT, a magnetohydrodynamic model including argon arc plasma and steel wire and the droplet is constructed by using two independent governing equations of gas and metal phase for the mass, momentum, and energy balance. Comparing the magnetic field controlled GMAW with conventional GMAW, the temperature field, current density distribution, electric potential field, static pressure field and also metal vapor mass fraction distribution are highlighted. It is shown that the metal transfer frequency decreases and droplet diameter increases with 180 A welding current when applying an external constant axial magnetic field 0.002 T. So, the arc length decreases before the detaching moment, the current density expands in the arc region and the voltage decreases. The centrifugal movement impedes the downward flow and transfers heat from the droplet center to the outside region.

Dynamics of Interaction of a Single Fiber with a Headset of a Sampling Drum

The article presents an analysis of the dynamics of interaction of a single fiber with the sampling drum of a headset during pneumomechanical spinning. The regularity is investigated and the equation of the movement of fibers on the surface of the tooth of the sampling drum headset is obtained. It was found that the dependences of the movement of fibers along the tooth at different angles of inclination, the distribution of fiber tension along the arc, and the distribution of fiber speeds in the region of the sampling arc have an increase property. As a result of the analysis of the tension and speed of the fibers, it was found that with the increase in the sampling zone, the tension force and speed of the fiber increase.

Characterisation of welded plate through micro-magnetic technique

Characterisation of the welded plate by Non-destructive testing technique are gaining more popularity over destructive testing. In this study, the variation in the hysteresis loop behaviour were examined with the variation of magnetic field intensity on the base metal, heat affected zone and weld metal regions of gas metal arc welded ferritic stainless steel plate. The behaviour of hysteresis loop characteristics such as average permeability, remanence and coercivity have been investigated and it was found that these characteristics depend upon the grain size and microhardness as well as magnetic field intensity. Coercivity of each region vary in proportion with the variation of magnetic field intensity and inversely proportional to the grain size, but the variation of other hysteresis loop characteristics with the magnetic field intensity in each region is irregular.

Eocene arc petrogenesis in Central Chile ( c. 33.6° S) and implications for the Late Cretaceous–Miocene Andean setting: tracking the evolving tectonic regime

The scarce Eocene geological record in the Andean region of Central Chile ( c. 33.6° S) is represented by the Estratos del Cordón de los Ratones unit. This is a c. 450 m thick, mainly volcanic, continental series with a bimodal character that hosts numerous subvolcanic intrusions. The igneous products show compositional features indicating a co-genetic character for the whole suite, relatively juvenile mantle signatures and arc-like affinities. This, along with age determinations of c. 42 Ma, indicate that the unit corresponds to the middle Eocene arc in the region. The geochemical data obtained complement the evolving arc magmatic record throughout Andean evolution. This allows us to track: (1) the earliest Late Cretaceous orogenic event; (2) neutral tectonic conditions from the latest Cretaceous to mid-Eocene times; (3) the Oligocene–early Miocene extensional episode; and (4) the onset of the prevailing compression. The record also indicates that the extensional event started no earlier than the mid-Eocene, with the deposition of the Estratos del Cordón de los Ratones, and no later than the earliest Oligocene. In addition, orogenic processes developed from early Miocene times are highlighted relative to those developed during the early Late Cretaceous, at least in the arc region. Supplementary material: Analytical methods (Item 1), the full dataset of U–Pb age determinations by SHRIMP (Item 2) and LA-ICP-MS (Item 3), and additional geochronological diagrams (Item 4) are available at https://doi.org/10.6084/m9.figshare.c.4710305