Reverse Zone Research Articles

Analysis of corneal surface shape following overnight orthokeratology with different optical zone diameters.

This study analyzed the corneal surface shape following overnight orthokeratology with different optical zone diameters. A total of 82 eyes belonging to 41 myopic children who completed 1 month of the orthokeratology (ortho-k) lens wear at the Eye Hospital of Wenzhou Medical University from January 2022 to January 2023 were retrospectively analyzed. According to the size of the base curve (BC) of ortho-k lens, patients were divided into BC 5.0 and BC 6.0 groups. The changes in decentration distance and corneal refraction of the two groups after the ortho-k lens wear were analyzed. Independent sample t-tests were used to compare these two outcome measures between the two groups. The decentration distance of BC 5.0 group (0.37 ± 0.19 mm) was significantly lower than that of BC 6.0 group (0.49 ± 0.25 mm, t = -2.330, p = 0.022). In the BC 5.0 group, the direction of decentration was superonasal in 3 cases, inferonasal in 2 cases, inferotemporal in 21 cases, and superotemporal in 6 cases. In the BC 6.0 group, the direction of decentration was superonasal in 2 cases, inferonasal in 2 cases, inferotemporal in 27 cases, and superotemporal in 19 cases. The optical zone area (8.19 ± 2.96 mm2) and reverse curve zone area (30.05 ± 6.74 mm2) in the BC 5.0 group were significantly lower than in the BC 6.0 group (10.42 ± 2.03 mm2, t = -4.043, p < 0.001; 38.21 ± 4.77 mm2, t = -6.422, p < 0.001). The change in the rate of refraction in the horizontal direction in BC 5.0 group were significant higher than in BC 6.0 group. Base curve 5.0 mm ortho-k lens is better positioned than BC 6.0 mm lens. A small BC ortho-k forms a smaller optical zone and reverse curve area, which might get a greater aiameter of alignment curve to facilitate positioning better than the traditional BC lens. In addition, a small BC lens increases positive refraction in the peripheral area, resulting in a greater negative pressure than the traditional BC lens.

Magnetostratigraphy of the upper Jurassic and Lower Cretaceous deposits of the Bolshekhetskaya structural terrace

Relevance. The confinement of hydrocarbon deposits to certain stratigraphic horizons, poor knowledge of the northeast of Western Siberia and adjacent territories, including the magnetostratigraphic method, with their oil and gas potential (over the past 10 years, four unique hydrocarbon deposits have been discovered here), the boreal nature of the deposits, and the need for remote magnetostratigraphic correlations. Aim. To create a magnetostratigraphic reference section of the northeast of Western Siberia. Objects. Sections of deep wells of the Pendomayakhskaya, Vostochno Suzunskaya, Vostochno Lodochnaya and Gorchinskaya areas of the Bolshekhetskaya structural terrace, which exposed the Lower Cretaceous and upper parts of the Upper Jurassic (Yanovstan Formation) deposits. Methods. Paleomagnetic studies were carried out according to standard methods and included sampling of core samples with an "up-down" orientation, sample preparation (kappametry, marking of samples, photographing, sawing), measurement of magnetic susceptibility, temporary cleaning (the samples were located along the field during a week, then a week-against the field with determination of residual magnetization), complete demagnetization by alternating magnetic field, plotting of complete demagnetization, mass cleaning, determination of components of natural residual magnetization, assessment of paleomagnetic stability, identification of forward and reverse polarity zones, construction of paleomagnetic sections. To construct the magnetostratigraphic sections given in this article, the paleomagnetic and biostratigraphic data are linked. For this purpose, magnetochrons were identified using biostratigraphic analysis. Results. The authors have compiled a composite magnetostratigraphic section of the boundary Jurassic-Cretaceous deposits of the Bolshekhetskaya structural terrace and identified four magnetozones with subzones of direct and reverse polarity, compared with the Berriasian ammonite scale. The high information content of the results of magnetostratigraphy research under boreal conditions was noted.

Cylindrical cavity expansion-contraction solutions in undrained MCC soils with the auxiliary variable approach

Cylindrical cavity exhibits non-self-similarity during contraction process following expansion. Previous studies solve this problem with total strain approach and simple constitutive models, but the approach is not applicable when using an advanced constitutive model. This paper presents a semi-analytical solution for a cylindrical cavity undergoing expansion-contraction in undrained soils with auxiliary variable approach, incorporating the Modified Cam-Clay (MCC) model. The stress states around the cavity are formed by the superposition of initial and superimposed stress states. By treating superimposed effective stresses as self-similar, a semi-analytical solution is derived for solving the cavity expansion-contraction problem. The elastoplastic stress-strain relationship is formulated as a set of first-order differential equations, which can be solved as an initial value problem though Runge-Kutta (RK) method. Then the stress distribution around the cavity during expansion-contraction process can be determined. To validate the proposed approach, a series of well-conduced self-boring pressuremeter (SBP) tests are used to verify the proposed approach, which shows good agreements. Additionally, a FEM simulation incorporating the MCC model is performed, and the simulation results are presented to carry out parametric studies on soil parameters. A significant influence on the range of the plastic and reverse plastic zones is shown for overconsolidation ratio, while the in-situ coefficient of the earth pressure only quantitatively affects the stress distribution.

Efficacy of orthokeratology lens with the modified small treatment zone on myopia progression and visual quality: a randomized clinical trial

BackgroundTo evaluate the long-term effectiveness of orthokeratology (ortho-K) lenses with small treatment zone (STZ) or conventional treatment zone (CTZ) in controlling axial elongation in children with myopia as well as the impact on visual quality. We also sought to determine the effect of retinal visual signal quality on axial elongation.MethodsThis is a prospective randomized controlled study. A total of 140 participants (age ranging from 8 to 12 years) were randomly assigned to wear either STZ or CTZ ortho-K lenses. STZ ortho-K lenses design was achieved by changing the depth of reverse zone and the sagitta height of the optical zone. Using the IOL-Master 500, axial length (AL) was measured at baseline and after 6, 12 and 18 months of ortho-K treatment. Spherical aberration (SA) and corneal topographic parameters were obtained by the Pentacam anterior segment analyzer at baseline and the 1-month follow-up visit, and optical qualities were assessed by optical quality analysis system-II (OQAS-II) at baseline and after 1 month of lens wearing. Optical quality parameters mainly included the modulation transfer function (MTF) cutoff, Strehl ratio (SR), objective scattering index (OSI), and predicted visual acuity (PVA).ResultsA total of 131 participants completed the study, including 68 in the STZ group and 63 in the CTZ group. The STZ group had significantly reduced AL elongation compared to the CTZ group after treatment (12 months: 0.07 ± 0.11 mm vs. 0.14 ± 0.12 mm, P = 0.002; 18 months: 0.17 ± 0.15 mm vs. 0.26 ± 0.16 mm, P = 0.002). The topography in the STZ group showed a smaller treatment zone (TZ) diameter (2.50 ± 0.23 mm vs. 2.77 ± 0.18 mm, P < 0.001), a wider defocus ring width (2.45 ± 0.28 mm vs. 2.30 ± 0.30 mm, P = 0.006), and larger values of total amount of defocus (119.38 ± 63.71 D·mm2 vs. 91.40 ± 40.83 D·mm2, P = 0.003) and total SA (0.37 ± 0.25 μm vs. 0.25 ± 0.29 μm, P = 0.015), compared with the CTZ group. Objective visual quality decreased in both groups (P < 0.001). This was evidenced by a greater decrease in MTF cutoff (− 14.24 ± 10.48 vs. − 10.74 ± 9.46, P = 0.047) and SR values (− 0.09 ± 0.07 vs. − 0.06 ± 0.07, P = 0.026), and an increase in OSI value (0.84 ± 0.72 vs. 0.58 ± 0.53, P = 0.019). PVA9% decreased significantly in the STZ group but not the CTZ group. A statistically significant negative correlation was found between the changes in total SA and MTF cutoff values (r = − 0.202, P = 0.025). AL changes were associated with sex, change of MTF cutoff value, increment of total SA and TZ area.ConclusionsCompared with CTZ ortho-K lenses, STZ ortho-K lenses significantly inhibited axial elongation in children with myopia while moderately reducing their objective visual quality. Axial elongation was affected by retinal visual quality, and it may be a possible mechanism for ortho-K slowing myopia progression.Trial registration This trial is registered at Chinese Clinical Trial Registry on November 5, 2019 with trial registration number: ChiCTR1900027218. https://www.chictr.org.cn/showproj.html?proj=45380

Effects of submergence ratio on flow around a circular pier in combined wave–current flows using particle image velocimetry

The present study illustrates an experimental investigation of flow hydrodynamics in the vicinity of a submerged circular pier across various submergence levels under only current and wave–current combined flow conditions. The instantaneous velocity data are collected using particle image velocimetry for three distinct frequencies of waves to determine the influence of wave superimposition on the current-induced turbulence parameters. The distribution of phase averaged turbulence quantities, such as mean velocities, Reynolds shear stress, turbulent kinetic energy, flow patterns, and vorticity analysis by Q-criterion, are presented. The results provide insight into the impacts of wave frequency and submergence ratio on the formation of horseshoe vortices, trailing vortex, and reverse flow zones. From the results it is observed that a decrease in the submergence level of the structure causes the formation of strong horseshoe vortices and reverse flow zones in the absence of waves. Also, an increase in wave frequency intensifies the turbulence kinetic energy at the upstream of the pier and eddy generation behind the pier. The present findings highlight the effects of pier submergence and wave characteristics, such as frequency, wave height, and wave period, on flow patterns and turbulent flow characteristics and aid in the design of marine structures. Furthermore, experimental data serve as a valuable resource for validating theoretical or mathematical models related to combined wave–current environments.

The Influence of Pump-Turbine Specific Speed on Hydraulic Transient Processes

The main porpose of this paper is to perform and present at transient process analysis on the influence of different specific speeds (nq) of the three-model pump-turbines that may implemented at the hydropower pump storage plant (HPSP) Bajina Basta, Serbia. The intention is to analyze the operation regimes along the S-shaped characteristic curve, which creates difficulties in calculations during the load-rejection process. These problems are manifested by an unusual increase in water pressure, followed by an increase in machine vibrations, thus threatening the stability of machine operation. The subject of this research is the four-quadrant (4Q) characteristic curves, presented in the form of Suter curves (the head and momentum parameters (Wh and Wm), in dependence of angle (θ)) for different wicket gate openings, of the three pump-turbine models with different specific speeds (nq = 27, nq = 38 and nq = 50). These 4Q characteristics are used as input data for numerical code developed to calculate the simultaneous load rejection of both pump-turbines. The numerical code is based on the method of characteristics and applied to the test case at HPSP. This is especially relevant when dealing with characteristic S-shaped curves that may lead to serious instability in operation during the transient process. The calculation results show changes in the pressure, speed of rotation and discharge of the machine operation regimes, but the important findings are reflected in further application of the results to determine the parametric flow and speed (Q11 and n11) trajectories of the operating points, where the unstable behavior of a pump-turbine operating in turbine mode is presented and periodically the trajectories also pass through the reverse pump zone.

Tailored micromixing in chemically patterned microchannels undergoing electromagnetohydrodynamic flow.

The study unveils a simple, non-invasive method to perform micromixing with the help of spatiotemporal variation in the Lorentz force inside a microchannel decorated with chemically heterogeneous walls. Computational fluid dynamics simulations have been utilized to investigate micromixing under the coupled influence of electric and magnetic fields, namely, electromagnetohydrodynamics, to alter the direction of the Lorentz force at the specific locations by creating the reverse flow zones where the pressure gradient, . The study explores the impact of periodicity, distribution, and size of electrodes alongside the magnitude of applied field intensity, the flow rate of the fluid, and the nature of the electric field on the generation of the mixing vortices and their strength inside the microchannels. The results illustrate that the wall heterogeneities can indeed enforce the formation of localized on-demand vortices when the strength of the localized reverse flow overcomes the inertia of the mainstream flow. In such a scenario, while the vortex size and strength are found to increase with the size of the heterogeneous electrodes and field intensities, the number of vortices increases with the number of heterogeneous electrodes decorated on the channel wall. The presence of a non-zero pressure-driven inflow velocity is found to subdue the strength of the vortices to restrict the mixing facilitated by the localized variation of the Lorentz force. Interestingly, the usage of an alternating current (AC) electric field is found to provide an additional non-invasive control on the mixing vortices by enabling periodic changes in their direction of rotation. A case study in this regard discloses the possibility of rapid mixing with the usage of an AC electric field for a pair of miscible fluids inside a microchannel.

Structural context of the Flatreef in the Northern Limb of the Bushveld Complex

AbstractThe Flatreef occurs at a depth of 700 m under the farm Turfspruit 241 KR in the Northern Limb of the Bushveld Complex. The Flatreef forms part of the Platreef of the Northern Limb, which contains magmatic rocks of the Rustenburg Layered Suite of the Bushveld Complex. The structure of the Flatreef is a flat-lying to gently westerly dipping monoclinal to open fold, 1 km wide and 6 km long. Distinctive features within the Flatreef include the development of cyclical magmatic layering with locally thickened pyroxenitic layers, and associated economically significant poly-metallic mineralisation. Geophysical evidence, exploration drill core, and recent underground exposure show that deformation had a major influence on the Flatreef mineralization. Block faulting and first generation folding affected the orientation and shape of the sedimentary host-rock sequence prior to intrusion of the Rustenburg Layered Suite. These structural and host-rock elements controlled the intrusion of the Lower Zone, and to a lesser degree, the Critical Zone correlatives of the Bushveld Complex in the Northern Limb. During intrusion reverse faults and shear zones and a second generation of folds were active, as well as local extension along layering. Syn-magmatic deformation on these structures led to laterally extensive stratal thickening across them, including the Merensky-Reef correlative that forms part of the Flatreef. This deformation was likely to have been driven by subsidence of the Bushveld complex. Many of these structures were intruded by granitic magmas during the late stages of intrusion, and they were reactivated during extension after intrusion. Thus, structures were active before, during and after the intrusion of Northern Limb, and the structural evolution determined the current geometry and mineral endowment of the Flatreef.

Thrust-related metamorphism in Carboniferous slates of southern Patagonia (South America): the fate of forearc successions

The Devonian to early Carboniferous western margin of Patagonia (South America) includes a NW–SE-trending magmatic arc associated with a NE-dipping palaeo-subduction zone. Along the Andean region of southern Patagonia, the Eastern Andean Metamorphic Complex developed in a forearc position and consists of a succession of very low- to low-grade metaturbidite–metabasic rocks emplaced from the Devonian to Carboniferous. There are significant uncertainties surrounding this metamorphic complex, mainly related to the tectonosedimentary setting of the basin and the subsequent conditions of deformation and metamorphism, which hinder our understanding of the orogenic architecture. To reveal the links between tectonics and metamorphism, we conducted a structural analysis and sampled metapelites to measure the illite crystallinity along a regional structural cross-section in the Eastern Andean Metamorphic Complex. Our analysis reveals broadly lower to upper anchizonal metamorphism roughly synchronous with deformation along northwards-verging thrusts. These findings support the development of a forearc hyperextended basin that was subsequently closed during the Gondwanide Orogeny (late Paleozoic), a model that reconciles previous proposals suggesting passive margin v. back-arc basin models. This closure led to the emplacement of supra-subduction zone ophiolites and turbidites over the continent through the landwards migration of brittle–ductile reverse shear zones. Supplementary material: Measurements of the Kübler index are available at https://doi.org/10.6084/m9.figshare.c.7160849 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Modeling and Programming of a Spiral Winding Cycle Using a Robotic Arm

This article is devoted to solving the problem of manufacturing products from carbon fiber composite materials, which are obtained as a result of layer-by-layer laying of carbon fiber with impregnation of their binder components. This paper presents a description of the process of spiral winding of products on a cylindrical mandrel and the mathematical model, which takes into account the coefficient of friction and the necessary reverse zones in which the tape will not slip. The model is implemented as a Python program and is capable of simulating and visualizing the step-by-step winding of a carbon tape on a cylindrical surface. It is possible to optimize the friction coefficient to ensure the tightest winding of subsequent passes. The program takes into account reverse zones, which are calculated taking into account the friction coefficient of the cylindrical mandrel. Based on the simulated winding process, a control program for the robotic arm is generated. The performance of the proposed model and its implementation was tested on a test bench with a robot.

Low-Cycle Fatigue Behavior of Hydrostatic Extruded AZ80 Mg Alloy

The fatigue properties of conventional and hydrostatic extruded AZ80 Mg alloy were fully studied under strain-controlled mode. The hydrostatic extrusion can effectively increase the tensile strength, but decrease the elongation. Consequently, the low cycle fatigue lifespan of the hydrostatic extruded specimens was shorter than that of the conventional extruded ones. The Manson-Coffin-Basquin relationship was adopted to describe the fatigue lifespan of the extruded AZ80 alloys. Finally, the fracture surfaces were observed by scanning electron microscope. The fatigue crack stable propagation zone of the hydrostatic extruded sample has decreased significantly compared with that of the conventional extruded sample. The hydrostatic extruded specimen has small reverse plastic zone size, which leads to microscopically rough fatigue crack propagation zone.

Experimental investigation of a grid plasma jet array in a turbulent boundary layer for skin-friction drag reduction

Toward turbulent skin-friction drag reduction, a novel layout of plasma actuator with a grid anode is devised (grid edge length: L), capable of producing an array of wall-normal plasma jets. The characteristics of this plasma jet array and its interaction with a turbulent boundary layer are investigated experimentally with a particle imaging velocimetry. Results show that the quiescent flow field of the plasma actuator is dominated by a standing vortex ring attached at the inner sides of the square grid, a wall-normal jet flow issued from the grid center, and a downwash flow between adjacent grids. When a tandem array of 11 plasma jets are issued into the cross flow, an equilibrium stage is reached after the third jet. In this stage, the main body of the wall-normal jet bends noticeably to the cross flow, and its leeward side hosts a reverse flow zone, extending downstream to form a slender low-speed wedge (LSW). Two vortical structures are prominent: the streamwise counter-rotating vortex pair residing in the two sides of the jet body, and the arch-shape negative spanwise vortex situated on the LSW root. In the grid-middle plane, the production of turbulence is enhanced across the entire boundary layer, and a second production peak is identified at y+=26. Reduction of the spanwise-averaged wall shear stress is achieved downstream of plasma actuation at x/L≥19.4, and part of the drag reduction fruit earned by ejection is offset by the spanwise transportation of high-velocity fluids toward the middle plane.

Effect of atomizing gas type on kerosene spray combustion using gas-blast atomizer: A comparative numerical study

In order to attain optimal combustion efficiency, minimal pollutant emissions, and reliable stability in gas turbines, a computational model was developed to study the combustion and atomization characteristics of liquid fuel (Kerosene). Seven different atomizing gases were considered, namely, air, ammonia, hydrogen, natural gas, superheated steam, oxygen, and nitrogen. The work aims to investigate the potential of hydrogen in contrast to the other atomizing gases, in minimizing pollutant concentrations in the combustion exhaust considering the associated cost implications. A 3D cylindrical combustor with a gas blast atomizer was employed while maintaining a constant air swirl number. The total thermal load across all tests was kept constant by varying the liquid kerosene flow rate. The simulations analyzed various parameters in order to address the combustion characteristics, such as reverse flow zone (RFZ), recirculated flow mass ratio, flow pathlines, temperature maps, centreline axial temperatures, outlet temperatures, species concentrations, and droplets characteristics. The results showed that the flame temperature reached its peak when hydrogen was utilized. When using combustible atomizing gases, the CO and CO2 concentrations at the exit of the combustor tube were generally lower. However, the CO concentration is notably higher when air is employed, unlike other gases such as nitrogen, oxygen, and natural gas, which showed decreased CO levels. Remarkably, the CO concentration experiences a significant decline of about 98% when natural gas is utilized. The average concentration of NOx is highest when oxygen and hydrogen are used as atomizing gases, but it experiences a significant decrease of approximately 75% when air is employed instead. It can be deduced that different gases such as hydrogen gas have a possibility as an option and sustainable atomizing gases on spray performance.

Devonian to Early Carboniferous Retreating—Advancing Subduction Switch in the Northwestern Patagonia Accretionary Orogen: U‐Pb and Lu‐Hf Isotopic Insights

AbstractIn this contribution, we present new early middle Devonian igneous and metaigneous units with a major juvenile magmatic source input in the North Patagonian Massif, which were discovered through U‐Pb and Lu‐Hf zircon analyses. Afterward, we assessed their tectonic implications for northwestern Patagonia and then for southern South America, combining our results with available database information consisting of igneous crystallization ages and isotopic data of the Devonian to early Carboniferous magmatic units, tectonic‐metamorphic analyses, and thermochronologic record. This study allows for distinguishing retreating and advancing subduction switching in northwestern Patagonia (38°30′ to 44°S) and a contrasting coetaneous evolution for basement outcrops exposed further north (27°30′ and 37°30′S). The early middle Devonian (400–380 Ma) northwestern Patagonian magmatism is characterized by widespread magmatism and positive εHf–εNd linked to forearc and backarc magmatism that evolved within a retreating subduction stage. A tectonic switching toward advancing orogeny stage began in the late Devonian, evidenced by a lull in magmatic activity with a negative εHf–εNd trend, possibly contemporaneous with the first tectonic‐metamorphic event in western Patagonia. An early Carboniferous magmatic gap, followed by the subsequent development of the main foliation in the basement during the Carboniferous‐Permian period, denotes the acme of this contractional stage. In contrast, the Devonian period in the northern segment is characterized by mostly negative εHf–εNd values, reverse shear zone activity in the foreland, and an inboard magmatism migration, evidencing a compressive tectonic setting that changed to an extensional configuration in the early Carboniferous with widespread arc magmatism development.

Water-blocking characteristics of fault zones with different structural combination of cementation degree

Recently, deep coal mining has posed a significant challenge owing to the threat of water inrush from highly pressured aquifers in the floor strata. Water inrush in the floor strata is often associated with the structural characteristics of the underlying fault zones. The permeability of these fault zones is a critical factor in determining their potential as conduits for water flow. The variation in permeability is attributed to the varying cementation degree across different locations within the fault zones. Hence, this study is based on the key stratum theory and introduces the concept of a water-blocking key stratum within fault zones. This research focuses on the engineering context of the 16th coal seam above the lower coal seam in the 10603 working face of the Yangcun Coal Mine's tenth mining area. The study investigates the activation characteristics of the 10605F5 reverse fault zone, which cuts through the working face. Various methods, including test of simulation of similar materials and numerical simulations, are employed to analyse the hydraulic pressure distribution and the impact of mining activities on the water-blocking key stratum within the 10605F5 reverse fault zone. The research findings will provide valuable insights for preventing fault activation and water inrush.

On the delineation of the flow separation zone in open-channel confluences

In the context of a T-shaped open-channel confluence, where the tributary flow separates at the downstream junction edge and creates a separation zone in the post-confluence channel, this paper provides a critical reflection upon the terminology and the delineation methods for the separation zone and its proxies: the recirculation zone and the reverse flow zone. Following the fluid-mechanical literature on flow separation, the separation zone is delineated by a dividing surface formed by the three-dimensional (3D) streamlines separating from the downstream junction edge. Based on a dense 3D time-averaged velocity field obtained from a Large-Eddy Simulation of a lab-style confluence flow, the separation zone turns out to be open. Near the bed, the dividing surface exhibits a gap, through which mainly tributary fluid enters the separation zone, leading to a limited discharge flowing through that zone. Downstream of the section where the merging flows are the most contracted, the dividing surface does not reattach to the inner bank, prohibiting the determination of a maximum length of the separation zone. Downstream of that section, the dividing surface gradually loses its role as a skeleton for the separation zone shear layer. Due to mixing, the separation zone and the adjacent maximum velocity zone gradually dissolve and transform into the flow recovery zone, as in a wake. By means of flow visualization with 3D streamlines, revealing different types of recirculating motions, the maximum recirculation zone extent is determined. Then three simplified methods commonly used in the literature to quantify the dimensions of the separation zone or its proxies are evaluated by comparison with the 3D streamline method. By adopting various simplifying assumptions about the flow, the pseudo-streamline method, the zero-unit-discharge method and the zero-velocity method yield definite reasonable maximum lengths for the recirculation zone and the reverse flow zone. With the exception of the zero-velocity method, all simplified methods yield reasonable estimates for the maximum widths and the corresponding contraction coefficients of the separation zone proxies. Still, contrary to the simplified methods, only the 3D streamline method can provide physical insight into the flow features occurring in the separation zone or its proxies.

Fatigue crack growth: Validation of the Kmax-ΔK approach using the GTN damage model

Considering cyclic plastic deformation as the single damage mechanism behind the fatigue crack growth (FCG), the effect of the mean stress is null in the absence of crack closure. In this study, an additional damage mechanism was introduced, predicting the effects of the growth, nucleation and coalescence of micro-voids. Using a non-local damage model, the reverse plastic zone was identified as the fatigue process zone, allowing to establish a relation to calculate its size. Considering aluminium alloy 2024-T351, the predictions are in close agreement with the experimental da/dN-ΔK curves, for distinct stress ratios. The results highlight that the effect of Kmax on the FCG rate is small in the absence of crack closure. On the other hand, modelling the contact between the crack flanks, the effect of Kmax on the FCG rate is amplified, i.e. the ΔK-Kmax plots for a given da/dN presented a Kmax dominance zone. The developed model suggests a three-parameter approach: ΔKeff -ΔK-Kmax.

Reduction of specific coke consumption in blast furnace by impact on thermal reverse zone

At the blast furnace of PJSC “Magnitogorsk Metallurgical Plant” (MMK), the specific consumption of coke was reduced by impact on thermal reverse zone (TRZ) by increasing the consumption of natural gas above 120 m3/t of cast iron under conditions of increased reactivity and reduced hot strength of coke. In the first pair of periods, an increase in CRI from 38.4 to 39.3 % with a decrease in CSR from 36.3 to 34.6 % was accompanied by an increase in the ratio of natural gas consumption and total oxygen entering the furnace from 0.43 to 0.45 by increasing the specific gas consumption from 123.2 to 133.5 m3/t of cast iron. The set of actions increased the TRZ length towards the blast-furnace mouth by 1.9 % with its unchanged location along the lower part. Reducing the heat consumption in the TRZ increased the temperature difference between gas and materials there by an average of 36 °С. In the second pair of periods, the consumption of natural gas was 143.9 m3/t of cast iron with a decrease in the oxygen content in the blast from 27.6 to 27.0. They were accompanied by the following changes in the processes under consideration: an increase in the length of the TRZ towards the blast-furnace mouth by 2.6 % and the distance from the tuyere hearth by 3.4 %, an increase in the degree of carbon reduction from 32.0 to 33.3 %, an insignificant (on average 0.3 °С) increase in the temperature difference of gas and materials in the TRZ. In the first pair of periods, reduction in the coke specific consumption was 4.7 kg/t of cast iron with an increase in furnace productivity by 27 t/day. Conditions and course of the processes of the second pair ensured a decrease in the coke specific consumption by 1.6 kg/t of cast iron and led to a decrease in cast iron production by 41 t/day.

Analysis of crack closure and wake of plasticity with the distributed dislocation technique

A new method for the analysis of plasticity-induced closure of finite cracks is developed based on the distributed dislocation technique. The method is applied to analyse closure and opening processes for an embedded fatigue crack propagating under constant amplitude cyclic loading. The obtained solution and presented results can serve as a benchmark for numerical procedures utilising the same yield-strip methodology. Comparison with past numerical studies reveals similar trends, though there are some differences in the crack tip opening values, particularly for low and negative R-ratios. The latter may indicate the need for a better approach to the discretisation of the contact, direct and reverse plasticity zones in the numerical procedures which utilise the same methodology. The developed method is general, and it can be adapted to evaluate the crack tip opening stress for other crack geometries and loading conditions.

Simultaneous sensing of strain and temperature based on the inline-MZI embedded point-shaped taper structure with low crosstalk.

An embedded spherical dot taper structure (EDT) based on the MZI principle is proposed in this paper, which is mainly fabricated by using two special arc discharges in the preparation process. The proposed structure involves two specialized arc discharge techniques. First, an oversaturated discharge fusion process creates a micro-arc spherical area on the fiber end face to form the first link type. Second, an unsaturated discharge-pulling taper fusion joint creates a local micro-extrusion operation on this micro-arc fiber end face to form the second link. The thermal stress from instantaneous discharge causes a reverse spherical expansion zone to form in the end face structure, similar to the micromachining of long-period fiber gratings that use local CO2 laser etching to create modulated zones. The study involves a mathematical and theoretical analysis of how geometric parameters in the spherical modulation zone impact the structure's characteristic spectrum. The research demonstrates the potential for this structure to function as a light-intensity modulated strain sensor device through both theoretical and experimental means. As per the experimental findings, the optimized structure displays a high level of strain sensing sensitivity at 0.03 dB/µε and temperature sensing sensitivity of 73 pm/°C (20°C-75°C) and 169 pm/°C (75°C-120°C). Additionally, it possesses excellent cross-sensitivity at only ∼0.0015 µε/°C. Therefore, this sensor presents a favorable option for strain and temperature synchronization sensing and monitoring components, and exhibits notable application prospects in precision engineering, which encompasses mechanical manufacturing, the power and electrical industry, healthcare domain, and certain specialized areas of small-scale precision engineering.