Single Pit Research Articles

Observation of natural convection and particle ejection from stainless steel single pits

Single pits were visually and electrochemically followed during their growth on a S41500 martensitic SS microelectrode. Solid particles were observed ejecting from the growing pit and after extraction, EDX determined they were mostly iron-based hydroxides/oxides. These particles were carried by fluid flow originating from the pit at a velocity of 21 μm/s. Finite element modeling confirmed the observed flow speeds are achievable by natural convection due to metal ion density gradients. While the pit solution does not experience flow, the bulk solution pH was observed to decrease illustrating how natural convection affects the bulk solution chemistry.

A phase field framework for corrosion fatigue of carbon steel

Corrosion fatigue damage occurs when metallic materials are subjected to cyclic loading in a corrosive medium. In this study, a phase field framework is proposed to predict the corrosion fatigue of carbon steels. The coupling effect of fatigue and corrosion is explicitly implemented in the proposed phase field framework by coupling the displacement field, electrochemical field and phase field. A degradation function of the interface free energy density with the consideration of elastic and plastic strain energies is introduced to account for the fatigue damage accumulated during the corrosion fatigue process. The applicability of this framework is validated by accurately capturing the pure fatigue and corrosion fatigue behaviors of compact tension specimens, particularly the acceleration effect of corrosion on the fatigue crack growth. The propagation morphology and rate of the corrosion fatigue crack in single pit and multiple pit models are studied. The distribution of stress state and strain energy density induces the directionality of crack propagation. The influence of loading frequency on the corrosion fatigue process is discussed in detail. Due to the corrosion-fatigue coupling effect, the corrosion rate increases with increasing of the loading frequency, resulting in an accelerated corrosion fatigue process. Moreover, the significance of the plasticity in the prediction of corrosion fatigue is emphasized.

EIS Investigation of a Single Pit on Cantor Alloy in Acidic Environment

High-entropy alloys (HEA) are an emerging class of materials with promising properties such as high strength and ductility, improved fatigue resistance, fracture toughness, and thermal stability. They show considerable potential for use as corrosion resistant alloys to support our infrastructure especially for use in extreme environments. In this work, we mainly focused on the typical Cantor alloy, which consists in a mixture of 5 elements CrMnFeCoNi in equimolar proportion. A huge amount of works has already been devoted to the study corrosion resistance of alloys in sulfuric acid [1] or in chloride containing solutions [2,3]. For the latter, the study of the pitting propagation remains challenging since this kind of corrosion initiates as a stochastic process.Electrochemical impedance spectroscopy (EIS) is intensively used as a tool for corrosion research and is well suited for the identification of complex mechanisms. However, data analysis remains difficult in the case of pitting studies, which can be described schematically as n anodic sites in parallel at different states of evolution. In this work we report on EIS analysis performed on a single pit (Fig. 1a) in order to describe the various step of its evolution as a function of time, but also as a function of various parameters such as the chloride ion concentration or the corrosion potential. Single pits were obtained by studying the breakdown of the passive film using the pumped-micropipette delivery/substrate collection (Pumped-MD/SC) mode of scanning electrochemical microscopy (SECM). A detailed mechanism is proposed to account for EIS results obtained on a single pit (Fig. 1b) in order to explain results on usuals EIS measurements.[1] J. Yang, J. Wu, C. Y. Zhang, S. D. Zhang, B. J. Yang, W. Emori et J. Q. Wang, « Effects of Mn on the electrochemical corrosion and passivation behavior of CoFeNiMnCr high-entropy alloy system in H2SO4 solution », Journal of Alloys and Compounds, 819, avril 2020, p. 152943, https://doi.org/10.1016/j.jallcom.2019.152943[2] Camila Boldrini Nascimento, Uyime Donatus, Carlos Triveño Ríos et Renato Altobelli Antunes, « Electronic properties of the passive films formed on CoCrFeNi and CoCrFeNiAl high entropy alloys in sodium chloride solution », Journal of Materials Research and Technology, 9, no 6, novembre 2020, p. 13879-92, https://doi.org/10.1016/j.jmrt.2020.10.002[3] Mengjiao Li, Qingjun Chen, Xia Cui, Xinyuan Peng et Guosheng Huang, « Evaluation of corrosion resistance of the single-phase light refractory high entropy alloy TiCrVNb0.5Al0.5 in chloride environment », Journal of Alloys and Compounds, 857, mars 2021, p. 158278, https://doi.org/10.1016/j.jallcom.2020.158278 Figure 1

Friction and Wear Mathematical Modeling and Optimization Design of Surface Microstructure Parameters of Unfolding Wheel based on Experiment and Numerical Simulation

Objective: In order to improve the friction-increasing and wear-reducing performance of the unfolding wheel surface, the surface microstructure of the unfolding wheel used in the detection of 8 kinds of steel balls was optimized by parameter matching. Method: Firstly, based on Hertz's theory, the contact area between steel balls of different sizes and the unfolding wheel are analyzed. The wear depth model is established based on Archard adhesive wear model. Secondly, the appropriate microstructure parameters for friction and wear experiments were selected. The finite element analysis software is used to simulate the stress on the surface of the microstructure unfolding wheel and calculate the wear depth. According to the experimental results, the relationship between friction coefficient, wear depth and microstructure parameters is obtained by data fitting, and the objective function of optimization design is established. Finally, based on the genetic algorithm DNSGA-II and Python, the parameters are optimized, and the optimal solution is obtained by using the TOPSIS method. Results: The feasibility of the simulation method is verified by friction and wear experiments, and the correctness of the optimization method is verified. Some existing patents on friction and wear of microstructure surfaces are introduced, and the future development of this field is prospected Conclusion: The research shows that the optimal parameters matching of microstructure for steel ball diameters of Ф16.6688 mm~Ф22.2250 mm: the shape is rhombus; the area of a single pit is close to the contact area, which is 0.0319 mm2 ~ 0.0554 mm2; the pit depth is 145 μm~150 μm, and the surface density of microstructure is (5.4~5.6) /mm2.

Selective Initiation of Corrosion Pits in Stainless Steel Using Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is a useful technique for determining variations in corrosion behavior across a surface. However, the numerous options for experimental parameters and little understanding of their effect on the corroding system render comparisons of results between studies difficult. Herein, we explore changes in corrosion behavior of two martensitic stainless steels, a cast CA6NM and a wrought S41500, as a result of the chosen experimental parameters, including scan rate, approach potential, surface oil immersion, and tip aperture diameter. The study demonstrates that these experimental parameters can be controlled to probe oxide passivation kinetics and single pitting events by changing the surface state and cathodic currents. We measured the pitting and repassivation kinetics of a single pit and determined the compositional change of the Al2O3 inclusion site initiation point. Hundreds of data points were measured within 17 h of experimental time on the stainless steel samples, allowing statistical averages of corrosion and pitting values. This work will open new avenues for fine-tuning various corrosion aspects at the microscale, thereby contributing to a deeper understanding of the corrosion processes and mechanisms of diverse materials.

Refractory Central Serous Retinal Detachment in the Presence of Optic Disc Pit – Case Report

Among congenital optic disc anomalies are megalopapilla, optic nerve aplasia and hypoplasia (de Morsier’s syndrome) and optic disc excavations. The latter are attributed to abnormal fetal fissure’s closure. There is a wide spectrum of these anomalies ranging from single optic disc pit, to multiple pits, to morning glory syndrome. Excavated defects of the optic disc are usually associated with retinal detachment in the macular region. It is usually confined to the macular region though a subtotal or total retinal detachment may occur. It requires treatment (a surgical approach in most cases) though a spontaneous resolution of the subretinal fluid within a short period of the detachment onset has been observed. We report a case of unilateral central serous retinal detachment in the presence of a bilateral optic disc pit refractory to primary treatment.

Single-Bubble Cavitation-Induced Pitting on Technical Alloys

Repeated single cavitation bubble experiments were performed primarily on 316L stainless steel, and some on nickel–aluminum–bronze (NAB) and pure aluminum. The bubble dynamics were recorded with two high-speed cameras and correlated with surface images, also acquired in situ. These experiments were performed for a range of stand-off distances γ (the ratio of the distance of the solid surface from the bubble to the bubble’s maximum radius) from 0.3 to 2.15. For all stand-off distances, single pits were the only surface change detected at the beginning of damage formation. Later phases of the collapse are not axisymmetric but show regions of “stronger” collapse, and the pits occur on the material underneath those regions. For γ < 0.4, the damage is attributed to the second collapse. For γ > 0.4, the first bubble collapse is most likely responsible for pitting. Shock-wave emission was detected from the collapse regions that were linked to the damage. On 316L, the pitting rate was found to be linearly dependent on the bubble radius, indicating a non-zero lower limit for the bubble radius below which pits do not occur. In terms of stand-off distance, the pitting rate (defined here as average pits per bubble) was non-monotonic, with maxima for bubbles initiated closest to the sample (γ = 0.3) and at γ = 1.4.

Structural displacement and deformation of adjacent shield tunnel induced by foundation pit excavation

Excavating a foundation pit close to a tunnel will unavoidably impact the nearby soil, causing the tunnel to shift and deform. Examining the longitudinal displacement and convergence deformation of a nearby shield tunnel during foundation pit excavation is crucial for maintaining safe operations. Nevertheless, most of the current research primarily focuses on the effects of a single foundation pit excavation on existing tunnels. This study examines and analyzes the effects of multiple foundation pit excavations on the displacement and deformation of pre-existing tunnels, using a project at a subway station as a case study. By employing the PLAXIS three-dimensional finite element software, a large-scale computational model based on the HS model is established, and then five dangerous working conditions are selected for simulation analysis. The research findings delineate that: (i) The displacement of the tunnel is affected by various factors. These encompass the magnitude of the foundation pit excavation, the positioning of the foundation pit excavation in relation to the tunnel, and the closeness of the tunnel to the foundation pit. (ii) The deformation encountered by the tunnel is largely influenced by external loads, where the scale of the unloading load primarily determines the deformation characteristics of the tunnel.

Fatigue of Bridge Steel Wire: A Corrosion Pit Evolution Model under the Effects of Wind and Vehicles

To investigate the damage evolution behavior of corroded steel wires under the influence of alternating loads, a damage evolution model for steel wires based on the theory of continuous damage mechanics was established. The damage evolution process at corrosion pits was simulated by using the element birth and death technique in ANSYS 2020R2. Then, a certain cable-stayed bridge was chosen as the research subject, the stress–time data of the sling were computed using a traffic–bridge–wind simulation analysis model, and the influence of corrosion pit distribution on the mechanical properties and fatigue life of wires under an alternating load was discussed. The results show that, in comparison to single-pitted steel wires, double-pits distributed circumferentially across the cross-section of the steel wires lead to more severe stress concentration, accelerating the damage evolution process and significantly reducing the fatigue life of the steel wires. Conversely, the stress concentration caused by double pits distributed along the longitudinal direction of steel wire is similar to that caused by single pits, and it will be even weaker than that caused by single pits with the change in the relative distance of the double pits. Based on the calculation results of the damage evolution model of steel wire, it was found that the corrosion pit crack nucleation life of steel wire under alternating load accounts for nearly 80% of the fatigue life of steel wire, and different corrosion pit distribution modes will significantly affect the fatigue life of steel wire.

A comprehensive study on the physicochemical characteristics of faecal sludge from septic tank and single pit latrine facilities in a typical semi-urban Indian town: a case study of Rajasthan, India

Faecal sludge (FS) samples were analysed to assess their characteristics. FS has high chemical oxygen demand, ranging from 4406 to 160 000 mg l−1, influenced by sludge age, sanitation type, and inflow/outflow to onsite sanitation contaminants.

A materials selection framework for fastener-in-panel geometries using FEM and LEFM, to mitigate coating degradation and environmentally assisted cracking

A finite element method (FEM) model was used to determine the potential, current, and current density distributions for a multi-material fastener/hole-in-plate configuration in an atmospheric environment. The plate consisted of bare Pyrowear 675 with or without a ZnNi coating, and the fastener consisted of Ti-6Al-4V with or without an anodization surface treatment. The potential distribution within the fastener hole was the focus of this work, as this region would represent the location of highest stress within the fastener/panel geometry. Separately, existing literature data were augmented by fracture mechanics-based evaluations of the environment-assisted cracking behavior of Pyrowear 675 as a function of electrode potential Pyrowear 675 in 3.0 M NaCl. Combining the fracture mechanics and FEM results allowed for a unified framework which was able to narrow a material selection matrix of 13 total scenarios to three scenarios, in an atmospheric environment of 0.6 M NaCl, specifically. The delayed drying out of occluded regions after the surface electrolyte has been evaporated was accounted for, with only one of the studied material selection combinations able to reduce the crack susceptibility under those conditions. A single pit within the fastener hole was also considered, and it was determined that the size of the pit had a larger impact on the potential than the location of the pit, which will aid in future computational assumptions.

Identification of the Overall Slope Pit Angle Value for Erosion Control in Disposal Land

Open-pit mining can cause changes in environmental conditions, especially in disposal land. The formation of gully erosion on disposal land tends to increase as the area of open land increases. The aim of this research is to calculate the amount of erosion and the geometry of the bench terrace as a form of recommendation for reducing the rate of erosion. The methodology used is the USLE (Universal Soil Loss Equation) method approach in predicting the amount of erosion and an empirical approach in providing recommendations to reduce the rate of erosion for conservation measures in the form of bench terraces. The results showed that the erosion formed on disposal land was 123.43 tons/ha/year with a range of 60-180 tons/ha/year in the category of moderate erosion hazard. While for the dimensions of bench terraces recommended on disposal land, the overall slope pit angle value was 46,60 with a maximum single slope pit angle on the bench of 600 (16.6%). Bench dimensions in the form of bench terraces will have a major influence on the overall slope pit angle value formed. The smaller the width of the bench formed with the single slope pit angle, the greater the value of the overall slope pit angle formed. In addition to the width of the bench that affects the value of the overall slope pit angle is the height of the disposal slope. The height of the disposal slope will be directly proportional to the decrease in the overall pit angle slope, to the number of benches formed. With soil conservation measures in the form of traditional terraces in the form of bench terraces with a value factor of 0.4 in open land without vegetation, it can decrease from 123.43% (tons/ha/year) to 49.37 tons/ha/year ranging from 15-60 tons/ha/year with the category of low erosion hazard level, and or about 39% reduction in erosion that occurs.

Polygonal concave wear and irregular packing behavior of grinding balls for vertical grinding mill

Grinding balls are an indispensable grinding medium in vertical grinding mills, grinding ore powder to target size. Some were severely worn and unrounded by iron ore from Anshan, China, during grinding operation in the vertical grinding mill (VTM-1500, Metso Outotec). Their service failure behavior was explored, based on classifying the wear shapes of the recovered grinding balls, combined with the ore-media operating behavior. The wear mechanism of the unroundness, invagination and the special-shaped reduction was verified by the three-dimensional (3D) wear sizes and position relationships of grinding balls. The main wear model of grinding balls was polygon wear, including pentagon shape and quadrangle shape. The minor wear form was abnormal wear, containing biconvex spindle contour wear and single pit contour wear induced by free wear distribution. Both mainly occurred on the packing protective surfaces, resulting in several normalized final shapes along with the wear progress. This investigation provides a theoretical basis for understanding the interaction behavior among slurry and grinding balls.

Remaining fatigue life assessment of corroded mooring chains using crack growth modelling

Failures caused by the combined actions of fatigue, corrosion and wear are important safety concerns for mooring chains used on floating structures in the oil and gas industry. Prediction of remaining corrosion fatigue life based on surface condition could therefore be a useful tool for the continued safe operation of corroded chains. This paper investigates the use of crack growth modelling for estimating the remaining corrosion fatigue life of mooring chains that exhibit significant pitting corrosion damage. A crack growth modelling approach is used to produce remaining fatigue life estimates for a selection of severely pitted mooring chains. Using fatigue crack growth rate test results for grade R4 high strength mooring chain steel, empirical crack growth laws are presented for free corrosion and cathodic protection conditions at load ratio R = 0.1. Two different methods for establishing equivalent cracks from surface scans of corrosion damage are presented. The mooring chains are proof loaded as part of their manufacturing process. Residual stresses introduced during this process have therefore been determined by finite element analysis and accounted for in the fatigue crack growth predictions. One of the equivalent crack models, accounting for the single dominant corrosion pit, provided quite accurate fatigue life predictions when compared with full scale test results.

Elite chariots and early horse transport at the Bronze Age burial site of Shijia

Horses and chariots played a crucial social, cultural and military role in the emergence and development of early states in China. Little research, however, has explored the life histories of individual chariot horses or assessed their role as working animals. Here, the authors present a detailed zooarchaeological and palaeopathological study of eight adult male horses, used for pulling chariots, recovered from a single chariot-horse pit at the burial site of Shijia in north-western China. The characterisation of key osteological differences between chariot horses and ridden horses is offered as a contribution to the toolkit available for the archaeological investigation of human-horse interactions around the globe.

Analysis of the flexural response of hybrid reinforced concrete beams with localized reinforcement corrosion

AbstractThis paper presents a modeling approach to analyze the flexural response of hybrid reinforced concrete beams with localized corrosion. A new mechanical model based on extensive uniaxial testing is proposed to describe the stress–strain relationship of corroded bars with a single pit. The proposed mechanical model is then incorporated into a sectional analysis to determine the moment curvature relationship of hybrid reinforced concrete sections with pitting corrosion. The actual crack pattern is used to divide a beam into discrete hinge elements which are then combined to compute the load–deflection response of statically determinate beams. The modeling approach is evaluated with available experimental data showing good predictive capabilities. A parametric study revealed the importance of the interaction between the tensile reinforcement ratio and the concrete postcracking residual stress. Furthermore, the deformation capacity of reinforcement bars with pitting corrosion levels beyond 0.25 was shown to have a dominant effect on the ultimate deflection of hybrid reinforced concrete beams.

Multidisciplinary analysis of pit craters at Hale Crater, Mars

Pit craters are circular to subcircular depressions that lack a rim and ejecta layer and typically have a conical shape. There are several mechanisms that can explain the formation of such depressions and they are associated with collapse due to the removal of subsurface material. Possible origins of pit craters include: volcanic processes (collapse of lava tubes, magmatic chambers, intrusion of dikes), karstic dissolution, extensional faulting or volatile processes.In this work, we study pit craters in the north-estern external slope of Hale Crater. We identified >40 pit craters that present unique morphological features in association with different landforms associated with volatile activity in the area. We identified moraine like ridges, gullies and aprons together with pits that represent an interesting suite of landforms. After producing a detailed geomorphic map, we classified the pits into: i) single pit craters, ii) chain pit craters, iii) complex pit craters and iv) elongated pit craters.We used DTMs to determine orientation and slopes of the pit craters-hosting terrains and to analyze elevation profiles of the different types of pits and their relation with the gullies and other features. In addition, we performed a spectral analysis using CRISM multispectral dataset in order to characterize the mineralogy of the sediments in the region and to identify any distinctive properties that could promote the formation of these depressions.Here, we propose that pit craters are stratigraphically on top of the ice-related landforms and present complex relationships with the gullies. The spatial relationship between the pits and these structures, along with the absence of evidence of present or past volcanic activity and the lack of evidence of any extensional faulting allows us to propose that the origin of the pit craters in the study area might be related to some volatile process. We propose here that these particular pit craters at Hale crater, are morphologically similar to Icelandic depressions located in a glacial environment. We conclude that the landforms found in the area are in close relation with glacial or periglacial conditions and pit craters might be formed by sublimation/melting of ground ice.

Effects on stone cell development and lignin deposition in pears by different pollinators.

The pear pulp is formed by the development of the ovary wall, which is the somatic cell of the female parent, and its genetic traits are identical to those of the female parent, so that its phenotypic traits should also be identical to those of the female parent. However, the pulp quality of most pears, especially the stone cell clusters (SCCs) number and degree of polymerization (DP), were significantly affected by the paternal type. Stone cells are formed by the deposition of lignin in parenchymal cell (PC) walls. Studies on the effect of pollination on lignin deposition and stone cell formation in pear fruit have not been reported. Methods: In this study, 'Dangshan Su' (P. bretschneideri Rehd.) was selected as the mother tree, while 'Yali' (P. bretschneideri Rehd.) and 'Wonhwang' (P. pyrifolia Nakai.) were used as the father trees to perform cross-pollination. We investigated the effects of different parents on SCCs number and DP, and lignin deposition by microscopic and ultramicroscopic observation. The results showed that the formation of SCCs proceeds was consistent in DY and DW, but the SCC number and DP in DY were higher than that in DW. Ultramicroscopy revealed that the lignification process of DY and DW were all from corner to rest regions of the compound middle lamella and the secondary wall, with lignin particles deposited along the cellulose microfibrils. They were alternatively arranged until they filled up the whole cell cavity to culminate in the formation of stone cells. However, the compactness of the wall layer of cell wall was significantly higher in DY than in DW. We also found that the pit of stone cell was predominantly single pit pair, they transported degraded material from the PCs that were beginning to lignify out of the cells. Stone cell formation and lignin deposition in pollinated pear fruit from different parents were consistent, but the DP of SCCs and the compactness of the wall layer were higher in DY than that in DW. Therefore, DY SCC had a higher ability to resist the expansion pressure of PC.

Mechanistic Model with Empirical Pitting Onset Approach for Detailed and Efficient Virtual Analysis of Atmospheric Bimetallic Corrosion.

A mechanistic model of atmospheric bimetallic corrosion with a simplified empirical approach to the onset of localized corrosion attacks is presented. The model was built for a typical bimetallic sample containing aluminum alloy 1050 and stainless steel 316L sheets. A strategy was developed that allowed the model to be calibrated against the measured galvanic current, geometrical corrosion attack properties, and corrosion products. The pitting-onset simplification sets all pits to be formed at a position near the nobler metal and treated all pits as being of the same shape and size. The position was based on the location of the highest pitting events and the pit attributes on an average of the deepest pits. For 5 h exposure at controlled RH (85%, 91%, and 97%) and salt load (86 μg NaCl/cm2), the model was shown to be promising: both for analysis of local bimetallic corrosion chemistry, such as pH and corrosion products, and for efficient assessment of pitting damage by computing a single largest pit depth. Parametric studies indicated that the pitting-onset approximation deviated the most at the beginning of exposure and when RH was below 91%.

Determination of the Influence of the Disturbance Caused by Traversing Cross-Type Deep Foundation Pit Excavations

Accurately recognizing the influence of excavation disturbance on the traversing cross-type deep foundation pit of the subway, determining the active range of the disturbance, and reasonably arranging the structure within its range can effectively ensure the safety of the project and save resources to achieve the goal of sustainable development. A three-dimensional model was established using the soil small strain hardening model to examine the subway deep foundation pit project in the CBD (central business district) core area of Fuzhou Coastal New City, where the soil is mainly soft soil with high natural water content, high compressibility, and weak permeability. The model was verified against the theoretical solution of Melan, and the deformation characteristics of the cross-asymmetric foundation pit excavation were analyzed. The results show that, due to repeated disturbance from excavation and unloading between the foundation pits, the soil arching effect, and changes in the boundary conditions, the structure at the intersection and the surrounding soil interact. The horizontal displacement of the retaining structure and the surrounding surface settlement are quite different from those observed from a single foundation pit excavation. For instance, the maximum horizontal displacement of profile 1-3 in Zone I decreases by 26.1%, while the maximum horizontal displacement of profile 1-1 in Zone II increases by 20.4%, and the maximum surface settlement around the profiles also has similar characteristics. The disturbance on the retaining structure and soil in different areas at the intersection can be divided into positive and negative effects. The active range of the “disturbance influence zone” is determined: the foundation pit of Metro Line 6 is 3.5 He and the foundation pit of Metro Line F1 is 3.0 He. Finally, the influence of changes in the groundwater level on the active range of the “disturbance influence zone” is discussed.