Pit Depth Research Articles

Rockburst criterion and evaluation method for potential rockburst pit depth considering excavation damage effect

Excavation-induced disturbances in deep tunnels will lead to deterioration of rock properties and formation of excavation damaged zone (EDZ). This excavation damage effect may affect the potential rockburst pit depth. Taking two diversion tunnels of Jinping II hydropower station for example, the relationship between rockburst pit depth and excavation damage effect is first surveyed. The results indicate that the rockburst pit depth in tunnels with severe damage to rock masses is relatively large. Subsequently, the excavation-induced damage effect is characterized by disturbance factor D based on the Hoek–Brown criterion and wave velocity method. It is found that the EDZ could be further divided into a high-damage zone (HDZ) with D = 1 and weak-damage zone (WDZ), and D decays from one to zero linearly. For this, a quantitative evaluation method for potential rockburst pit depth is established by presenting a three-element rockburst criterion considering rock strength, geostress and disturbance factor. The evaluation results obtained by this method match well with actual observations. In addition, the weakening of rock mass strength promotes the formation and expansion of potential rockburst pits. The potential rockburst pit depth is positively correlated with HDZ and WDZ depths, and the HDZ depth has a significant contribution to the potential rockburst pit depth.

Fracture prediction of corroded ZG300-500H cast steel with micromechanical fracture model

The effects of corrosion on the fracture prediction of steel are investigated. The power function for cast steel ZG300-500H in the acetic acid salt spray corrosion environment is fitted to illustrate the acceleration of the acetic acid salt spray corrosion test, and the statistical characteristics of the pit depth and pit diameter-depth ratio are analyzed. The material parameters of micromechanical fracture model under monotonic load are calibrated by tensile test and finite element analysis on smooth-notch tensile specimens. The VGM model and SMCS model can also be applied to predict the fracture of corroded ZG300-500H cast steel based on the random distribution model of corrosion pits. The finding is that the crack of the non-corroded single-notch specimens always initiates from the centre of the critical cross section. Corroded specimen cracks initiate from the severe corrosion areas. Once a crack is initiated, it always extends along the thickness and forms a visible crack. The subsequent crack propagation along the width direction can be simulated accurately.

Influence of structural defects toward the nickel-catalyzed etching behaviors of synthetic diamond

Diamond is an attractive material for next-generation wide-bandgap devices, while the top-down processing is very challenging due to its stable chemical and physical properties. Although the metal-catalyzed diamond etching process is quite promising to fabricate different atomic-flat surface structures, a clear understanding on the influence of various defects on the catalytic behaviors is so far missing. Here, metal-catalyzed (nickel (Ni), as the prototype) etching process of the synthetic diamond is investigated by electron microscopy. Our quasi in-situ observations showed that the Ni-catalyzed diamond etching behavior is lattice plane-dependent and the Ni nanoparticles (NPs) prefer to slide along the 〈110〉 orientations on the {111} surface. Moreover, the size, density and depth of the etching pits can be effectively modulated by the boron-doping level. The lateral movement of Ni NPs can be restricted by the planar defects, resulting in a larger etching rate along the twin planes/stacking faults. The grain boundaries of diamond were observed to act as a fast diamond-to-graphite transformation route. These results provide deep insights into the understanding of the role of defects in metal-catalyzed diamond etching, and could act as the basement of controllable etching in the diamond-based semiconductor industry.

A new method for constructing three dimensional rough surface topography with expected bearing capacity

Surface bearing ratio tp(c) or tp curve is often used to evaluate the bearing contact performance of rough surfaces, but currently it is difficult to invert the surface topography with the expected surface bearing ratio tp(c). Combining the definition of tp curve and the key coefficients in random process theory, roughness characteristic parameters (RCP) that directly regulate tp curve are found out to provide parameters for the active design model with expected tp(c). By calculating the surface height matrix satisfying the expected tp(c) and RCP with genetic algorithm, the active design method of surface topography gets constructed. Surface tp curves of grinding, shot peening, barrel finishing and active design are compared to verify the reliability of the method and the versatility of RCP. The results show: 1) RCP of tp curve are Sa (arithmetic mean height), Sq (root mean square height), Ssk (skew), Sku (kurtosis), Sp (maximum peak height) and Sv (maximum pit depth); 2) The surface topography of the expected tp(c) is basically consistent with the measured tp curve. The maximum relative errors of tp(c) and Sa are 5%, 1%, respectively. And the average relative errors are only 1.4% and 0.5%. The regulatory parameters influence in RCP on the surface bearing capacity is ranked as follows: Sa, Ssk, Sku, Sv, Sp. The new active design model provides method for constructing the expected bearing capacity surface and roughness interface mechanics’ study.

Concrete erosion mechanism and model research under the action of wind gravel flow in Gobi gale area

The surface covering of the Gobi gale area (GGA) primarily consists of medium-coarse sand and gravel, which can easily form a strong wind gravel flow (WGF) under the impact of high winds. Throughout the year, concrete bridge piers are exposed to WGF environments leading to severe erosion damage to their surface. This study investigates the influence of different gravel erosion parameters on concrete erosion wear (CEW) properties investigated through indoor erosion tests. It demonstrates that the concrete erosion rate (CER) initially increases and stabilizes over time. The higher the concrete strength class, the stronger its ability to resist erosion wear. The CER increased with the gravel attack angle and gravel flow. The erosion wind speed positively correlated with the CER, with a speed index between 2.13 and 2.96. When the gravel flow rate was the same, the mass loss of concrete primarily originated from the impact of small gravel. Although the size and depth of the erosion pits on the concrete surface are large under the impact of large-sized gravel, the mass loss is small. In addition, based on the bitter-deformation wear theory and the Oka erosion model, a concrete erosion model suitable for the WGF in Gobi was established. This study provides significant guidance for the protection and quality assurance of concrete structures in GGA.

Culicoides dokdoensis, sp. nov. (Diptera: Ceratopogonidae): A new biting midge species from Dokdo Island, Republic of Korea

AbstractRecent molecular approaches toward insect taxonomy are revealing cryptic diversity within biting midge genus Culicoides Latreille, 1809. A new biting midge species was collected from highly restricted area of Dokdo Island, East Sea of the Republic of Korea, and was identified as Culicoides dokdoensis, sp. nov., based on morphological characters and DNA barcoding. The specimens collected from the island were previously known as Culicoides circumscriptus Kieffer, 1918, a cosmopolitan blood‐feeder, due to its morphological similarity. However, the specimens from Dokdo Island can be distinguished from other congeners by the following characters: more curved arms in male aedeagus, wing spot pattern, sensory pit depth, and absence of a spermatheca neck in female. In addition, mitochondrial cytochrome c oxidase I sequence exhibited substantial genetic difference compared to C. circumscriptus populations from the Korean Peninsula, sufficiently supporting the genetic differentiation between the two species. The discovery of this cryptic species highlights the necessity of integrated taxonomy for Culicoides.

Impact of Desulfovibrio ferrophilus IS5 biocorrosion time on X80 carbon steel mechanical property degradation

Three different incubation times (7, 14 and 21 d) were used to immerse X80 carbon steel dogbone coupons in deoxygenated enriched artificial seawater at 28 °C inoculated with Desulfovibrio ferrophilus (strain IS5), a very corrosive sulfate reducing bacterium to cause microbiologically influenced corrosion (MIC). It was found that 21 d immersion had the largest weight loss (24.8 mg cm−2 equivalent to 0.55 mm/year corrosion rate), smallest sessile cell count (6.8 × 108 cell/cm2), deepest pit depth (30.6 μm), and most severe mechanical degradation (9 % loss in ultimate strength and 18 % loss in ultimate strain). Due to nutrient depletion in the static incubation system, corrosion rate and sessile cell count were the highest at 0.82 mm/year and 1.1 × 109 cell cm−2, respectively at 7 d. The results from scanning electron microscopy, X-ray photoelectron spectroscopy and confocal laser scanning microscopy analyses and electrochemical corrosion measurements supported the sessile cell counts and biocorrosion weight loss data.

Potential application of foveal structural measurements in treatment decision for retinopathy of prematurity: an OCT-based study

PurposeTo investigate foveal changes in infants with ROP not requiring treatment(nROP) and ROP infants needing treatment (tROP) using a handheld SD-OCT device.MethodWe performed horizontal SD-OCT scans through the fovea in 156 eyes of 81 infants diagnosed with ROP. Foveal immaturity indices including the presence of inner retinal layers (IRL), absence of foveal outer nuclear layers widening (ONL) and attenuation of hyperreflective outer segment layers (OS), presence and type of cystoid macular edema (CME), epiretinal membrane (ERM), foveal pit depth (FPD), foveal pit width (FPW) and central foveal thickness (CFT) were calculated. The multivariate logistic regression model was used to predict the need for treatment based on OCT measurements.ResultsThe shape of the foveolar pit was not significantly different among tROP and nROP groups (P-value = 0.287, Chi-square test). IRL extrusion was incomplete in both tROP and nROP groups (P-value = 0.0.41, Chi-square test). Nevertheless, the presence of thicker IRL was more frequent in the nROP group in comparison with the tROP group (100% vs.64.8%, P-value = 0.001). CME was observed in 29% of eyes in the tROP group and 40% of eyes in the nROP group; however, this difference was not statistically significant (P-value = 0.32, Chi-square test). ERM was detected in 15 (75%) and 84 (65.6%) eyes in the nROP and tROP groups, respectively (P-value = 0.39, Chi-square test). Multivariate logistic regression analyses showed that the need for treatment was significantly associated with gestational age (GA), CFT and FPD (P-values 0.001 and 0.002 respectively).ConclusionsThis study demonstrated GA, foveal pit depth and the central foveal thickness could accurately predict the need for treatment with sensitivity, specificity, and diagnostic accuracy of 97%, 65% and 91.7% respectively.

A method to calculate seismic behavior of a corroded beam-to-column joint considering distribution randomness of corrosion depth

When conventional uniform corrosion method and equivalent material property method are applied to predict the seismic performance of corroded steel beam-to-column joints, distribution randomness of corrosion depth can't be considered, once damage occurs at a position where there is a large corrosion pit, there will be a great error between the actual damage and the damage predicted by the two methods. The current work aims to overcome this problem. Firstly, accelerated corrosion test was conducted on mild steel coupons. Secondly, topography of the corrosion pits was scanned, and distribution characteristic of the corrosion depth was obtained. According to the distribution characteristic, a FE modeling method (namely, stochastic corrosion method) that considers distribution randomness of the corrosion depth was proposed. The proposed method, together with uniform corrosion method and equivalent material property method were then applied on the seismic performance prediction of a corroded steel beam-to-column joint. The results show that 1) The depth of the corrosion pits on the specimens subjected to accelerated corrosion approximately obeys lognormal distribution. 2) The corroded steel beam-to-column joints' hysteretic behavior predicted by stochastic corrosion method is more accurate than those predicted by the other two methods. Compared with uniform corrosion method, the maximum calculation accuracy improvement of stochastic corrosion method can reach 90%. 3) The reason which leads to prediction error of uniform corrosion method is that localized buckling of some positions on the structural member is overlooked, while the reason leads to prediction error of equivalent material property method is that the kinematic hardening parameter C is assumed to increase with the increase of corrosion time period. Both the prediction errors of the two methods increase with the increase of corrosion time.

Study of short-term corrosion behavior of Q345 steel in marine atmospheric environment

This work studied the corrosion behavior law of Q345 steel exposed to 120 days in Qingdao marine atmospheric environment and the differences in corrosion behavior between the sunlit and shaded sides. The corrosion behavior law of Q345 steel was studied in detail by using weight loss method, electrochemical test, SEM, XRD and ultra-depth microscope. We found that the weight loss curve of Q345 steel under short exposure time still conforms to the power function form, and the corrosion rate increases in the early stage (15 d, 30 d) and decreases in the later stage. The change trend of polarization resistance (Rp) and corrosion current density (Icorr) obtained by electrochemical test corresponds to it. There are significant differences in the morphology and phase composition of the corrosion products of Q345 steel sunlit and shaded sides. On the one hand, the color of the rust layer is not the same, and the rust layer of the shaded side is loose and easy to fall off, and the corrosion is more serious. The three-dimensional morphology map after rust removal showed that Q345 steel had obvious local corrosion in the early stage of corrosion, and the depth of the corrosion pit on the shaded side was greater than that on the sunlit side. On the other hand, the ratio of (β + s)/γ * on the shaded side was greater than that on the sunlit side, and the protection ability of the rust layer on the shaded side was weak. The corrosion characteristics of Q345 steel are different between the sunlit side and the shaded side, and the corrosion of the shaded side is more serious. In engineering applications, we should consider the consequences of this phenomenon.

Influence of Sulfate-Reducing Bacteria on Corrosion Behavior of EQ70 High-Strength Steel

This work examines corrosion behavior of EQ70 high-strength steel under anaerobic conditions in artificial seawater containing sulfate-reducing bacteria (SRB). Polarization and electrochemical impedance spectra (EIS) tests were conducted. The results reveal that corrosion rate initially decreased at the beginning of immersion. However, as the immersion time progressed, the corrosion rate of the high-strength steel increased, attributed to SRB reproduction. The scanning electron microscopy (SEM) results demonstrate that the corrosion was more severe in artificial seawater containing SRB compared to that of seawater without SRB. The morphologies of confocal laser scanning microscopy (CLSM) demonstrate that, after 15 days of immersion, the average depth of the corrosion pits on the sample in the artificial seawater containing SRB was nearly double that of the sample in the SRB-free seawater.

Electromagnetic-Actuated Soft Tactile Device Using a Pull–Push Latch Structure

Tactile devices composed of tactile pixels enable dynamic formulation of surface morphological features. It however remains a challenge for soft tactile devices to reliably achieve low-power control of each tactile pixel while maintaining high spatial resolution. In this paper, we proposed a novel pull-push latch structure and developed a programmable electromagnetic-actuated soft tactile device. Each tactile pixel of the device is individually controlled by a coil. The pull-push latch structure is capable of maintaining the pit depth of tactile pixels without energy consumption. By simultaneously controlling the current direction and on-off state of multiple coils, our tactile device with 3 mm spatial resolution can reliably form different tactile patterns. The energy consumption of a single coil is 59.15 mJ in a 6-s work cycle, which is about 0.34% of that of the tactile device without the latch structure. The user study indicates that the average discrimination accuracy of different patterns rendered by our tactile device is greater than 81%.

A Strain Transfer Model for Detection of Pitting Corrosion and Loading Force of Steel Rebar with Distributed Fiber Optic Sensor.

Steel rebar corrosion is one of the predominant factors influencing the durability of marine and offshore reinforced concrete structures, resulting in economic loss and the potential threat to human safety. Distributed fiber optic sensors (DFOSs) have gradually become an effective method for structural health monitoring over the past two decades. In this work, a strain transfer model is developed between a steel rebar and a DFOS, considering pitting-corrosion-induced strain variation in the steel rebar. The Gaussian function is first adopted to describe the strain distribution near the corrosion pit of the steel rebar and then is substituted into the governing equation of the strain transfer model, and the strain distribution in the DFOS is analytically obtained. Tensile tests are also conducted on steel rebars with artificially simulated corrosion pits, which are used to validate the developed model. The results show that the Gaussian function can be used to describe the strain variation near a corrosion pit with a depth less than 50% of the steel rebar diameter, and the strain distribution in the DFOS analytically determined based on the developed strain transfer model agrees well with the tensile test results. The corrosion pit depth and loading force in the steel rebars estimated based on the proposed model agree well with the actual values, and therefore, the developed strain transfer model is effective in detecting pitting corrosion and loading force in steel rebars.

Prediction of Crack Width in RC Piles Exposed to Local Corrosion in Chloride Environment.

A novel prediction model for crack development of reinforced concrete (RC) piles with localized chloride corrosion in the marine environment is proposed. A discrete method is used to solve the corrosion pit radius model and a crack extension model is developed to investigate the initiation and extension of cracks. The maximum corrosion degree of the reinforced concrete pile is predicted according to the limit crack criterion, and finally, a sensitivity analysis is carried out on the important parameters of crack extension. The results show that the radius of the corrosion pit, the depth corrosion pit, and the cross-sectional area loss of reinforcement gradually increase as the corrosion level increases. The loss of the local reinforcement section at crack initiation increases with the increase in the ratio of concrete cover to initial diameter and increases with the increase in the pitting factor. The required pit depth for reinforcement cracking increases with the increase in the ratio of concrete cover thickness to diameter. The loss of the cross-sectional area of reinforcement and the radius of the corrosion pit increase with the increase in the initial diameter of reinforcement. Increasing the pitting factor can reduce the pit depth and make the crack width develop faster before reaching the limit crack width. Increasing the concrete cover thickness can provide an improvement in the propagation of cracks. A comparative analysis shows that the localized corrosion pattern is more in conformity with marine engineering practice.

FEATURES OF GEOMORPHOLOGY STRUCTURE OF THE GNIVAN GRANITE QUARRY (VINNYTSIA REGION)

The Hnivan granite quarry is located in Vinnytsia district of Vinnytsia region. Geomorphologically, territory belongs to the western edge of the Dnieper Upland. Geostructurally, the quarry is located on the western edge of the Ukrainian shield, within the Podilsky megablock. Since the beginning of development, 7 rock horizons have been fully opened. As of today, the 8th horizon is being developed, and the development of the 9th horizon is planned in the future. The Hnivan quarry is a deep polygonal trapezoidal quarry in plan with many steps in profile. Morphometric characteristics of the Hnivan quarry and dump complex: the maximum length from north to south (including dumps of overburden strata) is 1 800 m; the maximum length of the quarry pit from north to south is 1 400 m, the maximum width from west to east is 900 m. The absolute heights within the mining are 230–255 m, the absolute height of the mine floor is 130 m. The depth of the quarry pit is currently about 105 m. The bottom is 97 meters below the level of the Southern Buh river. Quarry landforms are divided into produced relief forms, caused by anthropogenic denudation and bulked relief forms, created as a result of anthropogenic accumulation. The produced relief of the Hnivan quarry is represented by the bottom and walls. The bottom has a complex geometric shape of an elongated polygon from north to south. It consists of the bottom of the seventh developed horizon and the eighth horizon, where mining operations are carried out. Between these horizons, there is a step 15 m high. The surface of the bottom is flat, there are no internal dumps. The walls of the quarry are characterized by a multi-step shape in profile. They are approximately the same in height, steepness and nature of the processes. The structure of the walls in the upper parts, which are represented by ledges of overburden horizons, is different. The ancient steps of the mine walls are significantly disturbed by weathering, water erosion and gravitational processes. The produced relief forms of the quarry are represented by overburden dumps and processing plant dumps. All of them are located outside the quarry and are external dumps. Dumps of overburden strata are recultivated - stable and artificially forested. This example of carrying out reclamation works of a part of the quarry and dump complex can be a model for the improvement of anthropogenically disturbed territories. Key words: granite quarries; geomorphological structure; excavated relief; heaped relief; Hnivan.

Experimental study on the effect of water absorption level on rockburst occurrence of sandstone

To investigate the mechanism of rockburst prevention by spraying water onto the surrounding rocks, 15 experiments are performed considering different water absorption levels on a single face. High-speed photography and acoustic emission (AE) system are used to monitor the rockburst process. The effect of water on sandstone rockburst and the prevention mechanism of water on sandstone rockburst are analyzed from the perspective of energy and failure mode. The results show that the higher the absorption degree, the lower the intensity of the rockburst after absorbing water on single side of sandstone. This is reflected in the fact that with the increase in the water absorption level, the ejection velocity of rockburst fragments is smaller, the depth of the rockburst pit is shallower, and the AE energy is smaller. Under the water absorption level of 100%, the magnitude of rockburst intensity changes from medium to slight. The prevention mechanism of water on sandstone rockburst is that water reduces the capacity of sandstone to store strain energy and accelerates the expansion of shear cracks, which is not conducive to the occurrence of plate cracking before rockburst, and destroys the conditions for rockburst incubation.

Crystallographic orientation-dependent corrosion behavior of aluminum under residual stress

The role of residual stress in the crystallographic orientation-dependent corrosion behavior of Al at the pit initiation and propagation stages was investigated. A clear correlation between step dissolution of Al, the crystallographic orientation of Al, and residual stress was experimentally and theoretically demonstrated. Al atoms exhibit sequential dissolution behaviors, resulting in step configuration of the surface. Residual stress can slightly restrain or promote pit nucleation at the pit initiation stage, depending on its sign. However, on the step surface, residual stress is a primary factor that can decrease and increase the dissolution rates of atoms up to 10% during the pit propagation stage, regardless of the crystallographic orientation. Neighboring coordination numbers and distance between atoms were measured to elucidate the effects of crystallographic orientation and residual stress on the corrosion behavior of Al. Results of the work function and density of states calculations were adequately consistent with each other and supported the experimentally determined pit density and depth behaviors.

Tribological and dynamic performance analysis of rolling bearings with varied surface textures operating under lubricant contamination

This study aimed to evaluate the ability of textured rolling bearings to capture and store contaminants in a lubricant-contaminated state. Cylindrical thrust roller bearings (CTRBs) were selected for investigation, and circular textures were prepared on the bearing raceway surface using laser etching. The effects of pit location, diameter, depth, and area density on the tribological and dynamic performance of rolling bearings operating in a contaminated environment were examined. Results showed that adding texture only to the shaft washer raceway improved friction reduction and dynamic performance. Additionally, carefully designed textures could suppress vibration energy in the medium and high frequency bands of the bearing. Notably, the ability of the texture to capture contaminants was directly influenced by the diameter and area density of the pits. Furthermore, the relationship between the pits' depth and wear reduction capacity was closely linked to their diameter.

Justification of the innovative design of the skip winch with a body moved by a counterweight gravity drive

The article has to grapple with the problem of creating an economically efficient and environmentally friendly technological process for a development of solid minerals in open-pit mining. In many mining countries of the world today, the depth of many open pits is already 400–600 m or more. At the same time, the cost of transporting 1 ton of rock mass when operating a quarry whose depth is 400 m is 65–70 % of the total cost of extracting 1 ton of minerals. The object of research is technical devices for transport of rock masses in the technological process of development of solid useful deposits in open pit mining. The main reasons are the need to construct transport routes for them by withdrawing the sections of the rock mass on above them, as well their lifting capacity is limited because of they all do use highly energy-intensive machines for transporting rock minerals. In article has been justified a skip cable winch supplied with a wheels moving along on a railroad way by using only a gravitational counterweight device for transporting rock mass from a place of their formation to Earth surface. There have been created a prototype of a planar skip winch with four cables for practical implement in open-pit mining. The theoretical and experimental investigations of the prototype have being confirmed its performance. The created skip winch will accomplish its performancing without using any energy machines even under adverse climate conditions. Its affected would allow to make an open-pit effectiveness to soar and environmentally do friendly because of there are all but excluded any transport vehicles whether on gasoline or diesel oil

Long-term corrosion of abandoned offshore steel infrastructure

ABSTRACT A common practice in the offshore oil and gas (O&G) industry is to leave abandoned decommissioned pipelines and other steel infrastructure on the seafloor. Decisions about long-term environmental and other impacts and about the possibility of recovery require estimates of the likely long-term rate of deterioration, including corrosion loss and pit depth. These are considered as functions of time and environmental conditions including seawater temperature, dissolved oxygen concentration, salinity, seawater velocity, water pollution, microbiological activity, water depth, calcareous deposition and the effect of burial, all interpreted using established physico-chemical behaviour relevant for long-term exposures. Data for exposures up to some 600 years in seawaters are reviewed. Remaining research gaps and future perspectives of marine corrosion control are briefly discussed. Specific attention is given, by way of an example, to the influence on long-term durability of protective coatings and remnant cathodic protection, both areas in which further research is required.