Hard Spots Research Articles

Geographic distribution, prevalence, and incidence of citrus black spot caused by Phyllosticta citricarpa in Tunisia

AbstractCitrus black spot (CBS), caused by Phyllosticta citricarpa, is an important disease of citrus, an economically important fruit crop worldwide and particularly in Tunisia. CBS was recently detected in Tunisia and this study revealed that it is widespread in the governorates of Nabeul and Sousse. The highest incidence of CBS was found in the Bouargoub region (73.7%), while the lowest was observed in Soliman (25.0%) in the Nabeul governorate. The surveys revealed that CBS affected mainly lemon (Citrus limon). The symptoms of CBS observed were hard spots on fruits, twigs, and leaves, as well as false melanose on fruits. Symptoms were observed in both mature and immature citrus fruits, but disease incidence was higher in mature (97.0%) than that in immature fruits (2.95%). In this study, morphological and molecular identifications confirmed the presence of P. citricarpa. This is the first time that the extent of CBS has been documented in a Mediterranean citrus area.

Dielectric breakdown behavior of ferroelectric HfO2 capacitors by constant voltage stress studied by in situ laser-based photoemission electron microscopy

In situ laser-based photoemission electron microscopy observations with time-dependent dielectric breakdown measurements of TiN/Hf0.5Zr0.5O2(HZO)/TiN ferroelectric capacitors were performed to reveal the dielectric breakdown (DB) mechanism. We succeeded in visualizing the hard DB spots through the top electrode. We found that capacitors with short- and long-lifetime distributions were broken down near and far from the edge of the capacitors, respectively. This indicates that the DB is either topography-dependent or film-quality-dependent. This work demonstrates an effective method of detecting DB in a non-destructive manner to provide an insight for achieving higher endurance HfO2-based ferroelectric capacitors.

Research on the Influence of Pantograph Catenary Contact Loss Arcs and Zero-Crossing Stage on Electromagnetic Disturbance in High-Speed Railway

During train travel, various factors, such as body vibration, uneven contact lines, and hard spots on carbon sliding plates and over electric neutral zones, often lead to brief separation between the pantograph and the contact line, i.e., the pantograph catenary contact loss phenomenon. With the continuous increase in train speed and traction power, the probability of pantograph catenary contact loss occurrences rises with a gradual increase in the energy of electromagnetic radiation, making the pantograph catenary arc a primary source of interference affecting the electromagnetic safety of high-speed railways. Understanding the mechanism, characteristics, and influencing factors of electromagnetic interference caused by pantograph catenary contact loss discharges is of utmost importance for analyzing and resolving on-site equipment interference faults. Our analysis of the physical process of pantograph catenary contact loss reveals that when the distance between the pantograph and catenary is significant and the duration is lengthy, high-voltage breakdown occurs within the pantograph catenary gap as it comes close again after the complete extinguishing of the arc. To investigate the electromagnetic radiation characteristics resulting from high-voltage breakdown discharge arcs in the pantograph catenary contact loss process, we established a laboratory test platform for assessing the electromagnetic disturbance characteristics of high-voltage pantograph discharge. We designed a test procedure utilizing fixed-gap breakdown discharge to evaluate the impact of the arc zero-crossing stage on electromagnetic radiation disturbances. Our research indicates that when the pantograph catenary spacing remains constant, an increase in voltage level leads to an elevation in the current within the discharge circuit, resulting in an increased intensity of impulse radiation generated during pantograph catenary contact loss events. During the moment of gap breakdown, the antenna records the highest amplitude of electromagnetic radiation. Also, during the steady-state arc ignition phase of the pantograph catenary gap, the zero-crossing stage generates pulsed discharge currents within the circuit, accompanied by substantial electromagnetic radiation. As the arc current increases, the zero-crossing time shortens, and the pulse current during the zero-crossing process decreases, accompanied by a reduction in the excited electromagnetic radiation. These observations reveal novel characteristics of electromagnetic radiation disturbances during steady-state arc ignition. The outcomes of our study provide valuable insights that can contribute to our understanding of the characteristics and influencing factors of electromagnetic radiation in pantograph catenary contact loss discharges and offer theoretical guidance for the resolution of pantograph catenary contact loss interference faults.

Latest Developments in the Hardspot Inspection of heavy plates

Hard Spots are local areas with increased hardness on the surface of semi-finished or end products in steel manufacturing. The cause of these hard spots is attributed to effects in the casting or rolling process. In general, the occurrence of hard spots cannot be avoided completely in production of heavy plates. Therefore, in various current line-pipe specifications the topic ‘hard spots’ is discussed and there is actually a strong request for a suitable test method from end users as well as manufacturers of line pipes. The current presentation should give an update on the ongoing developments. Basis of all current approaches are electromagnetic inspection methods, based on the correspondence in between electrical and magnetic material properties and physical hardness. To be able to integrate an inspection into the production process, the so called rolling skin or mill scale, a thin surface layer of different iron oxides with different material properties to the base material, should not influence the inspection results. The inhomogeneities of this rolling skin, especially in conductivity and permeability, normally render standard eddy current inspection impossible. Additionally in the standard production process, the products were handled by large cranes, manipulating the plates by strong magnets. These magnets leave behind a significant residual magnetization. To overcome both problems the method uses a strong alternating magnetization to measure different resulting micro magnetic parameters. By combining these parameters, the mill scale as well as the residual magnetization effects can be minimized, so it gets possible to measure small local hardness variations on the plates. The presented paper describes the actual progress of the inspection method itself including the theoretical background as well as the calibration on artificial hard spots. Furthermore, an outlook will be given to the implementation in an automatic inline inspection system for plate mills.

The Effect of Temperature and Load on the Current Carrying and Erosion Behavior of Metal-Impregnated Pantograph Strip

As an important current-collecting component of the electric locomotive, the pantograph strip may increase its surface temperature due to catenary vibration, friction heat generation, arc burning, catenary hard spots, and other reasons during actual operation. Given the action of electric current, an electrochemical reaction is unavoidable on the contact surface. Under low voltage DC conditions, the influence of temperature and load on relevant electrical and tribological parameters of the pantograph strip was studied using self-developed multi-functional friction and wear tester and changing forward load, surface temperature, etc. The electrochemical reaction was performed at 3.5 wt% NaCl. The results showed that with the increase in temperature, the initial contact resistance, friction coefficient, wear, and corrosion resistance of the surface material of the sample decreased, and the wear amount increased significantly.

Elastic interactions of plastic events in strained amorphous solids before yield

It has been widely accepted that the plastic events of amorphous solids after mechanical yield belong to a highly correlated avalanche state. However, whether the plastic events before yield are correlated or not is still unsettled, leaving their interactions largely unexplored. In this paper, by means of atomistic simulations, typical ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ metallic glasses, as the model system, are sheared under athermal quasistatic limit to study these plastic events. The statistical analysis of both stress drops and waiting times reveals that plastic events before yield are in the correlated avalanche state and the interactions among them are mediated by the robust elasticity. The temporal correlation analysis of the nonaffine displacement fields further reveals that the elastic interactions are short-lived strong but long-standing weak, which results in the fractal morphology of potential energy landscape. By introducing vibrational modes to explore plastic events, we clearly exhibit the way how the elastic interactions organize the Eshelby-type shear transformations into avalanched plastic events. The correlation matrix, with its component being the dot product of the vibrational modes at different configurations, is defined to trace the evolution of vibrational modes during elastic deformation and across plastic events. Three reasons accounting for the robust elasticity are identified: (i) the limited destruction of plastic events on global elasticity, (ii) the persistent hard spots embedded in elastic matrix, and (iii) the self-recovery of elastic matrix during elastic deformation. Our results clarify the atomic-scale nature of both elastic deformation and plastic instabilities before yield in amorphous solids, providing fundamental information for the development of elastoplastic constitutive models.

Forensic Engineering Investigation of Factors Contributing to the Explosion of an International Natural Gas Pipeline

Following the explosion of a natural gas pipeline that resulted in extensive property damage, personal injury, and loss of life, a forensic engineering investigation was performed to determine factors that signifi-cantly contributed to the failure. Metallurgical analysis of the failure region resulted in the conclusion that the pipeline rupture was caused by hydrogen embrittlement acting on hard spots created during manufactur-ing. The next phase of this investigation involved root cause analysis of factors contributing to the pipeline rupture as well as evaluation of missed risk-reduction opportunities of the nondestructive analyses employed. It was ultimately determined that hydrogen embrittlement, caused by improper operation and maintenance procedures, resulted in an overabundance of hydrogen from excessive cathodic protection. Additionally, excessive operating pressure exceeded the resulting degraded ultimate capacity of the pipeline, which then manifested in the rupture of the natural gas pipeline and the ensuing explosion. It is recommended that op-erators exercise due diligence by considering the age of a pipeline when determining appropriate operating, monitoring, and maintenance procedures.

Failure analysis of truck steering knuckle

The steering knuckle of a truck with a load capacity of 22 tons broke during driving, and the wheel fell off; the truck had travelled only 1100 km. The composition, mechanical properties, fracture morphology, and microstructure of the failed parts were investigated. The results showed that the heat treatment of the steering knuckle is standardised. The composition of the raw material meets the relevant standard; however, spot segregation, pores, axial cracks, and inclusions appear in the raw material. Cracks originate from hard spots, which are caused by spot segregation, and surface defects, which are caused by pores. Axial cracks, pores, and inclusions can accelerate crack growth and cause rapid fracture of parts. According to the inspection and analysis results, we propose a product quality inspection and control scheme to the manufacturer.

Biocontrol of Phyllosticta citricarpa by Bacillus spp.: biological and chemical aspects of the microbial interaction

Citrus fruits are the most produced fruits in the world, but they are threatened by several pathogens, including the fungus Phyllosticta citricarpa, the causal agent of citrus black spot (CBS). The fungus affects most citrus species and the infection results in economic losses in citrus-producing areas. This disease causes the aesthetic depreciation of fresh fruit, impairing its commercialization. As an alternative to the use of synthetic fungicides to control the pathogen, the biological control, using bacteria of the genus Bacillus, is highlighted. Such microorganisms enable biocontrol by the production of volatile organic compounds (VOC) or non-volatile. Therefore, this work aimed to evaluate the production of VOC by isolates of Bacillus spp. grown in different culture media; to evaluate the effects of these compounds on the evolution of CBS lesions in orange fruits; to study the effects of VOC on resistance induction in orange fruits; to evaluate the effects of VOC on P. citricarpa morphology in CBS lesions, and to identify the produced VOC. Tryptone soya agar (TSA) and tryptone soya broth (TSB) media used to culture the bacterium resulted in up to 73% pathogen inhibition by VOC. Volatile compounds from Bacillus spp. ACB-65 and Bacillus spp. ACB-73 when cultured in TSB culture medium provided 86% inhibition of freckles that evolved to hard spots. The volatile fractions produced by the bacteria were identified as alcohols, ketones, amines, ethers, aldehydes and carboxylic acids that can serve as arsenal against the phytopathogen. The present work demonstrated the potential of VOC produced by Bacillus spp. in the control of P. citricarpa.

Effect of Intermetallics and Drill Materials on the Machinability of Al-Si Cast Alloys.

The present study was conducted on the machinability of 396 alloy (containing approximately 11% Si) and B319.2 alloy mainly to emphasize the effects of Fe-intermetallics, i.e., α-Fe, β-Fe, and sludge. The results demonstrate that the presence of sludge in the form of hard spots has a significant effect on cutting forces and tool life, in that it decreases drill life by 50% compared to the base alloy. The formation of the α-Fe phase in the M1 base alloy has a beneficial effect on tool life in that this alloy produces the highest number of holes drilled compared to alloys containing sludge or β-Fe; this result may be explained by the fact that the formation of the α-Fe intermetallic, with its rounded Chinese script morphology and its presence within α-Al dendrites, is expected to improve matrix homogeneity via hardening of the soft α-Al dendrites. Increasing the Fe-content from 0.5% to 1% in the 396-T6 alloy containing 0.5% Mn produces a distinct improvement in alloy machinability in terms of cutting force and tool life. The addition of Fe and/or Mn appears to have no discernible effect on the build-up edge area (BUE) and chip shape.

RESEARCH AND EXPERIMENTAL STUDIES OF STRESS-STRAIN STATE OF DISCRETE-CONTINUAL HARDENED MACHINE PARTS

Research and experimental studies of stress-strain state of discrete-continual hardened machine parts are presented in this work. This hardening method is distinguished by incorporation of numerous hard spots into the surface layer of one of the bodies. Meanwhile the other part is covered by a continuous corundum layer. Correspondingly, a network of microchannels for lubricant is formed between the bodies. Furthermore the contact loads are intensified in the vicinity of the harder material in the discrete zones. As a result the strength and durability of the loaded parts is increased. The technological parameters of the hardening process have great impact on the resulting characteristics. In particular, this concern the shape of the discrete hardening zones and the material properties of the corundum layer. These factors were varied in stress-strain analyses of the contacting bodies. The dependence of the stress-strain state characteristics on the varied parameters was established. The justified recommendations regarding the technological parameters of the discrete-continual hardening have been developed. Keywords: stress-strain state, discrete-continual hardening, contact interaction, finite element method, contact pressure, machine parts

Hydrogen assisted cracking driven by cathodic protection operated at near −1200 mV CSE – an onshore natural gas pipeline failure

A 22-inch onshore natural gas transmission pipeline in operation since 1960 experienced an in-service rupture in January of 2018. The rupture was caused by an axial crack located 150 km (93 miles) downstream of the closest compression station. While the root cause analysis of the rupture was being carried out, excavations of indications reported by a Hard Spot In-Line Inspection approximately 42 km (26 miles) downstream of the rupture found leaks from predominantly circumferential crack colonies mixed with spiderweb ones not associated with hard spots.The conclusion from this investigation is that the cracking mechanism for the in-service rupture and leaks is mainly hydrogen environment assisted cracking (HAC), with the hydrogen being generated by the cathodic protection. The root cause for the failures is the combination of an aged and defective coating and the cathodic protection (CP) system operated for decades at near the pipe-to-soil potential limit of −1200 mV CSE.An extensive literature search indicates that this investigation is the first fully documented case of an onshore transmission pipeline failure due to HAC driven by CP, with the cracks occurring in the pipe body of X52 steel, away from welds and not related with hard spots. The paper summarizes the approach used for the root cause analysis and the findings, where the implications in the management of the pipeline integrity of the pipeline system are discussed. The pipeline operator implemented a series of preventive and corrective measures, which included pressure testing, cathodic protection improvement, coating rehabilitation programs and In-Line Inspection programs.

A methodology to study high-speed pantograph-catenary interaction with realistic contact wire irregularities

In high-speed rail operations, the irregularity of the overhead system is a typical disturbance that affects the pantograph-catenary interaction performance. The existing methods, which treat the contact wire irregularities as hard spots, overestimate the negative effect of the irregularities on the contact force, leading to conservative results. In this work, a more accurate methodology aiming to include the effect of contact wire irregularities in the assessment of the pantograph-catenary dynamic performance is proposed. Measured contact wire irregularity data, collected from the Chinese high-speed network, is added to the initial configuration of the catenary model, through a developed Target Configuration Under Dead-loads (TCUD) method. This approach is used here to investigate the effect of the contact wire irregularities on the contact forces. The results indicate that the catenary imperfections have a direct impact on the pantograph-catenary interaction, leading to an increment of the contact forces amplitude, an increase of their standard deviation and an expansion of the contact forces range. A frequency analysis of the results shows that the contact wire irregularity increases the Power Spectral Density (PSD) peaks of the contact force at specific frequencies relevant to the span length and to the dropper spacing.

An Online Remote Verification System of Thermal Sources for Energy Harvesting Application

Several thermoelectric energy harvesting applications have been introduced recently, showing an increasing interest in thermoelectric energy, mainly using Thermoelectric generators (TEGs) that convert heat directly into electrical energy. Some examples of thermoelectric energy harvesting applications are in the human body, wearable devices, and aircraft. However, several studies and development steps are previously needed to build a complete thermal harvester to prove whether it can generate a useful amount of energy. In this context, a way to early verify the potential of a possible thermal source before building the thermal harvester is needed to save either time or funding resources. In this article, a complete system to verify the capabilities of thermal sources before building the final thermal harvester is presented. The proposed system runs a procedure of simultaneous sampling and emulating thermal gradients, that is, while the temperature gradient of the thermal source under test (TSUV) is sampled, the system emulates this gradient and applies it on a TEG, which can predict the potential of the TSUV. In addition, using long-range-based wireless connectivity, the proposed system operates remotely, meaning that the temperature gradient sampling process can be far away from the temperature gradient emulation process, allowing to evaluate thermal sources in very hard spots, for instance, inside building structures or faraway pipelines. Experimental results show the emulation of two potential thermal sources, namely, tree trunks and the back surface of the photovoltaic modules.

Influence of orientations biomimetic units processed by laser on wear resistance of 6082 aluminium alloy

Inspired by the wear-resistant non-smooth surfaces distributed with different hard spots in the nature, we used the laser processing technique to processed bionic units with different distributing orientations to simulate biological wear-resistant surface on the surface of 6082 Al alloy. In the study, a series of experiments were conducted including tension tests, wear tests and simulation analysis. The tensile performance and wear resistance of 6082 Al alloy were significantly improved by the bionic units and were maximized at the distributing angle of 30°, as the yield strength, fracture elongation, ultimate tensile strength and wear resistance were also improved respectively. In addition, the influence mechanism on the wear resistance of bionic units was explored.

Revisiting transport phenomena and their role in intermixing during dissimilar laser beam welding

A study was conducted in order to understand the intermixing during welding dissimilar steel materials in overlap condition. Based of a manganese steel, different combinations were investigated considering convective transport processes, local alloy constitution and mechanical properties, and the underlying metallurgical effects. The analysis reveal an uneven distribution of alloying elements where the ferritic and martensitic phases are largely suppressed. Micro hardness measurements show hard spots but leading to a ductile character of the weld metal. The investigation show the strong effects of the processing parameters on the degree of intermixing and the inhomogeneity of the weld metal.

Phomous rot is a dangerous disease of potato tubers

Goal. To establish the symptoms of pathogens of fomose rot on potato varieties of different resistance, to isolate pathogens from the genus Phoma, parasitizing on tubers and stems of plants.
 Methods. Symptoms of phomotic rot were determined visually by the determinant of diseases and the method of microbiological diagnosis was used. Pathogens were isolated from stems and tubers affected by fomose rot.
 Results. On the basis of psychopathological examination, it was experimentally proved for the first time in Ukraine that fomozna potato rot is widespread in commodity and seed potato plantings. The degree of harmfulness reaches 35%. Pathogens of the genus Phoma (Ph. Solanicola Prill. Et Del Ph tuberosa Malkomcon) affect potato stems and tubers. On the stems, the first symptoms appear as spots during the flowering phase of the plants, and on tubers the gangrene appears as round, depressed and hard spots, light or dark brown in color, on the top of which pycnids form. According to the harmfulness of the pathogen, the Polesye of Ukraine is divided into three zones: 1. The zone of strong development includes the Volyn and Zhytomyr regions, where the number of affected plants with phomosis exceeds 5%, affected tubers — 8—10%; 2. The zone of moderate development, it includes the Rivne and Khmelnitsky regions, where the number of plants affected by phomosis is 2—3%, and tubers during storage of the crop — 5—7%; 3. The zone of insignificant development of the disease includes Kiev and Chernihiv regions, where the number of plants affected by gangrene is up to 2%, and tubers after storage of the crop — up to 4%.
 Conclusions. According to the results of psychopathological surveys, three zones of development of fomose rot of potatoes (severe, moderate and minor damage to phomosis) were identified and a scheme for the development cycle of the infection of the genus Phoma (Solanicola Prill. et. Del. And Ph. Tuberosa Melh.) was established. Symptoms of fomose rot appear on the stems in the form of elongated blurry spots, on which pycnids form from light brown (Eurostar) to dark brown (Riviera) color. On potato tubers, fomosis appears in the form of round, hard, sunken spots of a dark color. It is proved that during the interaction of potato plants with pathogens of the genus Phoma complex physiological, biochemical and pathological processes occur that significantly reduce productivity, quality, taste and other economically valuable traits.

Effect of Cr, Mo and Al on Microstructure, Abrasive Wear and Corrosion Resistance of Ni-Mn-Cu Cast Iron.

Results of a study on influence of Cr, Mo and Al on the microstructure, abrasive wear and corrosion resistance of Ni-Mn-Cu cast iron in the as-cast and heat-treated conditions are presented. Because of the chilling effect of first two elements (tendency to create hard spots), graphitising Al was added to the alloys, with the highest concentration of Cr and Mo. All castings in the as-cast condition showed an austenitic matrix, guaranteeing good machinability. Heat treatment of raw castings, consisting in annealing at 500 °C for 4 h, resulted in partial transformation of austenite. As a result the carbon-supersaturated acicular ferrite, morphologically similar to bainitic ferrite was formed. The degree of this transformation increased with increasing concentrations of Cr and Mo, which successively decreased the thermodynamic stability of austenite. A change of matrix structure made it possible to significantly increase hardness and abrasive-wear resistance of castings. The largest increment of hardness and abrasion resistance was demonstrated by the castings with the highest total concentration of Cr and Mo with an addition of 0.4% Al. Introduction of Cr and Mo also resulted in an increase of corrosion resistance. In the heat-treated specimens, increasing the concentration of Cr and Mo resulted in a successive decrease of the depth of corrosion pits, with an increase in their number at the same time. This is very favourable from the viewpoint of corrosion resistance.

English

Students commonly develop alternative ideas about topics in science. According to constructivist view of learning, students’ alternative conceptions and misconceptions about the process of developing new knowledge should be highlighted. Remedy can be undertaken through conceptual change approach. In order to understand what factors causes 9th grade students to make mistakes in various sub concepts of shape of molecule, qualitative research design was followed. Misconceptions of the students about shape of the molecule were identified and analyzed. Accordingly, plan of action was framed for tackling each of the hard spots found among students. Lack of content information, previous knowledge, instructional approaches, process of assessment, cognitive and meta-cognitive strategies were attributed towards the cause of misconceptions.   Key words: Misconception, shape of molecule, constructivism.

Dry-Sliding Tribological Properties of TiAl Alloys and Ti2AlN/TiAl Composites at High Temperature

The dry-sliding tribological properties of TiAl alloy and its composite Ti2AlN/TiAl were investigated comparatively in the temperature range of 25-800 °C. The wear test results showed the wear resistance of TiAl alloy and Ti2AlN/TiAl composite from 25 to 400 °C was poor, but it improved obviously when temperature was above 600 °C. Also, 15 vol.% incorporation of Ti2AlN particles was beneficial to improve the friction and wear properties of TiAl. Protective oxide layer generated on the wear surface of 15 vol.% Ti2AlN/TiAl composite from 25 to 400 °C, hence, the wear resistance improved. Ti2AlN particles played a load-carrying role and inhabited the delamination of enamel layer effectively when the temperature was above 800 °C. Overall, Ti2AlN particles which acted as hard spots changed the state of wear surface and further provided a second phase strengthening effect, which resulted in the difference in tribological behaviors between TiAl alloy and its composite.