Black Spot Damage Research Articles

Development and Implementation of a Damage Model for Potato Tuber Blackspot in Discrete Element Method to Analyze Harvesting and Handling Processes

Highlights Method for determining the discoloration of potato tissue samples induced by mechanical stress. Model of the discoloration susceptibility of specific potato tissue. Particle segmentation algorithm in the Discrete Element Method for contact localization in post-processing. Development of the "Discrete Element Method Blackspot Potato Tuber Model" capable of predicting internal blackspot damage in potato tubers. Abstract. Blackspot damage caused by mechanical load during the harvesting and processing stages of potato tubers remains difficult to mitigate. Field tests are inadequate as it takes around two days to develop blackspot discoloration, making it unclear when and where the initial damage occurs. Particle simulation, particularly with the Discrete Element Method (DEM), offers opportunities to improve machine performance and reduce crop losses. However, the DEM cannot predict local blackspot damage, making it unsuitable for reducing potato tuber damage. To address this, the “DEM blackspot potato tuber model” presented in this contribution integrates a discoloration function and a segmentation algorithm of DEM particles to predict and analyze blackspot damage during harvesting and processing. Based on mechanical experiments on tuber tissues with different loading conditions, a discoloration function was proposed dependent on strain and strain rate. The segmentation algorithm adapts to the varying potato tuber particle size by varying the number of segments to generate segments of average blackspot size. Two different validation tests are used to identify the single and multiple impact capabilities of the model. The preliminary results show that the discoloration induced by single impact events is well predicted in terms of the number of damaged tubers as well as the average damage per tuber. Damage of multiple impacts is less accurately predicted since the model does not take into account the accumulation of damage. Keywords: Blackspot, Damage model, Discrete Element Method, Potato handling, Simulation.

Duration of fungicide spray program for the control of citrus black spot in sweet orange based on cultivar maturation and orchard age

Citrus black spot (CBS) damage and Phyllosticta citricarpa inoculum tend to increase in old orchards and in late-maturing cultivars of sweet orange. However, CBS control in São Paulo citrus belt is based on standard fungicide program of 180–220 days of fruit protection, regardless of cultivar and orchard age. This study aimed to investigate whether the protection period may be adjusted based on the cultivar maturation and age of orchards intended for juice processing. The efficacy of protection periods of 60, 100, 140, 180, 220 and 260 days was determined by assessing CBS incidence and severity and CBS-related fruit drop in 12 orchards over two seasons. The standard protection period, with 180 days targeted for mid-age and 220 days for old orchards, was the most cost effective for mid-season and late-maturing cultivars. These protection periods resulted in a significant reduction in CBS severity and fruit drop by up to ∼95% and ∼50%, respectively. For early-maturing cultivars, the duration of CBS spray program may be drastically reduced to 60 days for mid-age orchards and to 100 days for old orchards. These protection periods significantly reduced CBS severity and fruit drop by up to ∼92% and ∼50%, respectively. These adjustments in CBS fungicide protection period based on cultivar and orchard age may save up to US$14.3 million per season if adopted throughout the main Brazilian citrus belt. The results of this study allow citrus growers to save inputs, reduce costs, improve the operational efficiency within the farm and contribute to a more sustainable citrus industry.

Characterization of radiation damage in 3D printed SiC

• High-purity SiC composites fabricated by additive manufacturing were irradiated. • Radiation-induced defects are easily observed in α-SiC particles but not CVI matrix. • Defect swelling measured by STEM-EELS is similar in α-SiC particles and CVI matrix. • Defect types and swelling are consistent with other forms of nuclear-grade SiC. • Interface denuded zone reveals sink strength bias and relative defect-type mobility. The SiC fuel matrix for advanced gas-cooled high temperature reactors as part of the Transformational Challenge Reactor program serves as the fuel particle container structure, a barrier to fission gas release, and a heat transfer medium. Its performance is particularly important because the fuel matrix must demonstrate good structural stability and thermal behaviors. An additive manufacturing methodology combining a binder jet 3D printing process with chemical vapor infiltration (CVI) for the production of SiC was recently developed. In this study, post irradiation examination by transmission electron microscopy shows that defect accumulation within the printed particles is very similar to other forms of high-purity SiC. However, damage accumulation was not directly observed in the CVI matrix because black spot damage and dislocation loops are difficult to image within the nanoscale highly faulted CVI matrix and because interstitial defects may rapidly annihilate at the stacking faults. Therefore, electron energy loss spectroscopy (EELS) analysis was used to analyze defect swelling in both the printed particles and the CVI matrix. The EELS analysis helped reveal that the radiation-induced swelling in the CVI matrix is similar to that of the printed SiC particles. This work shows that 3D printed SiC has behavior that is comparable to SiC processed by other means and that 3D printing could serve as a suitable processing technique for high-purity SiC for nuclear applications.

Observations of He platelets during He ion irradiation in 3C SiC

Polycrystalline 3C SiC was irradiated and observed in-situ via Transmission Electron Microscopy with a 20 keV He ion beam at 400, 800, 1000 and 1200 °C at the Microscopes and Ion Accelerators for Materials Investigations facility. During the 400, 800, 1000 and 1200 °C irradiations, black-spot damage was observed at 3.1, 1.1, 2.1 and 2.1 dpa respectively. Helium bubbles were observed after 6.3 dpa at 400 °C and 2.1 dpa at 800 °C, and He platelets were seen after 1.1 dpa at 800, 1000 and 1200 °C but not observed during the 400 °C irradiation. This work shows for the first time, the preferential nucleation of platelets within stacking faults in 3C SiC. The dependence of He platelet diameter with temperature and dose has also been observed.

Reconditioning and weather conditions affect black spot damage during storage of potato (Solanum tuberosumL.) tubers

In potatoes (Solanum tuberosum L.), mechanical damage can cause the formation of black spots in the tuber flesh as the result of oxidation of phenolic compounds. This damage can result in substantial economic losses and degradation of quality. External factors contributing to the formation and the prevention of black spot damage (BSD) are not fully understood. The aim of this study was to determine the effect of weather conditions, using a hydrothermal coefficient, and of two potato tuber reconditioning methods on the formation of BSD. Five potato varieties were divided into high, moderate and low BSD susceptibility groups. The research was carried out over two growing seasons that differed greatly in precipitation and temperature. The black spot index was determined immediately after harvest and after 3 and 7months of storage. Two reconditioning methods, applied for 7days at 8°C and for 7days at 15 °C, were used for each variety. The incidence of BSD in susceptible varieties did not depend significantly on weather conditions, although statistically significant variation was observed. We found a correlation between the hydrothermal coefficient (dry conditions) and BSD in the Etiuda variety. There was no significant effect of storage time and temperature on BSD incidence in susceptible or moderately susceptible varieties. The reconditioning methods significantly reduced the formation of BSD in tubers after storage in all three groups. Regardless of the level of susceptibility of the variety, storage time and storage temperature, the most efficient treatment to limit BSD was reconditioning for 7days at 15 °C. Identification of the significant effects of weather, and strong reduction of BSD in tubers that had been reconditioned, allows examination of the underlying mechanisms. The described reconditioning method can lead to satisfactory reduction of BSD in potato tubers. Data from this research will be of interest to potato breeders, particularly if valuable alleles that affect this phenomeon can be isolated. © 2019 Society of Chemical Industry.

A Transmission Electron Microscopy study of the neutron-irradiation response of Ti-based MAX phases at high temperatures

Mn+1AXn phases, or simply MAX phases, are unique nanolayered materials that have been attracting the attention of the nuclear materials community worldwide due to the recent reports of superior radiation resistance compared to conventional ceramics. However, the knowledge and understanding of their response to neutron irradiation is fairly limited, in particular at high temperatures where MAX phases are expected to have high thermodynamic phase stability. In this paper, a complete and extensive study of neutron-irradiation effects at high temperatures on Ti-based MAX phases is presented. The MAX phases Ti3SiC2 and Ti2AlC were irradiated at 1273 K in the High-Flux Isotope Reactor located at the Oak Ridge National Laboratory up to 10 displacement per atom (dpa). Post-irradiation characterisation was performed within a Transmission Electron Microscope on both irradiated and pristine samples. Upon increasing the dose from 2 to 10 dpa, the areal density of black-spots in the Ti2AlC was observed to significantly increase while in the Ti3SiC2, disordered dislocation networks were observed. Regarding the Ti3SiC2, black-spot damage was observed to be concentrated within secondary phases, but absent in the matrix. Dislocation lines and loops were observed at both 2 and 10 dpa. The dislocation loops were identified to be of <a> type. At 2 dpa, stacking faults were observed in both materials, but were absent at 10 dpa. Cavities have also been observed, although no relationship with between size and dose was obtained. Finally, at 10 dpa, both MAX phases exhibited evidences of phase decomposition and irradiation-induced segregation. The presented results shed light on a very complex chain of radiation-induced defects in neutron-induced microstructures in both materials at high temperatures, and provide information that will enable better design of more radiation tolerant materials in the future.

Assessing the Neutron-Irradiation Resistance of Ti-Based MAX Phases at High Temperatures

Mn+1AXn phases, or simply MAX phases, are unique nanolayered materials that have been attracting the attention of the nuclear materials community worldwide due to the recent reports of superior radiation resistance compared to conventional ceramics. However, the knowledge and understanding of their response to neutron irradiation is fairly limited, in particular at high temperatures where MAX phases are expected to have high thermodynamic phase stability. In this paper, a complete and extensive study of neutron-irradiation effects at high temperatures on Ti-based MAX phases is presented. The MAX phases Ti3SiC2 and Ti2AlC were irradiated at 1273 K in the High-Flux Isotope Reactor located at the Oak Ridge National Laboratory up to 10 displacement per atom (dpa). Post-irradiation characterisation was performed within a Transmission Electron Microscope on both irradiated and pristine samples. Upon increasing the dose from 2 to 10 dpa, the areal density of black-spots in the Ti2AlC was observed to significantly increase while in the Ti3SiC2, disordered dislocation networks were observed. Regarding the Ti3SiC2, black-spot damage was observed to be concentrated within secondary phases, but absent in the matrix. Dislocation lines and loops were observed at both 2 and 10 dpa. The dislocation loops were identified to be of type. At 2 dpa, stacking faults were observed in both materials, but were absent at 10 dpa. Cavities have also been observed, although no relationship with between size and dose was obtained. Finally, at 10 dpa, both MAX phases exhibited evidences of phase decomposition and irradiation-induced segregation. The presented results shed light on a very complex chain of radiation-induced defects in neutron-induced microstructures in both materials at high temperatures, and provide information that will enable better design of more radiation tolerant materials in the future.

Enhanced Radiation Tolerance of Tungsten Nanoparticles to He Ion Irradiation.

Materials exposed to plasmas in magnetic confinement nuclear reactors will accumulate radiation-induced defects and energetically implanted gas atoms (from the plasma and transmutations), of which insoluble helium (He) is likely to be the most problematic. The large surface-area-to-volume ratio exhibited by nanoporous materials provides an unsaturable sink with the potential to continuously remove both point defects and He. This property enhances the possibilities for these materials to be tailored for high radiation-damage resistance. In order to explore the potential effect of this on the individual ligaments of nanoporous materials, we present results on the response of tungsten (W) nanoparticles (NPs) to 15 keV He ion irradiation. Tungsten foils and various sizes of NPs were ion irradiated concurrently and imaged in-situ via transmission electron microscopy at 750 °C. Helium bubbles were not observed in NPs with diameters less than 20 nm but did form in larger NPs and the foils. No dislocation loops or black spot damage were observed in any NPs up to 100 nm in diameter but were found to accumulate in the W foils. These results indicate that a nanoporous material, particularly one made up of ligaments with characteristic dimensions of 30 nm or less, is likely to exhibit significant resistance to He accumulation and structural damage and, therefore, be highly tolerant to radiation.

At harvest prediction of the susceptibility of potato varieties to blackspot after impact over long-term storage

The paper presents a prediction method of the susceptibility blackspot damage after impact of potato varieties for three- and seven-month storage of potato tubers at a temperature of 4 °C based on the geometric parameter of the microstructure of tuber parenchyma determined at harvest. Similar sized and shaped potato tubers of twenty eight cultivars harvested in 2012 and 2013 were analysed. Analyses of the tuber parenchyma microstructure were carried out using an optical confocal microscope for ten tubers of each variety. Cylindrical samples with a thickness of 1 mm and a diameter of 10 mm were collected from the perimedullary zone. Microscopic images of the structure were analysed. The size parameter of the cell cross-section surface area was determined two days after harvest, and the susceptibility of each variety to blackspot after impact was assessed after three and seven months of storage. The mean post-harvest size of the tuber parenchyma cells and the susceptibility to blackspot during storage are related. Tubers of varieties with smaller cells of the perimedullary zone tissue exhibited greater blackspot susceptibility during storage.

Natural losses in tuber weight during storage as a predictor of susceptibility to post-wounding blackspot in advanced potato breeding materials.

In potatoes, mechanical damage and the formation of black spots in the tuber flesh cause substantial economic losses and degradation of quality. The aim of this study was to determine the susceptibility of new potato genotypes (178 elite breeding lines) to blackspot damage after 7 months' storage at 5 and 8 °C, and to examine whether this susceptibility correlated with natural losses. The lowest index of blackspot damage after harvest was found in genotypes from the mid-late group of earliness and low-susceptibility group, and after storage in genotypes from the early group of earliness and low-susceptibility group. After storage at 5 °C tubers were characterized by a lower susceptibility to bruising compared with tubers stored at 8 °C. The storage temperature significantly affected the natural losses in advanced potato breeding materials after storage in the case of all earliness and susceptibility groups. The highest susceptibility to blackspot damage and natural losses occurred in potatoes stored at 8 °C (r = 0.85-0.91). Such a relationship was not observed in potatoes stored at 5 °C. For potato tubers susceptible to the formation of after-wounding blackspot, the natural losses arising as a result of storage at 8 °C can be used as a subjective method to evaluate the susceptibility of potatoes to the formation of black spots in the flesh. However, this observation needs further studies and stronger proof of this theory. © 2017 Society of Chemical Industry.

Correlation between cell size and blackspot of potato tuber parenchyma tissue after storage

Mechanical injuries are the main cause of damage and loss of quality of plant raw materials. Potatoes are susceptible to external and internal pressures, which cause bruising and fracture in soft tissues. The paper shows research concerning the relationship between geometrical parameters of the microstructure of potato tuber tissue and susceptibility of potatoes to blackspot damage after six months of storage. Twenty eight potato varieties from 2011 and 2012 crops in Poland were used in the experiment. The tubers had a similar size and shape. A TRSLM confocal microscope was used to study the microstructure of soft tissue in potato tubers and microscope images of the perimedullary zone of the tissue were analyzed.The study shows that there is a correlation between the size of perimedullary tissue cells in potato tubers and blackspot damage. Potato tubers with smaller cells of the perimedullary zone show higher susceptibility to blackspot damage, described by the blackspot index BIP, in comparison with potatoes with larger cells which were stored for six months.

Microstructural evolution in nickel alloy C-276 after Ar + ion irradiation

Irradiation damage in nickel alloy C-276 irradiated by 115 keV argon ions at room temperature with irradiation doses from 0.28 to 82.5 dpa has been investigated by transmission electron microscopy. Nano-scale black spot damage appeared at a dose higher than 0.83 dpa. Large interstitial-type dislocation loops were observed at the dose of 8.25 dpa. Both the density of dislocation loops and the density of network dislocations grew significantly with the increase of irradiation dose. However, the density of network dislocations declined at the dose of 27.5 dpa. But the total of dislocation density (density of dislocation lines plus density of dislocation loops) kept increasing and no signs of saturation were seen in the dose range explored. The results showed that the nickel alloy C-276 had good performance in delaying the development of black spots, dislocations and dislocation loops. However, original grains have formed into subgrains at the dose of 82.5 dpa, meaning that the grains in C-276 lost its structural integrity at doses higher than 82.5 dpa.

Structure and optical properties of sapphire implanted with boron at room temperature and 1000 °C

Many previous studies of ion-implanted sapphire have used gas-forming light ions or heavier metallic cations. In this study, boron (1017cm−2, 150keV) was implanted in c-axis crystals at room temperature, 500 and 1000°C as part of a continuing study of cascade density and “chemical” effects on the structure of sapphire. Rutherford backscattering-ion channeling (RBS-C) of the RT samples indicated little residual disorder in the Al-sublattice to a depth of 50–75nm but almost random scattering at the depth of peak damage energy deposition. The transmission electron micrographs contain “black-spot” damage features. The residual disorder is much less at all depths for samples implanted at 1000°C. The TEM photographs show a coarse “black-spot damage” microstructure. The optical absorption at 205nm is much greater than for samples implanted with C, N, or Fe under similar conditions.

Microstructural evolution of both as-irradiated and subsequently deformed microstructures of 316 L stainless steel irradiated at 30–160 °C at LANSCE

Specimens of 316L stainless steel were irradiated to 0.5–10.3dpa at 30–80°C with a mixture of 500–800MeV protons and spallation neutrons at the Los Alamos Neutron Science Center (LANSCE). Tensile test results of irradiated 316L reported earlier had showed hardening and embrittlement with increasing irradiation dose, with significant irradiation hardening occurring at a dose of as low as 0.5dpa. Transmission electron microscope (TEM) examination of the irradiated microstructure of 316L showed black-spot damage (small loops) and somewhat larger faulted Frank loops to produce the hardening. There was an initial decrease in uniform elongation at low dose levels from 49% (unirradiated) to 30% at 1.1dpa, followed by a second, rather abrupt contribution to ductility loss at higher doses (∼2.5dpa) from 21% at 2.5dpa to 0.5% at 3dpa. This second drop in ductility was not accompanied by any visible new or enhanced microstructural development. In the current study additional transmission electron microscope investigation was conducted on both as-irradiated and irradiated plus subsequently deformed 316L in the vicinity of the second abrupt ductility loss (∼2.5dpa). The steel was observed to deform mainly by twinning and no brittle phases were found in the deformation microstructure. It is proposed that gas accumulation with increasing dpa, especially of hydrogen, may be a contributor to this second abrupt decrease in uniform elongation. Although the retained gas (helium and hydrogen) levels approached ∼0.6at.% total at the highest exposure level, no discernible cavities were observed.

Microstructure of irradiated ferritic/martensitic steels in relation to mechanical properties

A review of the microstructure of irradiated reduced activation ferritic/martensitic steels is presented, with a focus on F82H. Because of its resistance to irradiation induced hardening, swelling and low irradiation induced temperature shift in the ductile to brittle transition, this class of steels is a candidate structural material in future fusion reactors. The microstructure induced by irradiation is investigated in order to identify the key elements to deformation mechanisms. The study is focussed on F82H irradiated between 0.5 and 9.2 dpa at temperatures between 250 and 310 °C. Irradiation induced dislocation loops, when resolvable in the TEM, are known to have a Burgers vector a 0 〈1 0 0〉 , while for the smallest visible defects, or ‘black spots,’ there is still an uncertainty on their type. Black spot damage, possibly due to dislocation loops or precipitates, is investigated. It is attempted to quantitatively relate the dislocation loops and the precipitates to the irradiation induced hardening.

Microstructural evolution in modified 9Cr–1Mo ferritic/martensitic steel irradiated with mixed high-energy proton and neutron spectra at low temperatures

Modified 9Cr–1Mo ferritic/martensitic steel was exposed at 32–57 °C to a mixed proton/neutron particle flux and spectrum at the Los Alamos Neutron Science Center. The microstructure of unirradiated 9Cr–1Mo consists of laths, dislocations and carbides. Examination of electron diffraction patterns obtained from extraction replicas of unirradiated 9Cr–1Mo revealed that the precipitate microstructure was primarily dominated by M 23C 6 carbides. The post-irradiation microstructure contained black-spot damage in addition to precipitates and dislocations. Examination of electron diffraction patterns revealed diffuse rings from M 23C 6 carbides, indicating amorphization and/or nanocrystallinity. Crystalline MC carbides were also found. No cavity formation was found although a significant amount of helium and hydrogen generation had been generated. TEM–EDS examination of extraction replicas for carbides from unirradiated and irradiated samples did not show any detectable changes in composition of either M 23C 6 or MC carbides. There was also no evident change in carbide size. Lattice images of M 23C 6 carbides revealed an amorphous microstructure following irradiation, but MC carbides were still crystalline.

A microstructural explanation for irradiation embrittlement of V-15Cr-5Ti

In order to explain severe degradation of mechanical properties, specimens of V-15Cr-5Ti have been examined by transmission electron microscopy following irradiation at 600°C to 14 dpa in FFTF. Specimens irradiated at 420 and 520°C were also examined to confirm density change measurements that indicated swelling levels as high as 2.5%. Following irradiation at 600°C, a complex microstructure was found that included a perfect dislocation network of line segments and loops, faulted loops, a high density of black spot damage and a high density of rod-shaped precipitates. Heat-to-heat variations did not appear to significantly alter these microstructural features; instead the density of large blocky precipitates, believed to be TiO 2, was found to have increased with increasing oxygen content. Only two of the specimens irradiated at 600°C contained voids, whereas none of the specimens irradiated at 420 or 520°C contained voids. Therefore, swelling as measured by density change is probably due to phase instability in these specimen conditions, and the hardening and irradiation embrittlement that has been observed can be explained by the microstructural development. Phase stability appears to be an important criterion in the design of vanadium alloys for fusion applications.

Microstructural examination of simple vanadium alloys irradiated in the FFTF/MOTA

A series of V alloys including pure and impure V and alloys with Mo, W, Cr, Ti and Y have been examined by transmission electron microscopy following irradiation in the FFTF/MOTA to 14 dpa at 870 K. All specimens were found to have developed features typical of radiation damage. Void, dislocation and precipitate structures were different even for specimens of similar composition. However, in general, specimens displayed precipitate development, often indicated by {001} stacking faults. About half of the alloys showed voids. Dislocation structures included large loops and dislocation tangles but much smaller loops similar to black spot damage could be frequently identified.

Electron microscopy of electron damage in tantalum carbide

An intermediate voltage (300-keV) transmission electron microscope was used to create carbon defects in situ in nearly stoichiometric tantalum carbide (TaC0.99). At room temperature, these defects appeared as black spot damage. Varying the accelerating voltage allowed us to determine the threshold energy for carbon displacement to be 23.2±1.1 eV. Electron irradiation at liquid-nitrogen temperature did not lead to the formation of observable defects. However, black spot damage became visible as the temperature of the specimen was raised to room temperature. Estimates of the size of defects produced were obtained by weak-beam dark-field imaging. These observations allowed us to assign a tentative physical interpretation to the three recovery stages seen in previous electron irradiation experiments using resistivity measurements.

Electron irradiation damage in quartz

Abstract Electron irradiation damage in quartz has been studied by transmission dectron microscopy as a function of accelerating voltage from 50650 kV at room temperature. Black spot damage was observed at all voltages, the damage rate being faster at higher accelerating voltages. In the voltage range 50-100 kV, black spots grew in size with time until they became resolvable as dislocation loops. However, in the higher voltage range, 350-650 kV, they were not clearly resolvable as dislocation loops Additional irradiation at all voltages gradually induced a crystalline-to-amorphous transition when the irradiated area became featureless and the crystalline diffraction pattern was replaced by amorphous rings. It was observed that the dose required for the transformation increased approximately linearly with increasing accelerating voltage. These results are discussed in terms of displacement damage and ionization damage processes.