bluuebunny/crossref_metadata_2025 huggingface dataset:
Bending Stiffness of Honeycomb Paperboard
Authors: Kmita-Fudalej Gabriela , Szewczyk Włodzimierz , Kołakowski Zbigniew
Published: December 2022

This article analyzes the influence of the initial deflection of the flat layers on the bending stiffness (BS) of honeycomb paperboards and presents two methods for its calculation. Both methods allow for the determination of BS in the main directions in the plane of the paperboard, i.e., the machine direction (MD) and the cross direction (CD). In addition, they have been verified by comparing the calculation results with the results of the BS measurements. The first method allowed for the calculation of the BS of cellular paperboard based on the mechanical properties of the paper used for its production. The second method allowed for the estimation of the BS of cellular paperboard based on the bending stiffness of other honeycomb paperboards with the same raw material composition and the same core cell size but with different thicknesses. In the first analytical method for the calculation of the bending stiffness of cellular paperboard, which does not include the deflections of the flat layers, the calculation results significantly differ from the measurement results, and they are overestimated. The second of the presented BS calculation methods allowed for a much more accurate assessment of paperboard’s bending stiffness depending on its thickness.
Sub-Surface Analysis of Grinding Burns with Barkhausen Noise Measurements
Authors: Sorsa Aki , Ruusunen Mika , Santa-aho Suvi , Vippola Minnamari
Published: December 2022

Barkhausen noise (BN) measurements are commonly used for surface characterisation. However, often there is also a need to verify the sub-surface region because detrimental tensile stresses may be present after different manufacturing steps. Especially in a grinding burn, the surface stress may be compressive, but it changes quickly into tensile stress below the surface. The aim of this study was to find out whether regular surface-sensitive BN measurement is also sensitive to the stresses below the surface caused by grinding burns. More specifically, the aim was to study the relationship between BN features and sub-surface stresses and to identify a model that estimates sub-surface stresses. Real samples were collected from an actual process. The samples were cylindrical samples manufactured from commercial alloyed AISI/SAE L6 steel that was through-hardened prior to grinding. Barkhausen noise measurements were carried out for 42 grinding burn locations followed by X-ray diffraction-based residual stress surface measurements and residual stress depth profiles. Depth information was obtained through step-by-step electrolytic removal of thin layers. The stress profiles were pre-processed through interpolation and averaged stress was calculated as a function of depth below the surface. Correlation analysis was carried out to evaluate the relationships between BN features and stress at different depths and among BN features. The main outcome of the analysis was that BN measurement is dominated by the sub-surface tensile stresses rather than the compressive stress at the surface. It was also noticed that BN features form two groups, corresponding to average Barkhausen activity and magnetising field strength leading to maximum Barkhausen activity. Models for stress at different steps were identified systematically. The performance of the models for sub-surface stresses was reasonable with R2 values of around 0.85 and root mean squared error (RMSE) values of around 95 MPa. Based on the results, it is concluded that BN measurement provides information about sub-surface stresses and that stress can be evaluated through straightforward modelling, allowing fast detection of grinding burns.
Effect of Heat Treatment on the Microstructure and Mechanical Properties of Additive Manufactured Ti-6.5Al-2Zr-1Mo-1V Alloy
Authors: Zhang Sheng , Zhang Yuqi , Qi Jinshun , Zou Zhiyi , Qian Yuanhong
Published: December 2022

Ti-6.5Al-2Zr-1Mo-1V (TA15), widely used in the aerospace industry, is a medium- to high-strength, near-α titanium alloy with high aluminium equivalent value. The TA15 fabricated via laser powder bed fusion (L-PBF) normally presents a typical brittle appearance in as-built status, with high strength and low ductility. In this study, the microstructure and properties of L-PBF TA15 were engineered by various heat treatments below the β-transus temperature (1022 °C). After heat treatment, the original acicular martensite gradually transforms into a typical lamellar α + β dual-phase structure. Withannealing temperature increases, the lamellar α phase thickened with a decreased aspect ratio. Globularisation of the α grain can be noticed when annealing above 800 °C, which leads to a balance between strength and ductility. After heat treatment between 800–900 °C, the desired combination of strength and ductility can be achieved, with elongation of about 12.5% and ultimate tensile strength of about 1100 Mpa.
Some Slippage Issues in High-Pressure Torsion Using Cu and Ti Samples as an Example
Authors: Gunderov Dmitriy , Asfandiyarov Rashid , Titov Vyacheslav , Gunderova Sofia , Astanin Vasily
Published: December 2022

The effect of slippage during High Pressure Torsion (HPT) of technically pure Ti and pure Cu samples was investigated. The “joint torsion of the disk halves” method was used to evaluate the effect of slippage. It was shown that slippage starts already at the early stages of HPT. With a further increase in the number of revolutions n, the slippage effect increases, and no torsional deformation occurs after n = 5. The slippage effect is explained by analyzing the surface friction forces between the sample and the anvil. However, studies via TEM and XRD have shown that the structure of Ti samples after HPT at the investigated conditions is grinded to a nanocrystalline state. A structure is formed in Ti similar to that observed after HPT by other authors. The dislocation density increases with increasing HPT degree from n = 5 to n = 10 revolutions, despite slippage. Consequently, despite slippage at HPT at n ≥ 5, deformation still occurs. The following assumptions are made to explain the accumulated strain in the sample at HPT. It is assumed that the planes of the upper and lower anvil during HPT are at a slight inclination relative to each other. Computer modeling using the Deform 3D software package has shown that this leads to the accumulations of significant strain during HPT.
Parametric Characterization of Machined Textured Surfaces
Authors: Pawlus Pawel , Reizer Rafal , Wieczorowski Michal
Published: December 2022

Surface topography in general is not easy to characterize due to a great number of different features that appear on it. It is still more challenging for machined textured surfaces that are of high functional significance for tribological purposes. For practical reasons, there is a need to describe such surfaces using only a small number of parameters. Which of them represent surface details the best is still an open issue. To find out which parameters can be the most suitable in that case, three groups of machined textured surfaces were prepared. They were plateau-honed cylinder surfaces made of gray cast iron, steel, and bronze surfaces with isolated dimples and steel surfaces after abrasive blasting followed by lapping. All of them were measured by means of a white light interferometer. Different parameters and relationships were evaluated and based on them correlation and regression analyses were used. The basic description contained statistically independent parameters that can be used in production control, while the wider description in scientific research. In general, parameters of random surfaces were more intercorrelated than those of surfaces with isolated dimples. As was found for the basic description of random two-process surfaces, five parameters were enough while description of textured surfaces with isolated oil pockets needed six. In wider, scientific description, regardless the surface type seven parameters contained the necessary information about the surface. It was also proved that a pair of parameters, the emptiness coefficient Sp/Sz and Sq/Sa, can describe the shape of the ordinate distribution of machined textured surfaces better than, for example, skewness Ssk and kurtosis Sku, commonly used for that purpose.
Flexural Tests for Efficiency Evaluation of Spike Anchors on CFRP-Strengthened Concrete
Authors: Llauradó Paula Villanueva , Porres Rafael Cascón , Blázquez Alberto Sanchidrián , Olalla Francisco Santos , Álvarez Fernando Gómez
Published: December 2022

Spike anchors are one of the most promising techniques to prevent or delay debonding in FRP reinforcement sheets. There are several parameters affecting the anchors’ capacity, such as the embedment length and dowel angle. Regardless of the anchors’ capacity, their contribution to the overall strength of the anchored joint is affected by a larger number of variables, including the bonded length behind the anchors, the number and arrangement of the anchors, and the contact surface between the anchor fan and the FRP sheet. This paper presents experimental results of 10 tests conducted on concrete beams. In the tests, anchored joints reached peak loads up to 155% of those of unanchored, bonded joints. The main finding of the research is that the bond length in front of and behind the anchors affects both the peak load and the overall behaviour, with unbonded anchored joints exhibiting a poor behaviour and premature slippage of the anchor, without achieving its failure due to fibre rupture.
Fabrication of Compliant and Transparent Hollow Cerebral Vascular Phantoms for In Vitro Studies Using 3D Printing and Spin–Dip Coating
Authors: Bisighini Beatrice , Di Giovanni Pierluigi , Scerrati Alba , Trovalusci Federica , Vesco Silvia
Published: December 2022

Endovascular surgery through flow diverters and coils is increasingly used for the minimally invasive treatment of intracranial aneurysms. To study the effectiveness of these devices, in vitro tests are performed in which synthetic vascular phantoms are typically used to reproduce in vivo conditions. In this paper, we propose a manufacturing process to obtain compliant and transparent hollow vessel replicas to assess the mechanical behaviour of endovascular devices and perform flow measurements. The vessel models were obtained in three main steps. First, a mould was 3D-printed in a water-soluble material; two techniques, fusion deposition modelling and stereolithography, were compared for this purpose. Then, the mould was covered with a thin layer of silicone through spin–dip coating, and finally, when the silicone layer solidified, it was dissolved in a hot water bath. The final models were tested in terms of the quality of the final results, the mechanical properties of the silicone, thickness uniformity, and transparency properties. The proposed approach makes it possible to produce models of different sizes and complexity whose transparency and mechanical properties are suitable for in vitro experiments. Its applicability is demonstrated through idealised and patient-specific cases.
The Effect of Ultrasonic Agitation on the Seedless Growth of Cu on Ru-W Thin Films
Authors: Santos Rúben F. , Oliveira Bruno M. C. , Ferreira Paulo J. , Vieira Manuel F.
Published: December 2022

Ru attracted considerable attention as a candidate to replace TaN as a diffusion barrier layer for Cu interconnect metallisation. The addition of W improves the diffusion barrier properties of Ru but appears to weaken the adhesion strength between the barrier and Cu and the direct (seedless) electroplatability behaviour. Although Cu can be directly electroplated on near equimolar Ru-W thin films, no complete substrate coverage is obtained. The understanding of Cu electrocrystallisation on Ru–W is essential to develop methods of fabricating thin, continuous, and well adherent films for advanced interconnect metallisation, where Ru–W thin films could be used as diffusion barriers. This work studies the effect of ultrasonic agitation on the growth of Cu films electroplated on Ru–W, namely on the impact on substrate coverage. Film structure, morphology and chemical composition were evaluated by digital and scanning and transmission electron microscopies, and X-ray diffraction. The results show that Cu particles decrease with increasing current density, but when no electrolyte agitation is applied, substrate coverage is incomplete in the central region, with openings around larger Cu particles, regardless of current density. Under ultrasonic agitation, substrate coverage is remarkably improved. An active particle detachment mechanism is proposed as responsible for attaining improved substrate coverage, only possible at intermediate current density. Lower current densities promote growth over nucleation, whereas higher currents result in extensive hydrogen reduction/formation. Ultrasonic agitation also enhances a preferential Cu growth along <111> direction.
Numerical Study on the Progressive Damage Behavior of the Interfacial Debonding between Shape Memory Alloy and Polymer Matrix
Authors: Li Hao , Jiang Cong , Yu Zhaogang , Wan Yun , Ma Yunsheng , Yang Zhaoyang
Published: December 2022

The shape memory alloy reinforced composites have promising application potential for aerospace, automotive and biomedical engineering, while the interfacial bonding performance between shape memory alloy and polymer matrix is crucial to the improvement on the mechanical properties. The interfacial bonding mechanical properties are not uniform on the interface between shape memory alloy and the polymer matrix due to the existence of internal defects. Based on the cohesive zone model, an innovative finite element model is proposed to simulate the progressive damage behavior of the interfacial debonding between shape memory alloy and polymer matrix. The good agreement between the numerical results and the available experimental results indicates the validation of the proposed model. The progressive damage and connection of different positions of the interface between shape memory alloy and polymer matrix result in the final interfacial debonding behavior. Further, the effects of the shape memory alloy length-diameter ratio and embedded depth on the interface performance between shape memory alloy and polymer matrix are investigated.
Influence of Stress Field and Temperature Field on Residual Stress of 2A14 Aluminum Alloy Based on In Situ SAXS Method
Authors: Yang Guanghui , Xue Bing , Li Zhengyi , Zhou Gang , Zhang Shaohua , Lu Ning , Wen Lei , Zhang Duzhou
Published: December 2022

In this paper, based on in situ synchrotron radiation SAXS technology, the effects of stress field, temperature field and thermo-mechanical coupling conditions on the evolution of residual stress are discussed, respectively. The results show that the continuous increase of the external load led to the increase of the residual stress perpendicular to the tensile direction of the 2A14 aluminum alloy, and when the external load closed to the yield strength, the change of the residual stress was no longer significant. Under the action of temperature, the residual stress of 2A14 aluminum alloy reduced after the process of heating–holding–cooling. Under the action of thermo-mechanical coupling, the recovery effect of aluminum alloy was triggered, the energy storage of deformation was released, the lattice strain was reduced and the residual stress introduced by external load was reduced.
Effect of Microstructural and Tribological Behaviors of Sputtered Titanium Carbide Thin Film on Copper Substrate
Authors: Ogunlana Musibau Olalekan , Muchie Mammo , Oladijo Oluseyi Philip , Erinosho Mutiu
Published: December 2022

Titanium carbide (TiC) thin films were deposited by radio frequency magnetron sputtering (RFMS) onto a copper substrate by using Argon (Ar) gas plasma at a gas flow rate of 10.0 sccm. The effect of time and temperature at a constant RF power on the structural and tribological properties were respectively investigated by atomic force spectroscopy (AFM), X–ray Diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, optical microscopy (OM), scanning electron microscopy (SEM) and tribological measurements. All films were tested to have crystal structures with the preferential plane (111) and dominant plane (200) grain orientations. Thus, plane (111) has phase identification of Cu(Cu16Ti)0.23 for some samples, whereas plane (200) has a phase identification of Cu(Cu0.997Ti0.003) and Cu(Cu0.923Ti0.077) for other samples. The lowest thin film roughness of 19.797 nm was observed in the sample, with RF power, sputtering time, and a temperature of 200 W, for two hours and 80 °C, respectively. The FTIR spectra of TiC films formed under different sputtering times (2–3 h) and temperatures (80 °C–100 °C) on Cu substrates at a constant sputtering power of 200 W in the range of 5000–500 cm−1. The peaks at 540 cm−1, 780 cm−1, and 1250 cm−1 are presented in the FTIR spectra and the formation of a Ti–C bond was observed. On the other hand, a sample was revealed to have the lowest wear volume of 5.1 × 10−3 mm3 while another sample was obtained with the highest wear volume of 9.3 × 10−3 mm3.
Mechanical and Water Absorption Properties of Waterborne Polyurethane/Graphene Oxide Composites
Authors: Baskakov Sergey A. , Baskakova Yulia V. , Dvoretskaya Elizaveta V. , Krasnikova Svetlana S. , Lesnichaya Valentina A. , Shulga Yury M. , Gutsev Gennady L.
Published: December 2022

Nanocomposites based on waterborne polyurethane (WPU) and graphene oxide (GO) have been synthesized and characterized. It was found that after the incorporation of GO, WPU films became mechanically more rigid, and the Young’s modulus increased by almost six times. It is shown that the lateral size of GO sheets influences the mechanical properties of WPU/GO composites. In particular, composites with larger lateral size of GO sheets have higher values of Young’s modulus. Additionally, if the mechanical properties are improved with the addition of GO additive, then water absorption decreases for WPU modified with small GO sheets whereas it increases for WPU modified with large GO sheets. Possible reasons for this behavior are discussed.
Compressive Strength and Chloride Resistance of Slag/Metakaolin-Based Ultra-High-Performance Geopolymer Concrete
Authors: Zhang Yufei , Chen Jiejing , Xia Jin
Published: December 2022

Ultra-high performance geopolymer concrete (UHPGC) has been favored due to its excellent sustainability and outstanding mechanical properties. This study was conducted to explore the mechanical and durability properties of slag/metakaolin-based UHPGC with steel fibers reinforcement. The uniaxial compression test and rapid chloride migration test were conducted to measure the compressive strength and chloride penetration resistance of UHPGC. A total of nine groups of mixture proportions were designed and tested to investigate the influences of steel fiber dosage and sodium hydroxide (NaOH) solution concentration. The results showed that an increased steel fiber dosage and alkali concentration can improve compressive strength, and the maximum compressive strength can reach more than 140 MPa. In addition, the rapid chloride migration test showed that the chloride penetration resistance of the slag/metakaolin-based concrete was moderate, with a non-steady chloride migration coefficient ranging from 6.5 × 10−12 m2/s to 14.1 × 10−12 m2/s. The increase in steel fiber volume content slightly enlarged chloride penetration depth, while the higher concentration of sodium hydroxide solution was beneficial as it improved chloride penetration resistance. The results suggest that although ultra-high compressive strength can be achieved, the durability issues of steel fiber reinforced slag/metakaolin-based geopolymer concrete still need considerable attention.
Effect of TaC Content on Microstructure and Properties of W-TaC Composites
Authors: Xu Kai , Zhang Yaning , Wang Dong , Jin Xing , Ding Xiang
Published: December 2022

Transition metal carbide reinforcement can improve the performance of pure W. W-(10–50) vol% TaC composites were prepared by spark plasma sintering at 2100 °C. The effect of TaC content on the microstructure, mechanical properties, and thermal conductivity of the composites was studied. The ablation resistance of the W-TaC composites was evaluated under an air plasma torch. The addition of TaC into the W matrix enhanced the densification of W-TaC composites, the density of W-40 vol% TaC composite exceeded 93%. TaC particles inhibited the growth of W grains during sintering. Reactive diffusion occurred between W and TaC, forming the solid solutions of (W,Ta)ss and (Ta,W)Css. W and TaC react to form the W2C phase at a TaC content of 50 vol%. The Vickers hardness of the composite increases from 3.06 GPa for WTA1 to 10.43 GPa for WTA5. The flexural strength reached 528 MPa in the W-40 vol% TaC composite. The thermal conductivity of W-20 vol% TaC composite was 51.2 ± 0.2 W·m−1·K−1 at 750 °C. The addition of TaC improved the ablation resistance of W-TaC composites. The mass ablation rate of W-30 vol% TaC composite was 0.0678 g·s−1. The ablation products were mainly W oxides and complex oxides of W-Ta-O.
Development and Implementation of Element Deletion Algorithm into an Open-Source Software Based on the Fracture Locus of Materials
Authors: Alomar Zaki , Maccioni Lorenzo , Concli Franco
Published: December 2022

An accurate fracture simulation is often associated with how reliably the material model is represented. Hence, many models dealing with the calibration of ductile damage of materials have already been developed to predict failure initiation. Nevertheless, the challenge remains in obtaining an accurate representation of the fracture growth. Herein, an element deletion algorithm is developed and implemented into finite element open-source software. The deleted elements are replaced by new cells made of a virtual low-stiffness material. To better visualize the failure progression, the final model excludes these virtual cells from the representation. The functionality of the algorithm is tested through a series of two-dimensional simulations on three different geometries with a well-known behavior under uniaxial tension. Moreover, the failure response of a three-dimensional lattice structure is numerically investigated and compared against experimental data. The results of the two-dimensional simulations showed the capability of the algorithm to predict the onset of failure, crack nucleation, and fracture growth. Similarly, the onset and the initial fracture region were accurately captured in the three-dimensional case, with some convergence issues that prevent the visualization of the fracture growth. Overall, the results are encouraging, and the algorithm can be improved to introduce other computational functionalities.
Numerical Simulation of Thermal Conductivity and Thermal Stress in Lightweight Refractory Concrete with Cenospheres
Authors: Mačiūnas Darius , Nosewicz Szymon , Kačianauskas Rimantas , Boris Renata , Stonys Rimvydas
Published: December 2022

The main objective of this paper was to investigate the heat transfer of modified lightweight refractory concrete at the microscopic scale. In this work, such material was treated as a porous composite based on the compound of calcium aluminate cement and aluminosilicate cenospheres. The presence of air inclusions within the cenospheres was an essential factor in the reduction in thermal performance. Due to the intricacy of the subject investigated, our research employed numerical, theoretical, and experimental approaches. Scanning electron microscopy (SEM) imaging was performed to study the composite microstructure with a special focus on geometry, dimensions, and the distribution of cenospheres. Based on the experimental analysis, simplified geometrical models were generated to reproduce the main features of the composite matrix and cenospheres. A finite element framework was used to determine the effective thermal conductivity of such domains as well as the thermal stresses generated in the sample during the heat flow. A considerable difference in thermal properties was revealed by comparing the simulation results of the pure composite matrix and the samples, indicating a varying arrangement of cenosphere particles. The numerical results were complemented by a theoretical study that applied analytical models derived from the two-phase mixture theory—parallel and Landauer. A satisfactory agreement between numerical and theoretical results was achieved; however, the extension of both presented approaches is required.
Research Progress on Blue-Phase Liquid Crystals for Pattern Replication Applications
Authors: Wang Hao , Zhou Huimin , He Wanli , Yang Zhou , Cao Hui , Wang Dong , Li Yuzhan
Published: December 2022

Blue-Phase Liquid Crystals (BPLCs) are considered to be excellent 3D photonic crystals and have attracted a great deal of attention due to their great potential for advanced applications in a wide range of fields including self-assembling tunable photonic crystals and fast-response displays. BPLCs exhibit promise in patterned applications due to their sub-millisecond response time, three-dimensional cubic structure, macroscopic optical isotropy and high contrast ratio. The diversity of patterned applications developed based on BPLCs has attracted much attention. This paper focuses on the latest advances in blue-phase (BP) materials, including applications in patterned microscopy, electric field driving, handwriting driving, optical writing and inkjet printing. The paper concludes with future challenges and opportunities for BP materials, providing important insights into the subsequent development of BP.
Microstructures and Mechanical Properties of V-Modified Ti-Zr-Cu-Ni Filler Metals
Authors: Feng Lu , Liu Quanming , Long Weimin , Jia Guoxiang , Yang Haiying , Tang Yangyang
Published: December 2022

TA2 titanium alloy was brazed with Ti-Zr-Cu-Ni-V filler metals developed in a laboratory. The melting properties, the microstructures, phase compositions of filler metals and wettability, erosion properties, tensile properties of the brazed joint were studied in detail. The results show that with the increase of V content, the solidus–liquidus temperature of Ti-Zr-Cu-Ni-V filler metals increased, but the temperature difference basically remained unchanged, trace V element had a limited influence on the melting temperature range of Ti-Zr-Cu-Ni filler metals. The microstructure of Ti-Zr-Cu-Ni-1.5V filler metal was composed of Ti, Zr matrix, (Zr, Cu) solid solution and crystal phase. With the addition of V content, these phases containing V such as Ni3VZr2, NiV3, Ni2V in the molten filler metals increased. V was more inclined to combine with Ni to slow down the diffusion of Ni to titanium matrix. The wettability of filler metal with trace (≤0.5 wt.%) V to TA2 titanium alloy became worse, the wettability improved significantly with continuous increase of V content. The thickness of embrittlement layer and intergranular infiltration region decreased significantly by adding V. With the increase of V content, V could regulate the brazing interface reaction, more strengthened phases generated, which resulted the significant increase of the strength (302.72 MPa) and plasticity index (16.3%) of the brazed joint with Ti-Zr-Cu-Ni-1.5V filler metal.
Measurements of Surface Impedance in MgB2 in DC Magnetic Fields: Insights in Flux-Flow Resistivity
Authors: Alimenti Andrea , Torokhtii Kostiantyn , Vidal García Pablo , Silva Enrico , Grigoroscuta Mihai Alexandru , Badica Petre , Crisan Adrian , Pompeo Nicola
Published: December 2022

We present the multifrequency measurements of the surface resistance of spark-plasma-sintered MgB2 performed through a dielectric loaded resonator operating at 16.5 and 26.7 GHz. By normally applying magnetic fields ≤1.2 T to the sample surface, we drove it in the mixed state. By means of data-rooted analysis, we found that the sample vortex dynamics could be fully described within a single-component approach. Pinning phenomena were present and characterized by a depinning frequency smaller than the measurement ones. The multiband nature of the superconductor emerged in the flux-flow resistivity, whose field dependence could be interpreted well within theoretical models. By exploiting them, the upper critical field was extracted in the low-temperature range, which exhibited a consistent temperature trend with the values obtained at the onset of the resistive transition near Tc, and was well in line with literature data on other polycrystalline samples.
Investigations on Caesium Dispersion and Molybdenum Coating on SPIDER Components
Authors: Candela Valentina , Cavallini Caterina , Gasparrini Claudia , Armelao Lidia , Candeloro Valeria , Dalla Palma Mauro , Fadone Michele , Marcuzzi Diego , Pavei Mauro , Pepato Adriano , Pouradier Duteil Basile , Rancan Marzio , Rizzolo Andrea , Sartori Emanuele , Segalini Beatrice , Serianni Gianluigi , Spolaore Monica , Zorzi Federico , Sonato Piergiorgio
Published: December 2022

SPIDER is the 100 keV full-size Negative Ion Source prototype of the ITER Neutral Beam Injector, operating at Consorzio RFX in Padova, Italy. The largest Negative Ion Source in the world, SPIDER generates an RF driven plasma from which Deuterium or Hydrogen negative ions are produced and extracted. At the end of 2021, a scheduled long-term shutdown started to introduce major modifications and improvements aiming to solve issues and drawbacks identified during the first three years of SPIDER operations. The first action of the shutdown period was the disassembly and characterization of the SPIDER beam source after removal from the vacuum vessel and its placement inside the clean room. Each component was carefully assessed and catalogued, following a documented procedure. Some source components, i.e., the Plasma Grid, Extraction Grid and Bias Plate, revealed the presence of different and non-uniform red, white and green coatings that might be correlated to back-streaming positive ions impinging on grid surfaces, electrical discharges and caesium evaporation. Thus, several analyses have been carried out to understand the nature of such coatings, with the study still ongoing. The evidence of caesium evaporation and deposition on molybdenum-coated SPIDER components, such as the formation of oxides and hydroxides, is demonstrated through surface characterization analyses with the use of the Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS).
Investigation into Friction and Wear Characteristics of 316L Stainless-Steel Wire at High Temperature
Authors: Huang Mingji , Fu Yili , Qiao Xiaoxi , Chen Ping
Published: December 2022

The damping performance of metal rubber is highly correlated with the tribological properties of the internal metal wires. In this paper, the friction and wear characteristics of 316L stainless-steel wire are investigated under different temperatures, loads, crossing angles, and working strokes. Results show that the friction coefficient increases from 0.415 to 0.635 and the wear depth increases from 34 μm to 51 μm, with the temperature rising from 20 °C to 400 °C. High temperature will soften metal materials and promote the oxidation of metal. Softened materials can be easily sheared and removed under friction action, resulting in high wear depth. However, when a continuous oxide film with high hardness is formed under higher temperature, the oxide film can work as a wear-resisting layer to prevent further wear of the wire to a certain degree. At the same temperature, the loads, crossing angles, and working strokes change the wear resistance by affecting the surface stress, debris removal efficiency, etc., and high temperature will aggravate this change. The results pave the way for the design and selection of materials for high-temperature metal rubber components.
Hardening Mechanism of Coral Aggregates in Cement-Based Systems
Authors: Wang Huajin , Shi Minglei , Tian Xintao , Zhang Yue , Liu Jinyu
Published: December 2022

In terms of the infrastructure construction near coral reefs, native coral aggregates have been widely implemented as alternative efficient building materials to prepare the “coral concrete”. This study focused on the mechanical properties and hardening mechanism of coral particles under cement-based systems. Firstly, coral particles were divided into two categories: coral biological debris particles (calcium sand) and coral parent rock particles (limestone). Subsequently, several elementary laboratory tests were conducted to compare the physical and chemical properties of the samples. The results demonstrate that the specific surface area and open pores of coral particles are bigger than those of quartz sand. Moreover, the water absorption rate of debris and parent rock particles reach 9.9% and 22%, respectively. To further examine the hardening mechanism of coral particles, we carried out particle crushing strength tests, compressive strength tests and nanoindentation tests. Regardless of the tested groups and particle categories, the results show that the wrapped cement slurry universally demonstrated the successful enhancement of crushing strength σ0,d. Particularly, in the size range from 1.18–2.36 mm, wrapped particles of debris and parent rock both reached unusually high σ0,d values: 10.14 MPa and 8.74 MPa, respectively. However, in the size range from 9.5 mm to 16 mm, the σ0,d values of wrapped debris and parent rock reached 4.75 MPa and 3.18 MPa, respectively. According to the nanoindentation tests, the sub-microscopic strength of ITZs was enhanced to more than 1 GPa, which is higher than that of conventional concrete, in terms of the sample with 28-day maintenance. In conclusion, this study has provided a further basis for studying coral concrete material and its hardening mechanism.
Microstructure and Solute Segregation around the Melt-Pool Boundary of Orientation-Controlled 316L Austenitic Stainless Steel Produced by Laser Powder Bed Fusion
Authors: Sato Kazuhisa , Takagi Shunya , Ichikawa Satoshi , Ishimoto Takuya , Nakano Takayoshi
Published: December 2022

For this article, we studied the microstructure and solute segregation seen around the melt pool boundary of orientation-controlled 316L austenitic stainless steel produced by laser powder bed fusion, using transmission electron microscopy and energy-dispersive x-ray spectroscopy. We found that the solidification cellular microstructures could be visualized with the aid of solute segregation (Cr and Mo) during solidification. Mn–Si–O inclusions (10–15 nm in diameter) were distributed along the lamellar boundaries, as well as in the dislocation cell walls. It is believed that the grain growth of the inclusions can be effectively suppressed by rapid quenching during the laser powder-bed fusion process. A thin region without cellular microstructures was observed at the melt-pool boundary. The cellular spacing widened near the bottom of the melt-pool boundary, owing to the decrease in the cooling rate. Atomic-structure analysis at the lamellar boundary by high-resolution transmission electron microscopy revealed a local interfacial structure, which is complementary to the results of electron back-scatter diffraction.
Preparation of Nitrogen-doped Holey Multilayer Graphene Using High-Energy Ball Milling of Graphite in Presence of Melamine
Authors: Hendaoui Ali , Alshammari Abdullah
Published: December 2022

Holey graphene, consisting of graphene sheets with in-plane nanopores, has recently attracted more attention as it expands graphene applications to other fields inaccessible by the pristine graphene. To ensure an effective implementation of holey graphene in the market, it is crucial to explore new preparation methods that are simple, cost effective, eco-friendly, versatile, and scalable. While ball milling of graphite in presence of exfoliating agents was found very effective in the preparation of graphene (doped and undoped) and graphene-composites, this technique remains unexplored for the preparation of holey graphene. In the present work, Nitrogen-doped multilayer holey graphene sheets were prepared by an all-solid, one-step procedure based on high-energy ball milling of graphite as the starting material in presence of melamine in a shaker-type mill for 1 hour under ambient conditions. Melamine acted simultaneously as an exfoliating agent to enhance the exfoliation of graphene layers and a diluent to protect graphite against the continuous fragmentation into amorphous carbon during the high-energy “shock” mode of ball milling. The high-energy “shock” mode of ball milling of graphite in presence of melamine induced the formation of multilayer defective graphene as an intermediate product before being converted into N-doped multilayer holey graphene after the removal of the in-plane defects during the milling process. The characterization of the final product confirmed the formation of N-doped multilayer holey graphene with a content in nitrogen as high as 12.96 at.%, making it promising for energy storage and energy conversion applications.
Influence of Intrinsic Physicochemical Properties of Agroforestry Waste on Its Pyrolysis Characteristics and Behavior
Authors: Liu Hui , Zhao Baowei , Zhang Xin , Zhang Yin
Published: December 2022

To obtain a comprehensive understanding of the qualitative and quantitative effects of the intrinsic properties of biomass on its pyrolysis characteristics and assess the behavior of agroforestry waste, thermogravimetric analyses of three representative agroforestry wastes, namely rape (Brassica campestris L.) straw (RS), apple (Malus domestica) tree branches (ATB), and pine (Pinus sp.) sawdust (PS), were carried out by pyrolysis under dynamic conditions (30 to 900 °C) at different heating rates of 5, 10, and 15 °C·min−1. Correlation analysis showed that intrinsic physicochemical properties play distinct roles in different stages of pyrolysis. The ash content was negatively correlated with the temperature range (R2) of the second stage (190–380 °C) of pyrolysis. The lignin content and the amount of pyrolysis residues (RSS) were positively correlated. Kinetic triplets, including the activation energy (Ea), pre-exponential factor (A), and reaction model [f(α)], were obtained using different methods, including the Flynn–Wall–Ozawa (FWO), Freidman, Kissinger–Akahira–Sunose (KAS), and Starink methods. The mean activation energy (Ea[mean]) for RS, ATB, and PS calculated by the different methods ranged from 167.15 to 195.58 kJ·mol−1, 195.37 to 234.95 kJ·mol−1, and 191.27–236.45 kJ·mol−1, respectively. Correlation analysis of the intrinsic physicochemical characteristics and kinetic factors of agroforestry waste showed that the minimum Ea (Ea[min]) was significantly positively correlated with heat capacity (C0) and negatively correlated with thermal diffusivity (D). The Ea[mean] and the maximum value of Ea (Ea[max]) significantly positively correlated with the sum content of cellulose and lignin, indicating that the contents of cellulose and lignin determines the energy required for the pyrolysis process of agroforestry waste. The mechanism of degradation involves the diffusion model (D1, D2, and D3), the growth model (A4), and the geometrical contraction model (R3). These results indicate that the pyrolysis of agroforestry waste is a complex process due to the heterogeneity of its intrinsic physicochemical properties.
Numerical Estimation of SAR and Temperature Distributions inside Differently Shaped Female Breast Tumors during Radio-Frequency Ablation
Authors: Miaskowski Arkadiusz , Gas Piotr
Published: December 2022

Radio-frequency (RF) ablation is a reliable technique for the treatment of deep-seated malignant tumors, including breast carcinoma, using high ablative temperatures. The paper aims at a comparative analysis of the specific absorption rate and temperature distribution during RF ablation with regard to different female breast tumors. In the study, four tumor models equivalent to an irregular tumor were considered, i.e., an equivalent sphere and ellipsoid with the same surfaces and volumes as the irregular tumor and an equivalent sphere and ellipsoid inscribed in the irregular tumor. An RF applicator with a specific voltage, operating at 100 kHz inserted into the anatomically correct female breast, was applied as a source of electromagnetically induced heat. A conjugated Laplace equation with the modified Pennes equation was used to obtain the appropriate temperature gradient in the treated area. The levels of power dissipation in terms of the specific absorption rate (SAR) inside the naturalistically shaped tumor, together with the temperature profiles of the four simplified tumor models equivalent to the irregular one, were determined. It was suggested that the equivalent tumor models might successfully replace a real, irregularly shaped tumor, and the presented numeric methodology may play an important role in the complex therapeutic RF ablation process of irregularly shaped female breast tumors.
Investigations on Fatigue Life of Tube Connections Based on International Codes of Pressure Vessel
Authors: Su Wenxian , Cao Qinqin , Cui Gaoyu , Chen Zhiwei
Published: December 2022

The fatigue assessment of tube connections under cyclic pressure is discussed using four kinds of methods from ASME VIII-2 and EN 13445-3. FEA results are compared to the fatigue test, and some conclusions are obtained. Method 1 is the most widely used traditional method and can be used in both welded structures and unwelded structures. This method has simple operation, safety and reliability. Method 2 adopts the effective strain range to assess the fatigue for both the welded and the unwelded structure. This method is with high accuracy, good stability, safety and reliability, but the elastic–plastic analysis is very complicated. Method 3 adopts the equivalent structure stress to assess the fatigue of the welded, it is developed from fracture mechanics, and the procedure is also very complicated. Method 4 is a detailed assessment procedure for the welded and unwelded, and it is the most accurate, stable and reliable among the four methods.
UV-A,B,C Emitting Persistent Luminescent Materials
Authors: Sharma Suchinder K. , James Jinu , Gupta Shailendra Kumar , Hussain Shamima
Published: December 2022

The nearly dormant field of persistent luminescence has gained fresh impetus after the discovery of strontium aluminate persistent luminescence phosphor in 1996. Several efforts have been put in to prepare efficient, long decay, persistent luminescent materials which can be used for different applications. The most explored among all are the materials which emit in the visible wavelength region, 400–650 nm, of the electromagnetic spectrum. However, since 2014, the wavelength range is extended further above 650 nm for biological applications due to easily distinguishable signal between luminescent probe and the auto-fluorescence. Recently, UV-emitting persistent materials have gained interest among researchers’ due to their possible application in information storage, phototherapy and photocatalysis. In the present review, we summarize these recent developments on the UV-emitting persistent luminescent materials to motivate young minds working in the field of luminescent materials.
Thermomechanical Fatigue Testing on Fe-Mn-Si Shape Memory Alloys in Prestress Conditions
Authors: Marinopoulou Eva , Katakalos Konstantinos
Published: December 2022

Active materials have gained increasing momentum during the last decades due to their ability to act as sensors and actuators without the need for an external controlling system or an electronic signal. Shape memory alloys (SMAs), which are a subcategory of active materials, are slowly being introduced in the civil engineering sector in applications that refer to prestressing and strengthening of various structural elements. Low-cost iron-based SMAs are a good alternative to the Ni-Ti SMAs for such uses since the cost of large-scale civil engineering applications would otherwise be prohibitive. The scope of this study is the investigation of the thermomechanical response of the Fe-17Mn-5Si-10Cr-4Ni-1(V,C) ferrous SMA. In particular, this study focuses on the application of prestress, and on the alloy’s behavior under fatigue loadings. In addition, the effect of loading frequency on the recovery stress of the material is thoroughly investigated. Four dog-bone specimens were prepared and tested in low-cycle fatigue. All the experiments aimed at the simulation of prestress. The recovery stress was monitored after pre-straining and heating applied under strain–control conditions. The experimental results are promising in terms of the is situ prestress feasibility since the measured recovery stress values are satisfactory high.
Multi-Task Data Imputation for Time-Series Forecasting in Turbomachinery Health Prognostics
Authors: Chen Xudong , Ding Xudong , Wang Xiaofang , Zhao Yusong , Liu Changjun , Liu Haitao , Chen Kexuan
Published: December 2022

Time-series forecasting is the core of the prognostics and health management (PHM) of turbomachinery. However, missing data often occurs due to several reasons, such as the failure of sensors. These partially missing and irregular data greatly affect the quality of time-series modeling and prediction as most time-series models assume that the data are sampled uniformly over time. Meanwhile, the training process of models requires a large number of samples and time. Due to various reasons, it is difficult to obtain a significant amount of monitoring data, and the PHM of turbomachinery has high timeliness and accuracy requirements. To fix these problems, we propose a multi-task Gaussian process (MTGP)-based data imputation method that leverages knowledge transfer across multiple sensors and even equipment. Thereafter, we adopt long short-term memory (LSTM) neural networks to build time-series forecasting models based on the imputed data. In addition, the model integrates the methods of denoising and dimensionality reduction. The superiority of this integrated time-series forecasting framework, termed MT-LSTM, has been verified in various data imputation scenarios of a synthetic dataset and a real turbomachinery case.
Motion-Compensated PET Image Reconstruction via Separable Parabolic Surrogates
Authors: Protonotarios Nicholas E. , Kastis George A. , Fotopoulos Andreas D. , Tzakos Andreas G. , Vlachos Dimitrios , Dikaios Nikolaos
Published: December 2022

The effective resolution of positron emission tomography (PET) can be significantly degraded by patient motion during data acquisition. This is especially true in the thorax due to respiratory motion. This study concentrates on the improvement of motion correction algorithms both in terms of image quality and computational cost. In this paper, we present a novel motion-compensated image reconstruction (MCIR) algorithm based on a parabolic surrogate likelihood function instead of the loglikelihood function of the expectation maximization (EM) algorithm. The theoretical advantage of the parabolic surrogate algorithm lies within the fact that its loglikelihood is upper bounded by the EM loglikelihood, thus it will converge faster than EM. This is of particular importance in PET motion correction, where reconstructions are very computationally demanding. Relaxation parameters were also introduced to converge closer to the maximum likelihood (ML) solution and achieve lower noise levels. Image reconstructions with embedded relaxation parameters actually converged to better solutions than the corresponding ones without relaxation. Motion-compensated parabolic surrogates were indeed shown to accelerate convergence compared to EM, without reaching a limit cycle. Nonetheless, with the incorporation of ordered subsets in the reconstruction setting, the improvement was less evident.
Liouville-Type Theorem for Nonlinear Elliptic Equations Involving Generalized Greiner Operator
Authors: Shi Wei
Published: December 2022

In this paper, we study the Liouville-type behaviors of the generalized Greiner operators with nonlinear boundary value conditions. We use the technique based upon the method of moving planes.