Materials

14 pages, 4771 KiB

Open AccessArticle

Numerical Analysis of Keyhole and Weld Pool Behaviors in Ultrasonic-Assisted Plasma Arc Welding Process

by Junnan Qiao, Chuansong Wu and Yongfeng Li

Materials 2021, 14(3), 703; https://doi.org/10.3390/ma14030703 - 02 Feb 2021

Cited by 2 | Viewed by 2747

The acoustic radiation force driving the plasma jet and the ultrasound reflection at the plasma arc-weld pool interface are considered to modify the formulas of gas shear stress and plasma arc pressure on the anode surface in ultrasonic-assisted plasma arc welding (U-PAW). A [...] Read more.

The acoustic radiation force driving the plasma jet and the ultrasound reflection at the plasma arc-weld pool interface are considered to modify the formulas of gas shear stress and plasma arc pressure on the anode surface in ultrasonic-assisted plasma arc welding (U-PAW). A transient model taking into account the dynamic changes of heat flux, gas shear stress, and arc pressure on the keyhole wall is developed. The keyhole and weld pool behaviors are numerically simulated to predict the heat transfer and fluid flow in the weld pool and dynamic keyhole evolution process. The model is experimentally validated. The simulation results show that the acoustic radiation force increases the plasma arc velocity, and then increases both the plasma arc pressure and the gas shear stress on the keyhole wall, so that the keyholing capability is enhanced in U-PAW. Full article

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18 pages, 2974 KiB

Open AccessArticle

Effect of Wear Conditions, Parameters and Sliding Motions on Tribological Characteristics of Basalt and Glass Fibre Reinforced Epoxy Composites

by Anis Adilah Abu Talib, Aidah Jumahat, Mohammad Jawaid, Napisah Sapiai and Alcides Lopes Leao

Materials 2021, 14(3), 701; https://doi.org/10.3390/ma14030701 - 02 Feb 2021

Cited by 12 | Viewed by 2639

Abstract

Basalt fibre is a promising mineral fibre that has high potential to replace synthetic based glass fibre in today’s stringent environmental concern. In this study, friction and wear characteristics of glass and basalt fibres reinforced epoxy composites were studied and comparatively evaluated at [...] Read more.

Basalt fibre is a promising mineral fibre that has high potential to replace synthetic based glass fibre in today’s stringent environmental concern. In this study, friction and wear characteristics of glass and basalt fibres reinforced epoxy composites were studied and comparatively evaluated at two test stages. The first stage was conducted at fixed load, speed and distance under three different conditions; adhesive, abrasive and erosive wear, wherein each composite specimens slide against steel, silicon carbide, and sand mixtures, respectively. The second stage was conducted involving different types of adhesive sliding motions against steel counterpart; unidirectional and reciprocating motion, with the former varied at pressure—velocity (PV) factor; 0.23 MPa·m/s and 0.93 MPa·m/s, while the latter varied at counterpart’s configuration; ball-on-flat (B-O-F) and cylinder-on-flat (C-O-F). It was found that friction and wear properties of composites are highly dependent on test conditions. Under 10 km test run, Basalt fibre reinforced polymer (BFRP) composite has better wear resistance against erosive sand compared to Glass fibre reinforced polymer (GFRP) composite. In second stage, BFRP composite showed better wear performance than GFRP composite under high PV of unidirectional sliding test and under B-O-F configuration of reciprocating sliding test. BFRP composite also exhibited better friction properties than GFRP composite under C-O-F configuration, although its specific wear rate was lower. In scanning electron microscopy examination, different types of wear mechanisms were revealed in each of the test conducted. Full article

(This article belongs to the Special Issue Recycled and Sustainable Materials in Composite Design)

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17 pages, 3553 KiB

Open AccessFeature PaperArticle

Constitutive Models for the Tensile Behaviour of TRM Materials: Literature Review and Experimental Verification

by Maria Concetta Oddo, Giovanni Minafò and Lidia La Mendola

Materials 2021, 14(3), 700; https://doi.org/10.3390/ma14030700 - 02 Feb 2021

Cited by 7 | Viewed by 2064

Abstract

In recent years, the scientific community has focused its interest on innovative inorganic matrix composite materials, namely TRM (Textile Reinforced Mortar). This class of materials satisfies the need of retrofitting existing masonry buildings, by keeping the compatibility with the substrate. Different recent studies [...] Read more.

In recent years, the scientific community has focused its interest on innovative inorganic matrix composite materials, namely TRM (Textile Reinforced Mortar). This class of materials satisfies the need of retrofitting existing masonry buildings, by keeping the compatibility with the substrate. Different recent studies were addressed to improve the knowledge on their mechanical behaviour and some theoretical models were proposed for predicting the tensile response of TRM strips. However, this task is complex due to the heterogeneity of the constituent materials and the stress transfer mechanism developed between matrix and fabric through the interface in the cracked stage. This paper presents a state-of-the-art review on the existing constitutive models for the tensile behavior of TRM composites. Literature experimental results of tensile tests on TRM coupons are presented and compared with the most relevant analytical models proposed until now. Finally, a new experimental study is presented and its results are used to further verify the reliability of the literature expressions. Full article

(This article belongs to the Special Issue Fiber Reinforced Materials for Buildings Strengthening)

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20 pages, 7019 KiB

Open AccessArticle

Reinforcing Mechanisms of Coir Fibers in Light-Weight Aggregate Concrete

by Xiaoxiao Zhang, Leo Pel, Florent Gauvin and David Smeulders

Materials 2021, 14(3), 699; https://doi.org/10.3390/ma14030699 - 02 Feb 2021

Cited by 14 | Viewed by 2822

Abstract

Due to the requirement for developing more sustainable constructions, natural fibers from agricultural wastes, such as coir fibers, have been increasingly used as an alternative in concrete composites. However, the influence of coir fibers on the hydration and shrinkage of cement-based materials is [...] Read more.

Due to the requirement for developing more sustainable constructions, natural fibers from agricultural wastes, such as coir fibers, have been increasingly used as an alternative in concrete composites. However, the influence of coir fibers on the hydration and shrinkage of cement-based materials is not clear. In addition, limited information about the reinforcing mechanisms of coir fibers in concrete can be found. The goal of this research is to investigate the effects of coir fibers on the hydration reaction, microstructure, shrinkages, and mechanical properties of cement-based light-weight aggregate concrete (LWAC). Treatments on coir fibers, namely Ca(OH)₂ and nano-silica impregnation, are applied to further improve LWAC. Results show that leachates from fibers acting as a delayed accelerator promote cement hydration, and entrained water by fibers facilitates cement hydration during the whole process. The drying shrinkage of LWAC is increased by adding fibers, while the autogenous shrinkage decreases. The strength and toughness of LWAC are enhanced with fibers. Finally, three reinforcement mechanisms of coir fibers in cement composites are discussed. Full article

(This article belongs to the Special Issue Advances in Natural Fibers and Polymers)

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14 pages, 3644 KiB

Open AccessArticle

Mechanical and Material Properties of Mortar Reinforced with Glass Fiber: An Experimental Study

by Marcin Małek, Mateusz Jackowski, Waldemar Łasica, Marta Kadela and Marcin Wachowski

Materials 2021, 14(3), 698; https://doi.org/10.3390/ma14030698 - 02 Feb 2021

Cited by 39 | Viewed by 4050

Abstract

The progressive increase in the amount of glass waste produced each year in the world made it necessary to start the search for new recycling methods. This work summarizes the experimental results of the study on mortar samples containing dispersed reinforcement in the [...] Read more.

The progressive increase in the amount of glass waste produced each year in the world made it necessary to start the search for new recycling methods. This work summarizes the experimental results of the study on mortar samples containing dispersed reinforcement in the form of glass fibers, fully made from melted glass waste (bottles). Mortar mixes were prepared according to a new, laboratory-calculated recipe containing glass fibers, granite as aggregate, polycarboxylate-based deflocculant and Portland cement (52.5 MPa). This experimental work involved three different contents (600, 1200, and 1800 g/m³) of recycled glass fibers. After 28 days, the mechanical properties such as compressive, flexural, and split tensile strength were characterized. Furthermore, the modulus of elasticity and Poisson coefficient were determined. The initial and final setting times, porosity, and pH of the blends were measured. Images of optical microscopy (OM) were taken. The addition of glass fibers improves the properties of mortar. The highest values of mechanical properties were obtained for concrete with the addition of 1800 g/m³ of glass fibers (31.5% increase in compressive strength, 29.9% increase in flexural strength, and 97.6% increase in split tensile strength compared to base sample). Full article

(This article belongs to the Special Issue Recent Developments on High-Performance Fiber-Reinforced Concrete: Hybrid Mixes and Combinations with Other Materials)

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14 pages, 2569 KiB

Open AccessArticle

Testing and Assessing Method for the Resistance of Wood-Plastic Composites to the Action of Destroying Fungi

by Anna Wiejak and Barbara Francke

Materials 2021, 14(3), 697; https://doi.org/10.3390/ma14030697 - 02 Feb 2021

Cited by 6 | Viewed by 2508

Abstract

Durability tests against fungi action for wood-plastic composites are carried out in accordance with European standard ENV 12038, but the authors of the manuscript try to prove that the assessment of the results done according to these methods is imprecise and suffers from [...] Read more.

Durability tests against fungi action for wood-plastic composites are carried out in accordance with European standard ENV 12038, but the authors of the manuscript try to prove that the assessment of the results done according to these methods is imprecise and suffers from a significant error. Fungi exposure is always accompanied by high humidity, so the result of tests made by such method is always burdened with the influence of moisture, which can lead to a wrong assessment of the negative effects of action fungus itself. The manuscript has shown a modification of such a method that separates the destructive effect of fungi from moisture accompanying the test’s destructive effect. The functional properties selected to prove the proposed modification are changes in the mass and bending strength after subsequent environmental exposure. It was found that intensive action of moisture measured in the culture chamber of about (70 ± 5)%, i.e., for 16 weeks, at (22 ± 2) °C, which was the fungi culture, which was accompanying period, led to changes in the mass of the wood-plastic composites, amounting to 50% of the final result of the fungi resistance test, and changes in the bending strength amounting to 30–46% of the final test result. As a result of the research, the correction for assessing the durability of wood-polymer composites to biological corrosion has been proposed. The laboratory tests were compared with the products’ test results following three years of exposure to the natural environment. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)

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2 pages, 162 KiB

Open AccessEditorial

Next-Generation Materials for Energy Storage and Conversion

by Il Tae Kim

Materials 2021, 14(3), 696; https://doi.org/10.3390/ma14030696 - 02 Feb 2021

Cited by 1 | Viewed by 1713

Abstract

n/a Full article

(This article belongs to the Special Issue Next-Generation Materials for Energy Storage and Conversion)

16 pages, 4902 KiB

Open AccessArticle

Parameters Identification of High Temperature Damage Model of X12 Alloy Steel for Ultra-Supercritical Rotor Using Inverse Optimization Technique

by Xuewen Chen, Kexue Du, Yuqing Du, Tingting Lian, Jiqi Liu, Rongren Bai, Zhipeng Li, Yisi Yang and Dongwon Jung

Materials 2021, 14(3), 695; https://doi.org/10.3390/ma14030695 - 02 Feb 2021

Cited by 1 | Viewed by 1894

Abstract

X12 alloy steel is a new generation material for manufacturing ultra-supercritical generator rotors. Cracks will appear on the forgings during the forging process and the rotors will be scrapped in serious cases. To optimize the forging process of the rotor and avoid the [...] Read more.

X12 alloy steel is a new generation material for manufacturing ultra-supercritical generator rotors. Cracks will appear on the forgings during the forging process and the rotors will be scrapped in serious cases. To optimize the forging process of the rotor and avoid the occurrence of crack defects in the hot forming process, based on Oyane damage model, a high temperature damage model of X12 alloy steel was proposed by introducing the influences of temperature and strain rate on the damage evolution. A reverse analysis method was proposed to determine the critical damage value of Oyane damage model by comparing experimental and simulated fracture displacement in the tensile tests. Then, the critical damage value was determined as a function of temperature and strain rate. The high temperature damage model was combined to the commercial finite element software FORGE^® to simulate the high temperature tensile test. The accuracy of the damage model was verified by comparing the difference of the fracture displacement between simulated and experimental samples. Additionally, as stress triaxiality is a significant factor influencing the damage behavior of ductile materials, the effects of temperature and strain rate on the stress triaxiality of X12 alloy steel was analyzed by simulating the high temperature tensile process, and the damage mechanism of X12 alloy steel under high stress triaxiality was analyzed by SEM (Scanning Electron Microscope). Full article

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9 pages, 2144 KiB

Open AccessArticle

Tuning the Magnetic Properties of Two-Dimensional MXenes by Chemical Etching

by Kemryn Allen-Perry, Weston Straka, Danielle Keith, Shubo Han, Lewis Reynolds, Bhoj Gautam and Daniel E. Autrey

Materials 2021, 14(3), 694; https://doi.org/10.3390/ma14030694 - 02 Feb 2021

Cited by 32 | Viewed by 3884

Abstract

Two-dimensional materials based on transition metal carbides have been intensively studied due to their unique properties including metallic conductivity, hydrophilicity and structural diversity and have shown a great potential in several applications, for example, energy storage, sensing and optoelectronics. While MXenes based on [...] Read more.

Two-dimensional materials based on transition metal carbides have been intensively studied due to their unique properties including metallic conductivity, hydrophilicity and structural diversity and have shown a great potential in several applications, for example, energy storage, sensing and optoelectronics. While MXenes based on magnetic transition elements show interesting magnetic properties, not much is known about the magnetic properties of titanium-based MXenes. Here, we measured the magnetic properties of Ti₃C₂T_x MXenes synthesized by different chemical etching conditions such as etching temperature and time. Our magnetic measurements were performed in a superconducting quantum interference device (SQUID) vibrating sample. These data suggest that there is a paramagnetic-antiferromagnetic (PM-AFM) phase transition and the transition temperature depends on the synthesis procedure of MXenes. Our observation indicates that the magnetic properties of these MXenes can be tuned by the extent of chemical etching, which can be beneficial for the design of MXenes-based spintronic devices. Full article

(This article belongs to the Section Materials Chemistry)

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17 pages, 2384 KiB

Open AccessArticle

New Model for Analytical Predictions on the Bending Capacity of Concrete Elements Reinforced with FRP Bars

by Kostiantyn Protchenko, Przemysław Leśniak, Elżbieta Szmigiera and Marek Urbański

Materials 2021, 14(3), 693; https://doi.org/10.3390/ma14030693 - 02 Feb 2021

Cited by 7 | Viewed by 2529

Abstract

Many studies on Fibre-Reinforced Polymers Reinforced Concrete (FRP-RC) beams tested in flexure have been performed by various researchers around the world. This work presents the results of statistical and mathematical analyses based on experimental data; 102 samples were collected and supplemented from 16 [...] Read more.

Many studies on Fibre-Reinforced Polymers Reinforced Concrete (FRP-RC) beams tested in flexure have been performed by various researchers around the world. This work presents the results of statistical and mathematical analyses based on experimental data; 102 samples were collected and supplemented from 16 different scientific papers. The load capacity of the beams determined on the basis of the tests was compared with the load capacity calculated on the basis of the recommendations of ACI 440.1R-15. The results obtained from experimental studies showed that for 91.4% of the samples, the underestimation of the load capacity on average was equal to 15.2% of theoretical, and for 33.3% of the beams, the load capacity was overestimated by 26.7%. The paper proposes a new empirical coefficient incorporating material parameters to be implemented into ACI 440.1R-15 flexural design approach in order to improve the accuracy of this model in scope of the nominal flexural strength capacity of FRP-reinforced beams estimation. Modifications to flexural design of FRP-RC beams with the use of ACI 440.1R-15 design code were proposed. As a result, the reliability of the analytical model is increased; therefore, the new model guarantees higher safety and cost efficiency of designed concrete structures reinforced with FRP bars. Full article

(This article belongs to the Special Issue Fiber Reinforced Polymers for Structural Strengthening)

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15 pages, 4456 KiB

Open AccessEditor’s ChoiceArticle

Phase Formation and Thermal Stability of Reactively Sputtered YTaO₄–ZrO₂ Coatings

by Bastian Stelzer, Katrin Pingen, Marcus Hans, Damian M. Holzapfel, Silvia Richter, Joachim Mayer, Konda Gokuldoss Pradeep and Jochen M. Schneider

Materials 2021, 14(3), 692; https://doi.org/10.3390/ma14030692 - 02 Feb 2021

Cited by 6 | Viewed by 2724

Abstract

Y_(1−x)/2Ta_(1−x)/2Zr_xO₂ coatings with 0 to 44 mol% ZrO₂ were synthesized by sputtering. Phase-pure M’-YTaO₄ coatings were obtained at a substrate temperature of 900 °C. Alloying with ZrO₂ resulted in the growth of [...] Read more.

Y_(1−x)/2Ta_(1−x)/2Zr_xO₂ coatings with 0 to 44 mol% ZrO₂ were synthesized by sputtering. Phase-pure M’-YTaO₄ coatings were obtained at a substrate temperature of 900 °C. Alloying with ZrO₂ resulted in the growth of M’ along with t-Zr(Y,Ta)O₂ for ≤15 mol%, while for ≥28 mol%, ZrO₂ X-ray diffraction (XRD) phase-pure metastable t was formed, which may be caused by small grain sizes and/or kinetic limitations. The former phase region transformed into M’ and M and the latter to an M’ + t and M + t phase region upon annealing to 1300 and 1650 °C, respectively. In addition to M and t, T-YTa(Zr)O₄ phase fractions were observed at room temperature for ZrO₂ contents ≥28 mol% after annealing to 1650 °C. T phase fractions increased during in situ heating XRD at 80 °C. At 1650 °C, a reaction with the α-Al₂O₃ substrate resulted in the formation of AlTaO₄ and an Al-Ta-Y-O compound. Full article

(This article belongs to the Section Thin Films and Interfaces)

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19 pages, 61873 KiB

Open AccessArticle

Lath Martensite Microstructure Modeling: A High-Resolution Crystal Plasticity Simulation Study

by Francisco-José Gallardo-Basile, Yannick Naunheim, Franz Roters and Martin Diehl

Materials 2021, 14(3), 691; https://doi.org/10.3390/ma14030691 - 02 Feb 2021

Cited by 15 | Viewed by 7170

Abstract

Lath martensite is a complex hierarchical compound structure that forms during rapid cooling of carbon steels from the austenitic phase. At the smallest, i.e., ‘single crystal’ scale, individual, elongated domains, form the elemental microstructural building blocks: the name-giving laths. Several laths of nearly [...] Read more.

Lath martensite is a complex hierarchical compound structure that forms during rapid cooling of carbon steels from the austenitic phase. At the smallest, i.e., ‘single crystal’ scale, individual, elongated domains, form the elemental microstructural building blocks: the name-giving laths. Several laths of nearly identical crystallographic orientation are grouped together to blocks, in which–depending on the exact material characteristics–clearly distinguishable subblocks might be observed. Several blocks with the same habit plane together form a packet of which typically three to four together finally make up the former parent austenitic grain. Here, a fully parametrized approach is presented which converts an austenitic polycrystal representation into martensitic microstructures incorporating all these details. Two-dimensional (2D) and three-dimensional (3D) Representative Volume Elements (RVEs) are generated based on prior austenite microstructure reconstructed from a 2D experimental martensitic microstructure. The RVEs are used for high-resolution crystal plasticity simulations with a fast spectral method-based solver and a phenomenological constitutive description. The comparison of the results obtained from the 2D experimental microstructure and the 2D RVEs reveals a high quantitative agreement. The stress and strain distributions and their characteristics change significantly if 3D microstructures are used. Further simulations are conducted to systematically investigate the influence of microstructural parameters, such as lath aspect ratio, lath volume, subblock thickness, orientation scatter, and prior austenitic grain shape on the global and local mechanical behavior. These microstructural features happen to change the local mechanical behavior, whereas the average stress–strain response is not significantly altered. Correlations between the microstructure and the plastic behavior are established. Full article

(This article belongs to the Special Issue Micromechanics: Experiment, Modeling and Theory)

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12 pages, 5178 KiB

Open AccessArticle

Chemical Reaction and Ion Bombardment Effects of Plasma Radicals on Optoelectrical Properties of SnO₂ Thin Films via Atomic Layer Deposition

by Pao-Hsun Huang, Zhi-Xuan Zhang, Chia-Hsun Hsu, Wan-Yu Wu, Chien-Jung Huang and Shui-Yang Lien

Materials 2021, 14(3), 690; https://doi.org/10.3390/ma14030690 - 02 Feb 2021

Cited by 9 | Viewed by 2979

Abstract

In this study, the effect of radical intensity on the deposition mechanism, optical, and electrical properties of tin oxide (SnO₂) thin films is investigated. The SnO₂ thin films are prepared by plasma-enhanced atomic layer deposition with different plasma power from [...] Read more.

In this study, the effect of radical intensity on the deposition mechanism, optical, and electrical properties of tin oxide (SnO₂) thin films is investigated. The SnO₂ thin films are prepared by plasma-enhanced atomic layer deposition with different plasma power from 1000 to 3000 W. The experimental results show that plasma contains different amount of argon radicals (Ar*) and oxygen radicals (O*) with the increased power. The three deposition mechanisms are indicated by the variation of Ar* and O* intensities evidenced by optical emission spectroscopy. The adequate intensities of Ar* and O* are obtained by the power of 1500 W, inducing the highest oxygen vacancies (O_V) ratio, the narrowest band gap, and the densest film structure. The refractive index and optical loss increase with the plasma power, possibly owing to the increased film density. According to the Hall effect measurement results, the improved plasma power from 1000 to 1500 W enhances the carrier concentration due to the enlargement of O_V ratio, while the plasma powers higher than 1500 W further cause the removal of O_V and the significant bombardment from Ar*, leading to the increase of resistivity. Full article

(This article belongs to the Special Issue Atomic Layer Deposition Technique in Material Science)

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19 pages, 3244 KiB

Open AccessArticle

Strength Parameters of Foamed Geopolymer Reinforced with GFRP Mesh

by Rafał Krzywoń and Szymon Dawczyński

Materials 2021, 14(3), 689; https://doi.org/10.3390/ma14030689 - 02 Feb 2021

Cited by 12 | Viewed by 2394

Abstract

The foaming of geopolymers lowers their density, thus opening up new environmental benefits, including acoustic and thermal insulation. At the same time, foaming disturbs the homogeneity of the material, which worsens the strength parameters, and particularly those related to tension, which can be [...] Read more.

The foaming of geopolymers lowers their density, thus opening up new environmental benefits, including acoustic and thermal insulation. At the same time, foaming disturbs the homogeneity of the material, which worsens the strength parameters, and particularly those related to tension, which can be improved by introducing reinforcement. This paper presents the results of research on foamed geopolymers reinforced with glass fiber meshes, a type of reinforcement that provides an adequate bond. The samples tested here were based on three types of coal fly ash, and were foamed with varying doses of hydrogen peroxide. Samples were cured at 40 °C and were tested after 28 days of maturing at ambient temperature. The strength parameters of the synthesized geopolymers were determined via laboratory testing, and were used to evaluate load-bearing capacity models of the tested samples reinforced with glass fiber mesh. The results showed the importance of the type of ash on the strength properties and efficiency of reinforcement. At the same time, a slight deterioration in the glass fibers was noticed; this was caused by the presence of sodium hydroxide solution, which was used as an activator. Full article

(This article belongs to the Special Issue Research and Development of Modified Building Materials)

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16 pages, 8053 KiB

Open AccessArticle

The Effect of Torsional Vibration in Longitudinal–Torsional Coupled Ultrasonic Vibration-Assisted Grinding of Silicon Carbide Ceramics

by Yurong Chen, Honghua Su, Jingyuan He, Ning Qian, Jiaqing Gu, Jiuhua Xu and Kai Ding

Materials 2021, 14(3), 688; https://doi.org/10.3390/ma14030688 - 02 Feb 2021

Cited by 14 | Viewed by 2554

Abstract

Rotary longitudinal–torsional coupled ultrasonic vibration-assisted grinding (LTUAG) is a new manufacturing method that can improve the grinding ability of silicon carbide ceramics. However, compared with longitudinal ultrasonic vibration-assisted grinding (LUAG), the role of torsional vibration in the grinding process is unclear. In this [...] Read more.

Rotary longitudinal–torsional coupled ultrasonic vibration-assisted grinding (LTUAG) is a new manufacturing method that can improve the grinding ability of silicon carbide ceramics. However, compared with longitudinal ultrasonic vibration-assisted grinding (LUAG), the role of torsional vibration in the grinding process is unclear. In this study, an effective method for measuring longitudinal–torsional coupled ultrasonic vibration amplitude and an experimental setup for measuring actual amplitude during grinding are proposed. The trajectory of the abrasive grains under the same grinding parameters and the same longitudinal amplitude during LTUAG and LUAG are analysed. Ultrasonic amplitude curves under the condition of tool rotation are then measured and analysed. Finally, the effect of torsional vibration on grinding force and surface roughness under the same grinding conditions is explained. Experimental analysis shows that the introduction of torsional vibration has little effect on the trajectory length and does not change the number of interference overlaps between abrasive grain tracks. Torsional vibration will only increase the cutting speed during grinding and reduce the undeformed chip thickness, which will reduce the grinding force and improve the surface roughness of LTUAG. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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15 pages, 3631 KiB

Open AccessArticle

Atomic Force Microscopy Investigation of the Interactions between the MCM Helicase and DNA

by Amna Abdalla Mohammed Khalid, Pietro Parisse, Barbara Medagli, Silvia Onesti and Loredana Casalis

Materials 2021, 14(3), 687; https://doi.org/10.3390/ma14030687 - 02 Feb 2021

Cited by 1 | Viewed by 2338

Abstract

The MCM (minichromosome maintenance) protein complex forms an hexameric ring and has a key role in the replication machinery of Eukaryotes and Archaea, where it functions as the replicative helicase opening up the DNA double helix ahead of the polymerases. Here, we present [...] Read more.

The MCM (minichromosome maintenance) protein complex forms an hexameric ring and has a key role in the replication machinery of Eukaryotes and Archaea, where it functions as the replicative helicase opening up the DNA double helix ahead of the polymerases. Here, we present a study of the interaction between DNA and the archaeal MCM complex from Methanothermobacter thermautotrophicus by means of atomic force microscopy (AFM) single molecule imaging. We first optimized the protocol (surface treatment and buffer conditions) to obtain AFM images of surface-equilibrated DNA molecules before and after the interaction with the protein complex. We discriminated between two modes of interaction, one in which the protein induces a sharp bend in the DNA, and one where there is no bending. We found that the presence of the MCM complex also affects the DNA contour length. A possible interpretation of the observed behavior is that in one case the hexameric ring encircles the dsDNA, while in the other the nucleic acid wraps on the outside of the ring, undergoing a change of direction. We confirmed this topographical assignment by testing two mutants, one affecting the N-terminal β-hairpins projecting towards the central channel, and thus preventing DNA loading, the other lacking an external subdomain and thus preventing wrapping. The statistical analysis of the distribution of the protein complexes between the two modes, together with the dissection of the changes of DNA contour length and binding angle upon interaction, for the wild type and the two mutants, is consistent with the hypothesis. We discuss the results in view of the various modes of nucleic acid interactions that have been proposed for both archaeal and eukaryotic MCM complexes. Full article

(This article belongs to the Special Issue Application of Scanning Probe Techniques in the Study of Biomaterials and Biomechanisms)

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24 pages, 2342 KiB

Open AccessArticle

Laboratory Test to Evaluate the Resistance of Cementitious Materials to Biodeterioration in Sewer Network Conditions

by Amr Aboulela, Matthieu Peyre Lavigne, Amaury Buvignier, Marlène Fourré, Maud Schiettekatte, Tony Pons, Cédric Patapy, Orlane Robin, Mansour Bounouba, Etienne Paul and Alexandra Bertron

Materials 2021, 14(3), 686; https://doi.org/10.3390/ma14030686 - 02 Feb 2021

Cited by 8 | Viewed by 2986

Abstract

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are [...] Read more.

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are proven to not be representative of the actual deterioration phenomena in real sewer conditions, a biological test–named the Biogenic Acid Concrete (BAC) test–was developed at the University of Toulouse to reproduce the biological reactions involved in the process of concrete biodeterioration in sewers. The test consists in trickling a solution containing a safe reduced sulfur source onto the surface of cementitious substrates previously covered with a high diversity microbial consortium. In these conditions, a sulfur-oxidizing metabolism naturally develops in the biofilm and leads to the production of biogenic sulfuric acid on the surface of the material. The representativeness of the test in terms of deterioration mechanisms has been validated in previous studies. A wide range of cementitious materials have been exposed to the biodeterioration test during half a decade. On the basis of this large database and the expertise gained, the purpose of this paper is (i) to propose a simple and robust performance criterion for the test (standardized leached calcium as a function of sulfate produced by the biofilm), and (ii) to demonstrate the repeatability, reproducibility, and discriminability of the test method. In only a 3-month period, the test was able to highlight the differences in the performances of common cement-based materials (CEM I, CEM III, and CEM V) and special calcium aluminate cement (CAC) binders with different nature of aggregates (natural silica and synthetic calcium aluminate). The proposed performance indicator (relative standardized leached calcium) allowed the materials to be classified according to their resistance to biogenic acid attack in sewer conditions. The repeatability of the test was confirmed using three different specimens of the same material within the same experiment and the reproducibility of the results was demonstrated by standardizing the results using a reference material from 5 different test campaigns. Furthermore, developing post-testing processing and calculation methods constituted a first step toward a standardized test protocol. Full article

(This article belongs to the Special Issue Concrete and Construction Materials)

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19 pages, 10962 KiB

Open AccessArticle

A Study on Machining Performances of Micro-Drilling of Multi-Directional Carbon Fiber Reinforced Plastic (MD-CFRP) Based on Nano-Solid Dry Lubrication Using Graphene NanoPlatelets

by Jin Woo Kim, Jungsoo Nam, Jaehun Jeon and Sang Won Lee

Materials 2021, 14(3), 685; https://doi.org/10.3390/ma14030685 - 02 Feb 2021

Cited by 12 | Viewed by 3010

Abstract

The objective of this study is to investigate the tribological behavior of graphene nanoplatelets (xGnPs) as nano-solid lubricants, and to evaluate their applicability to the micro-drilling of multi-directional carbon fiber-reinforced plastic (MD-CFRP). To verify the tribological effect of nano-solid lubricants, three kinds of [...] Read more.

The objective of this study is to investigate the tribological behavior of graphene nanoplatelets (xGnPs) as nano-solid lubricants, and to evaluate their applicability to the micro-drilling of multi-directional carbon fiber-reinforced plastic (MD-CFRP). To verify the tribological effect of nano-solid lubricants, three kinds of xGnPs (xGnP C-750, xGnP M-5, and xGnP H-5), multiwall carbon nanotubes (MWCNTs), and hBN are compared by the ball-on-plate test. Of these, three xGnPs are selected as nano-solid lubricants to investigate the micro-drilling performance of MD-CFRP using nano-solid dry lubrication, and the experimental results demonstrate that all xGnPs can enhance lubrication action in terms of surface quality (delamination, uncut fiber, and inner surface) and tool wear. In particular, larger graphene nanoplatelets (xGnP M-5 and xGnP H-5) are superior to the smaller one (xGnP C-750) by guaranteeing enhanced sliding action between the tool grain and the CFRP composite. Full article

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10 pages, 2162 KiB

Open AccessArticle

4H-SiC Drift Step Recovery Diode with Super Junction for Hard Recovery

by Xiaoxue Yan, Lin Liang, Xinyuan Huang, Heqing Zhong and Zewei Yang

Materials 2021, 14(3), 684; https://doi.org/10.3390/ma14030684 - 02 Feb 2021

Cited by 4 | Viewed by 2692

Abstract

Silicon carbide (SiC) drift step recovery diode (DSRD) is a kind of opening-type pulsed power device with wide bandgap material. The super junction (SJ) structure is introduced in the SiC DSRD for the first time in this paper, in order to increase the [...] Read more.

Silicon carbide (SiC) drift step recovery diode (DSRD) is a kind of opening-type pulsed power device with wide bandgap material. The super junction (SJ) structure is introduced in the SiC DSRD for the first time in this paper, in order to increase the hardness of the recovery process, and improve the blocking capability at the same time. The device model of the SJ SiC DSRD is established and its breakdown principle is verified. The effects of various structure parameters including the concentration, the thickness, and the width of the SJ layer on the electrical characteristics of the SJ SiC DSRD are discussed. The characteristics of the SJ SiC DSRD and the conventional SiC DSRD are compared. The results show that the breakdown voltage of the SJ SiC DSRD is 28% higher than that of the conventional SiC DSRD, and the dv/dt output by the circuit based on SJ SiC DSRD is 31% higher than that of conventional SiC DSRD. It is verified that the SJ SiC DSRD can achieve higher voltage, higher cut-off current and harder recovery characteristics than the conventional SiC DSRD, so as to output a higher dv/dt voltage on the load. Full article

(This article belongs to the Special Issue Silicon Carbide: From Fundamentals to Applications)

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7 pages, 2026 KiB

Open AccessArticle

Influence of Gas Annealing on Sensitivity of AlN/4H-SiC-Based Temperature Sensors

by Seung-Woo Jung, Myeong-Cheol Shin, Michael A. Schweitz, Jong-Min Oh and Sang-Mo Koo

Materials 2021, 14(3), 683; https://doi.org/10.3390/ma14030683 - 02 Feb 2021

Cited by 9 | Viewed by 2455

Abstract

In this study, the physical and electrical characteristics of an AlN/4H-SiC Schottky barrier diode-based temperature sensor annealed in various gas atmospheres were investigated. An aluminum nitride (AlN) thin film was deposited on a 4H-SiC substrate via radio-frequency sputtering followed by annealing in N [...] Read more.

In this study, the physical and electrical characteristics of an AlN/4H-SiC Schottky barrier diode-based temperature sensor annealed in various gas atmospheres were investigated. An aluminum nitride (AlN) thin film was deposited on a 4H-SiC substrate via radio-frequency sputtering followed by annealing in N₂ or O₂ gas. The chemical composition of the film was determined by X-ray photoelectron spectroscopy (XPS) before and after annealing, and its electrical properties were evaluated by plotting a current–voltage (I–V) curve. The voltage–temperature (V–T) characteristics of the sensor were extracted from the current–voltage–temperature (I–V–T) plots constructed in the temperature range between 475 and 300 K in steps of 25 K. Sensitivities of 9.77, 9.37, and 2.16 mV/K were obtained for the as-grown, N₂-annealed, and O₂-annealed samples, respectively. Full article

(This article belongs to the Special Issue SiC Materials and Applications)

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20 pages, 10086 KiB

Open AccessArticle

Machine Vision for As-Built Modeling of Complex Draped Composite Structures

by Oliver Döbrich, Ayoh Anderegg, Nicolas Gort and Christian Brauner

Materials 2021, 14(3), 682; https://doi.org/10.3390/ma14030682 - 02 Feb 2021

Cited by 4 | Viewed by 2081

Abstract

The transition in the use of fiber composite structures from special applications to application in the mass market is accompanied by high demands in quality assurance. The consequential costs of unclear process design, unknown fiber orientations, and uncertainty regarding the effects of any [...] Read more.

The transition in the use of fiber composite structures from special applications to application in the mass market is accompanied by high demands in quality assurance. The consequential costs of unclear process design, unknown fiber orientations, and uncertainty regarding the effects of any fiber angle deviations can lead to market considerations (higher costs/time for development) in mass production that advise against the use of fiber composites, despite their superiority compared with conservative materials. Active monitoring of the deposited reinforcement layers and an evaluation of the real fiber orientation can form the basis of a robust industrial use of fiber composites by a first-time right production that is able to reduce the process variability. This paper describes the application of an image analysis system to provide both geometric topology and local reinforcement fiber orientation feedback to a finite-element (FE) model. The application during an industrial composite part production is described, and the possibilities of using it for the improvement of the lightweight character, the reduction of rejects, and the realization of a quality management system are shown. The determined component data are made directly available for use in numerical simulations and, thus, they serve as a non-destructive evaluation of the components under real conditions in which all production-dependent influences that affect the fiber orientation are incorporated. Full article

(This article belongs to the Special Issue Numerical and Analytical Modeling of Anisotropic Fiber-Based Materials)

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11 pages, 3720 KiB

Open AccessArticle

The Concurrent Sintering-Crystallization Behavior of Fluoride-Containing Wollastonite Glass-Ceramics

by Chuanhui Li, Peng Li, Jianliang Zhang, Fengjuan Pei, Xingchen Gong, Wei Zhao, Bingji Yan and Hongwei Guo

Materials 2021, 14(3), 681; https://doi.org/10.3390/ma14030681 - 02 Feb 2021

Cited by 2 | Viewed by 1851

Abstract

The fabrication of well densified wollastonite with smooth appearance by direct sintering method is still a challenge due to the competitive behaviors between sintering and crystallization. In this study, the coarser glass frits with a size of 1–4 mm are subjected to heat [...] Read more.

The fabrication of well densified wollastonite with smooth appearance by direct sintering method is still a challenge due to the competitive behaviors between sintering and crystallization. In this study, the coarser glass frits with a size of 1–4 mm are subjected to heat treatment at different temperatures. An attempt of integrating differential thermal analyzer with a slag melting temperature characteristic tester was exploited to monitor the heat and geometry changes during the heating. The results showed that the addition of CaF₂ can significantly promote the crystallization of wollastonite at 940 °C, while hindering the sintering ability. At higher temperature, the increase of CaF₂ acts as flux and favors the formation of eutectics, leading to a decline in the precipitation amount of wollastonite. The predominated liquid sintering brought fast shrinkage. It was found out that high content of CaF₂ narrows the dense sintering temperature range and results in uneven surfaces. In order to obtain wollastonite glass-ceramics with smooth appearance, the maximum content of CaF₂ in sintering glass-ceramics should be limited to 2 wt.%. Full article

(This article belongs to the Section Construction and Building Materials)

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9 pages, 649 KiB

Open AccessTechnical Note

Calorimetric Studies of Magnesium-Rich Mg-Pd Alloys

by Adam Dębski, Sylwia Terlicka, Władysław Gąsior, Wojciech Gierlotka, Magda Pęska, Julita Dworecka-Wójcik and Marek Polański

Materials 2021, 14(3), 680; https://doi.org/10.3390/ma14030680 - 02 Feb 2021

Cited by 2 | Viewed by 2318

Abstract

Solution calorimetry with liquid aluminum as the bath was conducted to measure the enthalpy of a solution of magnesium and palladium as well as the standard formation enthalpies of selected magnesium-palladium alloys. These alloys were synthesized from pure elements, which were melted in [...] Read more.

Solution calorimetry with liquid aluminum as the bath was conducted to measure the enthalpy of a solution of magnesium and palladium as well as the standard formation enthalpies of selected magnesium-palladium alloys. These alloys were synthesized from pure elements, which were melted in a resistance furnace that was placed in a glove box containing high-purity argon and a very low concentration of impurities, such as oxygen and water vapor. A Setaram MHTC 96 Line evo drop calorimeter was used to determine the energetic effects of the solution. The enthalpies of the Mg and Pd solutions in liquid aluminum were measured at 1033 K, and they equaled −8.6 ± 1.1 and −186.8 ± 1.1 kJ/mol, respectively. The values of the standard formation enthalpy of the investigated alloys with concentrations close to the Mg₆Pd, ε, Mg₅Pd₂, and Mg₂Pd intermetallic phases were determined as follows: −28.0 ± 1.2 kJ/mol of atoms, −32.6 ± 1.6 kJ/mol of atoms, −46.8 ± 1.4 kJ/mol of atoms, and −56.0 ± 1.6 kJ/mol of atoms, respectively. The latter data were compared with existing experimental and theoretical data from the literature along with data calculated using the Miedema model. Full article

(This article belongs to the Section Materials Chemistry)

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17 pages, 4573 KiB

Open AccessArticle

Functionalization Mechanism of Reduced Graphene Oxide Flakes with BF₃·THF and Its Influence on Interaction with Li⁺ Ions in Lithium-Ion Batteries

by Łukasz Kaczmarek, Magdalena Balik, Tomasz Warga, Ilona Acznik, Katarzyna Lota, Sebastian Miszczak, Anna Sobczyk-Guzenda, Karol Kyzioł, Piotr Zawadzki and Agnieszka Wosiak

Materials 2021, 14(3), 679; https://doi.org/10.3390/ma14030679 - 02 Feb 2021

Cited by 2 | Viewed by 2451

Abstract

Doping of graphene and a controlled induction of disturbances in the graphene lattice allows the production of numerous active sites for lithium ions on the surface and edges of graphene nanolayers and improvement of the functionality of the material in lithium-ion batteries (LIBs). [...] Read more.

Doping of graphene and a controlled induction of disturbances in the graphene lattice allows the production of numerous active sites for lithium ions on the surface and edges of graphene nanolayers and improvement of the functionality of the material in lithium-ion batteries (LIBs). This work presents the process of introducing boron and fluorine atoms into the structure of the reduced graphene during hydrothermal reaction with boron fluoride tetrahydrofuran (BF₃·THF). The described process is a simple, one-step synthesis with little to no side products. The synthesized materials showed an irregular, porous structure, with an average pore size of 3.44–3.61 nm (total pore volume (BJH)) and a multi-layer structure and a developed specific surface area at the level of 586–660 m²/g (analysis of specific surface Area (BET)). On the external surfaces, the occurrence of irregular particles with a size of 0.5 to 10 µm was observed, most probably the effect of doping the graphene structure and the formation of sp³ hybridization defects. The obtained materials show the ability to store electric charge due to the development of the specific surface area. Based on cyclic voltammetry, the tested material showed a capacity of 450–550 mAh/g (charged up to 2.5 V). Full article

(This article belongs to the Special Issue Processing and Thermal Properties of Hybrid Composites)

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14 pages, 1667 KiB

Open AccessArticle

Copper–Calcium Hydroxide and Permanent Electrophoretic Current for Treatment of Apical Periodontitis

by Agron Meto, Etleva Droboniku, Elisabetta Blasi, Bruna Colombari, Emiljano Tragaj, Gabriele Cervino, Luca Fiorillo and Aida Meto

Materials 2021, 14(3), 678; https://doi.org/10.3390/ma14030678 - 02 Feb 2021

Cited by 11 | Viewed by 2721

Abstract

Endodontic failure has been and continues to be a problem for endodontics-specialists. Complicated anatomy, numerous foramens, and accessory canals are an environment for microorganisms to infect the teeth. The purpose of the present work was to evaluate the regeneration of copper–calcium hydroxide (Cupral)-endodontically [...] Read more.

Endodontic failure has been and continues to be a problem for endodontics-specialists. Complicated anatomy, numerous foramens, and accessory canals are an environment for microorganisms to infect the teeth. The purpose of the present work was to evaluate the regeneration of copper–calcium hydroxide (Cupral)-endodontically treated teeth diagnosed with apical periodontitis using an electrophoresis technique. In total, 132 patients, aging from 19 to 65 years old, underwent endodontic treatment mono- and multi-radicular teeth, with complicated canals from January 2019 to June 2020. The patients were divided into two groups: (i) the control group—which included 54 patients (n = 62 teeth) receiving endodontic paste (Calcipast + 1) and, as final filling, the AH-Plus^TM cement—and (ii) the Cupral group, which included 78 patients (n = 80 teeth) receiving Cupral paste plus the electrophoretic current and, as final filling, the Atacamit-alkaline cement. The clinical cases were periodically observed along an 18-month follow-up period via radiography. Data were expressed as focal size of the lesions (mean ± standard error (SEM) of all the radiographic outcomes) observed in each group at each interval point. Statistical analysis was performed using the Student’s t-test that allowed us to compare the control and Cupral groups; the statistical significance was set at p < 0.05 and p < 0.01, where the latter was highly significant. Before treatments, the focal sizes were 4.8 mm and 4.95 mm for control and Cupral-treated groups, respectively. After 6 months, the mean focal sizes were 3.9 mm and 2.14 mm for the control and Cupral groups, respectively. After 12 months, in the control group, the mean focal size was measured at 2.8 mm, while, in Cupral group, the lesion size decreased down to 0.31 mm and a highly dynamic regeneration of the destructive focal-bone occurred. After 18 months, the lesions were further significantly reduced in the control group (mean values of 2.62 mm), while they were barely detectable in the Cupral group (0.2 mm). In conclusion, we provide initial evidence that the Cupral-electrophoresis methodology is effective in treating destructive periodontitis of teeth with problematic canals up to 18 months, thus allowing teeth preservation. Full article

(This article belongs to the Special Issue Dental Materials in Endodontic and Post-endodontic Therapy)

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15 pages, 5552 KiB

Open AccessArticle

Preparation and Tensile Properties of Novel Porous Plates Made by Stainless Steel Wire Mesh and Powder Composites

by Shengcun Lin and Zhaoyao Zhou

Materials 2021, 14(3), 677; https://doi.org/10.3390/ma14030677 - 01 Feb 2021

Cited by 4 | Viewed by 2105

Abstract

Porous metal materials have important mechanical properties, and there are various manufacturing methods to produce them. In this paper, a porous, thin strip was fabricated by the composite rolling of stainless steel wire mesh and stainless steel powder. Then, a porous plate of [...] Read more.

Porous metal materials have important mechanical properties, and there are various manufacturing methods to produce them. In this paper, a porous, thin strip was fabricated by the composite rolling of stainless steel wire mesh and stainless steel powder. Then, a porous plate of stainless steel wire mesh and powder composite (SWMPC) was prepared by folding, pressing, and vacuum sintering the thin strip, and its structural characteristics and permeability were studied. The effects of the gap of the roller, gap of the powder box, number of layers by folding, and sintering parameters on the porosity and mechanical properties were also studied. The results indicated that the permeability increased with the increasing of porosity. Sintering parameters had a great influence on the mechanical properties. The larger the roll gap, the higher the porosity and the weaker the mechanical properties. As the gap of the powder box increased, the porosity decreased and the mechanical properties improved. The number of layers had no effect on the porosity. The first three stages of tensile curves of 10 and 15 layers were deformation stages and generally coincided, the time was short at the fracture stage. However, the mechanical properties got a raise when layers was 15. Full article

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13 pages, 3644 KiB

Open AccessArticle

Reusable Sensor for Strontium Sulfate Scale Monitoring in Seawater

by Abdellatif Bouchalkha, Radouane Karli and Khalid Alhammadi

Materials 2021, 14(3), 676; https://doi.org/10.3390/ma14030676 - 01 Feb 2021

Cited by 2 | Viewed by 2562

Abstract

The onset of scaling in oil pipelines can halt or drastically reduce oil production, causing huge financial losses and delays. Current methods used to monitor scaling can take weeks, while the scaling process only takes few hours. The proposed sensor is designed for [...] Read more.

The onset of scaling in oil pipelines can halt or drastically reduce oil production, causing huge financial losses and delays. Current methods used to monitor scaling can take weeks, while the scaling process only takes few hours. The proposed sensor is designed for online monitoring of strontium ions concentration in seawater as an early scaling indicator. The sensor operates in the GHz range by probing the shift in the resonance frequency due to changes in the ionic concentrations of the medium. The results show selective sensitivity to changes in the strontium ions concentration even in the presence of many other ions found in seawater. The measured sensitivity is found to be stable and linear with a detection level of better than 0.08% (0.042 mol/L) of strontium ions in seawater. This work demonstrates a robust GHz sensor for strontium sulfate scale monitoring and early detection, which could be used in the oil industry to prevent huge production losses. These results could also be extended further to target the monitoring of other ions in different industrial sectors. Full article

(This article belongs to the Special Issue Materials for Sources and Detectors in the GIGA-TERA-MIR Range 2020)

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11 pages, 8525 KiB

Open AccessEditor’s ChoiceArticle

Effect of the Particle Size and Matrix Strength on Strengthening and Damage Process of the Particle Reinforced Metal Matrix Composites

by Zhiyu Yang, Jianzhong Fan, Yanqiang Liu, Junhui Nie, Ziyue Yang and Yonglin Kang

Materials 2021, 14(3), 675; https://doi.org/10.3390/ma14030675 - 01 Feb 2021

Cited by 21 | Viewed by 2693

Abstract

Roles of the particle, strengthening, and weakening during deformation of the particle reinforced metal matrix composite, were studied using in situ technique. Composites with three different strengths Al-Cu-Mg alloy matrices reinforced by three sizes SiC particles were manufactured and subjected to in situ [...] Read more.

Roles of the particle, strengthening, and weakening during deformation of the particle reinforced metal matrix composite, were studied using in situ technique. Composites with three different strengths Al-Cu-Mg alloy matrices reinforced by three sizes SiC particles were manufactured and subjected to in situ tensile testing. Based on in situ observation, damage process, fraction and size distribution of the cracked particles were collected to investigate the behavior of the particle during composite deformation. The presence of the particle strengthens the composite, while the particle cracking under high load weakens the composite. This strengthening to weakening transformation is controlled by the damage process of the particle and decided by the particle strength, size distribution, and the matrix flow behavior together. With a proper match of the particle and matrix, an effective strengthening can be obtained. Finally, the effective match range of the particle and the matrix was defined as a function of the particle size and the matrix strength. Full article

(This article belongs to the Special Issue Advanced Composite Materials: Theory, Design and Applications)

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30 pages, 7098 KiB

Open AccessEditor’s ChoiceReview

Silk-Based Materials for Hard Tissue Engineering

by Vanessa J. Neubauer, Annika Döbl and Thomas Scheibel

Materials 2021, 14(3), 674; https://doi.org/10.3390/ma14030674 - 01 Feb 2021

Cited by 29 | Viewed by 4156

Abstract

Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based [...] Read more.

Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based materials are promising for bone tissue regeneration as they fulfill several of such necessary requirements, and they are non-toxic and biodegradable. They can be processed into a variety of morphologies such as hydrogels, particles and fibers and can be mineralized. Therefore, silk-based materials are versatile candidates for biomedical applications in the field of hard tissue engineering. This review summarizes silk-based approaches for mineralized tissue replacements, and how to find the balance between sufficient material stiffness upon mineralization and cell survival upon attachment as well as nutrient supply. Full article

(This article belongs to the Special Issue Silk-Based Biomaterials)

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16 pages, 3929 KiB

Open AccessEditor’s ChoiceArticle

Coaxial Monitoring of AISI 316L Thin Walls Fabricated by Direct Metal Laser Deposition

by Vito Errico, Sabina Luisa Campanelli, Andrea Angelastro, Michele Dassisti, Marco Mazzarisi and Cesare Bonserio

Materials 2021, 14(3), 673; https://doi.org/10.3390/ma14030673 - 01 Feb 2021

Cited by 24 | Viewed by 2664

Abstract

Direct metal laser deposition (DMLD) is an additive manufacturing technique suitable for coating and repair, which has been gaining a growing interest in 3D manufacturing applications in recent years. However, its diffusion in the manufacturing industry is still limited due to technical challenges [...] Read more.

Direct metal laser deposition (DMLD) is an additive manufacturing technique suitable for coating and repair, which has been gaining a growing interest in 3D manufacturing applications in recent years. However, its diffusion in the manufacturing industry is still limited due to technical challenges to be solved—both the sub-optimal quality of the final parts and the low repeatability of the process make the DMLD inadequate for high-value applications requiring high-performance standards. Thus, real-time monitoring and process control are indispensable requirements for improving the DMLD process. The aim of this study was the optimization of deposition strategies for the fabrication of thin walls in AISI 316L stainless steel. For this purpose, a coaxial monitoring system and image processing algorithms were employed to study the melt pool geometry. The comparison tests carried out highlighted how the region-based active contour algorithm used for image processing is more efficient and stable than others covered in the literature. The results allowed the identification of the best deposition strategy. Therefore, it is shown how this monitoring methodology proved to be suitable for designing and implementing the right building strategy for DMLD manufactured 3D components. A fast and stable image processing method was achieved, which can be considered for future closed-loop monitoring in real-time applications. Full article

(This article belongs to the Special Issue Laser Deposition Processes)

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