Materials

16 pages, 6254 KiB

Open AccessArticle

Microstructure and Abrasive Wear Resistance of Various Alloy Hardfacings for Application on Heavy-Duty Chipper Tools in Forestry Shredding and Mulching Operations

by Ladislav Falat, Miroslav Džupon, Miroslava Ťavodová, Richard Hnilica, Veronika Ľuptáčiková, Lucia Čiripová, Viera Homolová and Katarína Ďurišinová

Materials 2019, 12(13), 2212; https://doi.org/10.3390/ma12132212 - 9 Jul 2019

Cited by 16 | Viewed by 3760

Abstract

Five different alloy hardfacings on 16MnCr5 grade low-carbon ferritic–pearlitic steel were investigated in terms of their abrasive wear resistance in laboratory testing conditions. The selected hardfacing materials, namely “E520 RB”, “RD 571”, “LNM 420FM”, “E DUR 600”, and “Weartrode 62”, were individually deposited [...] Read more.

Five different alloy hardfacings on 16MnCr5 grade low-carbon ferritic–pearlitic steel were investigated in terms of their abrasive wear resistance in laboratory testing conditions. The selected hardfacing materials, namely “E520 RB”, “RD 571”, “LNM 420FM”, “E DUR 600”, and “Weartrode 62”, were individually deposited onto plain ground-finish surfaces of 10 mm thick steel plate samples. The studied hardfacings were fabricated using several different welding methods and process parameters proposed by their industrial manufacturers. In the present comparative study, the results obtained from laboratory abrasive wear tests of the investigated hardfacings were analyzed and discussed in relation to their microstructure, hardness, and wear mechanism characteristics. Regardless of great variety in microstructure and chemical composition of individual hardfacing materials, the results clearly indicated the governing factor for the wear resistance improvement to be the overall carbon content of the used hardfacing material. Thus it has been shown that the “E520 RB” hardfacing exhibited the highest abrasive wear resistance thanks to its appropriate hardness and beneficial “ledeburite-type” eutectic microstructure. Full article

(This article belongs to the Special Issue Tribology: Friction and Wear of Engineering Materials)

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13 pages, 5158 KiB

Open AccessArticle

Surface Roughness Characterisation and Analysis of the Electron Beam Melting (EBM) Process

by Manuela Galati, Paolo Minetola and Giovanni Rizza

Materials 2019, 12(13), 2211; https://doi.org/10.3390/ma12132211 - 9 Jul 2019

Cited by 67 | Viewed by 6407

Abstract

Electron Beam Melting (EBM) is a metal powder bed fusion (PBF) process in which the heat source is an electron beam. Differently from other metal PBF processes, today, EBM is used for mass production. As-built EBM parts are clearly recognisable by their surface [...] Read more.

Electron Beam Melting (EBM) is a metal powder bed fusion (PBF) process in which the heat source is an electron beam. Differently from other metal PBF processes, today, EBM is used for mass production. As-built EBM parts are clearly recognisable by their surface roughness, which is, in some cases, one of the major limitations of the EBM process. The aim of this work is to investigate the effects of the orientation and the slope of the EBM surfaces on the surface roughness. Additionally, the machine repeatability is studied by measuring the roughness of surfaces built at different positions on the start plate. To these aims, a specific artefact was designed. Replicas of the artefact were produced using an Arcam A2X machine and Ti6Al4V powder. Descriptive and inferential statistical methods were applied to investigate whether the surface morphology was affected by process factors. The results show significant differences between the upward and downward surfaces. The upward surfaces appear less rough than the downward ones, for which a lower standard deviation was obtained in the results. The roughness of the upward surfaces is linearly influenced by the sloping angle, while the heat distribution on the cross-section was found to be a key factor in explaining the roughness of the downward surfaces. Full article

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

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13 pages, 2112 KiB

Open AccessArticle

Femtosecond Laser Nano/Micro Textured Ti6Al4V Surfaces—Effect on Wetting and MG-63 Cell Adhesion

by Georg Schnell, Susanne Staehlke, Ulrike Duenow, J. Barbara Nebe and Hermann Seitz

Materials 2019, 12(13), 2210; https://doi.org/10.3390/ma12132210 - 9 Jul 2019

Cited by 45 | Viewed by 5735

Abstract

Nano- and microstructured titanium surfaces have recently attracted attention in the field of regenerative medicine because of the influence which surface characteristics such as roughness and wettability can have on cellular processes. This study focuses on the correlation of surface properties (wettability and [...] Read more.

Nano- and microstructured titanium surfaces have recently attracted attention in the field of regenerative medicine because of the influence which surface characteristics such as roughness and wettability can have on cellular processes. This study focuses on the correlation of surface properties (wettability and nano/micro texture) of laser-structured Ti6Al4V samples with pronounced cell adhesion. Samples were structured with multiple laser parameters in order to create a range of surface properties. Surface characterization was performed by contact angle measurements 1 and 7 days after laser processing. The arithmetic mean roughness of the material surface in an area (Sa) was determined by means of confocal laser scanning microscopy (CLSM). Immediately after wettability tests of the laser-structured surfaces, in vitro experiments with human MG-63 osteoblasts were carried out. For this purpose, the cell morphology and actin cytoskeleton organization were analyzed using CLSM and scanning electron microscopy. On rough microstructures with deep cavities, the cell growth and spreading were inhibited. An improved cellular adhesion and growth on nanostructured and sinusoidal microstructured surfaces could be demonstrated, regardless of hydrophilicity of the surfaces. Full article

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24 pages, 9057 KiB

Open AccessArticle

Generalized Softened Variable Angle Truss Model for RC Hollow Beams under Torsion

by Luís Bernardo

Materials 2019, 12(13), 2209; https://doi.org/10.3390/ma12132209 - 9 Jul 2019

Cited by 3 | Viewed by 2839

Abstract

In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to [...] Read more.

In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to cover RC hollow beams under torsion. The modification of the calculation procedure, in order to account for the specific behavior of RC hollow beams for low loading levels, as well as the final solution procedure, is presented. The theoretical predictions from the extended GSVATM are compared with experimental results of RC hollow beams under torsion found in the literature. Good agreement is observed between the experimental and theoretical results, for both high and low loading levels. Full article

(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)

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12 pages, 11437 KiB

Open AccessArticle

An Experimental Study on Micro-Milling of a Medical Grade Co-Cr-Mo Alloy Produced by Selective Laser Melting

by Gabriele Allegri, Alessandro Colpani, Paola Serena Ginestra and Aldo Attanasio

Materials 2019, 12(13), 2208; https://doi.org/10.3390/ma12132208 - 9 Jul 2019

Cited by 44 | Viewed by 5023

Abstract

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this [...] Read more.

Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this field, micro-milling can be used for the creation of micro-scale details on the printed parts, not obtainable with Additive Manufacturing techniques. In particular, there is a lack of scientific research in the field of the fundamental material removal mechanisms involving micro-milling of Co-Cr-Mo alloys. Therefore, this paper presents a micro-milling characterization of Co-Cr-Mo samples produced by Additive Manufacturing with the Selective Laser Melting (SLM) technique. In particular, microchannels with different depths were made in order to evaluate the material behavior, including the chip formation mechanism, in micro-milling. In addition, the resulting surface roughness (Ra and Sa) and hardness were analyzed. Finally, the cutting forces were acquired and analyzed in order to ascertain the minimum uncut chip thickness for the material. The results of the characterization studies can be used as a basis for the identification of a machining window for micro-milling of biomedical grade cobalt-chromium-molybdenum (Co-Cr-Mo) alloys. Full article

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

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8 pages, 3312 KiB

Open AccessArticle

Analysis of the Basal Plane Dislocation Density and Thermomechanical Stress during 100 mm PVT Growth of 4H-SiC

by Johannes Steiner, Melissa Roder, Binh Duong Nguyen, Stefan Sandfeld, Andreas Danilewsky and Peter J. Wellmann

Materials 2019, 12(13), 2207; https://doi.org/10.3390/ma12132207 - 9 Jul 2019

Cited by 19 | Viewed by 5146

Abstract

Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial [...] Read more.

Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial to grow SiC suitable for device manufacturing. In this paper, the impact of the cooldown step in PVT-growth on the defect distribution is investigated utilizing two similar SiC seeds and identical growth parameters except for a cooldown duration of 40 h and 70 h, respectively. The two resulting crystals were cut into wafers, which were characterized by birefringence imaging and KOH etching. The initial defect distribution of the seed wafer was characterized by synchrotron white beam X-ray topography (SWXRT) mapping. It was found that the BPD density increases with a prolonged cooldown time. Furthermore, small angle grain boundaries based on threading edge dislocation (TED) arrays, which are normally only inherited by the seed, were also generated in the case of the crystal cooled down in 70 h. The role of temperature gradients inside the crystal during growth and post-growth concerning the generation of shear stress is discussed and supported by numerical calculations. Full article

(This article belongs to the Special Issue Silicon Carbide and Related Materials for Energy Saving Applications—Select Papers from E-MRS 2019—Symposium “Silicon Carbide and Related Materials for Energy Saving Applications")

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7 pages, 1729 KiB

Open AccessLetter

A New Broadband and Strong Absorption Performance FeCO₃/RGO Microwave Absorption Nanocomposites

by Wei Huang, Shicheng Wei, Yujiang Wang, Bo Wang, Yi Liang, Yuwei Huang and Binshi Xu

Materials 2019, 12(13), 2206; https://doi.org/10.3390/ma12132206 - 9 Jul 2019

Cited by 23 | Viewed by 3206

Abstract

A novel composite of FeCO₃ nanoparticles, which are wrapped with reduced graphene oxide (RGO), is fabricated using a facile one-spot solvothermal method. The composite consists of a substrate of RGO and FeCO₃ nanoparticles that are embedded in the RGO layers. The [...] Read more.

A novel composite of FeCO₃ nanoparticles, which are wrapped with reduced graphene oxide (RGO), is fabricated using a facile one-spot solvothermal method. The composite consists of a substrate of RGO and FeCO₃ nanoparticles that are embedded in the RGO layers. The experimental results for the FeCO₃/RGO composite reveal a minimum refection loss (−44.5 dB) at 11.9 GHz when the thickness reaches 2.4 mm. The effective bandwidth is 7.9 GHz between 10.1 and 18 GHz when the refection loss was below −10 dB. Compared to GO and RGO, this type of composite shows better microwave absorption thanks to improved impedance matching. Overall, this thin and lightweight FeCO₃/RGO composite is a promising candidate for absorbers that require both strong and broad absorption. Full article

(This article belongs to the Special Issue Carbon Based Functional Microwave Shields)

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19 pages, 6823 KiB

Open AccessFeature PaperArticle

Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel

by István Mészáros and Bálint Bögre

Materials 2019, 12(13), 2205; https://doi.org/10.3390/ma12132205 - 9 Jul 2019

Cited by 16 | Viewed by 3748

Abstract

The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat [...] Read more.

The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat treatment for the eutectoidal phase transformation. Samples were cold rolled at seven different rolling reductions which was followed by heat treatment at five different temperatures. The second sample set was prepared to determine the activation energy of the eutectoidal decomposition process using the Arrhenius equation. Samples were cold rolled at seven different rolling reductions and were heat treated at the same temperature during eight different terms. A third sample set was made to study how another plastic-forming technology, beside the cold rolling, can influence the eutectoidal decomposition. Samples were elongated by single axis tensile stress and were heat treated at the same temperature. The results of the first and the third sample sets were compared. The rest δ-ferrite contents were calculated using the results of AC and DC magnetometer measurements. DC magnetometer was used as a feritscope device in this work. Light microscope and electron back scattering diffraction (EBSD) images demonstrated the process of the eutectoidal decomposition. The thermoelectric power and the hardness of the samples were measured. The results of the thermoelectric power measurement were compared with the results of the δ-ferrite content measurement. The accurate value of the coercive field was determined by a Foerster-type DC coercimeter device. Full article

(This article belongs to the Special Issue Advances in Duplex Stainless Steels)

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17 pages, 1920 KiB

Open AccessArticle

Methanol Dehydration to Dimethyl Ether on Zr-Loaded P-Containing Mesoporous Activated Carbon Catalysts

by José Palomo, José Rodríguez-Mirasol and Tomás Cordero

Materials 2019, 12(13), 2204; https://doi.org/10.3390/ma12132204 - 9 Jul 2019

Cited by 25 | Viewed by 4248

Abstract

Activated carbons have been prepared by the chemical activation of olive stones with phosphoric acid and loaded with Zr. The addition of Zr to the phosphorus-containing activated carbons resulted in the formation of zirconium phosphate surface groups. Gas phase methanol dehydration has been [...] Read more.

Activated carbons have been prepared by the chemical activation of olive stones with phosphoric acid and loaded with Zr. The addition of Zr to the phosphorus-containing activated carbons resulted in the formation of zirconium phosphate surface groups. Gas phase methanol dehydration has been studied while using the prepared Zr-loaded P-containing activated carbons as catalysts. Carbon catalysts showed high steady-state methanol conversion values, which increased with Zr loading up to a limit that was related to P content. The selectivity towards dimethyl ether was higher than 95% for all Zr loadings. Zirconium phosphate species that were present on catalysts surface were responsible for the catalytic activity. Full article

(This article belongs to the Special Issue Advanced Carbon Materials For Catalytical Applications)

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13 pages, 4880 KiB

Open AccessArticle

Effect of CNTs in Copper Matrix on Mechanical Characteristics and Tribological Behavior under Dry Sliding and Boundary Lubrication Conditions

by Lin Zhao, Pingping Yao, Haibin Zhou, Taimin Gong, Minwen Deng, Zhongyi Zhang, Yelong Xiao, Hui Deng, Yang Li and Fenghua Luo

Materials 2019, 12(13), 2203; https://doi.org/10.3390/ma12132203 - 9 Jul 2019

Cited by 10 | Viewed by 3387

Abstract

In the present work, the mechanical and tribological properties of carbon nanotube (CNT)-reinforced Cu matrix composites featuring 0–1.8 vol% CNTs prepared by spark plasma sintering under dry sliding and boundary lubrication conditions were investigated. The results of microstructure revealed that the bonding interface [...] Read more.

In the present work, the mechanical and tribological properties of carbon nanotube (CNT)-reinforced Cu matrix composites featuring 0–1.8 vol% CNTs prepared by spark plasma sintering under dry sliding and boundary lubrication conditions were investigated. The results of microstructure revealed that the bonding interface in Cu/CNT composites was very well established. Additionally, the addition of CNTs has a positive effect on improving the hardness and tensile strength of the composites, while the stress–strain response quasi-static tensile test confirms the same results. CNTs are proved to lead to certain self-lubrication. The addition of CNTs could result in decreased coefficient of friction (COF) and wear rates by reducing adhesive wear under dry sliding conditions, while the oil lubricating film was the major reason for decreased COF under boundary lubrication conditions. Full article

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18 pages, 17966 KiB

Open AccessArticle

Obtaining Nanoparticles of Chilean Natural Zeolite and its Ion Exchange with Copper Salt (Cu²⁺) for Antibacterial Applications

by Judith Vergara-Figueroa, Serguei Alejandro-Martín, Héctor Pesenti, Fabiola Cerda, Arturo Fernández-Pérez and William Gacitúa

Materials 2019, 12(13), 2202; https://doi.org/10.3390/ma12132202 - 9 Jul 2019

Cited by 22 | Viewed by 4740

Abstract

This article describes the production of nanoparticles of Chilean natural zeolite, using three size reduction methods: Ball mill, microgrinding, and microfluidization. Morphological characterization of samples indicated an average diameter of 37.2 ± 15.8 nm of the zeolite particles. The size reduction and chemical [...] Read more.

This article describes the production of nanoparticles of Chilean natural zeolite, using three size reduction methods: Ball mill, microgrinding, and microfluidization. Morphological characterization of samples indicated an average diameter of 37.2 ± 15.8 nm of the zeolite particles. The size reduction and chemical treatments did not affect the morphology or integrity of the zeolite. An increase of the zeolite samples’ Si/Al ratio was observed after the acid treatment and was confirmed by SEM-EDX analysis. Moreover, the effectiveness of the copper salt ion exchange (Cu²⁺) to the zeolite nanoparticles was analyzed by SEM-EDX. XRD analysis indicated that clinoptilolite and mordenite are the main phases of Chilean natural zeolite, and the crystalline structure was not affected by the modification processes. The FTIR characterization showed the presence of chemical bonds of copper with the zeolite nanoparticle framework. The ion-exchanged zeolite nanoparticles were evaluated for antibacterial behavior by the disc diffusion method. Additionally, the minimum inhibitory concentration and minimum bactericidal concentration were obtained. Microbiological assays with copper-exchanged nanozeolites showed an antimicrobial activity with a bactericidal effect against Escherichia coli and Staphylococcus aureus, which are the primary pathogens of food and are also resistant to multiple drugs. In this study, a new application for natural nanozeolites is demonstrated, as the incorporated copper ions (Cu²⁺) in nanozeolites registered a productive antibacterial activity. Full article

(This article belongs to the Collection Porous Materials and Nanozeolites)

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19 pages, 5840 KiB

Open AccessArticle

SEM Image Analysis in Permeable Recycled Concretes with Silica Fume. A Quantitative Comparison of Porosity and the ITZ

by Manuel J. Chinchillas-Chinchillas, Carlos A. Rosas-Casarez, Susana P. Arredondo-Rea, José M. Gómez-Soberón and Ramón Corral-Higuera

Materials 2019, 12(13), 2201; https://doi.org/10.3390/ma12132201 - 8 Jul 2019

Cited by 48 | Viewed by 6181

Abstract

Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to [...] Read more.

Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to evaluate the porosity in the interfacial transition zones. The porosity of the cement paste, the aggregate and the interfacial transitional zones (ITZ) of a PC with recycled coarse aggregates (RCA) and silica fume (SF) is measured by means of image analysis–scanning electron microscope (IA)-(SEM) and by mapping the chemical elements with an SEM-EDS (energy dispersive spectrometer) detector microanalysis linked to the SEM and, as a contrast, the mercury intrusion porosimetry technique (MIP). In the IA process, a “mask” was created for the aggregate and another for the paste, which determined the porosity percentage (for the anhydrous material and the products of hydration). The results showed that using SF caused a reduction (32%) in the cement paste porosity in comparison with the PC with RA. The use of RA in the PC led to a significant increase (190%) in the porosity at different thicknesses of ITZ compared with the reference PC. Finally, the MIP study shows that the use of SF caused a decrease in the micropores, mesopores and macropores. Full article

(This article belongs to the Special Issue Properties and Novel Applications of Recycled Aggregates)

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17 pages, 6904 KiB

Open AccessArticle

Evolution of Power Losses in Bending Rolled Fully Finished NO Electrical Steel Treated under Unconventional Annealing Conditions

by Ivan Petryshynets, František Kováč, Ján Füzer, Ladislav Falat, Viktor Puchý and Peter Kollár

Materials 2019, 12(13), 2200; https://doi.org/10.3390/ma12132200 - 8 Jul 2019

Cited by 3 | Viewed by 3163

Abstract

Currently, the non-oriented (NO) iron-silicon steels are extensively used as the core materials in various electrical devises due to excellent combination of their mechanical and soft magnetic properties. The present study introduces a fairly innovative technological approach applicable for fully finished NO electrical [...] Read more.

Currently, the non-oriented (NO) iron-silicon steels are extensively used as the core materials in various electrical devises due to excellent combination of their mechanical and soft magnetic properties. The present study introduces a fairly innovative technological approach applicable for fully finished NO electrical steel before punching the laminations. It is based on specific mechanical processing by bending and rolling in combination with subsequent annealing under dynamic heating conditions. It has been revealed that the proposed unconventional treatment clearly led to effective improvement of the steel magnetic properties thanks to its beneficial effects involving additional grain growth with appropriate crystallographic orientation and residual stress relief. The philosophy of the proposed processing was based on employing the phenomena of selective grain growth by strain-induced grain boundary migration and a steep temperature gradient through the cross-section of heat treated specimens at dynamic heating conditions. The stored deformation energy necessary for the grain growth was provided by plastic deformation induced within the studied specimens during the bending and rolling process. The magnetic measurements clearly show that the specimens treated according to our approach exhibited more than 17% decrease in watt losses in comparison with the specimens treated by conventional heat treatment leading only to stress relief without additional grain growth. Full article

(This article belongs to the Collection Magnetoelastic Materials)

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16 pages, 5793 KiB

Open AccessArticle

Friction Behavior of Silver Perrhenate in Oil as Lubricating Additive for Use at Elevated Temperatures

by Junhai Wang, Ting Li, Tingting Yan, Xiaoyi Wei, Xin Qu and Shuai Yuan

Materials 2019, 12(13), 2199; https://doi.org/10.3390/ma12132199 - 8 Jul 2019

Cited by 5 | Viewed by 3160

Abstract

In this study, we use an aqueous solution synthesis method to prepare silver perrhenate powders and suspend them into a poly alpha olefin (PAO) base oil with polyoxyethylene octylphenyl ether. Four ball tests and ball-on-disk reciprocating mode are performed to determine how silver [...] Read more.

In this study, we use an aqueous solution synthesis method to prepare silver perrhenate powders and suspend them into a poly alpha olefin (PAO) base oil with polyoxyethylene octylphenyl ether. Four ball tests and ball-on-disk reciprocating mode are performed to determine how silver perrhenate performs tribologically as a lubricating additive over a wide range of temperatures. The physical and chemical properties, as well as the lubricating mechanisms of the silver perrhenate additive, are characterized via X-ray diffraction, scanning electron microscope, Fourier transformation infrared spectroscopy, Raman spectrum, and X-ray photoelectron spectroscopy. The four-ball test results demonstrate that the oil added with silver perrhenate additive is more effective than the base oil in reducing friction and improving wear resistance, and provides the best lubricating performance when at a concentration of 0.5 wt%. The reciprocating mode findings indicate that the hybrid lubricant exhibits distinctively better tribological properties than the base oil at high temperatures, and its low shear strength and chemical inertness allow for low friction at elevated temperatures. The resulting silver perrhenate layer that incorporates native superalloy oxides on the worn surface can provide lubrication by serving as a barrier that prevents direct contact between the rubbing surfaces at elevated temperatures. Full article

(This article belongs to the Special Issue Tribology: Friction and Wear of Engineering Materials)

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22 pages, 3927 KiB

Open AccessArticle

An Efficient Beam Element Based on Quasi-3D Theory for Static Bending Analysis of Functionally Graded Beams

by Hoang Nam Nguyen, Tran Thi Hong, Pham Van Vinh and Do Van Thom

Materials 2019, 12(13), 2198; https://doi.org/10.3390/ma12132198 - 8 Jul 2019

Cited by 38 | Viewed by 4039

Abstract

In this paper, a 2-node beam element is developed based on Quasi-3D beam theory and mixed formulation for static bending of functionally graded (FG) beams. The transverse shear strains and stresses of the proposed beam element are parabolic distributions through the thickness of [...] Read more.

In this paper, a 2-node beam element is developed based on Quasi-3D beam theory and mixed formulation for static bending of functionally graded (FG) beams. The transverse shear strains and stresses of the proposed beam element are parabolic distributions through the thickness of the beam and the transverse shear stresses on the top and bottom surfaces of the beam vanish. The proposed beam element is free of shear-looking without selective or reduced integration. The material properties of the functionally graded beam are assumed to vary according to the power-law index of the volume fraction of the constituents through the thickness of the beam. The numerical results of this study are compared with published results to illustrate the accuracy and convenience rate of the new beam element. The influence of some parametrics on the bending behavior of FGM beams is investigated. Full article

(This article belongs to the Special Issue Advances in Structural Mechanics Modeled with FEM)

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20 pages, 5791 KiB

Open AccessFeature PaperReview

New Perspectives in the Use of Biomaterials for Periodontal Regeneration

by Federico Ausenda, Giulio Rasperini, Raffaele Acunzo, Angelina Gorbunkova and Giorgio Pagni

Materials 2019, 12(13), 2197; https://doi.org/10.3390/ma12132197 - 8 Jul 2019

Cited by 45 | Viewed by 11514

Abstract

Periodontitis is a disease with a high prevalence among adults. If not treated, it can lead to loss of teeth. Periodontal therapy aims at maintaining patient’s teeth through infection control and correction of non-maintainable anatomies including—when possible—regeneration of lost periodontal tissues. The biological [...] Read more.

Periodontitis is a disease with a high prevalence among adults. If not treated, it can lead to loss of teeth. Periodontal therapy aims at maintaining patient’s teeth through infection control and correction of non-maintainable anatomies including—when possible—regeneration of lost periodontal tissues. The biological regenerative potential of the periodontium is high, and several biomaterials can be utilized to improve the outcome of periodontal therapy. Use of different natural and synthetic materials in the periodontal field has been studied for many years. The main materials used today in periodontology analyzed in this review are: Resorbable and non-resorbable barrier membranes; autogenous, allogeneic, xenogeneic, and alloplastic bone substitutes; biological agents, such as amelogenins; platelet-derived growth factor; bone morphogenic proteins; rh fibroblast growth factor 2; teriparatide hormone; platelet concentrates; and 3D scaffolds. With the development of new surgical techniques some concepts on periodontal regeneration that were strictly applied in the past seem to be not so critical today. This can have an impact on the materials that are needed when attempting to regenerate lost periodontal structures. This review aims at presenting a rationale behind the use of biomaterials in modern periodontal regeneration Full article

(This article belongs to the Special Issue Biomaterials and Biological Mediators for Periodontal and Bone Regeneration)

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14 pages, 3350 KiB

Open AccessArticle

Field Test of Self-Cleaning Zr-Modified-TiO₂-SiO₂ Films on Glass with a Demonstration of Their Anti-Fogging Effect

by Andraž Šuligoj, Olena Pliekhova, Nives Vodišek, Mohor Mihelčič, Angelja K. Surca, Roman Kunič, Barbara Šubic, Jernej Starman, Aleš Ugovšek and Urška Lavrenčič Štangar

Materials 2019, 12(13), 2196; https://doi.org/10.3390/ma12132196 - 8 Jul 2019

Cited by 9 | Viewed by 3644

Abstract

The number of commercial products claiming self-cleaning properties is rising and testing of long-term activity and durability of such coatings needs to be addressed more. The time-dependent changes of different characteristics like haze, transparency, and color are essential for transparent glazing materials. Herein, [...] Read more.

The number of commercial products claiming self-cleaning properties is rising and testing of long-term activity and durability of such coatings needs to be addressed more. The time-dependent changes of different characteristics like haze, transparency, and color are essential for transparent glazing materials. Herein, we aimed to examine whether the laboratory results obtained on the Zr-modified-titania-silica (TiZr) self-cleaning materials would translate to larger-scale outdoor-exposed testing. TiZr thin films were deposited via spraying onto float glass window surfaces and exposed into three different environments for 20 months. For comparison, a commercially available active SGG BIOCLEAN^TM glass and standard float glass were simultaneously exposed in the same conditions. It was shown that the self-cleaning property of either a commercial product or TiZr-coated float glass was not considerably effective in real field test conditions, although the previous laboratory tests showed pronounced photocatalytic activity of TiZr thin films. The inclination angle; however, was shown to have a considerable effect on the self-cleaning ability of samples, as did the rain patterns during the testing period. On the other hand, the anti-fogging effect of our TiZr material was very well expressed in controlled laboratory conditions (measuring droplet formation time) as well as in the real outdoor environment. Full article

(This article belongs to the Special Issue Self-Cleaning Surfaces)

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9 pages, 2496 KiB

Open AccessArticle

Porous Open-Сell UHMWPE: Experimental Study of Structure and Mechanical Properties

by Alexei I. Salimon, Eugene S. Statnik, Michael Yu. Zadorozhnyy, Fedor S. Senatov, Dmitry D. Zherebtsov, Alexander A. Safonov and Alexander M. Korsunsky

Materials 2019, 12(13), 2195; https://doi.org/10.3390/ma12132195 - 8 Jul 2019

Cited by 16 | Viewed by 4878

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that is widely used as bulk material in reconstructive surgery for structural replacements of bone and cartilage. Porous UHMWPE can be used for trabecular bone tissue replacement, and it can be used in living [...] Read more.

Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that is widely used as bulk material in reconstructive surgery for structural replacements of bone and cartilage. Porous UHMWPE can be used for trabecular bone tissue replacement, and it can be used in living cell studies as bioinert 3D substrate permeable to physiological fluids. It is important to develop techniques to govern the morphology of open-cell porous UHMWPE structures (pore size, shape, and connectivity), since this allows control over proliferation and differentiation in living cell populations. We report experimental results on the mechanical behavior of porous open-cell UHMWPE obtained through sacrificial removal (desalination) of hot-molded UHMWPE-NaCl powder mixtures with pore sizes in the range 75 µm to 500 µm. The structures were characterized using SEM and mechanically tested under static compression and dynamic mechanical analysis (DMA), bending, and tensile tests. Apparent elastic modulus and complex modulus were in the range of 1.2 to 2.5 MPa showing a weak dependence on cell size. Densification under compression caused the apparent elastic modulus to increase to 130 MPa. Full article

(This article belongs to the Special Issue Bone Biomaterials)

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12 pages, 7975 KiB

Open AccessArticle

Fabrication of 50.0 μm Ultra-Fine Pure Rhodium Wire, Using a Multi-Pass Wire Drawing Process, for Probe Card Pins

by Sang-Kon Lee, In-Kyu Lee, Sung-Yun Lee and Sun-Kwang Hwang

Materials 2019, 12(13), 2194; https://doi.org/10.3390/ma12132194 - 8 Jul 2019

Cited by 5 | Viewed by 3588

Abstract

Rhodium is a rare material that is widely used in electrical and electronic components due to its excellent mechanical and electrical properties. Ultra-fine rhodium wires in particular are widely used in electronic components. In this study, a multi-pass wire drawing process was designed [...] Read more.

Rhodium is a rare material that is widely used in electrical and electronic components due to its excellent mechanical and electrical properties. Ultra-fine rhodium wires in particular are widely used in electronic components. In this study, a multi-pass wire drawing process was designed to fabricate ultra-fine pure rhodium wire with a diameter of 50.0 µm from an initial diameter of 80.0 µm, which is used as probe card pins. An elastic–plastic finite element (FE) analysis was performed to validate the pass schedule that was designed for this study. A fine wire drawing experiment was also carried out to verify the effectiveness of the designed process. As a result, the ultra-fine rhodium wire was fabricated using the design process without wire breaks and the diameter of the final drawn wire was 47.80 µm. Full article

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

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14 pages, 8671 KiB

Open AccessArticle

Numerical Simulation, Machining and Testing of a Phase Change Heat Sink for High Power LEDs

by Jianhua Xiang, Haoxing Zheng, Yipin Wang, Chunliang Zhang, Chao Zhou and Conggui Chen

Materials 2019, 12(13), 2193; https://doi.org/10.3390/ma12132193 - 8 Jul 2019

Cited by 2 | Viewed by 3166

Abstract

Thermal management is crucial to guarantee the normal operation of light-emitting diodes (LEDs) Phase change heat sink is superior to traditional metal solid heat sink due to very small thermal resistance. In this study, a new type of phase change heat sink for [...] Read more.

Thermal management is crucial to guarantee the normal operation of light-emitting diodes (LEDs) Phase change heat sink is superior to traditional metal solid heat sink due to very small thermal resistance. In this study, a new type of phase change heat sink for high power LEDs is first designed. Then, the fabrication process of boiling structures at the evaporation surface of the phase change heat sink is discussed and analyzed. To make a comparison and deep discussion, the machining process is simulated through the FEM (finite element analysis) software, DEFORM-3D. Last but not least, heat transfer performance of the fabricated phase change heat sink is tested. Results have shown that the designed new type of phase change heat sink has superior heat transfer performance and is suitable for heat dissipation of high-power LEDs. Full article

(This article belongs to the Special Issue Advanced Materials and Devices in Solid State Lighting)

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24 pages, 11692 KiB

Open AccessArticle

Effective Design of the Graded Strut of BCC Lattice Structure for Improving Mechanical Properties

by Long Bai, Changyan Yi, Xiaohong Chen, Yuanxi Sun and Junfang Zhang

Materials 2019, 12(13), 2192; https://doi.org/10.3390/ma12132192 - 8 Jul 2019

Cited by 82 | Viewed by 6766

Abstract

In order improve the poor mechanical properties of the body-centred cubic (BCC) lattice structure, which suffers from the stress concentration effects at the nodes of the BCC unit cell, a graded-strut design method is proposed to increase the radii corner of the BCC [...] Read more.

In order improve the poor mechanical properties of the body-centred cubic (BCC) lattice structure, which suffers from the stress concentration effects at the nodes of the BCC unit cell, a graded-strut design method is proposed to increase the radii corner of the BCC nodes, which can obtain a new graded-strut body-centred cubic (GBCC) unit cell. After the relative density equation and the force model of the structure are obtained, the quasi-static uniaxial compression experiments and finite element analysis (FEA) of GBCC samples and BCC samples are performed. The experimental results show that for the fabricated samples with the same relative density, the GBCC can increase the initial stiffness by at least 38.20%, increase the plastic failure strength by at least 34.12%, compared with the BCC. Coupled experimental and numerical results not only suggest that the GBCC has better mechanical and impact resistance properties than the BCC, but also indicate that as the radii corner increases, the stress concentration effect at the node and the mechanical properties will be improved, which validates the proposed design method for graded-strut unit cells and can provide guidance for the design and future research on ultra-light lattice structures in related fields. Full article

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9 pages, 2523 KiB

Open AccessCommunication

Loading Graphene Quantum Dots into Optical-Magneto Nanoparticles for Real-Time Tracking In Vivo

by Yu Wang, Nan Xu, Yongkai He, Jingyun Wang, Dan Wang, Qin Gao, Siyu Xie, Yage Li, Ranran Zhang and Qiang Cai

Materials 2019, 12(13), 2191; https://doi.org/10.3390/ma12132191 - 8 Jul 2019

Cited by 13 | Viewed by 3571

Abstract

Fluorescence imaging offers a new approach to visualize real-time details on a cellular level in vitro and in vivo without radioactive damage. Poor light stability of organic fluorescent dyes makes long-term imaging difficult. Due to their outstanding optical properties and unique structural features, [...] Read more.

Fluorescence imaging offers a new approach to visualize real-time details on a cellular level in vitro and in vivo without radioactive damage. Poor light stability of organic fluorescent dyes makes long-term imaging difficult. Due to their outstanding optical properties and unique structural features, graphene quantum dots (GQDs) are promising in the field of imaging for real-time tracking in vivo. At present, GQDs are mainly loaded on the surface of nanoparticles. In this study, we developed an efficient and convenient one-pot method to load GQDs into nanoparticles, leading to longer metabolic processes in blood and increased delivery of GQDs to tumors. Optical-magneto ferroferric oxide@polypyrrole (Fe₃O₄@PPy) core-shell nanoparticles were chosen for their potential use in cancer therapy. The in vivo results demonstrated that by loading GQDs, it was possible to monitor the distribution and metabolism of nanoparticles. This study provided new insights into the application of GQDs in long-term in vivo real-time tracking. Full article

(This article belongs to the Special Issue Advanced Materials in Drug Release and Drug Delivery Systems)

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15 pages, 2285 KiB

Open AccessReview

Effects of Hot Sterilization on Torsional Properties of Endodontic Instruments: Systematic Review with Meta-Analysis

by Mario Dioguardi, Diego Sovereto, Riccardo Aiuto, Luigi Laino, Gaetano Illuzzi, Enrica Laneve, Bruna Raddato, Vito Carlo Alberto Caponio, Antonio Dioguardi, Khrystyna Zhurakivska, Giuseppe Troiano and Lorenzo Lo Muzio

Materials 2019, 12(13), 2190; https://doi.org/10.3390/ma12132190 - 8 Jul 2019

Cited by 10 | Viewed by 3813

Abstract

Sterilization is a fundamental step in the reuse of endodontic instruments. The sterilization procedure involves disinfection, cleaning, washing, drying, packaging, and sterilization by heat. Heat sterilization can lead to changes in the physical and mechanical properties of dental instruments. These changes can affect [...] Read more.

Sterilization is a fundamental step in the reuse of endodontic instruments. The sterilization procedure involves disinfection, cleaning, washing, drying, packaging, and sterilization by heat. Heat sterilization can lead to changes in the physical and mechanical properties of dental instruments. These changes can affect the external surfaces via micropitting, corrosion, a reduction in cutting capacity, and/or an influence on the resistance to cyclic fatigue or to torsional fatigue. In this study, we examined the modification of the torsional properties of endodontic instruments after hot sterilization, and compared the properties with instruments not subjected to hot sterilization cycles in terms of resistance to torsional fatigue and deflection angle in NiTi and steel instruments. The following work was performed based on the PRISMA indications. Studies were identified through bibliographic research using electronic databases. A total of 725 records were identified in the PubMed and Scopus databases. A total of 685 records remained after exclusion by year of publication (1979 to 2019). With the application of the eligibility criteria (all articles pertaining to the issue of sterilization in endodontics), we found 146 articles, which decreased to 130 articles after elimination of duplications. There were 45 articles that studied the influences of sterilization procedures on the physical and mechanical characteristics of the instruments, and 12 that measured parameters related to resistance to torsional fatigue. Applying the inclusion and exclusion criteria resulted in a total of eight articles for quantitative analysis. The meta-analysis results show a pejorative effect of torsional fatigue for NiTi instruments subjected to heat sterilization compared to the non-sterilized control. Full article

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14 pages, 3319 KiB

Open AccessArticle

Graphene Quantum Dots as Nanozymes for Electrochemical Sensing of Yersinia enterocolitica in Milk and Human Serum

by Sumeyra Savas and Zeynep Altintas

Materials 2019, 12(13), 2189; https://doi.org/10.3390/ma12132189 - 8 Jul 2019

Cited by 85 | Viewed by 6666

Abstract

The genus Yersinia contains three well-recognized human pathogens, including Y. enterocolitica, Y. pestis, and Y. pseudotuberculosis. Various domesticated and wild animals carry Yersinia in their intestines. Spread to individuals arises from eating food or water contaminated by infected human or [...] Read more.

The genus Yersinia contains three well-recognized human pathogens, including Y. enterocolitica, Y. pestis, and Y. pseudotuberculosis. Various domesticated and wild animals carry Yersinia in their intestines. Spread to individuals arises from eating food or water contaminated by infected human or animal faeces. Interaction with infected pets and domestic stock may also lead to infection. Yersinia is able to multiply at temperatures found in normal refrigerators; hence, a large number of the bacteria may be present if meat is kept without freezing. Yersinia is also rarely transmitted by blood transfusion, because it is able to multiply in stored blood products. Infection with Yersinia can cause yersiniosis, a serious bacterial infection associated with fever, abdominal pain and cramps, diarrhea, joint pain, and symptoms similar to appendicitis in older children and adults. This paper describes a novel immunosensor approach using graphene quantum dots (GQDs) as enzyme mimics in an electrochemical sensor set up to provide an efficient diagnostic method for Y. enterecolitica. The optimum assay conditions were initially determined and the developed immunosensor was subsequently used for the detection of the bacterium in milk and human serum. The GQD-immunosensor enabled the quantification of Y. enterocolitica in a wide concentration range with a high sensitivity (LOD_milk = 5 cfu mL⁻¹ and LOD_serum = 30 cfu mL⁻¹) and specificity. The developed method can be used for any pathogenic bacteria detection for clinical and food samples without pre-sample treatment. Offering a very rapid, specific and sensitive detection with a label-free system, the GQD-based immunosensor can be coupled with many electrochemical biosensors. Full article

(This article belongs to the Special Issue Nanomaterials in Health Care Diagnostics)

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13 pages, 9943 KiB

Open AccessArticle

Mechanical Properties and Microstructures of Laser–TIG Welded ME21 Rare Earth Mg Alloy

by Taotao Li, Gang Song, Zhaodong Zhang and Liming Liu

Materials 2019, 12(13), 2188; https://doi.org/10.3390/ma12132188 - 8 Jul 2019

Cited by 8 | Viewed by 3168

Abstract

The microstructural and mechanical properties of laser–tungsten inert gas (TIG) hybrid welding of Mg alloy sheets for automobiles are investigated in the present work, including AZ31 and ME21, AZ31 and AZ31, ME21 and ME21, and corresponding comparisons were carried out. The results show [...] Read more.

The microstructural and mechanical properties of laser–tungsten inert gas (TIG) hybrid welding of Mg alloy sheets for automobiles are investigated in the present work, including AZ31 and ME21, AZ31 and AZ31, ME21 and ME21, and corresponding comparisons were carried out. The results show that columnar crystals appear in the ME21/ME21 and ME21/AZ31 heat-affected zones, and no columnar crystals formed in the AZ31/AZ31 fusion zone under a constant heat ratio of arc to laser. Heat accumulation in a narrow area and the undercooling degree are the two main factors for the formation of columnar crystal. The ME21/ME21 joint has a tensile strength of up to 185.2 MPa, which is about 81.8% of that of the ME21 base metal (BM-ME21). The tensile strength of the ME21/AZ31 joint (158.8 MPa) is lower than that of the ME21/ME21 joint. The fracture of the ME21/ME21 and ME21/AZ31 joints occurs at the junction of the columnar crystal and the heat-affected zone. The microhardness of the ME21/AZ31 joint presents a low–high–low–high trend from BE-ME21 to BE-AZ31, and the distribution of the ME21/AZ31 welded joint microhardness in the cross-section presents a low–high–low trend. The ME21/ME21 weld seam is composed of an AlCe₃ intermetallic compound, Mn particles, and α-Mg, and the ME21/AZ31 weld seam is composed of a α-Mg, Mg₁₇Al₁₂, and AlCe₃ intermetallic compound. Full article

(This article belongs to the Special Issue Laser Materials Fabrication and Joining)

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12 pages, 1059 KiB

Open AccessArticle

Effectiveness of Low-Level Laser Therapy during Tooth Movement: A Randomized Clinical Trial

by Gaetano Isola, Marco Matarese, Francesco Briguglio, Vincenzo Grassia, Giacomo Picciolo, Luca Fiorillo and Giovanni Matarese

Materials 2019, 12(13), 2187; https://doi.org/10.3390/ma12132187 - 8 Jul 2019

Cited by 37 | Viewed by 5075

Abstract

The present study evaluated the effects of low-level laser therapy (LLLT) by means of a diode laser in accelerating orthodontic tooth movement (OTM). After extraction of the first upper premolars for orthodontic purpose, 82 maxillary canines which needed distalization were analyzed in 41 [...] Read more.

The present study evaluated the effects of low-level laser therapy (LLLT) by means of a diode laser in accelerating orthodontic tooth movement (OTM). After extraction of the first upper premolars for orthodontic purpose, 82 maxillary canines which needed distalization were analyzed in 41 enrolled patients (21 males, 20 females, mean age 13.4 ± 2.1 years). On all experimental sites, an orthodontic force of 50/N was applied by a nickel-titanium (NiTi) closed coil spring (G&H, Franklin, IN, USA) in order to obtain the space closure. Using a split mouth randomized design, the test side was treated using a diode laser (Wiser Laser Doctor Smile, Brendola, Italy) operating at 810 nm wavelength in continuous wave mode at both the buccal and palatal side on three points/side (distal, medial and mesial) (1 W output power, continuous wave of 66.7 J/cm², energy density of 8 J) at baseline and at 3, 7, and 14 days and every 15 days until the space closed. On the control side, the opposite selected canine was treated only using orthodontic traction. The primary outcome chosen was the overall time needed to complete the levelling and closing space, measured on a study cast. The secondary outcome chosen was the evaluation of pain levels related to tooth traction, using a Visual Analogue Scale (VAS), recorded at 3, 7, and 14 days after treatments. The mean space closures of the maxillary canines were comparable between groups [Test, 4.56 mm (95% CI 3.9–4.8); Control, 4.49 mm (95% CI 3.8–4.7), p = 0.456]. The laser group yielded less mean time [84.35 ± 12.34 days (95% CI 79.3–86)] to accomplish space closure compared to the control group [97.49 ± 11.44 days (91.7–102.3)] (p < 0.001). The test side showed a significant reduction in the average range of dental pain at 3 [Test, 5.41 (95% CI 5.1–5.6); Control, 7.23 (95% CI 6.9–7.6), p < 0.001], 7 [Test, 4.12 (95% CI 3.8–4.7); Control, 5.79 (95% CI 5.4–5.8), p < 0.001], and at 14 days [Test, 2.31 (95% CI 1.8–2.3); Control, 3.84 (95% CI 3.3–4.2), p < 0.001] after treatment (p < 0.001). This study demonstrates that the use of LLLT therapy was effective in accelerating tooth movement and reducing pain levels related to OTM. Full article

(This article belongs to the Special Issue Advanced Materials for Oral and Dentofacial Surgery)

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20 pages, 5329 KiB

Open AccessArticle

Hot Deformation Behavior of Q345 Steel and Its Application in Rapid Shear Connection

by Mengwei Wu, Shuangjie Zhang, Shibo Ma, Huajun Yan, Wei Wang and Qiang Li

Materials 2019, 12(13), 2186; https://doi.org/10.3390/ma12132186 - 7 Jul 2019

Cited by 9 | Viewed by 3205

Abstract

The high-temperature deformation behavior of Q345 steel is detected by a Gleeble-3800 thermal simulator. The Arrhenius constitutive equation for high-temperature flow stress and the dynamic recrystallization model are constructed. With the secondary development technology, customized modifications are made on existing Deform-3D software. The [...] Read more.

The high-temperature deformation behavior of Q345 steel is detected by a Gleeble-3800 thermal simulator. The Arrhenius constitutive equation for high-temperature flow stress and the dynamic recrystallization model are constructed. With the secondary development technology, customized modifications are made on existing Deform-3D software. The constructed constitutive model and dynamic recrystallization model are embedded into Deform-3D to realize the secondary development of Deform-3D. The grain size and volume percentage distribution of dynamic recrystallization are obtained by simulating the shear connection process at high temperature and high speed. The results show that the constitutive equation and the dynamic recrystallization model constructed in this paper can be used to predict the evolution of the microstructure. The difference between the prediction results and the experimental data is about 3%. The accuracy of Arrhenius constitutive equation, dynamic recrystallization model and the feasibility of software secondary development are verified. Full article

(This article belongs to the Special Issue Development of the Rolling Process in Metallic Materials)

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23 pages, 9485 KiB

Open AccessReview

Graphene Oxide and Its Inorganic Composites: Fabrication and Electrorheological Response

by Yu Zhen Dong, Joo Nyeon Kim and Hyoung Jin Choi

Materials 2019, 12(13), 2185; https://doi.org/10.3390/ma12132185 - 7 Jul 2019

Cited by 18 | Viewed by 4606

Abstract

Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the [...] Read more.

Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the fabrication mechanisms of GO/inorganic composites and their ER response when suspended in a non-conducting medium, including steady shear flow curves, dynamic yield stress, On-Off tests, and dynamic oscillation analysis. Furthermore, the morphologies of these composites, dielectric properties, and sedimentation of the ER fluids are covered. Full article

(This article belongs to the Special Issue Graphene Oxide: Synthesis, Reduction, and Frontier Applications)

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18 pages, 5278 KiB

Open AccessArticle

Durability of Steel Fiber-Reinforced Concrete Containing SiO₂ Nano-Particles

by Peng Zhang, Qingfu Li, Yuanzhao Chen, Yan Shi and Yi-Feng Ling

Materials 2019, 12(13), 2184; https://doi.org/10.3390/ma12132184 - 7 Jul 2019

Cited by 86 | Viewed by 4813

Abstract

An experimental study was conducted to investigate the effect ofnano-SiO₂ and steel fiber content on the durability of concrete. Five different dosages of nano-SiO₂ particles and five volume dosages of steel fiber were used. The durability of concretes includes permeability resistance, [...] Read more.

An experimental study was conducted to investigate the effect ofnano-SiO₂ and steel fiber content on the durability of concrete. Five different dosages of nano-SiO₂ particles and five volume dosages of steel fiber were used. The durability of concretes includes permeability resistance, cracking resistance, carbonation resistance, and freezing-thawing resistance, and these were evaluated by the water permeation depth, number of cracks, total cracking area per unit area of the specimens, carbonation depth of the specimens, and the relative dynamic elastic modulus of the specimens after freezing-thawing cycles, respectively. The results indicate that the addition of nano-SiO₂ particles significantly improves the durability of concrete when the content of nano-SiO₂ is limited within a certain range. With the increase of nano-SiO₂ content, the durability of concrete first increases and then decreases. An excessive number of nano-SiO₂ particles could have an adverse effect on the durability of the concrete. The addition of the correct amount of steel fibers improves the carbonation resistance of concrete containing nano-particles, but excessive steel fiber reduces the carbonation resistance. Moreover, the addition of steel fibers reduces the permeability resistance of concrete containing nano-particles. The incorporation of steel fiber enhanced the freezing-thawing resistance and cracking resistance of concrete containing nano-particles. With increasing steel fiber content, the freezing-thawing resistance of the concrete containing nano-particles increases, and the cracking resistance of the concrete decreases gradually. Full article

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

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15 pages, 10232 KiB

Open AccessArticle

Comparison of Mechanical Properties and Energy Absorption of Sheet-Based and Strut-Based Gyroid Cellular Structures with Graded Densities

by Dawei Li, Wenhe Liao, Ning Dai and Yi Min Xie

Materials 2019, 12(13), 2183; https://doi.org/10.3390/ma12132183 - 7 Jul 2019

Cited by 148 | Viewed by 9304

Abstract

Bio-inspired functionally graded cellular materials (FGCM) have improved performance in energy absorption compared with a uniform cellular material (UCM). In this work, sheet-based and strut-based gyroid cellular structures with graded densities are designed and manufactured by stereo-lithography (SLA). For comparison, uniform structures are [...] Read more.

Bio-inspired functionally graded cellular materials (FGCM) have improved performance in energy absorption compared with a uniform cellular material (UCM). In this work, sheet-based and strut-based gyroid cellular structures with graded densities are designed and manufactured by stereo-lithography (SLA). For comparison, uniform structures are also designed and manufactured, and the graded structures are generated with different gradients. The mechanical behaviors of these structures under compressive loads are investigated. Furthermore, the anisotropy and effective elastic modulus of sheet-based and strut-based unit gyroid cellular structures are estimated by a numerical homogenization method. On the one hand, it is found from the numerical results that the sheet-based gyroid tends to be isotropic, and the elastic modulus of sheet-based gyroid is larger than the strut-based gyroid at the same volume fraction. On the other hand, the graded cellular structure has novel deformation and mechanical behavior. The uniform structure exhibits overall deformation and collapse behavior, whereas the graded cellular structure shows layer-by-layer deformation and collapse behavior. Furthermore, the uniform sheet-based gyroid is not only stiffer but also better in energy absorption capacity than the uniform strut-based gyroid structure. Moreover, the graded cellular structures have better energy absorption capacity than the uniform structures. These significant findings indicate that sheet-based gyroid cellular structure with graded densities have potential applications in various industrial applications, such as in crashworthiness. Full article

(This article belongs to the Section Advanced Materials Characterization)

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