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Materials, Volume 13, Issue 20 (October-2 2020) – 226 articles

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Cover Story (view full-size image) The performance of electrochemical devices is strongly affected by the transport properties of the [...] Read more.
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Open AccessArticle
Effect of the Drying Method of Pine and Beech Wood on Fracture Toughness and Shear Yield Stress
Materials 2020, 13(20), 4692; https://doi.org/10.3390/ma13204692 - 21 Oct 2020
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Abstract
The modern wood converting processes consists of several stages and material drying belongs to the most influencing future performances of products. The procedure of drying wood is usually realized between subsequent sawing operations, affecting significantly cutting conditions and general properties of material. An [...] Read more.
The modern wood converting processes consists of several stages and material drying belongs to the most influencing future performances of products. The procedure of drying wood is usually realized between subsequent sawing operations, affecting significantly cutting conditions and general properties of material. An alternative methodology for determination of mechanical properties (fracture toughness and shear yield stress) based on cutting process analysis is presented here. Two wood species (pine and beech) representing soft and hard woods were investigated with respect to four diverse drying methods used in industry. Fracture toughness and shear yield stress were determined directly from the cutting power signal that was recorded while frame sawing. An original procedure for compensation of the wood density variation is proposed to generalize mechanical properties of wood and allow direct comparison between species and drying methods. Noticeable differences of fracture toughness and shear yield stress values were found among all drying techniques and for both species, but only for beech wood the differences were statistically significant. These observations provide a new highlight on the understanding of the effect of thermo-hydro modification of wood on mechanical performance of structures. It can be also highly useful to optimize woodworking machines by properly adjusting cutting power requirements. Full article
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Open AccessArticle
Data Merging of AE Sensors with Different Frequency Resolution for the Detection and Identification of Damage in Oxide-Based Ceramic Matrix Composites
Materials 2020, 13(20), 4691; https://doi.org/10.3390/ma13204691 - 21 Oct 2020
Viewed by 226
Abstract
In this paper, acoustic emission data fusion based on multiple measurements is presented for damage detection and identification in oxide-based ceramic matrix composites. Multi-AE (acoustic emission) sensor fusion is considered with the aim of a better identification of damage mechanisms. In this context, [...] Read more.
In this paper, acoustic emission data fusion based on multiple measurements is presented for damage detection and identification in oxide-based ceramic matrix composites. Multi-AE (acoustic emission) sensor fusion is considered with the aim of a better identification of damage mechanisms. In this context, tensile tests were conducted on ceramic matrix composites, fabricated with 3M™ Nextel™ 610 fibers and aluminosilicate matrix, with two kinds of AE sensors. Redundant and complementary sensor data were merged to enhance AE system capability and reliability. Data fusion led to consistent signal clustering with an unsupervised procedure. A correlation between these clusters and the damage mechanisms was established thanks to in situ observations. The complementarity of the information from both sensors greatly improves the characterization of sources for their classification. Moreover, this complementarity allows features to be perceived more precisely than using only the information from one kind of sensor. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle
Morphological, Chemical, and Biological Investigation of Ionic Substituted, Pulse Current Deposited Calcium Phosphate Coatings
Materials 2020, 13(20), 4690; https://doi.org/10.3390/ma13204690 - 21 Oct 2020
Viewed by 199
Abstract
Ionic substituted calcium phosphate coatings (iCP) have been prepared by the electrochemical pulse current deposition technique with an alternate pulse on and off time of 5 ms onto a titanium alloy substrate. The elemental distribution and morphology of the deposited layers have been [...] Read more.
Ionic substituted calcium phosphate coatings (iCP) have been prepared by the electrochemical pulse current deposition technique with an alternate pulse on and off time of 5 ms onto a titanium alloy substrate. The elemental distribution and morphology of the deposited layers have been extensively studied by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM). The crystallinity and phase structure of iCPs have been investigated by X-ray diffraction (XRD). The corrosion characteristics and biodegradability of coatings have been determined by electrochemical measurements, recording potentiodynamic curves in a physiological solution over a long-term immersion period. The cell viability tests confirmed that the iCP coating was biocompatible, while the corrosion tests proved its biodegradable characteristic. In our paper, we compare the morphological, chemical, and biological characteristics of silver and zinc substituted calcium phosphate layers deposited by the electrochemical method. Full article
(This article belongs to the Special Issue Surface Modifications and Coatings for Bioactive Implants)
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Open AccessArticle
Metal Nanoparticles Formation from Nickel Hydroxide
Materials 2020, 13(20), 4689; https://doi.org/10.3390/ma13204689 - 21 Oct 2020
Viewed by 242
Abstract
In this study, the mechanism of nickel nanoparticle formation from its hydroxide was analyzed. Metallic nickel nanoparticles were obtained through the hydroxide’s reduction under hydrogen. Nickel hydroxides were produced from nickel (II) nitrate hexahydrate and NaOH by deposition under various initial conditions. The [...] Read more.
In this study, the mechanism of nickel nanoparticle formation from its hydroxide was analyzed. Metallic nickel nanoparticles were obtained through the hydroxide’s reduction under hydrogen. Nickel hydroxides were produced from nickel (II) nitrate hexahydrate and NaOH by deposition under various initial conditions. The influence of washing treatment on the dispersion of obtained nickel powders was studied. The washing procedure of precipitates was carried out by centrifugation, ultrasonic treatment, and decantation. X-ray diffractometry, transmission electron microscopy, low-temperature nitrogen adsorption, infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy methods were used for nanoparticle characterization. Based on the resulting data, a model of the Ni(OH)2 aggregate structure after deposition was proposed. The number of nickel hydroxide particles required to form one nickel nanoparticle was estimated, and a model of its formation was proposed. Full article
(This article belongs to the Special Issue Metallurgy of Non-ferrous, Rare and Precious Metals)
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Open AccessArticle
Treatment of Osseous Defects after Mandibular Third Molar Removal with a Resorbable Alloplastic Grafting Material: A Case Series with 1- to 2-Year Follow-Up
Materials 2020, 13(20), 4688; https://doi.org/10.3390/ma13204688 - 21 Oct 2020
Viewed by 308
Abstract
Mandibular third molar (M3) surgical extraction may cause periodontal complications on the distal aspect of the root of the adjacent mandibular second molar (M2). Patients older than 26 years with periodontal pathology on the distal surface of the M2 and a horizontal/mesioangular impacted [...] Read more.
Mandibular third molar (M3) surgical extraction may cause periodontal complications on the distal aspect of the root of the adjacent mandibular second molar (M2). Patients older than 26 years with periodontal pathology on the distal surface of the M2 and a horizontal/mesioangular impacted M3 may benefit from bone regenerative therapy at the time of surgery. In this prospective case series, an alloplastic fully resorbable bone grafting material, consisting of beta-tricalcium phosphate (β-TCP) and calcium sulfate (CS), was used for the treatment of the osseous defects after the removal of horizontal or mesioangular M3s in 4 patients older than 26 years. On presentation, the main radiological finding in all patients, indicating periodontal pathology, was the absence of bone between the crown of the M3 and the distal surface of the root of the M2. To evaluate the treatment outcome, bone gain (BG) was assessed by recording the amount of bone defect (BD) at the time of surgical removal (T0) and at the time of final follow-up (T1) 1 or 2 years post-operatively. The healing in all cases was uneventful, with no complications associated with the use of the alloplastic grafting material. Clinical and radiological examination at T1 revealed that all extraction sites were adequately restored, with significant BG of 6.07 ± 0.28 mm. No residual pathological pockets on the distal surface of the M2 were detected. Pocket depth (PD) at T1 was 2 ± 0.71 mm. Within the limitations of this case series, the results suggest that β-TCP/CS can support new bone formation at M3 post-extraction sites where bone regeneration methods are indicated, thus reducing the risk of having persistent or developing new periodontal problems at the adjacent M2. Full article
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Open AccessArticle
Effect of Yttrium and Rhenium Ion Implantation on the Performance of Nitride Ceramic Cutting Tools
Materials 2020, 13(20), 4687; https://doi.org/10.3390/ma13204687 (registering DOI) - 21 Oct 2020
Viewed by 229
Abstract
In the paper, the results of experimental investigations of ion implanted cutting tools performance are presented. The tools, made out of Si3N4 with additives typically used for turning of Ti-6Al-4V alloy, underwent implantation with ions of yttrium (Y+) [...] Read more.
In the paper, the results of experimental investigations of ion implanted cutting tools performance are presented. The tools, made out of Si3N4 with additives typically used for turning of Ti-6Al-4V alloy, underwent implantation with ions of yttrium (Y+) and rhenium (Re+) using the metal vapor vacuum arc method. Distribution of ions on the tool surface was measured. The cutting tools were tested in turning process with measurement of cutting forces and analysis of wear. A rather unexpected result was the increased wear of the tool after Y+ implantation with 1 × 1017 ion/cm2. It was demonstrated, however, that the tool after Y+ 2 × 1017 ion/cm2 ion implantation provided the best machining performance. Full article
(This article belongs to the Special Issue Machinability of Metallic Materials and Composites)
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Open AccessArticle
The Effects of Hybridisation of Composites Consisting of Aramid, Carbon, and Hemp Fibres in a Quasi-Static Penetration Test
Materials 2020, 13(20), 4686; https://doi.org/10.3390/ma13204686 - 21 Oct 2020
Viewed by 191
Abstract
The quasi-static penetration properties of hybrid laminates were experimentally investigated. Aramid fabrics, carbon fabrics, and short hemp fibres were applied as the reinforcements of hybrid and non-hybrid composite laminates with polyurethane–polyurea (PUR/PUA) matrix. The laminates were made by hand, in a mould. They [...] Read more.
The quasi-static penetration properties of hybrid laminates were experimentally investigated. Aramid fabrics, carbon fabrics, and short hemp fibres were applied as the reinforcements of hybrid and non-hybrid composite laminates with polyurethane–polyurea (PUR/PUA) matrix. The laminates were made by hand, in a mould. They were cured at room temperature for 24 h. Hybrid laminates consisted of aramid and carbon layers in two different configurations, i.e., aramid at the innermost layers and outermost layers. Aramid/PUR/PUA and carbon/PUR/PUA composites were fabricated for comparison purposes. Laminates were also prepared via an analogue sequence of laying the reinforcement layers with the addition of 5% by weight of hemp fibres in the PUR/PUA matrix. Quasi-static penetration tests (QSPT) were conducted using a tensile testing machine with a surface-hardened, hemispherical, steel punch (9 mm diameter tip), reflecting the geometry of the Parabellum projectile. A quasi-static puncture test was carried out until the laminate was perforated. The ratio between the support span (Ds) and the punch diameter (Dp) was SPR = Ds/Dp = 5.0. The results showed the influences of laminate hybridisation on the values of absorbed energy, punch shear strength, and damage mechanism in the QSPT test. The addition of hemp fibres to aramid laminates resulted in a positive hybridisation effect. The order of layers of aramid and carbon fabrics in hybrid laminates influenced the results obtained in the QSPT test. Full article
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Open AccessArticle
Mitigating Portland Cement CO2 Emissions Using Alkali-Activated Materials: System Dynamics Model
Materials 2020, 13(20), 4685; https://doi.org/10.3390/ma13204685 - 21 Oct 2020
Viewed by 217
Abstract
While alkali-activated materials (AAMs) have been hailed as a very promising solution to mitigate colossal CO2 emissions from world portland cement production, there is lack of robust models that can demonstrate this claim. This paper pioneers a novel system dynamics model that [...] Read more.
While alkali-activated materials (AAMs) have been hailed as a very promising solution to mitigate colossal CO2 emissions from world portland cement production, there is lack of robust models that can demonstrate this claim. This paper pioneers a novel system dynamics model that captures the system complexity of this problem and addresses it in a holistic manner. This paper reports on this object-oriented modeling paradigm to develop a cogent prognostic model for predicting CO2 emissions from cement production. The model accounts for the type of AAM precursor and activator, the service life of concrete structures, carbonation of concrete, AAM market share, and policy implementation period. Using the new model developed in this study, strategies for reducing CO2 emissions from cement production have been identified, and future challenges facing wider AAM implementation have been outlined. The novelty of the model consists in its ability to consider the CO2 emission problem as a system of systems, treating it in a holistic manner, and allowing the user to test diverse policy scenarios, with inherent flexibility and modular architecture. The practical relevance of the model is that it facilitates the decision-making process and policy making regarding the use of AAMs to mitigate CO2 emissions from cement production at low computational cost. Full article
(This article belongs to the Special Issue Advanced Cement and Concrete Composites)
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Open AccessArticle
Influence of Vinyl Polysiloxane Impression Techniques on Marginal Fit of Metal Frameworks for Fixed Partial Dentures
Materials 2020, 13(20), 4684; https://doi.org/10.3390/ma13204684 - 21 Oct 2020
Viewed by 174
Abstract
Impression technique is one of the factors affecting restoration fit accuracy, which is a major aspect influencing its survival. The purpose of this study is to compare, in vivo, the effect of two commonly used Vinyl Polysiloxane (VPS) impression techniques on the metal [...] Read more.
Impression technique is one of the factors affecting restoration fit accuracy, which is a major aspect influencing its survival. The purpose of this study is to compare, in vivo, the effect of two commonly used Vinyl Polysiloxane (VPS) impression techniques on the metal framework fitting of fixed partial dentures. Ninety-two consecutive patients, diagnosed as partially edentulous, treated by fixed partial denture restorations, participated in the study. Group 1-impressions (n = 44) were subjected to the 1-step technique, while group 2 impressions (n = 48) were subjected the 2-step technique. Three accuracy assessment common methods: probe, tactile sense and radiographic test, were used to validate the clinical fit of the metal framework. Misfit was defined as even one test failure. Twenty-one (22.8%) out of 92 metal frameworks exhibited metal frameworks misfit, whereas the other 71 (77.2%) were found to be accurate. Group 1 presented significantly (p = 0.04) more metal frameworks misfit, 14/44 (31.8%) vs. 7/48 (14.6%). Restoration location (maxilla vs. mandible) had no statistically significant impact on the results (p = 0.461). The use of the VPS putty/wash 2-step impression technique is recommended to improve the clinical fit of fixed partial denture restorations. Full article
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Open AccessArticle
On the Impact of Substrate Uniform Mechanical Tension on the Graphene Electronic Structure
Materials 2020, 13(20), 4683; https://doi.org/10.3390/ma13204683 - 21 Oct 2020
Viewed by 221
Abstract
Employing density functional theory calculations, we obtain the possibility of fine-tuning the bandgap in graphene deposited on the hexagonal boron nitride and graphitic carbon nitride substrates. We found that the graphene sheet located on these substrates possesses the semiconducting gap, and uniform biaxial [...] Read more.
Employing density functional theory calculations, we obtain the possibility of fine-tuning the bandgap in graphene deposited on the hexagonal boron nitride and graphitic carbon nitride substrates. We found that the graphene sheet located on these substrates possesses the semiconducting gap, and uniform biaxial mechanical deformation could provide its smooth fitting. Moreover, mechanical tension offers the ability to control the Dirac velocity in deposited graphene. We analyze the resonant scattering of charge carriers in states with zero total angular momentum using the effective two-dimensional radial Dirac equation. In particular, the dependence of the critical impurity charge on the uniform deformation of graphene on the boron nitride substrate is shown. It turned out that, under uniform stretching/compression, the critical charge decreases/increases monotonically. The elastic scattering phases of a hole by a supercritical impurity are calculated. It is found that the model of a uniform charge distribution over the small radius sphere gives sharper resonance when compared to the case of the ball of the same radius. Overall, resonant scattering by the impurity with the nearly critical charge is similar to the scattering by the potential with a low-permeable barrier in nonrelativistic quantum theory. Full article
(This article belongs to the Special Issue Carbon-Based Materials)
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Open AccessArticle
Preliminary Study on the Capability of the Novel Near Solidus Forming (NSF) Technology to Manufacture Complex Steel Components
Materials 2020, 13(20), 4682; https://doi.org/10.3390/ma13204682 - 21 Oct 2020
Viewed by 223
Abstract
The benefits of the novel Near Solidus Forming (NSF) process has shown previously in its ability to produce steel components with comparable as-forged mechanical properties but with a cost reduction of 10–15%. This study further pushes the NSF technology to produce parts that [...] Read more.
The benefits of the novel Near Solidus Forming (NSF) process has shown previously in its ability to produce steel components with comparable as-forged mechanical properties but with a cost reduction of 10–15%. This study further pushes the NSF technology to produce parts that are conventionally difficult to produce via conventional methods. A 2.7 kg 42CrMo4 steel grade component was manufactured into a complex geometry using only a 400t press. Different manufacturing parameters were evaluated to show their influence on the process and final component. A combination of X-ray fluorescence (XRF), optical microscopy and SEM analysis of the microstructure was also conducted revealing the deformation pattern of the material and shedding some light on how the material evolves during the process. The successful forging of these components shows the capability to produce previously deemed difficult geometries, with much a lower specification forging press, in a single deformation. Full article
(This article belongs to the Special Issue Forging Processes of Materials)
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Open AccessArticle
Tropisms of the Dowser Texture
Materials 2020, 13(20), 4681; https://doi.org/10.3390/ma13204681 - 21 Oct 2020
Viewed by 219
Abstract
Due to its low symmetry C2v, the dowser texture is characterised by a 2D unitary vector field or alternatively by a unitary complex field. For the same symmetry reasons, the dowser texture is sensitive, in first order, to perturbations such [...] Read more.
Due to its low symmetry C2v, the dowser texture is characterised by a 2D unitary vector field or alternatively by a unitary complex field. For the same symmetry reasons, the dowser texture is sensitive, in first order, to perturbations such as thickness gradients, electric fields or flows. We will focus on corresponding properties called respectively: cuneitropism, electrotropism and rheotropism. In particular we will show that topological defects, known as dowsons or monopoles, can be manipulated by means of these tropisms. Full article
(This article belongs to the Special Issue Stimuli Responsive Liquid Crystals)
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Open AccessArticle
Evaluation of the Milling Accuracy of Zirconia-Reinforced Lithium Silicate Crowns Fabricated Using the Dental Medical Device System: A Three-Dimensional Analysis
Materials 2020, 13(20), 4680; https://doi.org/10.3390/ma13204680 - 21 Oct 2020
Viewed by 175
Abstract
This study aimed to analyze the milling accuracy of lithium disilicate and zirconia-reinforced silicate crown fabricated using chairside computer-aided design/manufacturing (CAD/CAM) system. Mandibular left first premolar was selected for abutment. A master model was obtained for digital impression using an intraoral scanner, and [...] Read more.
This study aimed to analyze the milling accuracy of lithium disilicate and zirconia-reinforced silicate crown fabricated using chairside computer-aided design/manufacturing (CAD/CAM) system. Mandibular left first premolar was selected for abutment. A master model was obtained for digital impression using an intraoral scanner, and crowns were designed using a CAD software design program. Amber Mill (AM), IPS e max CAD (IPS), and CELTRA DUO (CEL) were used in the CAD/CAM system, and a total 45 crowns (15 crowns each for AM, IPS, and CEL) was fabricated. Milling accuracy was analyzed with respect to trueness, measured by superimposing CAD design data and scan data through a three-dimensional program to compare the outer and inner surfaces and internal and external parts, thereby acquiring both quantitative and qualitative data. Data were analyzed using the non-parametric test and Kruskal–Wallis H test. In addition, the Mann–Whitney U test was used by applying the level of significance (0.05/3 = 0.016) adjusted by post-analysis Bonferroni correction. All the measured parts of the lithium disilicate and zirconia-reinforced silicate crowns showed statistically significant differences (p < 0.05). The lithium disilicate (AM and IPS) materials showed superior milling accuracy than the zirconia-reinforced lithium silicate (CEL) materials. Full article
(This article belongs to the Section Biomaterials)
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Open AccessFeature PaperArticle
Simvastatin Induces In Vitro Mineralization Effects of Primary Human Odontoblast-Like Cells
Materials 2020, 13(20), 4679; https://doi.org/10.3390/ma13204679 - 20 Oct 2020
Viewed by 237
Abstract
Simvastatin (SV) is an often prescribed statin reducing the LDL-concentration in circulating blood. The aim of this study was to evaluate the pleiotropic effects of SV to primary human odontoblast-like cells. Twenty four wisdom teeth of different subjects were extracted and the pulp [...] Read more.
Simvastatin (SV) is an often prescribed statin reducing the LDL-concentration in circulating blood. The aim of this study was to evaluate the pleiotropic effects of SV to primary human odontoblast-like cells. Twenty four wisdom teeth of different subjects were extracted and the pulp tissue was removed and minced under sterile conditions. After mincing, the requested cells were passaged according to established protocols. Osteoblastic marker (ALP conversion), viability and mineralization were determined at days 14, 17 and 21 after simvastatin exposition (0.01 µM, 0.1 µM, 1.0 µM, 2.0 µM). The sample size per group was 24 cultures with three replicates per culture for ALP-conversion and mineralization and 6 replicates for viability. A Kruskal–Wallis test was used for statistical analysis. After adding SV, viability was significantly (p < 0.01) decreased in a time- and dose-dependent manner, whereas after 21 days, mineralization was significant (p < 0.01). ALP-conversion in groups with SV concentrations of 1 and 2 µM SV was significantly (p < 0.01) increased. Pleiotropic effects regarding mineralization in higher SV concentrations were possibly induced via alternative mineralization pathways as almost equal elevations of ALP conversion were not evident in the control and experimental groups. Full article
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Open AccessArticle
Dry Rolling/Sliding Wear of Bainitic Rail Steels under Different Contact Stresses and Slip Ratios
Materials 2020, 13(20), 4678; https://doi.org/10.3390/ma13204678 - 20 Oct 2020
Viewed by 244
Abstract
This study aims to deeply understand the effect of contact stress and slip ratio on wear performances of bainitic rail steels. The results showed that the wear loss increased as the contact stress and slip ratio increased. Based on the surface damage morphology [...] Read more.
This study aims to deeply understand the effect of contact stress and slip ratio on wear performances of bainitic rail steels. The results showed that the wear loss increased as the contact stress and slip ratio increased. Based on the surface damage morphology and microstructural analyses, it revealed that the rolling contact fatigue wear mechanism played a significant role under the low slip ratio, but the dominant wear mechanism transferred to the abrasive wear at the high slip ratio. Meanwhile, the bainitic steel specifically presented worse wear resistance under the abrasive wear mode. Compared with the influence of a slip ratio, the increase in contact stress led to severer plastic flows and contributed to the propagation of cracks. In addition, the contact stress and slip ratio had the opposite effect on the friction coefficient, that is, the friction coefficient of bainitic steels behaved the inverse proportion with the contact stress, but positive proportion with the slip ratio. At last, the increase in slip ratio had more significant effect on the reduction of retained austenite (RA) than the enlargement of contact stress due to the fact that the RA would probably be removed before the martensitic transformation occurred under the abrasive wear mechanism. Full article
(This article belongs to the Special Issue Friction and Wear of Materials Surfaces)
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Open AccessArticle
Addressing H-Material Interaction in Fast Diffusion Materials—A Feasibility Study on a Complex Phase Steel
Materials 2020, 13(20), 4677; https://doi.org/10.3390/ma13204677 - 20 Oct 2020
Viewed by 330
Abstract
Hydrogen embrittlement (HE) is one of the main limitations in the use of advanced high-strength steels in the automotive industry. To have a better understanding of the interaction between hydrogen (H) and a complex phase steel, an in-situ method with plasma charging was [...] Read more.
Hydrogen embrittlement (HE) is one of the main limitations in the use of advanced high-strength steels in the automotive industry. To have a better understanding of the interaction between hydrogen (H) and a complex phase steel, an in-situ method with plasma charging was applied in order to provide continuous H supply during mechanical testing in order to avoid H outgassing. For such fast-H diffusion materials, only direct observation during in-situ charging allows for addressing H effects on materials. Different plasma charging conditions were analysed, yet there was not a pronounced effect on the mechanical properties. The H concentration was calculated while using a simple analytical model as well as a simulation approach, resulting in consistent low H values, below the critical concentration to produce embrittlement. However, the dimple size decreased in the presence of H and, with increasing charging time, the crack propagation rate increased. The rate dependence of flow properties of the material was also investigated, proving that the material has no strain rate sensitivity, which confirmed that the crack propagation rate increased due to H effects. Even though the H concentration was low in the experiments that are presented here, different technological alternatives can be implemented in order to increase the maximum solute concentration. Full article
(This article belongs to the Special Issue Recent Advances in Mechanisms of Fracture and Fatigue)
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Open AccessArticle
Large-Beam Picosecond Interference Patterning of Metallic Substrates
Materials 2020, 13(20), 4676; https://doi.org/10.3390/ma13204676 - 20 Oct 2020
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Abstract
In this paper, we introduce a method to efficiently use a high-energy pulsed 1.7 ps HiLASE Perla laser system for two beam interference patterning. The newly developed method of large-beam interference patterning permits the production of micro and sub-micron sized features on a [...] Read more.
In this paper, we introduce a method to efficiently use a high-energy pulsed 1.7 ps HiLASE Perla laser system for two beam interference patterning. The newly developed method of large-beam interference patterning permits the production of micro and sub-micron sized features on a treated surface with increased processing throughputs by enlarging the interference area. The limits for beam enlarging are explained and calculated for the used laser source. The formation of a variety of surface micro and nanostructures and their combinations are reported on stainless steel, invar, and tungsten with the maximum fabrication speed of 206 cm2/min. The wettability of selected hierarchical structures combining interference patterns with 2.6 µm periodicity and the nanoscale surface structures on top were analyzed showing superhydrophobic behavior with contact angles of 164°, 156°, and 150° in the case of stainless steel, invar, and tungsten, respectively. Full article
(This article belongs to the Special Issue Advances in Laser Processing)
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Open AccessArticle
Experimental Determination of the Manson−Coffin Curves for an Original Unconventional Vehicle Frame
Materials 2020, 13(20), 4675; https://doi.org/10.3390/ma13204675 - 20 Oct 2020
Viewed by 181
Abstract
This article is divided into two parts—in the first part, authors inform about their testing device that enables the acquisition of results from uniaxial and multiaxial fatigue tests (the bending−torsion combination). We present the approaches used during designing and building the testing device. [...] Read more.
This article is divided into two parts—in the first part, authors inform about their testing device that enables the acquisition of results from uniaxial and multiaxial fatigue tests (the bending−torsion combination). We present the approaches used during designing and building the testing device. The direct implementation of the research in the second part will concentrate on implementing the acquired results for the frame design of a vehicle worked out by the authors. The three-wheeled vehicle has the front steered wheel suspended in an unconventional way. This original design can cause an increased load on the vehicle’s frame. This can be apparent mainly during driving through curves. Therefore, the fatigue curves of the tested material (EN AW 6063) will be implemented from the point of view of its usability in operation. A vehicle frame is most often loaded by bending and torsion. The authors assess the influence of welding on the fatigue life of this unique unconventional vehicle by determining the fatigue curves of the material for its production. The stresses achieved on the test specimens fully correspond to the load of the frame (in welds) during its operation. Full article
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Open AccessArticle
The Effect of the Addition of Polypropylene Fibers to Primer on the Pull-Off Strength of Epoxy Resin Coatings
Materials 2020, 13(20), 4674; https://doi.org/10.3390/ma13204674 - 20 Oct 2020
Viewed by 192
Abstract
This article describes the effect of adding polypropylene fibers to primer on the pull-off strength of epoxy resin coatings. Investigated primers were laid on substrates made of cement mortar and cement slurry. The primer was made of epoxy resin modified with the addition [...] Read more.
This article describes the effect of adding polypropylene fibers to primer on the pull-off strength of epoxy resin coatings. Investigated primers were laid on substrates made of cement mortar and cement slurry. The primer was made of epoxy resin modified with the addition of 0.5%, 1%, 1.5% and 2% of polypropylene fibers. One reference sample was made without the addition of fibers. Then, an epoxy resin coating was applied to each substrate. Four pull-off strength tests were performed for each material configuration. For this purpose, an automatic device for measuring the pull-off strength of the coatings was used. The results were compared with the results obtained for the reference sample. The optimum content of polypropylene fibers was found to be in the range of 0.5–1.0 wt. % of the mass of the resin. One percent of fibers was optimum for the epoxy resin laid on the cement slurry, while 0.5 wt. % of fibers was optimum for the mortar substrate. The addition of a higher amount of polypropylene fibers resulted in a lower pull-off strength of coatings than for the reference sample. Full article
(This article belongs to the Special Issue Advanced Civil Engineering Materials: From Synthesis to Application)
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Open AccessArticle
Surface Activation of Polylactic Acid-Based Wood-Plastic Composite by Atmospheric Pressure Plasma Treatment
Materials 2020, 13(20), 4673; https://doi.org/10.3390/ma13204673 - 20 Oct 2020
Viewed by 243
Abstract
Wood-plastic composite (WPC) based on a polylactic acid (PLA) matrix is a promising material since it is biobased, degradable, sustainable, and 3D printable. However, due to its coloring, visible layers after 3D-printing, and small build volumes of these printers, a coating or gluing [...] Read more.
Wood-plastic composite (WPC) based on a polylactic acid (PLA) matrix is a promising material since it is biobased, degradable, sustainable, and 3D printable. However, due to its coloring, visible layers after 3D-printing, and small build volumes of these printers, a coating or gluing of parts might be required. This study investigates the influence of a dielectric barrier discharge (DBD) plasma treatment of PLA-based WPC to activate the surface and improve, e.g., coating capabilities. X-ray photoelectron spectroscopy (XPS) measurements showed the oxidation of the surface due to the formation of carbonyl and carboxyl groups. Laser scanning microscopy revealed a surface roughening after the treatment. Contact angles of water and diiodomethane decreased significantly after the plasma treatment and the consecutively calculated surface free energy increased. Finally, two practical adhesion tests revealed an improvement of the applied acrylic dispersion coating’s adhesion to the WPC surface: The assigned cross-cut class improved, and the pull-off strength increased from 1.4 to 2.3 N/mm2. Full article
(This article belongs to the Special Issue Advances in Natural Fibers and Polymers)
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Open AccessArticle
Imidazolium-Based Ionic Liquid as Efficient Corrosion Inhibitor for AA 6061 Alloy in HCl Solution
Materials 2020, 13(20), 4672; https://doi.org/10.3390/ma13204672 - 20 Oct 2020
Viewed by 185
Abstract
The corrosion inhibition performance of an imidazolium-based ionic liquid (IL), 1-butyl-3-methylimidazolium thiocyanate (BMIm), was studied on AA 6061 alloy in 1 M HCl solution at 303 K, 333 K, and 363 K by gravimetric tests, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) analysis. [...] Read more.
The corrosion inhibition performance of an imidazolium-based ionic liquid (IL), 1-butyl-3-methylimidazolium thiocyanate (BMIm), was studied on AA 6061 alloy in 1 M HCl solution at 303 K, 333 K, and 363 K by gravimetric tests, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) analysis. Scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) were used to detect the surface morphologies and chemical composition of the surface films. The results indicate that this IL inhibits AA 6061 corrosion in acid with maximum inhibition efficiencies of 98.2%, 86.6%, and 41.2% obtained at 303 K, 333 K, and 363 K respectively. Inhibition efficiency generally decreased with increasing immersion time; the major exception was at 303 K, whereby the inhibition efficiency was detected to increase with immersion time from 30 to 90 min and then decrease slightly beyond 90 min. The results indicate that BMIm is a mixed-type inhibitor with a predominant effect on cathodic reactions. Surface morphology analyses by SEM revealed less surface damage in the presence of the inhibitor. XPS analysis established the development of a protective film on the AA 6061 surface which was hydrophobic in nature. Full article
(This article belongs to the Special Issue Corrosion of Nonferrous Metals and Their Alloys)
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Open AccessArticle
Fabrication and Characterisation of Aligned Discontinuous Carbon Fibre Reinforced Thermoplastics as Feedstock Material for Fused Filament Fabrication
Materials 2020, 13(20), 4671; https://doi.org/10.3390/ma13204671 - 20 Oct 2020
Viewed by 262
Abstract
In this work, aligned discontinuous fibre composite (ADFRC) tapes were developed and investigated as precursors for a novel 3D printing filament. ADFRCs have the potential to achieve mechanical performance comparable to continuous fibre reinforced composites, given sufficient fibre length and high level of [...] Read more.
In this work, aligned discontinuous fibre composite (ADFRC) tapes were developed and investigated as precursors for a novel 3D printing filament. ADFRCs have the potential to achieve mechanical performance comparable to continuous fibre reinforced composites, given sufficient fibre length and high level of alignment, and avoid many of the manufacturing difficulties associated with continuous fibres, e.g., wrinkling, bridging and corner radii constraints. Their potential use for fused filament fabrication (FFF) techniques was investigated here. An extensive down-selection process of thermoplastic matrices was performed, as matrix properties significantly impact both the processing and performance of the filament. This resulted in four candidate polymers (ABS, PLA, Nylon, PETG) which were used to manufacture ADFRC tapes with a Vf of 12.5% using the high performance discontinuous fibre (HiPerDiF) technology and an in-house developed continuous consolidation module. Tensile stiffness and strength up to 30 GPa and 400 MPa respectively were recorded, showing that a discontinuous fibre filament has the potential to compete with continuous fibre filaments. Full article
(This article belongs to the Special Issue Additive Manufacturing of Fiber Composites)
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Open AccessArticle
Stribeck Curve of Magnetorheological Fluid within Pin-on-Disc Configuration: An Experimental Investigation
Materials 2020, 13(20), 4670; https://doi.org/10.3390/ma13204670 - 20 Oct 2020
Viewed by 218
Abstract
The paper focuses on the coefficient of friction (COF) of a magnetorheological fluid (MRF) in the wide range of working conditions across all the lubrication regimes—boundary, mixed, elastohydrodynamic (EHD), and hydrodynamic (HD) lubrication, specifically focused on the common working area of MR damper. [...] Read more.
The paper focuses on the coefficient of friction (COF) of a magnetorheological fluid (MRF) in the wide range of working conditions across all the lubrication regimes—boundary, mixed, elastohydrodynamic (EHD), and hydrodynamic (HD) lubrication, specifically focused on the common working area of MR damper. The coefficient of friction was measured for MR fluids from Lord company with concentrations of 22, 32, and 40 vol. % of iron particles at temperatures 40 and 80 °C. The results were compared with a reference fluid, a synthetic liquid hydrocarbon PAO4 used as a carrier fluid of MRF. The results show that at boundary regime and temperature 40 °C all the fluids exhibit similar COF of 0.11–0.13. Differences can be found in the EHD regime, where the MR fluid COF is significantly higher (0.08) in comparison with PAO4 (0.04). The COF of MR fluid in the HD regime rose very steeply in comparison with PAO4. The effect of particle concentration is significant in the HD regime. Full article
(This article belongs to the Section Smart Materials)
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Open AccessArticle
Ground Tire Rubber Modified by Ethylene-Vinyl Acetate Copolymer: Processing, Physico-Mechanical Properties, Volatile Organic Compounds Emission and Recycling Possibility
Materials 2020, 13(20), 4669; https://doi.org/10.3390/ma13204669 - 20 Oct 2020
Viewed by 185
Abstract
Ground tire rubber (GTR) was reclaimed and modified with 10 phr of ethylene-vinyl acetate copolymer via low-temperature extrusion process. Processing, physico-mechanical properties, volatile organic compounds emission, and recycling possibility were investigated. In order to better understand the impact of used modifiers, their efficiency [...] Read more.
Ground tire rubber (GTR) was reclaimed and modified with 10 phr of ethylene-vinyl acetate copolymer via low-temperature extrusion process. Processing, physico-mechanical properties, volatile organic compounds emission, and recycling possibility were investigated. In order to better understand the impact of used modifiers, their efficiency was compared with trans-polyoctenamer, which is an additive that is commercially dedicated to waste rubber recycling. The results showed that a relatively small amount of ethylene-vinyl acetate copolymer improves the mechanical properties of modified reclaimed GTR and also allows further recycling by multiple processing without the deterioration of performance after three cycles. Full article
(This article belongs to the Special Issue Recent Advances in Rubber Recycling)
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Open AccessEditorial
Special Issue: Mechanical Properties in Progressive Mechanically Processed Metallic Materials
Materials 2020, 13(20), 4668; https://doi.org/10.3390/ma13204668 - 20 Oct 2020
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Abstract
The research and development of modern metallic materials imparts not only the introduction of innovative alloys and compounds, but also the increasing lifetime of existing materials via optimized deformation processing. Among the essential features of progressive metallic materials used for modern applications are [...] Read more.
The research and development of modern metallic materials imparts not only the introduction of innovative alloys and compounds, but also the increasing lifetime of existing materials via optimized deformation processing. Among the essential features of progressive metallic materials used for modern applications are enhanced mechanical properties, but also other high-level functional characteristics, such as thermal–physical parameters, corrosion rate, and electric resistance. The properties of materials and alloys ensue from their structures, which can primarily be affected by the preparation/production process. The Special Issue “Mechanical Properties in Progressive Mechanically Processed Metallic Materials” was established to present recent developments and innovations particularly in the engineering field. The Special Issue comprises papers dealing with modern materials, such as metallic composites and pseudoalloys, as well as developments in various processing technologies. Full article
Open AccessArticle
Effect of Rotation of the Principal Stress Axes Relative to the Material on the Evolution of Material Properties in Severe Plastic Deformation Processes
Materials 2020, 13(20), 4667; https://doi.org/10.3390/ma13204667 - 20 Oct 2020
Viewed by 228
Abstract
Severe plastic deformation (SPD) processes are widely used for improving material properties. A distinguishing feature of many SPD processes is that the principal axes of the stress tensor intensively rotate relative to the material. Nevertheless, no measure of this rotation is involved in [...] Read more.
Severe plastic deformation (SPD) processes are widely used for improving material properties. A distinguishing feature of many SPD processes is that the principal axes of the stress tensor intensively rotate relative to the material. Nevertheless, no measure of this rotation is involved in the constitutive equations that predict the evolution of material properties. In particular, a typical way of describing the effect of SPD processes on material properties is to show the dependence of various parameters that characterize these properties on the equivalent strain. However, the same level of the equivalent strain can be achieved in a process in which the principal axes of the stress tensor do not rotate relative to the material. It is, therefore, vital to understand which properties are dependent and which properties are independent of the rotation of the principal axes of the stress tensor relative to the material. In the present paper, a new multistage SPD process is designed such that the principal stress axes do not rotate relative to the material during each stage of the process but the directions of the major and minor principal stresses interchange between two subsequent stages. The process is practically plane strain, and it may be named the process of upsetting by V-shape dies. In addition, axisymmetric compression by Rastegaev’s method is conducted. In this case, the principal stress axes are fixed in the material throughout the entire process of deformation. Material properties and microstructure generated in the two processes above are compared to reveal the effect of the rotation of the principal stress axes relative to the material on the evolution of these properties. Full article
(This article belongs to the Special Issue Forging Processes of Materials)
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Open AccessArticle
Wetting Kinetics and Microstructure Analysis of BNi2 Filler Metal over Selective Laser Melted Ti-6Al-4V Substrate
Materials 2020, 13(20), 4666; https://doi.org/10.3390/ma13204666 - 20 Oct 2020
Viewed by 177
Abstract
The wetting kinetics of nickel-based filler metal (BNi2) over selective laser-melted Ti-6Al-4V (SLMed TC4) titanium alloy in a protective argon atmosphere is experimentally investigated using a real-time in situ hot stage equipped with an optical microscope. The spreading processes at different temperatures are [...] Read more.
The wetting kinetics of nickel-based filler metal (BNi2) over selective laser-melted Ti-6Al-4V (SLMed TC4) titanium alloy in a protective argon atmosphere is experimentally investigated using a real-time in situ hot stage equipped with an optical microscope. The spreading processes at different temperatures are similar, and the overall wetting/spreading process can be roughly divided into three stages: (i) an initial stage, (ii) a rapid spreading stage, and (iii) an asymptotic stage. Moreover, the wetting kinetics of the BNi2/SLMed TC4 system can be expressed by empirical power exponential function Rn~t with n = ~1. In the process of spreading, Ti-based solid solution (Ti(ss)) and intermetallic compound (Ti2Ni and TiB2) were formed at the interface within the reaction domain, and the phase transition of α’ martensitic to α-Ti and β-Ti also took place. The influence of elevated temperature on the spreading and wetting kinetics of the BNi2/SLMed TC4 system was studied, and the results show that the increase of temperature has a slightly promoting effect on the spreading, but a limited impact on the value of n. In addition, the spreading and wetting kinetics of BNi2/SLMed TC4 system are similar to those of BNi2 on conventional forged TC4 substrate. Full article
(This article belongs to the Special Issue Dynamic Behaviour of Metallic Materials)
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Open AccessArticle
Surfactant Effects on the Synthesis of Redox Bifunctional V2O5 Photocatalysts
Materials 2020, 13(20), 4665; https://doi.org/10.3390/ma13204665 - 20 Oct 2020
Viewed by 202
Abstract
Novel V2O5 bifunctional photocatalysts were prepared following a wet chemical process with the addition of anionic or non-ionic surfactants into the precursor solution and further heating under reflux. Detailed characterization and investigation of the relevant light-matter interactions proved that surfactants [...] Read more.
Novel V2O5 bifunctional photocatalysts were prepared following a wet chemical process with the addition of anionic or non-ionic surfactants into the precursor solution and further heating under reflux. Detailed characterization and investigation of the relevant light-matter interactions proved that surfactants addition had a strong impact on the morphology, while also affecting the crystallinity, the optoelectronic properties, and the surface chemistry of the novel photocatalysts. The most efficient photocatalyst (T80) was based on tween 80, a surface-active agent employed for the first time in the synthesis of vanadium oxide materials. T80 presented crystalline nature without structural defects, which are usually centers of e − h+ recombination. This material also exhibited small crystal size, high porosity, and short migration paths for the charge carriers, enabling their effective separation during photocatalysis. Under UV light illumination, T80 was capable to reduce hexavalent chromium to trivalent up to 70% and showed high yields in degrading methylene blue azo-dye and tetracycline antibiotic water pollutants. This remarkably high bifunctional performance defines T80 as a promising and capable photocatalytic material for both advanced oxidation and reduction processes (AOPs-ARPs). Full article
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Open AccessArticle
Experimental Investigation on Machinability of Aluminum Alloy during Dry Micro Cutting Process Using Helical Micro End Mills with Micro Textures
Materials 2020, 13(20), 4664; https://doi.org/10.3390/ma13204664 - 19 Oct 2020
Viewed by 203
Abstract
Aluminum alloy material is widely used in the electronics, weapons, aviation and aerospace industries, due to its medium strength, good corrosion resistance, good toughness and excellent oxidation properties. With the trend of product miniaturization, micro cutting has become the mainstream technique for fabricating [...] Read more.
Aluminum alloy material is widely used in the electronics, weapons, aviation and aerospace industries, due to its medium strength, good corrosion resistance, good toughness and excellent oxidation properties. With the trend of product miniaturization, micro cutting has become the mainstream technique for fabricating micro parts and components, so it is very meaningful and vital to work on removing the cutting fluid from the micro cutting process and make it totally sustainable and eco-friendly. In this work, an attempt has been made to fabricate micro textures onto the rear surface of helical micro end mills with diameters of less than 1 mm. Micro textures in the form of grooves were fabricated using a noncontact low speed wire electrical discharge turning technique. Dry micro cutting experiments were carried out on an aluminum alloy material using helical micro end mills with micro textures and the dry micro cutting surface quality and tool wear have been investigated. The influence of dry micro cutting parameters on the surface roughness parameters were also investigated. Experimental results showed that the Sa and Sq can be reduced to be about 1.56 μm and 2.08 μm, respectively. Contrasting results indicate that the implantation of micro textures does not deteriorate the dry micro cutting surface but improves the machined surface consistency of an aluminum alloy workpiece. The tool wear on helical micro end mills with micro textures involved in the dry micro cutting process of Al 6061 mainly include rear frictional wear, oxidation wear and diffusion wear. Full article
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Open AccessCommunication
Surface Piezoelectricity and Pyroelectricity in Centrosymmetric Materials: A Case of α-Glycine
Materials 2020, 13(20), 4663; https://doi.org/10.3390/ma13204663 - 19 Oct 2020
Viewed by 299
Abstract
Surface pyroelectricity and piezoelectricity induced by water incorporation during growth in α-glycine were investigated. Using the periodic temperature change technique, we have determined the thickness (~280 µm) of the near surface layer (NSL) and its pyroelectric coefficient (160 pC/(K × cm2) [...] Read more.
Surface pyroelectricity and piezoelectricity induced by water incorporation during growth in α-glycine were investigated. Using the periodic temperature change technique, we have determined the thickness (~280 µm) of the near surface layer (NSL) and its pyroelectric coefficient (160 pC/(K × cm2) at 23 °C) independently. The thickness of NSL remains nearly constant till 60 °C and the pyroelectric effect vanishes abruptly by 70 °C. The piezoelectric effect, 0.1 pm/V at 23 °C measured with an interferometer, followed the same temperature dependence as the pyroelectric effect. Abrupt disappearance of both effects at 70 °C is irreversible and suggests that water incorporation to α-glycine forms a well defined near surface phase, which is different form α-glycine because it is polar but it too close to α-glycine to be distinguished by X-ray diffraction (XRD). The secondary pyroelectric effect was found to be <14% of the total, which is unexpectedly small for a material with a large thermal expansion coefficient. This implies that water incorporation infers minimal distortions in the host lattice. This finding suggests a path for the control of the piezoelectric and pyroelectric effects of the crystals using stereospecific incorporation of the guest molecules. Full article
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