Materials

22 pages, 6094 KiB

Open AccessArticle

Stabilisation/Solidification of the Zn-Contaminated Loess Silt in View of the Mechanical Properties

by Agnieszka Lal and Joanna Fronczyk

Materials 2024, 17(24), 6266; https://doi.org/10.3390/ma17246266 (registering DOI) - 21 Dec 2024

The effectiveness of the stabilisation/solidification process depends upon a number of factors, the most significant of which are the type of binder, contaminants, and soil undergoing treatment. In accordance with the principles of sustainable construction, alternatives to cement are sought after, with the [...] Read more.

The effectiveness of the stabilisation/solidification process depends upon a number of factors, the most significant of which are the type of binder, contaminants, and soil undergoing treatment. In accordance with the principles of sustainable construction, alternatives to cement are sought after, with the objective of achieving the lowest environmental impact while maintaining a high level of strength and effective binding of the contaminant. In the study of the stabilisation/solidification of zinc-contaminated loess, incinerated sewage sludge fly ash with reactive magnesia was selected as the binder, and the UCS of the mixtures and microstructure was verified after 28 days of treatment. The values obtained were related to the strength of a reference sample and exhibited by S/S products using Portland cement. The findings verified the effectiveness of the selected materials in the S/S process. Following a 28-day treatment with 30 and 45% IFA and MgO in a 2:1 ratio, the samples were classified as a hard subgrade, suitable for civil engineering purposes, due to the UCS values achieved, ranging from 0.52 to 0.9 MPa. Furthermore, a correlation between the UCS values and the water content was identified, and the mineralogical composition of S/S products was determined with the use of the XRD technique. Full article

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16 pages, 22059 KiB

Open AccessArticle

Influence of Scanning Strategy on Residual Stresses in Laser-Based Powder Bed Fusion Manufactured Alloy 718: Modeling and Experiments

by Carl-Johan Hassila, Andreas Malmelöv, Carl Andersson, Johan Hektor, Martin Fisk, Andreas Lundbäck and Urban Wiklund

Materials 2024, 17(24), 6265; https://doi.org/10.3390/ma17246265 (registering DOI) - 21 Dec 2024

Abstract

In additive manufacturing, the presence of residual stresses in produced parts is a well-recognized phenomenon. These residual stresses not only elevate the risk of crack formation but also impose limitations on in-service performance. Moreover, it can distort printed parts if released, or in [...] Read more.

In additive manufacturing, the presence of residual stresses in produced parts is a well-recognized phenomenon. These residual stresses not only elevate the risk of crack formation but also impose limitations on in-service performance. Moreover, it can distort printed parts if released, or in the worst case even cause a build to fail due to collision with the powder scraper. This study introduces a thermo-mechanical finite element model designed to predict the impact of various scanning strategies in order to mitigate the aforementioned unwanted outcomes. The investigation focuses on the deformation and residual stresses of two geometries manufactured by laser-based powder bed fusion (PBF-LB). To account for relaxation effects during the process, a mechanism-based material model has been implemented and used. Additionally, a purely mechanical model, based on the inherent strain method, has been calibrated to account for different scanning strategies. To assess the predicted residual stresses, high-energy synchrotron measurements have been used to obtain values for comparison. The predictions of the models are evaluated, and their accuracy is discussed in terms of the physical aspects of the PBF-LB process. Both the thermo-mechanical models and the inherent strain method capture the trend of experimentally measured residual stress fields. While deformations are also adequately captured, there is an overall underprediction of their magnitude. This work contributes to advancing our understanding of the thermo-mechanical behavior in PBF-LB and provides valuable insights for optimizing scanning strategies in additive manufacturing processes. Full article

(This article belongs to the Special Issue Current and Future Trends in Additive Manufacturing)

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10 pages, 342 KiB

Open AccessArticle

Numerical Analysis of the Influence of Air Flow Rate on the Development of the Porous Structure of Activated Carbons Prepared from Macadamia Nut Shells

by Mirosław Kwiatkowski and Guojie Zhang

Materials 2024, 17(24), 6264; https://doi.org/10.3390/ma17246264 (registering DOI) - 21 Dec 2024

Abstract

This paper presents the numerical analysis of the influence of air flow rate on the porous structure development of activated carbons prepared from macadamia nut shells. The analyses based on nitrogen and carbon dioxide isotherms were carried out by the new numerical clustering-based [...] Read more.

This paper presents the numerical analysis of the influence of air flow rate on the porous structure development of activated carbons prepared from macadamia nut shells. The analyses based on nitrogen and carbon dioxide isotherms were carried out by the new numerical clustering-based adsorption analysis method. Therefore, it was possible to evaluate the porous structure with high precision and reliability. In particular, the results obtained showed that activated carbon prepared at an air flow rate of 700 cm³/min has the highest adsorption capacity with respect to this adsorbate, but with surface heterogeneity. On the other hand, numerical analysis based on carbon dioxide adsorption isotherms showed that the activated carbon with the highest adsorption capacity towards carbon dioxide is the sample obtained at an air flow rate of 500 cm³/min. The analyses conducted have shown that too high an air flow rate causes a violent oxidation reaction, leading to uncontrolled burning of the carbonaceous substance and destruction of the structure of the smallest micropores. Full article

(This article belongs to the Special Issue Adsorption Materials and Their Applications (2nd Edition))

27 pages, 12398 KiB

Open AccessArticle

Shape Optimization and Experimental Investigation of Glue-Laminated Timber Beams

by Paweł Szeptyński, Dorota Jasińska and Leszek Mikulski

Materials 2024, 17(24), 6263; https://doi.org/10.3390/ma17246263 (registering DOI) - 21 Dec 2024

Abstract

This study investigated the optimal shape of glue-laminated timber beams using an analytical model of a slender beam, taking into account the anisotropy of its strength properties as well as boundary conditions at the oblique bottom face of the beam. A control theory [...] Read more.

This study investigated the optimal shape of glue-laminated timber beams using an analytical model of a slender beam, taking into account the anisotropy of its strength properties as well as boundary conditions at the oblique bottom face of the beam. A control theory problem was formulated in order to optimize the shape of the modeled beam. Two optimization tasks were considered: minimizing material usage (

V_{m i n}

) for a fixed load-carrying capacity (LCC) of the beam and maximizing load-bearing capacity (

Q_{m a x}

) for a given volume of the beam. The optimal solution was found using Pontryagin’s maximum principle (PMP). Optimal shapes were determined using Dircol v. 2.1 software and then adjusted according to a 3D finite element analysis (FEA) performed in Abaqus. The final shapes obtained through this procedure were used in the CNC-based production of three types of nine beams: three reference rectangular beams, three

V_{m i n}

beams, and three

Q_{m a x}

beams. All specimens were subjected to a four-point bending test. The experimental results were contrasted with theoretical assumptions. Optimization reduced material usage by ca. 12.9% while preserving approximately the same LCC. The maximization of LCC was found to be rather unsuccessful due to the significant dependence of the beams’ response on the highly variable mechanical properties of GLT. Full article

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17 pages, 10704 KiB

Open AccessArticle

Compressive Load Capacity of Concrete Structures Made of Hollow Blocks with Voids Filled with Concrete of Various Features

by Vadim Griniov, Kseniya Yurkova and Rafał Prusak

Materials 2024, 17(24), 6262; https://doi.org/10.3390/ma17246262 (registering DOI) - 21 Dec 2024

Abstract

A masonry made of hollow concrete blocks in modern constructions differs from the traditional one in that the empty space (up to 70%) makes it possible to create complex high-strength load-bearing structures by filling the voids with monolithic or reinforced concrete. The aim [...] Read more.

A masonry made of hollow concrete blocks in modern constructions differs from the traditional one in that the empty space (up to 70%) makes it possible to create complex high-strength load-bearing structures by filling the voids with monolithic or reinforced concrete. The aim of this study was to examine specimens of concrete structures made of hollow blocks with voids filled with concretes with various features. The research methodology is based on the results of numerical and experimental tests. Laboratory studies were conducted to determine the influence of the concrete filling on strength, deformability and the nature of destruction of the experimental specimens. The numerical analysis was performed on the basis of FEM with the use of the ANSYS 2021 R1 software. The method for determining the load capacity of multi-component structures using strain diagrams of constituent materials has been improved. There is strong agreement between the numerical and experimental results for all masonry prisms. Additionally, a good correlation was observed between the experimental results and the analytical calculations performed using the proposed methodology. Full article

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13 pages, 3689 KiB

Open AccessArticle

Propagation of a Fatigue Crack Through a Hole

by Diogo Neto, Joel Jesus, Ricardo Branco, Edmundo Sérgio and Fernando Antunes

Materials 2024, 17(24), 6261; https://doi.org/10.3390/ma17246261 (registering DOI) - 21 Dec 2024

Abstract

The stop-hole technique is a well-known strategy to extend the fatigue life of cracked components. The ability to estimate fatigue life after the hole is important for safety reasons. The objective here is to develop strategies for the accurate prediction of initiation and [...] Read more.

The stop-hole technique is a well-known strategy to extend the fatigue life of cracked components. The ability to estimate fatigue life after the hole is important for safety reasons. The objective here is to develop strategies for the accurate prediction of initiation and propagation life ahead of the stop-hole. Experimental work was developed in a Compact-Tension (CT) specimen made of 7050-T7451 aluminium alloy and with a 3 mm diameter hole. A total number of 625,000 load cycles were required to re-initiate the crack after the hole. Crack initiation life after the hole was estimated using the Theory of Critical Distances combined with the Smith–Watson–Topper parameter. A value of a₀ = 31.83 µm was obtained for El Haddad parameter, which was used to define the critical distance. The predicted life was found to be only 4% lower than the experimental value. The fatigue crack growth (FCG) rate was calculated using a node release strategy, assuming that cyclic plastic deformation is the main damage mechanism and that cumulative plastic strain is the crack driving parameter. A good agreement was found between the numerical predictions of da/dN and the experimental results. The main result, however, is the proposed methodology, which allows predicting the initiation and propagation lives in notched components. Full article

(This article belongs to the Special Issue Fatigue Crack Growth in Metallic Materials (Volume II))

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12 pages, 5814 KiB

Open AccessArticle

Transformations in the Ti-6Al-4V Alloy Studied Using Dilatometry Supported by Acoustic Emission

by Małgorzata Łazarska, Janusz Musiał, Tomasz Tański and Zbigniew Ranachowski

Materials 2024, 17(24), 6260; https://doi.org/10.3390/ma17246260 (registering DOI) - 21 Dec 2024

Abstract

This paper presents the results of research on the kinetics of transformations in the two-phase (α + β) Ti-6Al-4V alloy. The transformation start and end temperatures during heating at different rates were determined using a dilatometer. A modified dilatometer was employed, equipped with [...] Read more.

This paper presents the results of research on the kinetics of transformations in the two-phase (α + β) Ti-6Al-4V alloy. The transformation start and end temperatures during heating at different rates were determined using a dilatometer. A modified dilatometer was employed, equipped with an acoustic emission measurement apparatus and software enabling the assessment of sample dimensional changes during heating and cooling. The results were obtained in the form of dilatometric curves. Additionally, the occurrence of the transformation was confirmed by acoustic emission signals. In the study of the Ti-6Al-4V alloy, acoustic emission refers to the application of this non-destructive technique to monitor the alloy’s behavior during thermal processes. As the temperature increased, regardless of the heating rate, the α→β transformation was observed to occur after exceeding 900 °C. Within the transformation range, acoustic emission signals were recorded. Moreover, it was found that the applied research methods enabled the identification of signal components originating from the transformation. The application of acoustic methods in the analysis of phase transformations opens new possibilities for their use in industry. Full article

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18 pages, 40755 KiB

Open AccessArticle

Effects of Temperature and Water Vapor Content on Microstructure, Mechanical Properties and Corrosion Behavior of C/C-SiC Composites

by Yanbin Wei, Zhiyong Ye, Yalei Wang, Xiang Xiong, Zaidong Liu, Jinming Wang and Tongqi Li

Materials 2024, 17(24), 6259; https://doi.org/10.3390/ma17246259 (registering DOI) - 21 Dec 2024

Abstract

Carbon-fiber-reinforced carbon and silicon carbide (C/C-SiC) composites were prepared using chemical vapor infiltration (CVI) combined with reactive melt infiltration (RMI). The microstructure and flexural properties of C/C-SiC composites after oxidation in different temperature water vapor environments were studied. The results indicate that the [...] Read more.

Carbon-fiber-reinforced carbon and silicon carbide (C/C-SiC) composites were prepared using chemical vapor infiltration (CVI) combined with reactive melt infiltration (RMI). The microstructure and flexural properties of C/C-SiC composites after oxidation in different temperature water vapor environments were studied. The results indicate that the difficulty of oxidation in water vapor can be ranked from easy to difficult in the following order: carbon fiber (CF), pyrolytic carbon (PyC), and ceramic phase. The surface CFs become cone-shaped under corrosion. PyC has a slower oxidation rate and lower degree of oxidation compared to CF. The SiO₂ layer formed by the oxidation of SiC and residual Si was insufficient to fully cover the surface of CFs and PyC. As the temperature increased, the oxide film thickened, but the corrosion degree of CF and PyC intensified, and the flexural performance continuously deteriorated. The flexural strength of C/C-SiC composites was 271.86 MPa at room temperature. Their strength retention rates were all higher than 92.19% after water vapor corrosion at 1000 °C, still maintaining the “pseudoplastic” fracture characteristics. After water vapor corrosion at 1200 °C, the CFs inside the composites sustained more severe damage, with a strength retention rate as low as 48.75%. The fracture mode was also more inclined towards brittle fracture. Full article

(This article belongs to the Special Issue Damage, Fracture and Fatigue of Ceramic Matrix Composites (CMCs))

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16 pages, 2080 KiB

Open AccessArticle

Preparation and Properties of Sulfur-Modified Alite Calcium Sulfoaluminate Cement

by Xiaodong Li, Guodong Kang, Shang Dou, Bing Ma, Jin Tang, Hao Zhou, Houhu Zhang, Jiaqing Wang and Xiaodong Shen

Materials 2024, 17(24), 6258; https://doi.org/10.3390/ma17246258 (registering DOI) - 21 Dec 2024

Abstract

Alite calcium sulfoaluminate (ACSA) cement is an innovative and environmentally friendly cement compared to ordinary Portland cement (OPC). The synthesis and hydration of ACSA clinkers doped with gradient sulfur were investigated. The clinker compositions and hydrated pastes were characterized by X-ray diffraction (XRD), [...] Read more.

Alite calcium sulfoaluminate (ACSA) cement is an innovative and environmentally friendly cement compared to ordinary Portland cement (OPC). The synthesis and hydration of ACSA clinkers doped with gradient sulfur were investigated. The clinker compositions and hydrated pastes were characterized by X-ray diffraction (XRD), isothermal calorimetry, mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) to analyze its mineral contents, hydration products, heat release, pore structure, and microstructure. The compressive strength and linear expansion of ACSA mortars were tested for their mechanical properties. Results showed that clinkers doped with 2 wt.% MgO can offset the hurdle that SO₃ caused to the formation of C₃S (tricalcium silicate). Clinkers with varying ratios of C₃S and C₄A₃$ (calcium sulfoaluminate) were obtained, achieving 58–70% C₃S and 2.0–5.6% C₄A₃$ in ACSA through adjusting the KH (lime saturation factor) values and SO₃ dosage. ACSA cement showed better early mechanical properties. The 0.93 KH value with 3% SO₃ dosage in the raw meal, which contains 63.9% C₃S and 2.98% C₄A₃$ in the clinker, reached an optimal compressive strength level at 1d (26.35 MPa) and at 3d (39.41 MPa), marking 30.45% and 18.70% increases compared to PII 52.5. The excellent early strength of ACSA cement may offer promising applications t increasing the incorporation of supplementary cementitious materials, thereby reduce pollution and carbon emissions. Full article

(This article belongs to the Special Issue Sustainable Pavement Materials: Design, Application and Performance Evaluation)

19 pages, 17625 KiB

Open AccessArticle

The Effect of Absorbed Hydrogen on the Rotors of Steel Machining Products During Powerful Turbo Aggregate Repairs

by Alexander I. Balitskii, Andriy M. Syrotyuk, Valerii O. Kolesnikov, Valentina O. Balitska, Ljubomyr M. Ivaskevych and Maria R. Havrilyuk

Materials 2024, 17(24), 6257; https://doi.org/10.3390/ma17246257 (registering DOI) - 21 Dec 2024

Abstract

Rotor shafts are the most heavily loaded and accident-prone parts of powerful turbine generators, which are cooled using hydrogen. To eliminate damage sustained during operations, repair work was carried out, including the removal of defective parts, surfacing, and turning. This study tested the [...] Read more.

Rotor shafts are the most heavily loaded and accident-prone parts of powerful turbine generators, which are cooled using hydrogen. To eliminate damage sustained during operations, repair work was carried out, including the removal of defective parts, surfacing, and turning. This study tested the machinability of the rotor shaft using prototypes made from 38KhN3MFA steel. A section of the shaft was degraded due to prolonged operation (250 thousand hours), and compared to the central part, a decrease in the average grain size from 21.57 μm to 12.72 μm and an increase in the amount of hydrogen absorbed during operation from 2.27 to 7.54 ppm were observed. With the frequency of dry turning increasing from 200 to 315 RPM, the chips changed their form from mostly rectangular with linear dimensions of 10 to 20 mm to large spiral rings with a diameter of 15 to 20 mm and a length of more than 50 mm. Cracks of 1 to 4 mm in length were found in most chip particles at both rotational speeds. Increasing the rotational speed from 200 to 315 and up to 500 RPM led to the formation of an oxide film on the surface of the specimens, as evidenced by the appearance of oxygen during local analyses of the elemental content on the chip surface. The saturation of specimens by hydrogen gas led to the formation of finer chips compared to the non-hydrated material, and the roughness of the machined surface increased at hydrogen contents of 6 and 8 ppm. In both dry and coolant cutting operations, surface roughness reflects the degradation of the rotor shaft or experimental prototypes due to hydrogenation, which can be used to diagnose the condition of the rotor after long-term operation. Full article

(This article belongs to the Collection Machining and Manufacturing of Alloys and Steels)

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16 pages, 4154 KiB

Open AccessArticle

Optimisation of Hot-Chamber Die-Casting Process of AM60 Alloy Using Taguchi Method

by Tomasz Rzychoń and Andrzej Kiełbus

Materials 2024, 17(24), 6256; https://doi.org/10.3390/ma17246256 (registering DOI) - 21 Dec 2024

Abstract

This paper presents the effect of hot-chamber HPDC (high-pressure die casting) process parameters on the porosity, mechanical properties, and microstructure of AM60 magnesium alloy. To reduce costs, a Taguchi design of the experimental method was used to optimise the HPDC process. Six parameters [...] Read more.

This paper presents the effect of hot-chamber HPDC (high-pressure die casting) process parameters on the porosity, mechanical properties, and microstructure of AM60 magnesium alloy. To reduce costs, a Taguchi design of the experimental method was used to optimise the HPDC process. Six parameters set at two levels were selected for optimisation, i.e., piston speed in the first phase, piston speed in the second phase, molten metal temperature, piston travel, mould temperature, and die-casting pressure (the pressure under the piston). Signal-to-noise (S/N) ratios were used to quantify the present variations. The significance of the influence of the HPDC parameters was assessed using statistical analysis of variance (ANOVA). The results showed that the die-casting pressure had the most significant influence on the porosity of the AM60 alloy. Moreover, piston speed in the first phase, second phase, and die-casting pressure had the most important effects on tensile strength. It is well known that porosity determines the mechanical properties of die castings; however, in AM60 alloy, changes in the HPDC parameters also contribute to microstructural changes, mainly through the formation of Externally Solidified Crystals. Full article

(This article belongs to the Special Issue Achievements in Foundry Materials and Technologies)

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19 pages, 50647 KiB

Open AccessArticle

Long-Pulse Thermography Application for Detection and Localisation of Embedded Optical Fibres into Glass Fibre Composite

by Katarzyna Majewska and Magdalena Mieloszyk

Materials 2024, 17(24), 6255; https://doi.org/10.3390/ma17246255 (registering DOI) - 21 Dec 2024

Abstract

Composites have found applications in critical components and require a high degree of safety and reliability. To ensure this, structural health monitoring systems based on optical fibres embedded within structures are installed for continuous monitoring. Infrared thermography is a non-destructive method that can [...] Read more.

Composites have found applications in critical components and require a high degree of safety and reliability. To ensure this, structural health monitoring systems based on optical fibres embedded within structures are installed for continuous monitoring. Infrared thermography is a non-destructive method that can be applied to inspect the internal structure after manufacturing and during operation. This paper presents an application of pulsed thermography for observing and evaluating the internal structure of glass fibre-reinforced polymer samples with different arrangements of embedded optical fibres. The goal of the paper is to study the feasibility of using pulsed thermography to distinguish optical fibres from glass textile fibre bundles, as well as to track the arrangement of the optical fibres. Full article

(This article belongs to the Special Issue Fabrication, Characterisation and Application of Fibre-Reinforced Polymers and Composites)

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13 pages, 26617 KiB

Open AccessArticle

Improving Corrosion Resistance of Rare Earth Zirconates to Calcium–Magnesium–Alumina–Silicate Molten Salt Through High-Entropy Strategy

by Cong Gui, Zi-Jian Peng, Jun-Teng Yao, Shu-Qi Wang, Zhan-Guo Liu, Ya-Ming Wang and Jia-Hu Ouyang

Materials 2024, 17(24), 6254; https://doi.org/10.3390/ma17246254 (registering DOI) - 21 Dec 2024

Abstract

The erosion caused by high-temperature calcium–magnesium–alumina–silicate (CMAS) has emerged as a critical impediment to the advancement of thermal barrier coating (TBC). In this study, a series of high-entropy rare earth zirconates, (La_0.2Sm_0.2Dy_0.2Er_0.2Gd_0.2)₂ [...] Read more.

The erosion caused by high-temperature calcium–magnesium–alumina–silicate (CMAS) has emerged as a critical impediment to the advancement of thermal barrier coating (TBC). In this study, a series of high-entropy rare earth zirconates, (La_0.2Sm_0.2Dy_0.2Er_0.2Gd_0.2)₂(Zr_1−xCe_x)₂O₇ (x = 0, 0.2, 0.4, 0.5) were synthesized through a solid-phase reaction, and their corrosion behavior against CMAS was investigated. Our findings demonstrate that numerous rare earth elements impede element diffusion, facilitate the formation of a compact oxide layer, and effectively hinder CMAS infiltration. Furthermore, rare earth elements with larger ionic radii exhibit enhanced solubility in apatite, whereas those with smaller ionic radii are more readily soluble in ZrO₂. In general, the utilization of the high-entropy strategy is an effective approach to significantly improving corrosion resistance against CMAS. Full article

(This article belongs to the Special Issue Corrosion Resistance Enhancement of the Materials Surface—Second Edition)

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15 pages, 5908 KiB

Open AccessArticle

Fabrication and Coating of Porous Ti6Al4V Structures for Application in PEM Fuel Cell and Electrolyzer Technologies

by Juan Villemur, Carlos Romero, Jose Manuel Crego and Elena Gordo

Materials 2024, 17(24), 6253; https://doi.org/10.3390/ma17246253 (registering DOI) - 21 Dec 2024

Abstract

The production of green hydrogen through proton exchange membrane water electrolysis (PEMWE) is a promising technology for industry decarbonization, outperforming alkaline water electrolysis (AWE). However, PEMWE requires significant investment, which can be mitigated through material and design advancements. Components like bipolar porous plates [...] Read more.

The production of green hydrogen through proton exchange membrane water electrolysis (PEMWE) is a promising technology for industry decarbonization, outperforming alkaline water electrolysis (AWE). However, PEMWE requires significant investment, which can be mitigated through material and design advancements. Components like bipolar porous plates (BPPs) and porous transport films (PTFs) contribute substantially to costs and performance. BPPs necessitate properties like corrosion resistance, electrical conductivity, and mechanical integrity. Titanium, commonly used for BPPs, forms a passivating oxide layer, reducing efficiency. Effective coatings are crucial to address this issue, requiring conductivity and improved corrosion resistance. In this study, porous Ti64 structures were fabricated via powder technology, treating them with thermochemical nitriding. The resulting structures with controlled porosity exhibited enhanced corrosion resistance and electrical conductivity. Analysis through scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), grazing incidence XRD and X-ray photoelectron spectroscopy (XPS) confirmed the effectiveness of the coating, meeting performance requirements for BPPs. Full article

(This article belongs to the Special Issue Select Papers in Electrochemical Energy Conversion and Storage Devices)

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19 pages, 7278 KiB

Open AccessArticle

Study on the Bending and Shear Behavior of a New Type of Wet Joint in Precast Concrete Deck for Composite Bridges

by Yan Wang, Long Hu, Wei Li, Guangshuai Zhang, Bin Han, Jin Di, Peng Fei, Xiaofeng Duan, Jinying Dong and Fengjiang Qin

Materials 2024, 17(24), 6252; https://doi.org/10.3390/ma17246252 (registering DOI) - 21 Dec 2024

Abstract

According to the mechanical characteristics of joints in steel–concrete composite bridge decks under the combined bending and shear, improved joint details with simple structure and convenient construction were studied, including lapped U-bars, lapped headed bars, and lapped hook bars. In order to test [...] Read more.

According to the mechanical characteristics of joints in steel–concrete composite bridge decks under the combined bending and shear, improved joint details with simple structure and convenient construction were studied, including lapped U-bars, lapped headed bars, and lapped hook bars. In order to test the mechanical properties of the three joint details and compare them with the existing lapped/welded linear bars, the tests of five specimens were carried out. The cracking load, ultimate load, failure mode, crack pattern, and reinforcement strain were analyzed. The test results showed that the joint with lapped U-bars and hook bars exhibited ductile failure, while the joint with lapped headed and lapped/welded linear bars exhibited brittle failure. The cracking load of the five specimens was basically the same. The crack first occurred at the interface of pre-cast concrete and wet joints. When the ultimate bearing capacity was reached, the vertical main cracks were generated near the interface of the lapped U-bars, lapped hook bars, and welded linear bars specimens. The diagonal cracks were generated at the wet joint of the lapped headed bars specimen and lapped linear bars specimen. The lapped U-bars specimen had the highest bearing capacity, which was 22.8%, 14.2%, 50.4%, and 32.1% higher than the capacities of the lapped headed bars, lapped hook bars, lapped linear bars, and welded linear bars specimens, respectively. The load–deflection curves and crack mode obtained from the FEM of the lapped U-bars joint specimen were consistent with the test results. The bearing capacity of the FEM (351.3 KN) was 1.8% less than the test result (357.6 KN), which indicates that the bearing capacity calculated by the finite element model is reliable. There are 80 models with varying lap lengths and concrete strengths. The self-organizing migrating algorithm was used to fit the coupling effect of lap length and concrete strength. Based on doubly reinforced beam flexural capacity formulas, a bearing capacity calculation for lapped U-bars joint was proposed. The mean value of the formula calculation result and the finite element result ratio is 1.03, and the variance is 0.0004. Full article

(This article belongs to the Special Issue Experimental Study, Numerical Simulation & Structural Applications of Construction Materials—2nd Edition)

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13 pages, 9916 KiB

Open AccessArticle

Low-Temperature Sintering and Microwave Dielectric Properties of Cu_xZn₁_−xTi₀_.2Zr₀_.8Nb₂O₈ Ceramics with the Aid of LiF

by Xing-Hua Ma, Qi Qu, Haitao Wu, Zhenlu Zhang and Xingyi Ma

Materials 2024, 17(24), 6251; https://doi.org/10.3390/ma17246251 (registering DOI) - 20 Dec 2024

Abstract

M²⁺N⁴⁺Nb₂O₈-type ceramics (where M = Mg, Ca, Mn, Co, Ni, Zn and N = Ti, Zr) are essential for satellite communication and mobile base stations due to their medium relative permittivity (ε_r) [...] Read more.

M²⁺N⁴⁺Nb₂O₈-type ceramics (where M = Mg, Ca, Mn, Co, Ni, Zn and N = Ti, Zr) are essential for satellite communication and mobile base stations due to their medium relative permittivity (ε_r) and high quality factor (Q × f). Although ZnTi_0.2Zr_0.8Nb₂O₈ ceramic exhibits impressive microwave dielectric properties, including an ε_r of 29.75, a Q × f of 107,303 GHz, and a τ_f of −24.41 ppm/°C, its sintering temperature of 1150 °C remains a significant barrier for integration into low-temperature co-fired ceramic (LTCC) technologies. To overcome this limitation, a strategy involving the partial substitution of Zn²⁺ with Cu²⁺ and the addition of LiF as a sintering aid was devised for ZnTi_0.2Zr_0.8Nb₂O₈. The dual impact of Cu²⁺ partial substitution and LiF as a sintering enhancer facilitated the successful sintering of Cu_0.3Zn_0.7Ti_0.2Zr_0.8Nb₂O₈ ceramics at a reduced temperature of 950 °C using the conventional solid-state reaction method. These ceramics exhibited excellent microwave dielectric properties. Notably, Cu_0.3Zn_0.7Ti_0.2Zr_0.8Nb₂O₈ ceramic with 40 mol% LiF addition demonstrated optimal microwave dielectric properties without any reaction with a silver electrode at a sintering temperature of 950 °C, yielding ε_r = 32, Q × f = 45,543 GHz, and τ_f = −43.5 ppm/°C. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

46 pages, 17108 KiB

Open AccessArticle

Predicting the Effect of RSW Parameters on the Shear Force and Nugget Diameter of Similar and Dissimilar Joints Using Machine Learning Algorithms and Multilayer Perceptron

by Marwan T. Mezher, Alejandro Pereira and Tomasz Trzepieciński

Materials 2024, 17(24), 6250; https://doi.org/10.3390/ma17246250 (registering DOI) - 20 Dec 2024

Abstract

Resistance spot-welded joints are crucial parts in contemporary manufacturing technology due to their ubiquitous use in the automobile industry. The necessity of improving manufacturing efficiency and quality at an affordable cost requires deep knowledge of the resistance spot welding (RSW) process and the [...] Read more.

Resistance spot-welded joints are crucial parts in contemporary manufacturing technology due to their ubiquitous use in the automobile industry. The necessity of improving manufacturing efficiency and quality at an affordable cost requires deep knowledge of the resistance spot welding (RSW) process and the development of artificial neural network (ANN)- and machine learning (ML)-based modelling techniques, apt for providing essential tools for design, planning, and incorporation in the welding process. Tensile shear force and nugget diameter are the most crucial outputs for evaluating the quality of a resistance spot-welded specimen. This study uses ML and ANN models to predict shear force and nugget diameter responses to RSW parameters. The RSW analysis was executed on similar and dissimilar AISI 304 and grade 2 titanium alloy joints with equal and unequal thicknesses. The input parameters included welding current, pressure, welding duration, squeezing time, holding time, pulse welding, and sheet thickness. Linear regression, Decision tree, Support vector machine (SVM), Random forest (RF), Gradient-boosting, CatBoost, K-Nearest Neighbour (KNN), Ridge, Lasso, and ElasticNet machine learning algorithms, along with two different structures of Multilayer Perceptron, were utilized for studying the impact of the RSW parameters on the shear force and nugget diameter. Different validation metrics were applied to assess each model’s quality. Two equations were developed to determine the shear force and nugget diameter based on the investigation parameters. The current research also presents a prediction of the Relative Importance (RI) of RSW factors. Shear force and nugget diameter predictions were examined using SHapley (SHAP) Additive Explanations for the first time in the RSW field. Trainbr as the training function and Logsig as the transfer function delivered the best ANN model for predicting shear force in a one-output structure. Trainrp with Tansig made the most accurate predictions for nugget diameter in a one-output structure and for shear force and diameter in a two-output structure. Depending on validation metrics, the Random forest model outperformed the other ML algorithms in predicting shear force or nugget diameter in a one-output model, while the Decision tree model gave the best prediction using a two-output structure. Linear regression made the worst ML predictions for shear force, while ElasticNet made the worst nugget diameter forecasts in a one-output model. However, in two-output models, Lasso made the worst predictions. Full article

(This article belongs to the Section Metals and Alloys)

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26 pages, 675 KiB

Open AccessReview

Implant Surface Decontamination Methods That Can Impact Implant Wettability

by Georgios E. Romanos, Lauren Mistretta, Allyson Newman, Danielle Ohana and Rafael A. Delgado-Ruiz

Materials 2024, 17(24), 6249; https://doi.org/10.3390/ma17246249 (registering DOI) - 20 Dec 2024

Abstract

This review addresses the effects of various decontamination methods on the wettability of titanium and zirconia dental implants. Despite extensive research on surface wettability, there is still a significant gap in understanding how different decontamination techniques impact the inherent wettability of these surfaces. [...] Read more.

This review addresses the effects of various decontamination methods on the wettability of titanium and zirconia dental implants. Despite extensive research on surface wettability, there is still a significant gap in understanding how different decontamination techniques impact the inherent wettability of these surfaces. Although the literature presents inconsistent findings on the efficacy of decontamination methods such as lasers, air-polishing, UV light, and chemical treatments, the reviewed studies suggest that decontamination alters in vitro hydrophilicity. Post-decontamination surface chemistry must be carefully considered when selecting optimal surface treatments for implant materials. Further in vitro investigations are essential to determine which approaches best enhance surface wettability, potentially leading to improved implant–tissue interactions in clinical settings. Full article

(This article belongs to the Special Issue Advanced Dental Materials for Oral Rehabilitation)

20 pages, 3525 KiB

Open AccessArticle

Method for the Mixing Design and Physical Characterization of Air-Foamed Lightweight Clay Concrete: A Response to the Issue of Recycling Dredged Sediments

by Agnès Zambon, Zoubir Mehdi Sbartaï and Nadia Sayouri

Materials 2024, 17(24), 6248; https://doi.org/10.3390/ma17246248 (registering DOI) - 20 Dec 2024

Abstract

From both economic and environmental points of view, the reuse of dredged sediments in the direct onsite casting of concrete represents a promising method for replacing sand. The aim of this study was to develop a cementitious material that (i) reuses the thin [...] Read more.

From both economic and environmental points of view, the reuse of dredged sediments in the direct onsite casting of concrete represents a promising method for replacing sand. The aim of this study was to develop a cementitious material that (i) reuses the thin particles of sediments; (ii) has a low density due to the incorporation of air foam in the material; and (iii) achieves a minimum mechanical strength of 0.5 MPa for embankment applications. This study focused on the characterization of a non-standard “concrete”, which is a mixture of a synthetic soil (80% montmorillonite and 20% calibrated sand) and cement. To reduce its density, air foam was incorporated into the material during the manufacturing process (air-foamed lightweight clay concrete—AFLCC). The study results highlight that a density around 1.2 (unit: g/cm³/1 g/cm³) can be obtained. This density reduction can be obtained with a certain degree of workability when the material is in a fresh state. To obtain this workability, a certain amount of water must be added; however, the addition of water has a significant impact on the compressive strength of the AFLCC. As such, a mathematical equation correlating the compressive strength, the density, and the percentage of cement is proposed in this study. The mechanical strength results of the AFLCC at different times, in conjunction with the Vicat results, show that the porosity created by the air foam has the effect of slowing down the hydration mechanism of the cement. The porosities obtained are consistent with the density results. The characteristic radii indicate large pore sizes for formulations with low fluidity in the fresh state when air bubbles are incorporated. Full article

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

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