Materials

49 pages, 14823 KiB

Open AccessReview

by Frank Czerwinski

Materials 2020, 13(15), 3441; https://doi.org/10.3390/ma13153441 - 04 Aug 2020

Cited by 86 | Viewed by 13422

Thermal stability, determining the material ability of retaining its properties at required temperatures over extended service time, is becoming the next frontier for aluminum alloys. Its improvement would substantially expand their range of structural applications, especially in automotive and aerospace industries. This report [...] Read more.

Thermal stability, determining the material ability of retaining its properties at required temperatures over extended service time, is becoming the next frontier for aluminum alloys. Its improvement would substantially expand their range of structural applications, especially in automotive and aerospace industries. This report explains the fundamentals of thermal stability; definitions, the properties involved; and the deterioration indicators during thermal/thermomechanical exposures, including an impact of accidental fire, and testing techniques. For individual classes of alloys, efforts aimed at identifying factors stabilizing their microstructure at service temperatures are described. Particular attention is paid to attempts of increasing the current upper service limit of high-temperature grades. In addition to alloying aluminum with a variety of elements to create the thermally stable microstructure, in particular, transition and rare-earth metals, parallel efforts are explored through applying novel routes of alloy processing, such as rapid solidification, powder metallurgy and additive manufacturing, engineering alloys in a liquid state prior to casting, and post-casting treatments. The goal is to overcome the present barriers and to develop novel aluminum alloys with superior properties that are stable across the temperature and time space, required by modern designs. Full article

(This article belongs to the Special Issue Lightweight Structural Materials for Automotive and Aerospace)

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31 pages, 4964 KiB

Open AccessReview

On the Factors Governing Austenite Stability: Intrinsic versus Extrinsic

by Binbin He

Materials 2020, 13(15), 3440; https://doi.org/10.3390/ma13153440 - 04 Aug 2020

Cited by 43 | Viewed by 4042

Abstract

In this review, we separate the different governing factors on austenite stability into intrinsic and extrinsic factors, depending on the domain defined by austenite grain boundaries. The different measuring techniques on the effectiveness of the governing factors in affecting the austenite stability are [...] Read more.

In this review, we separate the different governing factors on austenite stability into intrinsic and extrinsic factors, depending on the domain defined by austenite grain boundaries. The different measuring techniques on the effectiveness of the governing factors in affecting the austenite stability are discussed. On the basis of the austenite stability, a new alloy design strategy that involves the competition between the intrinsic and extrinsic factors to control the transformation-induced plasticity (TRIP) effect to realize the stronger the more ductile steel is proposed. The present review may provide new insights into the development of novel thermal-mechanical processing to advance the mechanical properties of steels for industrial applications. Full article

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21 pages, 6961 KiB

Open AccessArticle

Experimental Investigations Regarding the Structural Damage Monitoring of Strands Wire Rope within Mechanical Systems

by Carmen Debeleac, Silviu Nastac and Gina Diana Musca (Anghelache)

Materials 2020, 13(15), 3439; https://doi.org/10.3390/ma13153439 - 04 Aug 2020

Cited by 4 | Viewed by 2088

Abstract

This paper deals with the area of structural damage monitoring of steel strands wire ropes embedded into various equipment and mechanical systems. Of the currently available techniques and methods for wire ropes health monitoring, the authors focused on the group of techniques based [...] Read more.

This paper deals with the area of structural damage monitoring of steel strands wire ropes embedded into various equipment and mechanical systems. Of the currently available techniques and methods for wire ropes health monitoring, the authors focused on the group of techniques based on operational dynamics investigation of such systems. Beyond the capability and efficiency of both occasionally and continuously monitoring application, the dynamics-based methods are able to provide additional information regarding the structural integrity and functional operability of the entire ensemble embedding the wire ropes. This paper presents the results gained by the authors using a laboratory setup that can simulate the operational condition usually used for regular applications of wire ropes. The investigations were conducted on three directions of acquired signals post-processing. Firstly, the classical fast Fourier transform was used to evaluate the potential changes within the spectral distribution of transitory response. The other two directions involved high-order spectral analyses in terms of bi-spectrum and Wigner–Ville distribution and multi-scale analysis based methods such as complex wavelet cross-correlation and complex wavelet coherency. The results indicate that each direction of analysis can provide suitable information regarding potential wire rope damage, but the ensemble of post-processing methods offers supplementary precision. Full article

(This article belongs to the Special Issue Simulation and Analysis of Materials Failure Under Loading)

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11 pages, 1476 KiB

Open AccessArticle

Effect of Immiscible Secondary Fluid on Particle Dynamics and Coffee Ring Characteristics during Suspension Drying

by Kevin Injoe Jung, Baek Sung Park, Seong Jae Lee, Seung Man Noh and Hyun Wook Jung

Materials 2020, 13(15), 3438; https://doi.org/10.3390/ma13153438 - 04 Aug 2020

Cited by 4 | Viewed by 2396

Abstract

Particle motion and coffee ring patterns in water-borne suspensions of polystyrene (PS) particle added with small amounts of secondary hydrophobic decalin are investigated during the drying of the suspension droplets, mainly employing light scattering methods. Very tiny secondary fluid insertions via high-speed agitation [...] Read more.

Particle motion and coffee ring patterns in water-borne suspensions of polystyrene (PS) particle added with small amounts of secondary hydrophobic decalin are investigated during the drying of the suspension droplets, mainly employing light scattering methods. Very tiny secondary fluid insertions via high-speed agitation effectively link the particles through hydrophobic dissolution leading to the formation of multimodal particulate clusters, with resistance to the outward capillary flow and suppression of coffee ring formation after drying. The impact of decalin on particles is corroborated by actual images acquired from an optical profiler and a scanning electron microscope (SEM). The average particle motion inside the suspension changed by decalin was expressed in terms of mean square displacement (MSD) based on diffusing wave spectroscopy (DWS). Employing multispeckle diffusing wave spectroscopy (MSDWS), the rapid motion or β-relaxation of particles in various suspensions with and without decalin is quantified in early lag time during the drying of droplets. The change in particle dynamics during suspension drop drying, when adding a small secondary fluid, plays a key role in tuning coffee ring patterns. Full article

(This article belongs to the Special Issue Functional Coating Materials and Processing for Platform Technology)

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28 pages, 11178 KiB

Open AccessArticle

Experimental Investigation of NaOH and KOH Mixture in SCBA-Based Geopolymer Cement Composite

by Sardar Kashif Ur Rehman, Lahiba Imtiaz, Fahid Aslam, Muhammad Khizar Khan, Muhammad Haseeb, Muhammad Faisal Javed, Rayed Alyousef and Hisham Alabduljabbar

Materials 2020, 13(15), 3437; https://doi.org/10.3390/ma13153437 - 04 Aug 2020

Cited by 31 | Viewed by 4291

Abstract

This research aimed at exploring the effects of a mixture of sodium hydroxide (NaOH) and potassium hydroxide (KOH) activators in a sugar cane bagasse ash (SCBA)-based geopolymer cement paste. Bagasse ash replacement was 20% of cement by weight. The mixture of NaOH and [...] Read more.

This research aimed at exploring the effects of a mixture of sodium hydroxide (NaOH) and potassium hydroxide (KOH) activators in a sugar cane bagasse ash (SCBA)-based geopolymer cement paste. Bagasse ash replacement was 20% of cement by weight. The mixture of NaOH and KOH comprised 4, 8, and 12 M solutions with mixing percentages of 0%, 20%, 40%, 60%, 80%, and 100% for all possible combinations. A pH test was performed on each possible combination of solutions. A Chapelle’s test, XRD, X-ray fluorescence (XRF), and SEM analysis were used to check whether the SCBA exhibited pozzolanic reactivity. Subsequently, the SCBA geopolymer cement paste was tested for compressive strength, water absorption, permeable porosity, and sorptivity. It was estimated that the geopolymer cement paste exhibited higher absorption and sorptivity values than control mixtures when molarity increased. However, the samples prepared with combinations of the 8 M activator solution exhibited consistent absorption, sorptivity, and compressive strength values when compared to the control and other geopolymer mixtures with 4 and 12 M activator solutions. Thus, the two activator solutions G8N₄₀8K₆₀ and G8N₂₀8K₈₀—where GxN_ayK_b represents the geopolymer concrete sample prepared by adding solutions of two bases, i.e., ‘xN_ayK_b’ showing an ‘a’ percentage of ‘x’ molar NaOH and a ‘b’ percentage of ‘y’ molar KOH—were obtained as the optimum molar ratio of the activator in geopolymer concrete. The geopolymer cement pastes, along with the optimum and control samples, were further tested for concrete durability, SEM, and TGA tests. The G8N₂₀8K₈₀ sample exhibited a better mechanical and durability performance than the G8N₄₀8K₆₀ sample. The durability performance of the geopolymer concrete was also superior to ordinary concrete. Moreover, the geopolymer concrete achieved a 21% reduction in global warming potential compared to the control mixture. Thus, it can be concluded that the use of SCBA in geopolymer concrete can address the ash disposal and CO₂ emission problems with enhanced durability. Full article

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20 pages, 10722 KiB

Open AccessArticle

Investigation on the Residual Stresses and Fatigue Performance of Riveted Single Strap Butt Joints

by Jintong Liu, Anan Zhao, Zhenzheng Ke, Zhiqiang Li and Yunbo Bi

Materials 2020, 13(15), 3436; https://doi.org/10.3390/ma13153436 - 04 Aug 2020

Cited by 7 | Viewed by 2891

Abstract

In aircraft manufacturing, riveting is one of the most important connection ways to fasten the sheet metal parts. The riveted single strap butt joints are mainly used in the load-bearing components of the aircraft such as the fuselage and wing panels. The connection [...] Read more.

In aircraft manufacturing, riveting is one of the most important connection ways to fasten the sheet metal parts. The riveted single strap butt joints are mainly used in the load-bearing components of the aircraft such as the fuselage and wing panels. The connection quality and fatigue performance of the riveted joints directly affect the reliability and safety of the aircraft. In this paper, under the assumption of constant temperature, the fatigue strengthening mechanism of interference-fit riveting is introduced based on elastic-plastic mechanics and fracture mechanics. On this basis, the finite element (FE) models of the riveted single strap butt joints with various strap thickness and rivet sizes/arrangements are established. The residual stresses distribution around the riveted hole is analyzed. Furthermore, the fatigue tests of the riveted single strap butt joints with cyclic loading are carried out. The experimental results verified the correctness and effectiveness of the simulation model. Finally, the conclusion is drawn that increasing rivet size and strap thickness within the allowable weight range can improve the fatigue performance of the riveted single strap butt joints. The knowledge could be used to guide the structural design and optimization of the riveted butt joints against fatigue. Full article

(This article belongs to the Special Issue Advanced Manufacturing and Joining Technologies of Aluminum and Steel Sheets)

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13 pages, 4316 KiB

Open AccessArticle

Leachable Poly(Trimethylene Carbonate)/CaCO₃ Composites for Additive Manufacturing of Microporous Vascular Structures

by Zhengchao Guo, Dirk Grijpma and André Poot

Materials 2020, 13(15), 3435; https://doi.org/10.3390/ma13153435 - 04 Aug 2020

Cited by 5 | Viewed by 2344

Abstract

The aim of this work was to fabricate microporous poly(trimethylene carbonate) (PTMC) vascular structures by stereolithography (SLA) for applications in tissue engineering and organ models. Leachable CaCO₃ particles with an average size of 0.56 μm were used as porogens. Composites of photocrosslinkable [...] Read more.

The aim of this work was to fabricate microporous poly(trimethylene carbonate) (PTMC) vascular structures by stereolithography (SLA) for applications in tissue engineering and organ models. Leachable CaCO₃ particles with an average size of 0.56 μm were used as porogens. Composites of photocrosslinkable PTMC and CaCO₃ particles were cast on glass plates, crosslinked by ultraviolet light treatment and leached in watery HCl solutions. In order to obtain interconnected pore structures, the PTMC/CaCO₃ composites had to contain at least 30 vol % CaCO₃. Leached PTMC films had porosities ranging from 33% to 71% and a pore size of around 0.5 μm. The mechanical properties of the microporous PTMC films matched with those of natural blood vessels. Resins based on PTMC/CaCO₃ composites with 45 vol % CaCO₃ particles were formulated and successfully used to build vascular structures of various shapes and sizes by SLA. The intrinsic permeabilities of the microporous PTMC films and vascular structures were at least one order of magnitude higher than reported for the extracellular matrix, indicating no mass transfer limitations in the case of cell seeding. Full article

(This article belongs to the Special Issue Biodegradable and Biocompatible Polymer-Based Materials for Biomedical Engineering)

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17 pages, 2611 KiB

Open AccessArticle

Retentive Characteristics of a New Attachment System for Hybrid Dentures

by Christin Arnold, Charlotte Stampa, Ramona Schweyen, Jeremias Hey and Arne Boeckler

Materials 2020, 13(15), 3434; https://doi.org/10.3390/ma13153434 - 04 Aug 2020

Cited by 10 | Viewed by 2837

Abstract

Removable implant-anchored dentures have become an established treatment concept especially for older, multimorbid patients. This study investigates the retention force (RF) of two different attachment systems. A total of 96 specimens (n = 8 for each condition) were fabricated and RF was measured [...] Read more.

Removable implant-anchored dentures have become an established treatment concept especially for older, multimorbid patients. This study investigates the retention force (RF) of two different attachment systems. A total of 96 specimens (n = 8 for each condition) were fabricated and RF was measured under different conditions: fatigue (10,000 cycles dislodging), thermal undulation (5/55 °C, 5000 cycles) and implant-angulation (0°, 5°, 10°, 15°, 20°). The Novaloc system ((N), 0° and 15° abutments, yellow matrix (Y)) was compared to the Locator system ((L), pink (P) and orange (O)). Initial RFs (8.57 ± 0.99 N (NY), 19.39 ± 8.10 N (LP), 8.8 ± 5.28 N (LO)) were reduced by ageing simulation (26% (NY), 66% (LP), 89% (LO); p < 0.001). After thermocycling, Novaloc’s RFs decreased by 33% (p < 0.001) while the Locators’ RFs increased by 34% (LP: p = 0.002, LO: p = 0.148). In contrast to LP, the RFs of Novaloc abutments and LOs predominantly showed no clinically relevant dependence on implant angulation. Ageing processes tended to result in lower RFs at higher implant angulation. Thus, the Novaloc attachment system offers an alternative to Locator attachments. It is characterized by a comparatively continuous RF-curve over the entire wearing period. Future clinical studies have to be conducted to verify the in vitro demonstrated advantages of the Novaloc system. Full article

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20 pages, 5883 KiB

Open AccessArticle

Silk Fibroin/Collagen/Chitosan Scaffolds Cross-Linked by a Glyoxal Solution as Biomaterials toward Bone Tissue Regeneration

by Sylwia Grabska-Zielińska, Alina Sionkowska, Catarina C. Coelho and Fernando J. Monteiro

Materials 2020, 13(15), 3433; https://doi.org/10.3390/ma13153433 - 04 Aug 2020

Cited by 32 | Viewed by 3742

Abstract

In this study, three-dimensional materials based on blends of silk fibroin (SF), collagen (Coll), and chitosan (CTS) cross-linked by glyoxal solution were prepared and the properties of the new materials were studied. The structure of the composites and the interactions between scaffold components [...] Read more.

In this study, three-dimensional materials based on blends of silk fibroin (SF), collagen (Coll), and chitosan (CTS) cross-linked by glyoxal solution were prepared and the properties of the new materials were studied. The structure of the composites and the interactions between scaffold components were studied using FTIR spectroscopy. The microstructure was observed using a scanning electron microscope. The following properties of the materials were measured: density and porosity, moisture content, and swelling degree. Mechanical properties of the 3D materials under compression were studied. Additionally, the metabolic activity of MG-63 osteoblast-like cells on materials was examined. It was found that the materials were characterized by a high swelling degree (up to 3000% after 1 h of immersion) and good porosity (in the range of 80–90%), which can be suitable for tissue engineering applications. None of the materials showed cytotoxicity toward MG-63 cells. Full article

(This article belongs to the Special Issue Research of Organic Molecules and Materials for Biological Application)

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18 pages, 3428 KiB

Open AccessArticle

Compostable Polylactide and Cellulose Based Packaging for Fresh-Cut Cherry Tomatoes: Performance Evaluation and Influence of Sterilization Treatment

by Marco Rapisarda, Cristina Patanè, Alessandra Pellegrino, Angelo Malvuccio, Valeria Rizzo, Giuseppe Muratore and Paola Rizzarelli

Materials 2020, 13(15), 3432; https://doi.org/10.3390/ma13153432 - 04 Aug 2020

Cited by 16 | Viewed by 3900

Abstract

For food packaging, plastic materials display large appeal, mostly due to their versatility, mechanical, optical and barrier properties. However, they play an important role in environmental concerns and waste management issue. Compostable bioplastics represent alternative materials designed for a lower environmental impact. In [...] Read more.

For food packaging, plastic materials display large appeal, mostly due to their versatility, mechanical, optical and barrier properties. However, they play an important role in environmental concerns and waste management issue. Compostable bioplastics represent alternative materials designed for a lower environmental impact. In this work, a biobased compostable packaging, constituted by polylactide (PLA) trays and NatureFlex™ film, was evaluated for fresh-cut cherry tomato. A comparative analysis was accomplished using traditional packaging materials, that is, polyethylene terephtalate (PET) trays and polypropylene (PP Coex) film. Structural stability under food contact conditions, mechanical and physical-chemical properties were investigated. Tensile mechanical properties, puncture resistance, contact angle (CA) and attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), before and after UV or radiofrequency (RF) sterilization treatment, were evaluated. UV irradiation method resulted the less invasive one. Therefore, oxygen and water vapor transmission rate (OTR and WVTR), overall chemical migration test, biodegradation assessment by biochemical oxygen demand (BOD) according to ISO 14851 and disintegration test by ISO 20200 were carried out to establish the further influence of UV sterilization on the packaging. Overall, data showed that the biobased compostable packaging for a prolonged shelf-life of fresh-cut cherry tomato has better properties that were surprisingly enhanced by the UV treatment. Full article

(This article belongs to the Special Issue Biodegradable Polymers: From Synthesis to the Market)

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12 pages, 4951 KiB

Open AccessArticle

Influence of Superhydrophobic Coating on the Water Resistance of Foundry Dust/Magnesium Oxychloride Cement Composite

by Fajun Wang, Xiantao Zhu, Huangjuan Liu, Sheng Lei and Daqi Huang

Materials 2020, 13(15), 3431; https://doi.org/10.3390/ma13153431 - 04 Aug 2020

Cited by 6 | Viewed by 2261

Abstract

In this work, magnesium oxychloride cement (MOC) was used to realize the resource use of foundry dust (FD). Portland cement (PC)-based superhydrophobic coating was prepared on the surface of FD/MOC composite to improve the water resistance of the composite. First, the FD/MOC composites [...] Read more.

In this work, magnesium oxychloride cement (MOC) was used to realize the resource use of foundry dust (FD). Portland cement (PC)-based superhydrophobic coating was prepared on the surface of FD/MOC composite to improve the water resistance of the composite. First, the FD/MOC composites with different contents of FD were prepared. The phase structure of the composite was analyzed using X-ray diffraction (XRD). The microstructure of the cross-section and surface of the composite was observed using field emission scanning electron microscope (FE-SEM). The mechanical properties of the FD/MOC composites with different FD contents at different ages were tested and analyzed. Secondly, the superhydrophobic coating was prepared on the surface of MOC composite using silane/siloxane aqueous emulsion as the hydrophobic modifier, PC as the matrix and water as the solvent. The microstructure and chemical composition of the PC-based superhydrophobic coating were tested and analyzed. The results show that FD can significantly improve the early strength of the FD/MOC composite. The 28-day compressive strength of the FD/MOC composite decreases with increasing FD content. When the FD content is 30%, the 28-day compressive strength of the FD/MOC composite is as high as 75.68 MPa. Superhydrophobic coating can effectively improve the water resistance of the FD/MOC composite. The softening coefficient of the FD/MOC composite without superhydrophobic coating is less than 0.26, while that of the composite modified by superhydrophobic coating is greater than 0.81. Full article

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

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14 pages, 9517 KiB

Open AccessArticle

Experimental and Numerical Evaluation on Deformation and Fracture Mechanism of Cast Duplex Stainless Steel Tubular Specimen

by Zhenhua Li, Xinyu Wang, Tao Chen, Fan Feng, Pan Liu and Yonghao Lu

Materials 2020, 13(15), 3430; https://doi.org/10.3390/ma13153430 - 04 Aug 2020

Cited by 1 | Viewed by 2453

Abstract

The deformation behavior and fracture mechanism of cast duplex stainless steel tubular specimens under different tensile stages were investigated through experimental and numerical evaluation. The results showed that the axial stress was redistributed due to the necking of the tubular specimen, the axial [...] Read more.

The deformation behavior and fracture mechanism of cast duplex stainless steel tubular specimens under different tensile stages were investigated through experimental and numerical evaluation. The results showed that the axial stress was redistributed due to the necking of the tubular specimen, the axial stress near the internal wall was larger than those near the external wall, and its maximum axial stress was distributed between the internal wall and the center of the wall thickness. Microcracks and voids were initiated under the maximum shear stress along the δ/γ phase interface and propagated to the ferrite interior. The voids were connected and merged into the main crack through the propagation of the microcracks. Moreover, the main crack first propagated to the internal wall and then rapidly propagated to the external wall. The fracture morphology can be divided into three types: shear lip zones that can be found on both the internal and external walls, and shear lip zones that can be found on either only the internal wall or the external wall. Full article

(This article belongs to the Special Issue Damage Mechanisms and Failure Analysis in Materials)

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19 pages, 10247 KiB

Open AccessArticle

Selected Properties of the Surface Layer of C45 Steel Parts Subjected to Laser Cutting and Ball Burnishing

by Agnieszka Skoczylas and Kazimierz Zaleski

Materials 2020, 13(15), 3429; https://doi.org/10.3390/ma13153429 - 04 Aug 2020

Cited by 19 | Viewed by 2827

Abstract

In this article, we report the results of experimental studies on the impact of ball burnishing parameters on the roughness, microstructure and microhardness of the surface layer of laser-cut C45 steel parts. We also analysed the distribution of residual stresses generated in the [...] Read more.

In this article, we report the results of experimental studies on the impact of ball burnishing parameters on the roughness, microstructure and microhardness of the surface layer of laser-cut C45 steel parts. We also analysed the distribution of residual stresses generated in the surface layer of these parts. Laser-cut parts often require finishing to improve the quality of their surface. The tests performed in this study were aimed at assessing whether ball burnishing could be used as a finishing operation for parts of this type. Ball burnishing tests were performed on an FV-580a vertical machining centre using a mechanically controlled burnishing tool. The following parameters were varied during the ball burnishing tests: burnishing force F_n, path interval f_w and the diameter of the burnishing ball d_n. Ball burnishing of laser-cut C45 steel parts reduced the surface roughness parameters Sa and Sz by up to 60% in relation to the values obtained after laser cutting. Finish machining also led to the reorganization of the geometric structure of the surface, resulting in an increase in the absolute value of skewness Ssk. This was accompanied by an increment in microhardness (maximum microhardness increment was ΔHV = 95 HV0.05, and the thickness of the hardened layer was g_h = 40 µm) and formation of compressive residual stresses in the surface layer. Full article

(This article belongs to the Section Carbon Materials)

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24 pages, 2593 KiB

Open AccessReview

Incorporation of Alkali-Activated Municipal Solid Waste Incinerator Bottom Ash in Mortar and Concrete: A Critical Review

by Rawaz Kurda, Rui Vasco Silva and Jorge de Brito

Materials 2020, 13(15), 3428; https://doi.org/10.3390/ma13153428 - 03 Aug 2020

Cited by 22 | Viewed by 4081

Abstract

In the light of one of the most common waste management issues in urban areas, namely the elimination of municipal solid waste (MSW; about 486 kg of the waste per capita were generated in the EU in 2017), this study discusses one technique [...] Read more.

In the light of one of the most common waste management issues in urban areas, namely the elimination of municipal solid waste (MSW; about 486 kg of the waste per capita were generated in the EU in 2017), this study discusses one technique as an outlet in the construction industry for the by-product of the waste’s incineration in energy recovery facilities (i.e., MSW incinerator bottom ash—MIBA). There have been some investigations on the use of MIBA as partial replacement of cement to be used in cementitious composites, such as concrete and mortars. However, the waste’s incorporation ratio is limited since further products of hydration may not be produced after a given replacement level and can lead to an unsustainable decline in performance. In order to maximize the incorporation of MIBA, some research studies have been conducted on the alkali activation of the waste as precursor. Thus, this study presents an extensive literature review of the most relevant investigations on the matter to understand the material’s applicability in construction. It analyses the performance of the alkali-activated MIBA as paste, mortar, and concrete from different perspectives. This literature review was made using search engines of several databases. In each database, the same search options were repeated using combinations of various representative keywords. Furthermore, several boundaries were made to find the most relevant studies for further inspection. The main findings of this review have shown that the chemical composition and reactivity of MIBA vary considerably, which may compromise performance comparison, standardization and commercialization. There are several factors that affect the performance of the material that need to be considered, e.g., type and content of precursor, alkaline activator, curing temperature and time, liquid to solid ratio, among others. MIBA-based alkali-activated materials (AAM) can be produced with a very wide range of compressive strength (0.3–160 MPa). The main factor affecting the performance of this precursor is the existence of metallic aluminum (Al), which leads to damaging expansive reactions and an increase in porosity due to hydrogen gas generation stemming from the reaction with the alkaline activator. Several approaches have been proposed to eliminate this issue. The most effective solution was found to be the removal of Al by means of eddy current electromagnetic separation. Full article

(This article belongs to the Special Issue Low Carbon Cements)

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16 pages, 2687 KiB

Open AccessArticle

Influence of Backing Plate Support Conditions on Armor Ceramic Protection Efficiency

by Bowen Zhang, Yangwei Wang, Shaofeng Du, Zhikun Yang, Huanwu Cheng and Qunbo Fan

Materials 2020, 13(15), 3427; https://doi.org/10.3390/ma13153427 - 03 Aug 2020

Cited by 6 | Viewed by 2494

Abstract

The bilayer composite ceramic armor is widely used in the world, while the protection efficiency of the armor ceramic in it still confuses researchers. This study applied a numerical simulation method to produce a general equation that describes the relationship between the protection [...] Read more.

The bilayer composite ceramic armor is widely used in the world, while the protection efficiency of the armor ceramic in it still confuses researchers. This study applied a numerical simulation method to produce a general equation that describes the relationship between the protection efficiency of the armor ceramic and the supporting conditions of the backing plate, thereby enhancing the current understanding of the composite ceramic armor. The results indicated that the protection efficiency of the armor ceramic can be divided into three parts: (1) the basic protection efficiency, (2) the increment efficiency caused by inertial support, and (3) the increment efficiency caused by mechanical support. The inertial support is related to the density and thickness of the backing plate, and the mechanical support is related to the elastic modulus and yield strength of the backing plate materials. The inertial support exhibited a positive correlation with the protection efficiency of the armor ceramic before it reached the S_cr; after that, the protection efficiency of the armor ceramic would remain stable. In addition, the mechanical support showed a linear, positive correlation with the backing plate stress at ε₀. Full article

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14 pages, 5230 KiB

Open AccessArticle

Failure Analysis of a Flare Tip Used in Offshore Production Platform in Qatar

by Elsadig Mahdi and Ali Esmaeili

Materials 2020, 13(15), 3426; https://doi.org/10.3390/ma13153426 - 03 Aug 2020

Cited by 1 | Viewed by 6566

Abstract

An immature failure of a gas flare tip used in Qatar oil and gas offshore industry was investigated throughout this study. The design lifetime of the flare was fifteen years; however, it manifested immature failure resulting in a reduction of its lifetime to [...] Read more.

An immature failure of a gas flare tip used in Qatar oil and gas offshore industry was investigated throughout this study. The design lifetime of the flare was fifteen years; however, it manifested immature failure resulting in a reduction of its lifetime to ten years. The flare is composed of different parts where the upper flare body and wind deflector showed failure while other components were still healthy. The material used for the aforementioned failed parts was Incoloy 800H, which is a highly corrosion and high-temperature resistant steel alloy. The material was rolled up and welded together with different welding joints. The root cause of failure was identified by using chemical analysis and microstructural and mechanical characterizations. For the mechanical characterization, an optical microscope (OM) and scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) analyses were used for the specimen extracted from the failed part in order to ensure that the material mentioned by the manufacturer demonstrated the same metallurgical properties. For the mechanical characterization, two sets of specimens were used, one close to the failure region and the other far from the failure area. The chemical analysis revealed that the material was truthfully Incoloy 800H. The mechanical examination results showed a significant reduction of mechanical properties, i.e., the ultimate tensile strength (UTS) and microhardness dropped by 44% and 41% for samples close and far from the failure regions, respectively. Careful examination of the failed parts indicated that failure mostly took place in the vicinity of the welds, in particular near the joints. Improper joint designs, as well as a number of joints being designed in tiny areas, worsened the harmful effect of the heat-affected zone (HAZ), resulting in crack nucleation in the HAZ regions. The effect of welding in a combination of harsh service conditions of flare caused further crack extension where they merged, resulting in final immature failure. Full article

(This article belongs to the Special Issue Failure Mechanisms and Fatigue Life Prediction of Engineering Structures)

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16 pages, 7971 KiB

Open AccessArticle

Investigation of Phase Transformation of Fe65Ni35 Alloy by the Modified Pulse Method

by Janusz Terpiłowski, Stanisław Jóźwiak, Rafał Rudzki, Robert Szczepaniak and Grzegorz Woroniak

Materials 2020, 13(15), 3425; https://doi.org/10.3390/ma13153425 - 03 Aug 2020

Cited by 3 | Viewed by 2661

Abstract

This paper presents the possibility of using a modified-pulse method (MPM) determining the temperature characteristics of thermal diffusivity in order to identify phase transformations in metals. The experiment and attempt of phase identification were conducted for the Fe65Ni35 alloy in the 20–500 °C [...] Read more.

This paper presents the possibility of using a modified-pulse method (MPM) determining the temperature characteristics of thermal diffusivity in order to identify phase transformations in metals. The experiment and attempt of phase identification were conducted for the Fe65Ni35 alloy in the 20–500 °C temperature range during both sample heating and cooling. The estimated error of discrete thermal diffusivity measurements was less than 3%. The method allows us to narrow down the averaging of the interval of this value, as a function of temperature, in the range below 1 K. Recently published analysis of the phase diagrams of Fe–Ni alloys, and the results of the authors’ own research into the Fe65Ni35 alloy, showed very good correlation between changes occurring when heating the alloy and the equilibrium diagram provided by Cacciamani G., Dinsdale A., Palumbo M., and Pasturel A. (Intermetallics 18, 2010, 1148–1162) showing the position of phases with a crystal-lattice structure based on the face-centered cubic (FCC) cell. Full article

(This article belongs to the Section Advanced Materials Characterization)

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26 pages, 10941 KiB

Open AccessArticle

Constitutive Equations for Describing the Hot Compressed Behavior of TC4–DT Titanium Alloy

by Haoran Wang, Chunge Wang, Muyu Li, Rui Ma and Jun Zhao

Materials 2020, 13(15), 3424; https://doi.org/10.3390/ma13153424 - 03 Aug 2020

Cited by 8 | Viewed by 2379

Abstract

Isothermal hot compression tests of TC4–DT titanium alloy were performed under temperatures of 1203–1293 K and strain rates of 0.001–10 s⁻¹. The purpose of this study is to develop a new high-precision modified constitutive model that can describe the deformation behavior [...] Read more.

Isothermal hot compression tests of TC4–DT titanium alloy were performed under temperatures of 1203–1293 K and strain rates of 0.001–10 s⁻¹. The purpose of this study is to develop a new high-precision modified constitutive model that can describe the deformation behavior of TC4–DT titanium alloy. Both the modified strain-compensated Arrhenius-type equation and the modified Hensel–Spittel equation were established by revising the strain rate. The parameters in the above two modified constitutive equation were solved by combining regression analysis with iterative methods, which was used instead on the traditional linear regression methods. In addition, both the original strain-compensated Arrhenius-type equation and Hensel–Spittel equation were established to compare with the new modified constitutive equations. A comparison of the predicted values based on the four constitutive equations was performed via relative error, average absolute relative error (AARE) and the correlation coefficient (R). These results show the modified Arrhenius-type equation and the modified Hensel–Spittel equation is more accurate and efficient with a similar prediction accuracy. The AARE-value of the two modified constitutive equation is relatively low under various strain rates and their fluctuation is small as the strain rate changes. Full article

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20 pages, 5319 KiB

Open AccessArticle

Torsional Behaviour of Steel Fibre Reinforced Alkali Activated Concrete

by Chee Keong Lau, Trevor N. S. Htut, Jack J. Melling, Amin Chegenizadeh and Tian Sing Ng

Materials 2020, 13(15), 3423; https://doi.org/10.3390/ma13153423 - 03 Aug 2020

Cited by 4 | Viewed by 2999

Abstract

Nine alkali-activated concrete beams were produced and tested under pure torsional load to failure. The alkali-activated concrete beams were produced with following variables: (i) fibres only, (ii) conventionally reinforced or (iii) a hybrid of both fibres and conventional steel reinforcement. The fibres only [...] Read more.

Nine alkali-activated concrete beams were produced and tested under pure torsional load to failure. The alkali-activated concrete beams were produced with following variables: (i) fibres only, (ii) conventionally reinforced or (iii) a hybrid of both fibres and conventional steel reinforcement. The fibres only beams were found to have approximately 20% higher cracking torque than conventionally reinforced beams. However, fibres only beams were observed to have lower post crack ductility and inconsistent post crack behaviour, in comparison to conventionally reinforced alkali-activated concrete (AAC) beams. On the other hand, the hybrid reinforcements in AAC beams were found to demonstrate more ductile post crack behaviour consistently of the beams tested. Hybrid reinforcement was also shown to have 20% and 25% improvement in cracking and ultimate torque compared to conventionally reinforced, which suggests that it is suitable for industrial applications to improve structure capacity. The ultimate torque results of the beams were compared to an analytical model that considered the contribution of fibres. It was found that the ultimate torque of the hybrid reinforced beam has good correlation with the model but overestimated conventionally reinforced beams. Full article

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

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20 pages, 7350 KiB

Open AccessArticle

The Structural and Mechanical Properties of the UHMWPE Films Mixed with the PE-Wax

by Tarek Dayyoub, Leonid K. Olifirov, Dilyus I. Chukov, Sergey D. Kaloshkin, Evgeniy Kolesnikov and Saidkhodzha Nematulloev

Materials 2020, 13(15), 3422; https://doi.org/10.3390/ma13153422 - 03 Aug 2020

Cited by 15 | Viewed by 3727

Abstract

Since obtaining a highly oriented structure based on a large-scale commercial ultra-high molecular weight polyethylene (UHMWPE) is considered very difficult due to its high molecular weight and melting index, modifying the structure of these cheap commercial UHMWPE brands into a supra-molecular structure with [...] Read more.

Since obtaining a highly oriented structure based on a large-scale commercial ultra-high molecular weight polyethylene (UHMWPE) is considered very difficult due to its high molecular weight and melting index, modifying the structure of these cheap commercial UHMWPE brands into a supra-molecular structure with fiber-forming properties by adding a small amount of polyethylene wax (PE-wax) will provide the possibility to obtain highly oriented UHMWPE products with enhanced mechanical and tribological properties. In this work, highly oriented UHMWPE/PE-wax films were prepared. The PE-wax affected the UHMWPE as an intermolecular lubricant. The obtained lamellar structure of the UHMWPE/PE-wax composites had a better processability. The UHMWPE and UHMWPE/PE-wax structures for the xerogels and the films were studied by using differential scanning calorimetry and scanning electron microscopy. The PE-wax presence enhanced the mechanical properties of the UHMWPE/PE-wax films to a high degree. The highest average value of the tensile strength was 1320 MPa (an increase of 78%) obtained by adding a PE-wax content of 1.0 wt.%, and the highest average value of the Young’s modulus was 56.8 GPa (an increase of 71%) obtained by adding a PE-wax content of 2.0 wt.%. The addition of the PE-wax increased the work of fracture values of the UHMWPE/PE-wax films up to 233%. The formation of the cavities was observed in the virgin UHMWPE films more than in the UHMWPE/PE-wax films, and the whitening of the oriented films was related to the crystallization process more than to the cavitation phenomenon. The coefficient of friction of the oriented UHMWPE/PE-wax films improved by 33% in comparison with the isotropic UHMWPE, and by 7% in comparison with the oriented virgin UHMWPE films. Full article

(This article belongs to the Special Issue Advances in Polyethylene Based Composites)

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8 pages, 4331 KiB

Open AccessArticle

Investigating the Response of Human Neutrophils to Hydrophilic and Hydrophobic Micro-Rough Titanium Surfaces

by Karim El Kholy, Daniel Buser, Julia-Gabriella Wittneben, Dieter D. Bosshardt, Thomas E. Van Dyke and Michael J. Kowolik

Materials 2020, 13(15), 3421; https://doi.org/10.3390/ma13153421 - 03 Aug 2020

Cited by 9 | Viewed by 2724

Abstract

Various treatments have been used to change both the topography and chemistry of titanium surfaces, aiming to enhance tissue response and reduce healing times of endosseous implants. Most studies to date focused on bone healing around dental implants occurring later during the healing [...] Read more.

Various treatments have been used to change both the topography and chemistry of titanium surfaces, aiming to enhance tissue response and reduce healing times of endosseous implants. Most studies to date focused on bone healing around dental implants occurring later during the healing cascade. However, the impact of the initial inflammatory response in the surgical wound site on the success and healing time of dental implants is crucial for implant integration and success, yet it is still poorly understood. The purpose of this study was to investigate the effect of titanium surface hydrophilicity on the response of human neutrophils by monitoring oxygen radical production, which was measured as chemiluminescence activity. Materials and Methods: Neutrophils were isolated from human donors’ blood buffy coats using the double sucrose gradient method. Neutrophils were exposed to both hydrophilic and hydrophobic titanium surfaces with identical topographies in the presence and absence of human serum. This resulted in six experimental groups including two different implant surfaces, with and without exposure to human serum, and two control groups including an active control with cells alone and a passive control with no cells. Two samples from each group were fixed and analyzed by SEM. Comparisons between surface treatments for differences in chemiluminescence values were performed using analysis of variance ANOVA. Results and Conclusion: In the absence of exposure to serum, there was no significant difference noted between the reaction of neutrophils to hydrophilic and hydrophobic surfaces. However, there was a significant reduction in the mean and active chemiluminescence activity of neutrophils to serum-coated hydrophilic titanium surfaces than to serum-coated hydrophobic titanium surfaces. This suggests that surface hydrophilicity promotes enhanced adsorption of serum proteins, which leads to decreased provocation of initial immune cells and reduction of local oxygen radical production during wound healing. This can help explain the faster osseointegration demonstrated by hydrophilic titanium implants. Full article

(This article belongs to the Collection 3D Printing in Medicine and Biomedical Engineering)

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22 pages, 7640 KiB

Open AccessArticle

Effect of Graphene Family Materials on Multiple Myeloma and Non-Hodgkin’s Lymphoma Cell Lines

by Barbara Strojny, Sławomir Jaworski, Irena Misiewicz-Krzemińska, Isabel Isidro, Elizabeta A. Rojas, Norma C. Gutiérrez, Marta Grodzik, Piotr Koczoń, André Chwalibog and Ewa Sawosz

Materials 2020, 13(15), 3420; https://doi.org/10.3390/ma13153420 - 03 Aug 2020

Cited by 3 | Viewed by 2501

Abstract

The interest around the graphene family of materials is constantly growing due to their potential application in biomedical fields. The effect of graphene and its derivatives on cells varies amongst studies depending on the cell and tissue type. Since the toxicity against non-adherent [...] Read more.

The interest around the graphene family of materials is constantly growing due to their potential application in biomedical fields. The effect of graphene and its derivatives on cells varies amongst studies depending on the cell and tissue type. Since the toxicity against non-adherent cell lines has barely been studied, we investigated the effect of graphene and two different graphene oxides against four multiple myeloma cell lines, namely KMS-12-BM, H929, U226, and MM.1S, as well as two non-Hodgkin lymphoma cells lines, namely KARPAS299 and DOHH-2. We performed two types of viability assays, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide conversion) and ATP (adenosine triphosphate detection), flow cytometry analysis of apoptosis induction and cell cycle, cell morphology, and direct interaction analysis using two approaches—visualization of living cells by two different systems, and visualization of fixed and dyed cells. Our results revealed that graphene and graphene oxides exhibit low to moderate cytotoxicity against cells, despite visible interaction between the cells and graphene oxide. This creates possibilities for the application of the selected graphene materials for drug delivery systems or theragnostics in hematological malignancies; however, further detailed studies are necessary to explain the nature of interactions between the cells and the materials. Full article

(This article belongs to the Special Issue The Effect of Graphene on Cancer)

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12 pages, 5474 KiB

Open AccessArticle

Modification of Collagen Properties with Ferulic Acid

by Beata Kaczmarek, Katarzyna Lewandowska and Alina Sionkowska

Materials 2020, 13(15), 3419; https://doi.org/10.3390/ma13153419 - 03 Aug 2020

Cited by 17 | Viewed by 2692

Abstract

Collagen materials are widely used in biomedicine and in cosmetics. However, their properties require improvement for several reasons. In this work, collagen solution as well as collagen films were modified by the addition of ferulic acid (FA). Thin collagen films containing FA were [...] Read more.

Collagen materials are widely used in biomedicine and in cosmetics. However, their properties require improvement for several reasons. In this work, collagen solution as well as collagen films were modified by the addition of ferulic acid (FA). Thin collagen films containing FA were obtained by solvent evaporation. The properties of collagen solution have been studied by steady shear tests. The structure and surface properties of collagen thin films were studied. It was found that for collagen solution with 5% addition of FA, the apparent viscosity was the highest, whereas the collagen solutions with other additions of FA (1%, 2%, and 10%), no significant difference in the apparent viscosity was observed. Thin films prepared from collagen with 1 and 2% FA addition were homogeneous, whereas films with 5% and 10% FA showed irregularity in the surface properties. Mechanical properties, such as maximum tensile strength and elongation at break, were significantly higher for films with 10% FA than for films with smaller amount of FA. Young modulus was similar for films with 1% and 10% FA addition, but bigger than for 2% and 5% of FA in collagen films. The cross-linking of collagen with ferulic acid meant that prepared thin films were elastic with better mechanical properties than collagen films. Full article

(This article belongs to the Special Issue Research of Organic Molecules and Materials for Biological Application)

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17 pages, 4043 KiB

Open AccessArticle

A Systematic Study on Polymer-Modified Alkali-Activated Slag–Part II: From Hydration to Mechanical Properties

by Zichen Lu, Jan-Philip Merkl, Maxim Pulkin, Rafia Firdous, Steffen Wache and Dietmar Stephan

Materials 2020, 13(15), 3418; https://doi.org/10.3390/ma13153418 - 03 Aug 2020

Cited by 9 | Viewed by 2384

Abstract

The effect of styrene-acrylate (SA) polymer latex on alkali-activated slag (AAS) was systematically studied in the aspects of hydration, hydration products, pore structure and mechanical properties through the combined analytical techniques including calorimetry, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and mechanical measurement. [...] Read more.

The effect of styrene-acrylate (SA) polymer latex on alkali-activated slag (AAS) was systematically studied in the aspects of hydration, hydration products, pore structure and mechanical properties through the combined analytical techniques including calorimetry, X-ray diffraction, thermogravimetric analysis, mercury intrusion porosimetry, and mechanical measurement. It was found that the addition of SA does not retard the AAS hydration, but slightly accelerates it, possibly due to the increasing ion diffusion through the loosely structured hydration products. Pore structure analysis indicates that the addition of polymer increases the cumulative pore volume and the portion of pores with size >100 nm in the hardened AAS paste. The addition of SA latex results in a continuous decrease of the compressive strength, but the flexural strength firstly increases and then decreases with the increase of polymer dosage. The polymer dosage of 2.5 wt % is optimal when applying polymer latex in the AAS system in this study. Full article

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

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26 pages, 9150 KiB

Open AccessArticle

The 3D-Printed Bilayer’s Bioactive-Biomaterials Scaffold for Full-Thickness Articular Cartilage Defects Treatment

by Kittiya Thunsiri, Siwasit Pitjamit, Peraphan Pothacharoen, Dumnoensun Pruksakorn, Wasawat Nakkiew and Wassanai Wattanutchariya

Materials 2020, 13(15), 3417; https://doi.org/10.3390/ma13153417 - 03 Aug 2020

Cited by 28 | Viewed by 4142

Abstract

The full-thickness articular cartilage defect (FTAC) is an abnormally severe grade of articular cartilage (AC) injury. An osteochondral autograft transfer (OAT) is the recommended treatment, but the increasing morbidity rate from osteochondral plug harvesting is a limitation. Thus, the 3D-printed bilayer’s bioactive-biomaterials scaffold [...] Read more.

The full-thickness articular cartilage defect (FTAC) is an abnormally severe grade of articular cartilage (AC) injury. An osteochondral autograft transfer (OAT) is the recommended treatment, but the increasing morbidity rate from osteochondral plug harvesting is a limitation. Thus, the 3D-printed bilayer’s bioactive-biomaterials scaffold is of major interest. Polylactic acid (PLA) and polycaprolactone (PCL) were blended with hydroxyapatite (HA) for the 3D-printed bone layer of the bilayer’s bioactive-biomaterials scaffold (B-BBBS). Meanwhile, the blended PLA/PCL filament was 3D printed and combined with a chitosan (CS)/silk firoin (SF) using a lyophilization technique to fabricate the AC layer of the bilayer’s bioactive-biomaterials scaffold (AC-BBBS). Material characterization and mechanical and biological tests were performed. The fabrication process consists of combining the 3D-printed structure (AC-BBBS and B-BBBS) and a lyophilized porous AC-BBBS. The morphology and printing abilities were investigated, and biological tests were performed. Finite element analysis (FEA) was performed to predict the maximum load that the bilayer’s bioactive-biomaterials scaffold (BBBS) could carry. The presence of HA and CS/SF in the PLA/PCL structure increased cell proliferation. The FEA predicted the load carrying capacity to be up to 663.2 N. All tests indicated that it is possible for BBBS to be used in tissue engineering for AC and bone regeneration in FTAC treatment. Full article

(This article belongs to the Section Biomaterials)

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16 pages, 5340 KiB

Open AccessArticle

The Influence of Ag on the Microstructure and Properties of Cu-Ni-Si Alloys

by Beata Krupińska, Wojciech Borek, Mariusz Krupiński and Tatiana Karkoszka

Materials 2020, 13(15), 3416; https://doi.org/10.3390/ma13153416 - 03 Aug 2020

Cited by 4 | Viewed by 2162

Abstract

The influence of the mass concentration of Ag on properties of Cu-Ni alloys is investigated. The effect of silver addition on the structure and properties of Cu-2Ni-1Si alloys is determined. The scientific aim of this research is to determine how the addition of [...] Read more.

The influence of the mass concentration of Ag on properties of Cu-Ni alloys is investigated. The effect of silver addition on the structure and properties of Cu-2Ni-1Si alloys is determined. The scientific aim of this research is to determine how the addition of silver affects the mechanisms of strengthening silver-modified supersaturated, deformed, and aged Cu-2Ni-1Si alloys. The applied thermo-derivative analysis has allowed us to determine a range of the temperature values for the beginning and the end of crystallization, the phases and eutectics, and the effects of the modification on the solid fraction of the solidified alloy. In addition to the crystallization kinetics, the microstructure morphology, mechanical properties under real operating conditions, and the electrical conductivity have also been investigated. Moreover, the conducted research includes the impact of heat treatment and plastic deformation on the alloy structure and considers the type, share, and distribution of the intermetallic phases and structural stresses caused by coherent phases, as well as the effect of dislocations in the reinforcing phases during aging. Electron microscopy (SEM), micro-area analysis (EDS), optical microscopy, hardness measurements, and conductivity of the tested alloys are utilized to comment on these properties. Full article

(This article belongs to the Special Issue Progress in Plastic Deformation of Metals and Alloys)

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24 pages, 5794 KiB

Open AccessReview

Recent Advances and Trends of Nanofilled/Nanostructured Epoxies

by Mariaenrica Frigione and Mariateresa Lettieri

Materials 2020, 13(15), 3415; https://doi.org/10.3390/ma13153415 - 03 Aug 2020

Cited by 35 | Viewed by 4051

Abstract

This paper aims at reviewing the works published in the last five years (2016–2020) on polymer nanocomposites based on epoxy resins. The different nanofillers successfully added to epoxies to enhance some of their characteristics, in relation to the nature and the feature of [...] Read more.

This paper aims at reviewing the works published in the last five years (2016–2020) on polymer nanocomposites based on epoxy resins. The different nanofillers successfully added to epoxies to enhance some of their characteristics, in relation to the nature and the feature of each nanofiller, are illustrated. The organic–inorganic hybrid nanostructured epoxies are also introduced and their strong potential in many applications has been highlighted. The different methods and routes employed for the production of nanofilled/nanostructured epoxies are described. A discussion of the main properties and final performance, which comprise durability, of epoxy nanocomposites, depending on chemical nature, shape, and size of nanoparticles and on their distribution, is presented. It is also shown why an efficient uniform dispersion of the nanofillers in the epoxy matrix, along with strong interfacial interactions with the polymeric network, will guarantee the success of the application for which the nanocomposite is proposed. The mechanisms yielding to the improved properties in comparison to the neat polymer are illustrated. The most important applications in which these new materials can better exploit their uniqueness are finally presented, also evidencing the aspects that limit a wider diffusion. Full article

(This article belongs to the Special Issue Advances in Thermoset Materials)

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24 pages, 4710 KiB

Open AccessArticle

Experimental Investigation and Micromechanical Modeling of Elastoplastic Damage Behavior of Sandstone

by Chaojun Jia, Qiang Zhang and Susheng Wang

Materials 2020, 13(15), 3414; https://doi.org/10.3390/ma13153414 - 03 Aug 2020

Cited by 6 | Viewed by 2020

Abstract

The mechanical behavior of the sandstone at the dam site is important to the stability of the hydropower station to be built in Southwest China. A series of triaxial compression tests under different confining pressures were conducted in the laboratory. The critical stresses [...] Read more.

The mechanical behavior of the sandstone at the dam site is important to the stability of the hydropower station to be built in Southwest China. A series of triaxial compression tests under different confining pressures were conducted in the laboratory. The critical stresses were determined and the relationship between the critical stress and confining pressure were analyzed. The Young’s modulus increases non-linearly with the confining pressure while the plastic strain increment

N_{ϕ}

and the dilation angle ϕ showed a negative response. Scanning electron microscope (SEM) tests showed that the failure of the sandstone under compression is a coupled process of crack growth and frictional sliding. Based on the experimental results, a coupled elastoplastic damage model was proposed within the irreversible thermodynamic framework. The plastic deformation and damage evolution were described by using the micromechanical homogenization method. The plastic flow is inherently driven by the damage evolution. Furthermore, a numerical integration algorithm was developed to simulate the coupled elastoplastic damage behavior of sandstone. The main inelastic properties of the sandstone were well captured. The model will be implemented into the finite element method (FEM) to estimate the excavation damaged zones (EDZs) which can provide a reference for the design and construction of such a huge hydropower project. Full article

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

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28 pages, 13109 KiB

Open AccessArticle

Crosslinking of Chitosan with Dialdehyde Chitosan as a New Approach for Biomedical Applications

by Katarzyna Wegrzynowska-Drzymalska, Patrycja Grebicka, Dariusz T. Mlynarczyk, Dorota Chelminiak-Dudkiewicz, Halina Kaczmarek, Tomasz Goslinski and Marta Ziegler-Borowska

Materials 2020, 13(15), 3413; https://doi.org/10.3390/ma13153413 - 03 Aug 2020

Cited by 61 | Viewed by 6686

Abstract

Materials based on natural high molecular compounds are particularly interesting for biomedical applications. It is known that the cross-linking agent used for preparation of biomacromolecule-based materials is as important as used biopolymer. Therefore, natural cross-linkers containing reactive carbonyl groups are of great interest [...] Read more.

Materials based on natural high molecular compounds are particularly interesting for biomedical applications. It is known that the cross-linking agent used for preparation of biomacromolecule-based materials is as important as used biopolymer. Therefore, natural cross-linkers containing reactive carbonyl groups are of great interest especially for modifying properties of natural polysaccharides. One of the most popular cross-linking agents is glutaraldehyde. Nevertheless, the unreacted particles can be released from the cross-linked material and cause cytotoxic effects. This can be eliminated when using a cross-linker based e.g., on polysaccharides. This article describes quick and efficient synthesis of dialdehyde chitosan (DACS) and its application for the preparation of chitosan films. Materials obtained with different amount of DACS were fully characterized in terms of structure and surface morphology. Thermal and mechanical properties as well as hydrophilic character were also examined. The results obtained were compared with the materials obtained by cross-linking chitosan with low molecular weight glutaraldehyde and high molecular weight cross-linking agent based on polysaccharide–dialdehyde starch. Toxicity of all obtained materials was tested using the Microtox^® test. It has been shown that due to better mechanical, thermal and surface properties as well as lower toxicity, dialdehyde chitosan is a very promising crosslinking agent. Full article

(This article belongs to the Special Issue Research of Organic Molecules and Materials for Biological Application)

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21 pages, 8743 KiB

Open AccessArticle

Investigation on Surface Quality of a Rapidly Solidified Al–50%Si Alloy Component for Deep-Space Applications

by Oussama Chaieb, Oluwole A. Olufayo, Victor Songmene and Mohammad Jahazi

Materials 2020, 13(15), 3412; https://doi.org/10.3390/ma13153412 - 03 Aug 2020

Cited by 4 | Viewed by 2491

Abstract

To meet the requirements for high-performance products, the aerospace industry increasingly needs to assess the behavior of new and advanced materials during manufacturing processes and to ensure they possess adequate machinability, as well as high performance and an extensive lifecycles. Over the years, [...] Read more.

To meet the requirements for high-performance products, the aerospace industry increasingly needs to assess the behavior of new and advanced materials during manufacturing processes and to ensure they possess adequate machinability, as well as high performance and an extensive lifecycles. Over the years, industrial research works have focused on developing new alloys with an increased thermal conductivity as well as increased strength. High silicon content aluminum (Al–Si) alloys, due to their increased thermal conductivity, low coefficient of thermal expansion, and low density, have been identified as suitable materials for space applications. Some of these applications require the use of intricate parts with tight tolerances and surface integrity. These challenges are often tied to the machining conditions and strategies, as well as to workpiece materials. In this study, experimental milling tests were performed on a rapidly solidified (RS) Al–Si alloy with a prominent silicon content (over 50%) to address challenges linked to material expansion in deep space applications. The tests were performed using a polycrystalline cubic boron nitride (PCBN) tool coated with amorphous diamond to reduce tool wear, material adhesion, surface oxidation, and particle diffusion. The effects of cutting parameters on part surface roughness and microstructure were analyzed. A comparative analysis of the surface with a conventionally utilized Al6061-T6 alloy showed an improvement in surface roughness measurements when using the RS Al–Si alloy. The results indicated that lower cutting speed and feed rate on both conventional and RS Al–Si alloys produced a better surface finish. Reduced vibrations were also identified in the RS Al–Si alloy, which possessed a stable cutting time at low cutting speeds but only displayed notable vibrations at cutting speeds above 120 m/min. Full article

(This article belongs to the Special Issue Machinability of Metallic Materials and Composites)

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