Class Of Composites Research Articles

Direct Laser Writing of Chitosan-Borax Composites: Toward Sustainable Electrochemical Sensors.

In this study, the laser-induced graphitization process of sustainable chitosan-based formulations was investigated. In particular, optimal lasing conditions were investigated alongside the effect of borax concentration in the chitosan matrix. In all cases, it was found that the obtained formulations were graphitizable with a CO2 laser. This process gave rise to the formation of high surface area, porous, and electrically conductive laser-induced graphene (LIG) structures. It was found that borax, as a cross-linker of chitosan, enabled the graphitization process when its content was ≥30 wt % in the chitosan matrix, allowing the formation of an LIG phase with a significant content of graphite-like structures. The graphitization process was investigated by thermogravimetric analysis (TGA), Raman, X-ray photoemission (XPS), and Fourier transform infrared (FTIR) spectroscopies. LIG electrodes obtained from CS/40B formulations displayed a sheet resistance as low as 110 Ω/sq. Electrochemical characterization was performed after a 10 min electrode activation by cycling in 1 M KCl. A heterogeneous electron transfer rate, k0, of 4 × 10-3 cm s-1 was determined, indicating rapid electron transfer rates at the electrode surface. These results show promise for the introduction of a new class of sustainable composites for LIG electrochemical sensing platforms.

Population demography of the Blackbuck Antilope cervicapra (Cetartiodactyla: Bovidae) at Point Calimere Wildlife Sanctuary, India

Demographic research utilizing vital rates and life tables is a standard aspect of planning protection and management strategies for wildlife populations. The Blackbuck Antilope cervicapra population at Point Calimere Wildlife Sanctuary, Tamil Nadu, has undergone fluctuations in recent decades. The cause remains elusive, and conservation efforts may be hampered by a lack of population data. This study aimed to estimate demographic parameters using population count and age-sex classification data collected for the years 2017─2020. The overall mean population estimate derived from line-transect distance sampling was 719, with annual estimates of 716, 727, 711, and 722 for the years 2017–2020 respectively. In total, 64% of Blackbucks counted were adults, 19% subadults, and 17% fawns. Mortality was highest for adult and subadult classes for the composite female class, and fawn mortality was 20%. The net reproductive rate (R0) was as low as 3.28 offspring per generation contrasted with a rather longer mean generation time (G) as 4.75 years. Thus, the study observes a decrease in Blackbuck numbers postulated in earlier research to be driven principally by a conglomerate of factors, including reduction of usable space and interspecific resource competition. Our findings provide a baseline demography of the species and highlights the value of long-term demographic monitoring of age sex classes to understand the evolution of life histories.

Topology of WC/Co Interfaces in Cemented Carbides.

WC-Co cemented carbides build one of the important classes of metal matrix composites. We show in this paper that the use of machine vision methods makes it possible to obtain sufficiently informative statistical data on the topology of the interfaces between tungsten carbide grains (WC) and a cobalt matrix (Co). For the first time, the outlines of the regions of the cobalt binder were chosen as a tool for describing the structure of cemented carbides. Numerical processing of micrographs of cross sections of three WC-Co alloys, which differ in the average grain size, was carried out. The distribution density of the angles in the contours of cobalt "lakes" is bimodal. The peaks close to 110° (so-called outcoming angles) correspond to the contacts between the cobalt binder and the WC/WC grain boundaries. The peaks close to 240° (or incoming angles) correspond to the WC "capes" contacting the cobalt "lakes" and are determined by the angles between facets of WC crystallites. The distribution density of the linear dimensions of the regions of the cobalt binder, approximated with ellipses, were also obtained. The distribution density exponentially decreases with the lengths of the semi-axes of the ellipsoid, approximating the area of the cobalt binder. The possible connection between the obtained data on the shape of cobalt areas and the crack trajectories in cemented carbides is discussed.

Ceramics matrix composites for biomedical applications - a review

Composite materials have found varying applications in biomedical engineering. With their different physical, chemical, and mechanical properties, composites are produced to meet specific requirements for specific purposes. Synthetic materials are utilized in construction, such as automotive, buildings, mobile sector as well as bridges, aeronautics, naval (e.g., ships and boats), and biomedical sciences. Despite the fact that metallic, polymeric, and ceramic biomaterials have been used in medical facilities for decades for treatments including tissue repair and replacement, bone fixation, dental implants, and many others, composites are only now becoming widely known for orthopedic applications, a new generation of biocompatible, bioactive, as well as biodegradable metallic materials has recently been created. These ceramic materials are known for their strength and biocompatibility. Magnesium in its pure form, its alloys, and alloy-based composites are frequently employed in biomedical applications due to their high biocompatibility and moderate strength. This comprehensive research focuses on the mechanical (strength base) characteristics and corrosion resistance of several classes of biodegradable magnesium matrix composites. It also reviews the use of ceramic-based composites for biomedical applications. It concludes with the submission that ceramics-based composites are a welcomed mainstay in the biomedical world as a viable material. It is believed that this review will draw the attention of personnel to the gains of the adoption of ceramic matrix composites to biomedical applications.

Experimentally characterization and theoretical modeling of the electro-thermomechanical coupling of unimorph Shape Memory Active Hybrid composites

Shape memory alloy hybrid composites (SMAHC) are a class of smart composites with the ability to change their shape in response to external stimuli, such as heat or electric current, due to the thermoelastic phase transition of embedded filaments of a shape memory alloy. In this work, a multiphyical electro-thermomechanical SMAHC model, capable of describing the dynamic shape adaptive behavior of SMAHC on various length scales under the influence of external loads and ambient temperatures, is developed and experimentally validated. Activation and deactivation experiments were performed systematically for different geometries and all material parameters needed for validation purposes were measured.

IM Twenty-Four Steps Of Educational Innovation In Indonesia

This study aims to critically analyze educational innovation in Indonesia through twenty-four appropriate educational strategies. This type of research is library research. Collecting data by identifying discourse from books, papers or articles, journals, newspapers, the internet (web), or other information related to education. Data analysis used descriptive analysis, content analysis, and scientific critical analysis. The results of the study show that educational innovation in Indonesia can implement twenty-four educational strategies which include Personalization, Multi-Age Classes, Small Community Learning, Peer Group Learning, Small Group Learning Communities with other groups, Multidisciplinary Curriculum with Block Scheduling, Cooperative Learning, Cooperative Learning, Project Based Learning, Co-Teachers, Teaching Teams, Community Service Learning, Looping Partnerships, Business for Assessment, Resources, and Funding, Global Connections, Laptops, and Wireless Technology for Anywhere, Anytime Learning, Parental Involvement, Students Putting on Shows, Curriculum Life Skills (Non-Academic), Meaningful Career Counseling, Social/Emotional Counseling, Open Learning, Education to Serve Student Needs, Portfolio-Based Assessment and New Paradigm of School Buildings.

Variationally consistent modeling of a sensor-actuator based on shape-morphing from electro-chemical–mechanical interactions

This paper concerns the computational modeling of a class of carbon fiber composites, known as shape-morphing and strain-sensing composites. The actuating and sensing performance of such (smart) materials is achieved by the interplay between electrochemistry and mechanics, in particular the ability of carbon fibers to (de)intercalate Li-ions repeatedly. We focus on the actuation and sensing properties of a beam in conjunction with the appropriate “through-the-thickness” properties. Thus, the electro-chemo-mechanical analysis is essentially two-dimensional, and it is possible to rely heavily on the results in Carlstedt et al. (2020). More specifically, the cross-sectional design is composed of two electrodes, consisting of (partly) lithiated carbon fibers embedded in structural battery electrolyte (SBE), on either side of a separator. As a result, the modeling is hierarchical in the sense that (macroscale) beam action is combined with electro-chemo-mechanical interaction along the beam. The setup is able to work as sensor or actuator depending on the choice of control (and response) variables. Although quite idealized, this design allows for a qualitative investigation. In this paper we demonstrate the capability of the developed framework to simulate both the actuator and sensor modes. As proof of concept, we show that both modes of functionality can be captured using the developed framework. For the actuator mode, the predicted deformation is found to be in close agreement with experimental data. Further, the sensor-mode is found to agree with experimental data available in the literature.

ПОРІВНЯЛЬНИЙ АНАЛІЗ МЕТОДИК ВИМІРЮВАННЯ АДГЕЗІЇ РЕМОНТНИХ РОЗЧИНІВ З СУХИХ БУДІВЕЛЬНИХ СУМІШЕЙ ДО БЕТОННИХ ПОВЕРХОНЬ

The article provides a general assessment of the adhesion strength indicators of polymer-cement repair composites to the concrete base and determination of the degree of repeatability of test results when changing the methods of its measurement in accordance with Ukrainian and European standards. During experimental studies, data were obtained on the adhesive strength indicators of the same cement samples of repair mortars based on dry building mixtures for the repair and restoration of concrete and reinforced concrete structures and buildings under equal conditions using different measurement methods, a distribution was obtained by the received classes of repair composites, taking into account the requirements of both standards according to the indicator of adhesive strength. The obtained data show that according to the measurement method according to the Ukrainian standard, the vast majority of the examined samples of repair mortars based on dry construction mixtures showed similar measurement results, which indicates a high repeatability of the results of the measurement method. Also, a high percentage of adhesion loss according to the AF-S and CF-S classes and the number of structural classes among the studied composites remain among all the studied samples. The European measurement method on the same samples and reference concrete slabs showed a significantly higher number of samples with a deviation from the average adhesion index, a lower number of samples with a loss of adhesion according to the AF-S and CF-S classes, a lower number of structural classes of repair composites and, in general, has a significantly lower repeatability of measurement results. It has been established that some of the repair composites, which according to the requirements of the Ukrainian standard correspond to the highest structural class of the repair material РМ1 based solely on the adhesion index, can be classified only as materials of the R3 class according to the requirements of the European.

Variable-stiffness composites optimisation under multiple design requirements and loads

The aim of this paper is twofold. On the one hand, it presents a methodology for the deterministic optimisation of a general class of variable-stiffness composite (VSC) structures, including a solution obtained by using laminæ with a curvilinear fibres-path and variable-thickness, by considering different design requirements under multiple load cases. The considered framework is the multi-level design methodology based on the polar parameters (PPs) to describe the macroscopic behaviour of the VSC structure. Particularly, only the first-level problem is addressed in this work: the design variables are, thus, the PPs and the thickness of the VSC laminate, whose spatial distribution is described via basis spline (B-spline) surfaces. The goal is to minimise the mass of the VSC structure subject to design requirements on feasibility, strength, first buckling load and maximum curvature of the fibres-path. This latter is formulated as an equivalent (conservative) constraint in the PPs space, regardless of the fibres-path within each lamina. Moreover, a general formulation of the gradient of the requirements related to buckling load and strength is proposed, which takes advantage from the main properties of B-spline entities and PPs. On the other hand, this paper aims to propose a new benchmark problem that is representative of a panel belonging to the fuselage of a standard civil aircraft subjected to multiple loading conditions. To this end, a wide campaign of numerical tests has been performed by considering a sensitivity analysis of the optimised solution to: (a) the integer parameters involved in the definition of the B-spline entities describing the distribution of the PPs and, possibly, of the thickness, (b) the type of VSC structure, (c) the type of deterministic optimisation algorithm. The results can be used as a database to assess the effectiveness of different design strategies against the optimised solutions presented in this paper.

Design and Analysis of an Automobile Disc Brake Rotor by Using Hybrid Aluminium Metal Matrix Composite for High Reliability

Due to their superior capabilities for manufacturing lightweight automotive components, aluminium metal matrix composites have gained a lot of attention in the last few years. Aluminium metal matrix composites are an exceptional class of metal matrix composites that can solve all the major problems related to the automobile industry. Aluminium matrix composites in the disc braking system have already been employed and studied by many scientists. However, the developed materials are not yet always sufficiently accurate and reliable. In this article, a new enhanced metal matrix composite material is used and studied to improve the efficiency of an ordinary car’s braking system. To improve the accuracy of the designated braking system, an innovative hybrid aluminium matrix composite (Al6061/SiC/Gr)-based brake rotor has been developed, and its effectiveness has been determined by finite element analysis. From the simulation, the product performance confirmed that the hybrid aluminium matrix composite (Al6061/SiC/Gr)-based brake rotor has the potential to replace the standard cast iron brake disc. The new enhanced hybrid composite material used in this study can be used for the efficient design of various braking parts.

Smooth subvarieties of Jacobians

We give new examples of algebraic integral cohomology classes on smooth projective complex varieties that are not integral linear combinations of classes of smooth subvarieties. Some of our examples have dimension 6, the lowest possible. The classes that we consider are minimal cohomology classes on Jacobians of very general curves. Our main tool is complex cobordism.

Predicting the life cycle durability and ecological performance of cementitious coatings with a fuzzy‐stochastics–based approach

AbstractCementitious coating effectively prevents chloride‐induced corrosion in offshore reinforced concrete (RC) structures. Strain hardening cementitious composites (SHCC) is a class of advanced cementitious composites with superior ductility and durability. Due to the lack of long‐term test data, the current probability‐based design guidelines may not be applicable to SHCC coating. This paper develops a fuzzy‐stochastic–based approach to assess the durability performance of coatings using cement mortar and engineered cementitious composites (ECC), a specific type of SHCC. The age factor and the mean of chloride diffusion coefficient are modeled as fuzzy variables, and the chloride diffusion coefficient follows Gaussian distribution. Based on limited test data and subjective opinion, membership functions are proposed for the mean of initial chloride diffusion coefficient and the age factor of cement and ECC. To achieve equivalent durability performance of cement mortar coating, the amount of uncracked and cracked ECC coating are estimated to be around 33% and 25%, respectively. Based on equivalent durability performance, life cycle assessment (LCA) is conducted to compare the ecological performance of the two coatings. A case study, based on a 25‐m‐long simply supported box girder in Shenzhen Bay, is given to elaborate the proposed approach and the evaluation results of durability performance and ecological impacts.

ICT as a Didactic Tool to Facilitate the Learning Process in the Subject of Mathematics in Combined Classes

Information and Communication Technologies (ICT) has become a common entity in all aspects of life. The use of ICT has fundamentally changed the practices and procedures of almost all forms of endeavor within the learning process. The use of ICT in education lends itself to more learner-centered learning environments, and this often creates some convenience for teachers and students. On the other hand, with the small number of students, schools are facing the merging of several classes led by one teacher. A combined classroom is when students from more than one grade level learn from the same teacher, in the same classroom. Therefore, this study aims to explore the process of integrating ICT into teaching and learning practices in combined classrooms in the subject of mathematics. The study is a qualitative study that focuses on a case of elementary and lower secondary school "River Heroes" in the Republic of Kosovo. In this study, the descriptive survey method was chosen to evaluate teachers' experiences in the integration of ICT in the teaching and learning process in combined classes. The total number of participants in this study was 9 primary school teachers of this school. This particular study used interviews to collect qualitative data. The results of the study show that the use of technology in teaching can be a powerful tool to help students develop their mathematical skills, especially in schools with mixed classes. The results of this study can help the Ministry of Education, Science, and Technology, Municipal Directorates of Education, school teachers and principals, as well as other interested bodies to design intervention and rehabilitative measures related to the integration of ICT in teaching and learning, especially in combined classes.

Fabrication and characterization of hexagonal boron nitride/polyester composites to study the effect of filler loading and surface modification for microelectronic applications

AbstractThis work investigates a composite prepared with polyester and hexagonal boron nitride (hBN) in terms of the properties required in the material for microelectronics applications. The influence of filler loading and the surface treatment of hBN with a silane coupling agent (γ‐aminopropyl triethoxy silane) is studied. It has been observed that the silane‐modified hBN improves the compatibility and adhesion with the matrix as verified by SEM images. The experimental investigation reveals that the addition of hBN in polyester unwillingly rises the density, voids content, and water absorption rate. Though, the increment is limited with surface‐modified hBN. The material's mechanical properties improve with filler loading over a particular range of filler loading. The material's thermal conductivity and glass transition temperature increase with hBN content, whereas the coefficient of thermal expansion reduces. Polyester when filled with 40 wt% of the silane‐hBN, the thermal conductivity improves around six times that of unfilled polyester. The dielectric properties are marginally augmented with filler loading whereas, the increase in frequency results in the reduction of dielectric properties. It can be observed from the overall experimental analysis that the developed material can be used in different microelectronic applications.Highlights A new class of composite is developed with polyester and raw/modified hBN. Composite with modified hBN shows improved physical/mechanical properties. Thermal properties of polyester improved appreciably with treated hBN. The dielectric properties of composites remain well within the range. The fabricated composites are recommended for microelectronics applications.

Colloidal gelation with non-sticky particles

Colloidal gels are widely applied in industry due to their rheological character—no flow takes place below the yield stress. Such property enables gels to maintain uniform distribution in practical formulations; otherwise, solid components may quickly sediment without the support of gel matrix. Compared with pure gels of sticky colloids, therefore, the composites of gel and non-sticky inclusions are more commonly encountered in reality. Through numerical simulations, we investigate the gelation process in such binary composites. We find that the non-sticky particles not only confine gelation in the form of an effective volume fraction, but also introduce another lengthscale that competes with the size of growing clusters in gel. The ratio of two key lengthscales in general controls the two effects. Using different gel models, we verify such a scenario within a wide range of parameter space, suggesting a potential universality in all classes of colloidal composites.

Additive manufacturing of (TiB+TiC)/Ti6Al4V composites with tailored network reinforcement architecture

(TiB + TiC)/Ti6Al4V composites with controllable three-dimensional network structure were fabricated from mixed spherical Ti6Al4V and boron carbide (B4C) powders by laser directed energy deposition (LDED) based additive manufacturing process (AM). The (TiB + TiC) precipitates significantly refined the microstructure and aggregated at prior β grain boundaries forming network structure. The increase of the B4C content reduced the network size and the tensile performance of the composites was associated with the network size. (TiB + TiC) pinned on the network allowed specific strengthening effect, benefiting the enhancement in tensile strength of the composites, while the network structure together with α lamellae size gradient structure contributed to high uniform tensile ductility. This work demonstrates the significant potential of additive manufacturing process in creating a new class of metal matrix composites with tailored three-dimensional architecture.

Experimental studies on structural performance of precast concrete shear walls with innovative UHPC-based connections

Ultrahigh-Performance Concrete (UHPC) is an advanced class of cement-based composite that offers excellent bond performance with steel bars. When compared to conventional approaches, using UHPC-based connections for Precast Concrete Shear Walls (PCSWs) has the advantages of smaller bar lap-spliced lengths and greater tolerance to installation errors. In this study, a two-stage scheme was proposed. Firstly, the bond properties between lapped steel bars and UHPC were determined to provide guidelines for designing PCSWs. A total of 15 pullout samples were designed and tested under direct tension. Failure patterns including steel bar pullout, cover splitting, and steel bar rupture were summarized. The basic splice length of steel bars with diameters limited to 14 mm in UHPC should be at least 6 times the bar diameter. In the second stage, the seismic performance of PCSWs with UHPC-based connections was investigated. Two full-scale PCSWs and two monolithic walls were constructed and tested cyclically in axial compression ratios of 0.1 and 0.3. In PCSWs, the splice length of additional bars (the one-row) in UHPC was set as 10 times the diameter to allow for a safe margin. PCSWs with UHPC-based connections demonstrated higher load-carrying capacity, better ability to dissipate energy, and comparable ductility to monolithic counterparts. An evaluation of test results also met the acceptance criteria for shear wall systems that could be considered as structures assigned to high seismic performance.

Research on the Teaching Reform of Human Resource Management Curriculum Based on the Ideological and Political Education in the Course

Curriculum ideology and politics is an important measure and fundamental task to combine professional courses with ideological and political courses to carry out moral education and cultivate people in Chinese colleges and universities. Traditional teaching of human resource management neglects the cultivation of moral character. Therefore, it is necessary to reform the teaching of human resource management, and integrate ideological and political education into the whole process of teaching to improve the ideological and moral level of students. On the basis of analyzing the necessity of human resource management in curriculum ideology and politics construction, curriculum teaching reform is carried out. A new curriculum ideological and political education model that includes "teaching objective -- ideological and political content -- teaching means -- teaching evaluation" has been constructed. The content of the course is divided into 8 chapters, and the multi-level teaching objectives including "knowledge - skills - ideology and politics" have been clearly defined, and the triple teaching objectives of each chapter are clearly set. The ideological and political content has been integrated into the process of knowledge teaching by chapters. The modern educational technology and Internet platform technology are made full use of to optimize teaching methods, and heuristic and experiential teaching means are adopted, the combination of classroom and society is increased, and an assessment and evaluation system with diversified subjects is built with diversified subjects, a comprehensive assessment process, and diverse assessment methods, comprehensively evaluating students' learning outcomes from multiple dimensions, in order to improve the effectiveness of ideological and political education in human resource management courses. It is expected to provide a reference and basis for the construction of curriculum, ideological and political reform, the practice of socialist core values, and the realization of goals.

Augmented visualization by computer vision and chromatographic fingerprinting on comprehensive two-dimensional gas chromatographic patterns: Unraveling diagnostic signatures in food volatilome

Computer Vision is an approach of Artificial Intelligence (AI) that conceptually enables “computers and systems to derive useful information from digital images” giving access to higher-level information and “take actions or make recommendations based on that information”. Comprehensive two-dimensional chromatography gives access to highly detailed, accurate, yet unstructured information on the sample's chemical composition, and makes it possible to exploit the AI concepts at the data processing level (e.g., by Computer Vision) to rationalize raw data explorations. The goal is the understanding of the biological phenomena interrelated to a specific/diagnostic chemical signature. This study introduces a novel workflow for Computer Vision based on pattern recognition algorithms (i.e., combined untargeted and targeted UT fingerprinting) which includes the generation of composite Class Images for representative samples' classes, their effective re-alignment and registration against a comprehensive feature template followed by Augmented Visualization by comparative visual analysis. As an illustrative application, a sample set originated from a Research Project on artisanal butter (from raw sweet cream to ripened butter) is explored, capturing the evolution of volatile components along the production chain and the impact of different microbial cultures on the finished product volatilome. The workflow has significant advantages compared to the classical one-step pairwise comparison process given the ability to realign and pairwise compare both targeted and untargeted chromatographic features belonging to Class Images resembling chemical patterns from many different samples with intrinsic biological variability.

A novel seismic strengthening method for RC frames: Precast ultra-high performance concrete braces

A novel bracing method to strengthen the seismic behavior of reinforced concrete (RC) frames was developed in the study. The brace was made using steel reinforced ultra-high performance concrete (UHPC). UHPC is a class of tensile strain-hardening cementitious composites and has ultra-high compressive strength of greater than 120 MPa. To utilize the capacity of the UHPC brace prior to the onset of major inelastic response of the RC frame, a design method for the UHPC brace was established. In the developed strengthening method, the in-situ construction process was simplified by conveniently installing the precast UHPC brace using the UHPC connections that was constructed in-situ to link the UHPC brace to the frame. The performance of the UHPC bracing method was evaluated using cyclic loading tests on two frame specimens, i.e., a bare RC frame and a UHPC brace-strengthened RC frame. The test results showed that the UHPC brace effectively enhanced the initial stiffness, peak strength, and energy dissipation capacity of the original frame. Moreover, it successfully preserved the capacity of the columns when the UHPC brace was active without magnifying the shear demand in the columns. As a result, the strengthening method allowed the original columns to utilize their full force resisting capacity after the capacity of the UHPC brace was depleted. In addition to the experimental study, an analytical model, which was derived based on equilibrium, compatibility, and suitable material constitutive laws, was developed to reasonably evaluate the load-displacement response of RC frames strengthened with UHPC braces.