Polyoxometalate modified inorganic–organic nanocomposite materials for energy storage applications: A review

Modification of organic substrates with inorganic polyoxometalate (POM) clusters can be used to engineer nanocomposite materials with improved properties and diverse functionalities. This review will outline concepts and methodologies for fabricating POM based inorganic–organic composite materials with a special focus on the electrochemical functionality of these composites for energy storage applications. The strengths and limitations of three different fabrication techniques, chemisorption to a carbon surface, immobilization in a polymer matrix, and layer-by-layer self-assembly will be assessed. Furthermore, the latest developments in the use of POM nanocomposite materials in energy storage applications like electrochemical capacitors (ECs) and lithium ion batteries will be presented. This review will highlight the issues and challenges that need to be addressed to achieve inorganic–organic POM nanocomposites able to support high performance energy storage applications.     

Three-dimensional needle-punching for composites – A review

The current literature on three-dimensional (3D) needle-punched composites tends to address the aspects of preforms fabrication and composites characterization respectively. This paper aims to bring together these two aspects to provide readers with a comprehensive understanding of the subject of 3D needle-punched reinforcements for composites. Consequently, this paper contains a detailed outline of the current state of 3D needle-punched technology for manufacturing advanced composite preforms. Properties of 3D needle-punched composites and some of the predictive models available for determining these properties are also reviewed. To conclude, a number of current and potential applications of 3D needle-punched preforms for engineering composites are highlighted, and issues impeding the use of 3D needle-punched composites are also summarized.     

Bimodal microstructure – A feasible strategy for high-strength and ductile metallic materials

Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results on fcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo-mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.     

Auxetic materials — A review

Auxetic materials are endowed with a behavior that contradicts common sense, when subjected to an axial tensile load they increase their transverse dimension. In case of a compression load, they reduce their transverse dimension. Consequently, these materials have a negative Poisson’s ratio in such direction. This paper reviews research related to these materials. It presents the theories that explain their deformation behavior and reveals the important role represented by the internal structure. Their mechanical properties are explored and some potential applications for these materials are shown.     

Thermoplastic–epoxy interactions and their potential applications in joining composite structures – A review

This paper presents a literature survey on the theoretical backgrounds and the past research efforts in relation to the interactions between certain thermoplastics and epoxies, and their applications in polymer blending, epoxy toughening and composite joining. The main objectives are to understand the possible mechanisms of interfacial adhesion between thermoplastic and thermoset polymers, and also to explore the feasible approaches to improve interfacial adhesion for the purposes of joining fibre reinforced polymer (FRP) composite structures by fusion bonding. Further, it is expected that the review would provide some visions to the potential applications of the thermoplastic–thermoset interfacial interactions for the quick assembly of composite structures in cost-effective manufacturing of composite structures, through the uses of the technologies, such as thermoset composite fusion bonding, welding of thermoplastic composites with thermoset composites, and thermoplastic article attachment on thermoset composites.     

Flax fibre and its composites – A review

In recent years, the use of flax fibres as reinforcement in composites has gained popularity due to an increasing requirement for developing sustainable materials. Flax fibres are cost-effective and offer specific mechanical properties comparable to those of glass fibres. Composites made of flax fibres with thermoplastic, thermoset, and biodegradable matrices have exhibited good mechanical properties. This review presents a summary of recent developments of flax fibre and its composites. Firstly, the fibre structure, mechanical properties, cost, the effect of various parameters (i.e. relative humidity, various physical/chemical treatments, gauge length, fibre diameter, fibre location in a stem, oleaginous, mechanical defects such as kink bands) on tensile properties of flax fibre have been reviewed. Secondly, the effect of fibre configuration (i.e. in forms of fabric, mat, yarn, roving and monofilament), manufacturing processes, fibre volume, and fibre/matrix interface parameters on the mechanical properties of flax fibre reinforced composites have been reviewed. Next, the studies of life cycle assessment and durability investigation of flax fibre reinforced composites have been reviewed.     

Robust design – A concept for imperfection insensitive composite structures

Robust design is a philosophy that aims to ensure that a structure will be tolerant to unknown variations and imperfections. This is an important consideration as highly optimised critical structures are required to survive unexpected loading and operating conditions. In some ways, robust design appears to be similar to damage tolerant design but its application to aerospace structural design is neither well established nor understood. In order to demonstrate the differences between the two concepts, a stiffened composite panel has been analysed for damage tolerance and robustness properties. Damage tolerance has been studied experimentally with the panel subjected to impact damage. The effect of laminate stacking sequence on the robustness of the panel has been assessed using finite element analysis and a Robust Index applied to quantify the robustness. The differences between designs are discussed together with the possible future directions for robust design applied to aerospace composite structures.     

Advantages and challenges of relaxor-PbTiO3 ferroelectric crystals for electroacoustic transducers – A review

Relaxor-PbTiO₃ (PT) based ferroelectric crystals with the perovskite structure have been investigated over the last few decades due to their ultrahigh piezoelectric coefficients (d₃₃ > 1500 pC/N) and electromechanical coupling factors (k₃₃ > 90%), far outperforming state-of-the-art ferroelectric polycrystalline Pb(Zr,Ti)O₃ ceramics, and are at the forefront of advanced electroacoustic applications. In this review, the performance merits of relaxor-PT crystals in various electroacoustic devices are presented from a piezoelectric material viewpoint. Opportunities come from not only the ultrahigh properties, specifically coupling and piezoelectric coefficients, but through novel vibration modes and crystallographic/domain engineering. Figure of merits (FOMs) of crystals with various compositions and phases were established for various applications, including medical ultrasonic transducers, underwater transducers, acoustic sensors and tweezers. For each device application, recent developments in relaxor-PT ferroelectric crystals were surveyed and compared with state-of-the-art polycrystalline piezoelectrics, with an emphasis on their strong anisotropic features and crystallographic uniqueness, including engineered domain–property relationships. This review starts with an introduction on electroacoustic transducers and the history of piezoelectric materials. The development of the high performance relaxor-PT single crystals, with a focus on their uniqueness in transducer applications, is then discussed. In the third part, various FOMs of piezoelectric materials for a wide range of ultrasound applications, including diagnostic ultrasound, therapeutic ultrasound, underwater acoustic and passive sensors, tactile sensors, acoustic tweezers and ultrasonic motors, are evaluated to provide a thorough understanding of the materials’ behavior under operational conditions. Structure–property–performance relationships are then established. Finally, the impacts and challenges of relaxor-PT crystals are summarized to guide on-going and future research in the development of relaxor-PT crystals for the next generation electroacoustic transducers.     

Phase change material based cold thermal energy storage: Materials,techniques and applications – A review

This paper gives a comprehensive review on recent developments and the previous research studies on cold thermal energy storage using phase change materials (PCM). Such commercially available PCMs having the potential to be used as material for cold energy storage are categorised and listed with their melting point and latent heat of fusion. Also techniques for improving the thermo-physical properties of PCM such as heat transfer enhancement, encapsulation, inclusion of nanostructures and shape stabilization are reviewed. The effect of stability due to the corrosion of construction materials is also reported. Finally, different applications where the PCM can be employed for cold energy storage such as free cooling of building, air-conditioning, refrigerated trucks and cold packing are discussed.     

Two novel propylenedioxythiophene-based copolymers with donor–acceptor structures for organic solar cell materials

Two novel conjugated copolymers consisting of alternating electron-rich propylenedioxythiophene and electron-deficient 2,3-diphenyltheno[3,4-b]pyrazine or 6,7-diphenyl[1,2,5]thiadiazole units have been synthesized through palladium catalyzed Sonogashira triple-bond coupling reaction. The structures and properties of the two copolymers, P ₁ , P ₂ , were characterized by FT-IR, NMR, UV–Vis absorbance (Abs), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and cyclic voltammetry (CV). UV–Vis absorption spectra of the polymers show two absorption bands both in CHCl₃ solution and films. The absorption peak maxima of P ₁ , P ₂ are 600 nm, 766 nm in solution and 627 nm, 823 nm in films, respectively. Thermal gravimetric analysis demonstrates that the two polymers are stable below 300 °C. Cyclic voltammetry studies reveal that the band gaps of P ₁ , P ₂ are 1.62 eV and 1.50 eV, suggesting their potential for applications as organic solar cell materials.     

Mechanics of mechanically fastened joints in polymer–matrix composite structures – A review

As the applications of advanced composite structural materials continue to increase, so does the need to understand the mechanical behavior of mechanically fastened joints in such structures. The most recent and relevant review article on this subject was published more than a decade ago, but it was restricted to stress analysis and strength prediction of mechanically fastened joints in fiber-reinforced plastics. The present article attempts a more comprehensive review of recent literature in the broader area of mechanics of mechanically fastened joints in polymer–matrix composite structures. Since experimental characterization has traditionally played such a fundamental role in such studies, the article begins with a review of relevant mechanical test methods and standards. This is followed by a discussion of the mechanics aspects of design, including joint design methodologies, considerations of the influence of geometric effects, and fastener preload selection. The remaining sections are devoted to failure modes such as bearing failure, failure prediction for both statically and dynamically loaded joints, time-dependent joint preload relaxation, the effects of temperature and moisture on joint strength and failure, and non-destructive evaluation techniques for monitoring the joints. Finally, comments are offered regarding the most important remaining problems in this area, and recommendations for future work.     

Fatigue failure predictions for steels in the very high cycle region – A review and recommendations

Very high cycle fatigue properties of various steels were studied using findings of previous research and laboratory fatigue testing. First, experimental data for more than 550 specimens covering 25 high and medium strength steels were used to investigate the relationships between the applied stress, number of failure cycles, size of defects or inclusions at fracture origins and stress intensity factors. Using the results of the investigation of these data, general conclusions were arrived at for steels as a whole. It was observed that the size of the failure origin can be predicted using strength properties of steels. Existing methods for estimating major parameters such as size of failure origins and stress intensity factors were reviewed, new methods were proposed and their accuracy was verified using experimental data. Also, the possibility of simplifying existing formulae with substitutions for the major parameters was reviewed. Employing these major parameters, new formulae for predicting fatigue strengths of both medium and high strength steels were proposed. Predictions of these proposed formulae were compared with existing well known formulae using experimental data and statistical methods highlighting the simplicity and importance of the proposed formulae. The ability of employing the proposed formulae for predicting, “fatigue strengths that are more close to the real values” as well as “fatigue strengths that are more safe and conservative” was reviewed. Secondly, fatigue properties and failure causes of medium strength – low carbon structural steels that are usually used in civil engineering structures were investigated. For this investigation, 35 smooth specimens of five steels were tested using a rotating bending fatigue tester. It was observed that fatigue failures occur up to around 10⁷ cycles and that the failure originates from the surface. It was found that the formulae proposed are able to predict failures of these medium strengths steels. Slopes of stress life curves in the very high cycle fatigue regions were well predicted by these proposed formulae while the predictions were fairly aligned with values suggested in previous research. Finally, recommendations were given for employing suitable prediction methods considering safety and importance of components and structures.     

Relationship between concrete resistivity and corrosion rate – A literature review

The process of reinforcement corrosion in concrete is partially controlled by the transport of ions through the concrete microstructure. Ions are charged and the ability of a material to withstand transfer of charge is dependent upon the electrical resistivity. Thus, a connection could be expected between the corrosion process of steel embedded in concrete and the electrical resistivity of concrete. This paper reviews research concerning the relationship between corrosion rate and concrete resistivity. Overall, there exists an inverse proportional correlation between the parameters. However, the dependency varies between studies and one single relationship cannot be established between corrosion rate and resistivity. To address the variation, the article reviews and evaluates the influence of factors including the experimental setup, the concrete mix design and the cause of corrosion.     

Obsolescence – A review of the literature

Technology progress and fierce competitiveness between manufacturers creates intense pressues to innovatively develop and sell new products. These products could be household or industrial items, such as telephones, computers, machines, robots, unmanned aerial vehicle (UAV), motors, industrial processes, electronic devices, tools, and spare parts in general. The technological progress implies the use of the word “obsolescence.” The new products have higher performance metrics compared to the older units, such as reliability, resilience, memory capacity, improved material, precision, artificial intelligence, lower energy consumption, ergonomics, and safety. Therefore, obsolescence became a paradox in our daily life and industry. This paper presents a literature review of the main published works on obsolescence (1976–2020). Its typologies, consequences and replacement strategies are illustrated.     

Monitoring and control of coating and granulation processes in fluidized beds – A review

This review presents a compilation of works of the main techniques for monitoring and control fluidization regimes, particle size and moisture content during coating and granulation processes in the fluidized bed. The development of monitoring and control systems for coating and granulation of particles is highly desirable, not only to allow the operation in a stable bubbling fluidization regime, which intensifies heat and mass transfer, but also to ensure strict quality specifications for products, such as, uniform particle size distribution, low moisture content and good flowability. This paper focuses on the discussion of methods used and results obtained in studies on monitoring and control of granulation and coating process in the fluidized bed reported in the literature in the last decades. Pressure fluctuation signal analysis is widely discussed as a tool of regime monitoring. To monitor particle size, techniques such as, Near Infrared spectroscopy (NIR), Focused Beam Reflectance Measurements (FBRMs), among others are presented in detail. As for moisture content tracking, the methods are reviewed like acoustic signals, capacitance, microwave resonance and spectroscopy. It is evident that although these processes are highly complex, the techniques presented here have evolved mainly due to the efforts of several research groups, showing great potential for applications in industry, emphasizing the importance of this research field.     

Reliability in composites – A selective review and survey of current development

As a response to the rampant increase in research activity within reliability in the past few decades, and to the lack of a conclusive framework for composite applications, this article attempts to identify the most relevant reliability topics to composite materials and provide a selective review. Available reliability assessment methods are briefly explained, referenced and compared within an unified formulation. Recent developments to confer efficiency in computing reliability in large composite structures are also highlighted. Finally, some general conclusions are derived along with an overview of future directions of research within reliability of composite materials and their influence on design and optimization.     

A broad review about face recognition – feature extraction and recognition techniques

Abstract

Face recognition (FR) throws open a vast horizon of challenging tasks in the arena of facial image processing applications and computer visualisation, and hence has riveted keen interest during the last few years on account of its versatile applications in numerous spheres. Creating a useful facial design from initial face images is a very important gradient for victorious facial expression detection. Here, we furnish a report of several feature extraction and recognition methods which find themselves employed in the method of FR. The major aim of this survey is to assess the diverse FR methods according to their feature extraction and recognition techniques. From the analysis, we come to know about the feature extraction and recognition methods which have been elegant utilised in the FR procedure. They also vividly establish the technique which has performed excellently yielding superior FR precision by detecting face images more exactly. Moreover our study draws a concise picture of the feature extraction and recognition techniques and acts as a lodestar to the incoming intriguing investigators intending to increase their information about this innovative technique.     

Ti based biomaterials,the ultimate choice for orthopaedic implants – A review

The field of biomaterials has become a vital area, as these materials can enhance the quality and longevity of human life and the science and technology associated with this field has now led to multi-million dollar business. The paper focuses its attention mainly on titanium-based alloys, even though there exists biomaterials made up of ceramics, polymers and composite materials. The paper discusses the biomechanical compatibility of many metallic materials and it brings out the overall superiority of Ti based alloys, even though it is costlier. As it is well known that a good biomaterial should possess the fundamental properties such as better mechanical and biological compatibility and enhanced wear and corrosion resistance in biological environment, the paper discusses the influence of alloy chemistry, thermomechanical processing and surface condition on these properties. In addition, this paper also discusses in detail the various surface modification techniques to achieve superior biocompatibility, higher wear and corrosion resistance. Overall, an attempt has been made to bring out the current scenario of Ti based materials for biomedical applications.     

A matrix-form GSM–CFD solver for incompressible fluids and its application to hemodynamics

A GSM–CFD solver for incompressible flows is developed based on the gradient smoothing method (GSM). A matrix-form algorithm and corresponding data structure for GSM are devised to efficiently approximate the spatial gradients of field variables using the gradient smoothing operation. The calculated gradient values on various test fields show that the proposed GSM is capable of exactly reproducing linear field and of second order accuracy on all kinds of meshes. It is found that the GSM is much more robust to mesh deformation and therefore more suitable for problems with complicated geometries. Integrated with the artificial compressibility approach, the GSM is extended to solve the incompressible flows. As an example, the flow simulation of carotid bifurcation is carried out to show the effectiveness of the proposed GSM–CFD solver. The blood is modeled as incompressible Newtonian fluid and the vessel is treated as rigid wall in this paper.