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.     

Strategies to synthesise copper oxide nanoparticles and their bio applications – a review

Researchers have identified copper oxide nanoparticles (CuO-NPs) as a key of interest because of their unique shape- and size-dependent bio-medical properties. Researchers have discovered and invented a variety of methods for the synthesis of CuO-NPs under physical, chemical and biological approach. In this review paper, we give an overview of the preparation of CuO-NPs through various methods and also their applications in the bio-medical field. The main aim of this paper is to keep up to date with the myriad ongoing methods of NPs’ synthesis and also examine their applications, especially in the field of medicine.     

Strengthening in and fracture behaviour of CNT and carbon-fibre-reinforced epoxy–matrix hybrid composite

Advanced materials such as continuous fibre-reinforced polymer matrix composites offer significant enhancements in strength and fracture resistance properties as compared with their bulk, monolithic counterparts. In the present work, mode-I (tensile) fracture behaviour of the neat epoxy (without nano- or hybrid reinforcements), nanocomposite (with amino-functionalized multi-walled carbon nanotube (MWCNT) reinforcement to neat epoxy) and hybrid composite (with amino MWCNT and carbon fibre reinforcements to neat epoxy) along with their flexural strength and interlaminar shear strength has been reported and discussed. Limited topological studies have also been conducted to understand the nature of material fracture and its dependence on the notch orientation. The results thus obtained are analysed and discussed in detail to elucidate: (i) alignment of fibre and its influence on the anisotropy in strength and fracture resistance, (ii) dependence of notch root radii on the apparent fracture toughness and concurrence to strain-controlled fracture and (iii) finally, the nature of J–R curves. The results thus obtained have revealed that the resistance to fracture is significantly increased with the addition of amino-functionalized MWCNTs and carbon fibres. In the hybrid composite, fracture resistance is greater in the longitudinal orientation of fibres than in the transverse orientation and it exhibits a significantly higher strength–fracture toughness combination.     

Graphene-based materials and structures for energy harvesting with fluids – A review

Graphene and graphene-based systems have recently been recognized as promising platforms for energy harvesting, microelectronic components and energy storage owing to their excellent electrical and thermal conductivity, outstanding mechanical properties, good chemical stability, area adaptability, among other significant properties. Integration of energy harvesting systems relying on the graphene/graphene-based materials in contact with fluids has been emphasized in recent years, as well as their potential impact on electric energy generation for a wide range of applications (e.g. innovative medical devices, advanced electronic systems and highly-efficient transduction systems for renewable energy). This review summarizes, for the first time, major breakthroughs carried out in the scope of energy harvesting exploiting graphene-based material systems (comprising graphene films, graphene grids, graphene membranes, 3D graphene composites and tribological structures) in contact with ionic and non-ionic fluids. Several transduction mechanisms for energy harvesting have been thoroughly analyzed. Energy outputs, materials and structures, substrates, types of fluid, manufacture methodologies, and experimental test methodologies are systematically highlighted in this review. Finally, future research directions and innovative applications of these harvesters are proposed.     

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.     

Failure mechanisms in toughened epoxy resins—A review

The subject of improving the fracture toughness of brittle epoxy resins is receiving significant attention in order to improve the design strain of fiber-reinforced composites for aerospace structural applications. Various rubber-modified and particle-filled epoxy resins have been considered as candidate materials. Such modified resins have been observed to yield a ten- to thirty-fold increase in fracture toughness compared to the unmodified material. In order fully to utilize the potential of such materials, it is necessary to understand the failure mechanisms leading to the improvement in toughness. This paper provides a critical review of the existing theories that have been proposed for the various toughening mechanisms related to modified epoxy resins.     

Numerical modeling on concrete structures and steel–concrete composite frame structures

A steel–concrete composite fiber beam-column model is developed in this study. The composite fiber beam-column model consists of a preprocessor program that is used to divide a composite section into fibers and a group of uniaxial hysteretic material constitutive models coded in the user defined subprogram UMAT in ABAQUS. The steel–concrete composite fiber beam-column model is suitable for global elasto-plastic analysis on composite frames with rigid connections subjected to the combined action of gravity and cyclic lateral loads. The model is verified by a large number of experiments and the results show that the developed composite fiber model possesses better accuracy and broader applicability compared with a traditional finite element model. Although the fiber beam-column model neglects the slip between the steel beam and concrete slab, there are essentially no effects on the global calculation results of steel–concrete composite frames. The proposed model has a simple modeling procedure, high calculation efficiency and great advantage when it is used to analyze composite frames subjected to cyclic loading due to earthquake.     

A review of bast fibres and their composites. Part 2 – Composites

Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer matrix composites as they are perceived to be “sustainable”. The fibres are composed primarily of cellulose which potentially has a Young’s modulus of ～140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). Part 2 of this review will consider the prediction of the properties of natural fibre reinforced composites, manufacturing techniques and composite materials characterisation using microscopy, mechanical, chemical and thermal techniques. The review will close with a brief overview of the potential applications and the environmental considerations which might expedite or constrain the adoption of these composites.     

Fe–Ga–As precipitates and their magnetic domain structures in high-dose iron implanted GaAs

The integration of ferromagnetism with semiconductors to fabricate ferromagnetic semiconductors has been believed to be a potential way to make new spintronic devices. We have synthesized ferromagnetic Fe₃Ga_2−x As _x nanoparticles in the surface of GaAs by employing ion implantation and rapid thermal annealing processes. Transmission electron microscopy revealed that these nanoparticles exist only in the top surface of the GaAs samples, with sizes from several to hundreds of nanometers. They have two orientation relationships to the GaAs matrix: [1 − 210]_p//[011]_m, (10 − 10)_p//(−42 − 2)_m and (0002)_p//(11 − 1)_m; and [1 − 210]_p//[011]_m, (−1010)_p//(42 − 2)_m and (0002)_p//(−11 − 1)_m. The magnetic structures of the precipitates were studied by magnetic force microscopy. Results indicate that most of the ferromagnetic nanoparticles have single magnetic domains with their magnetic poles randomly orientated.     

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.     

A review of bast fibres and their composites. Part 1 – Fibres as reinforcements

Bast fibres are defined as those obtained from the outer cell layers of the stems of various plants. The fibres find use in textile applications and are increasingly being considered as reinforcements for polymer–matrix composites as they are perceived to be “sustainable”. The fibres are composed primarily of cellulose which potentially has a Young’s modulus of ～140 GPa (being a value comparable with man-made aramid [Kevlar/Twaron] fibres). The plants which are currently attracting most interest are flax and hemp (in temperate climates) or jute and kenaf (in tropical climates). This review paper will consider the growth, harvesting and fibre separation techniques suitable to yield fibre of appropriate quality. The text will then address characterisation of the fibre as, unlike man-made fibres, the cross section is neither circular nor uniform along the length.     

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.     

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.     

Formation of composite Cu–graphite and Cu–PTFE coatings and their tribological characterization

The Dynamic Chemical Plating (DCP) technique allows production of 2-μm copper films containing particles of graphite or PTFE in 18 and 15 min, respectively, at ambient temperature. DCP yields composites with particle-incorporation fractions of 12% for graphite micro-particles and 22% for PTFE nano-particles. The composite films show excellent tribological properties, acting as self-lubricating coatings with friction coefficients as low as 0.18.     

Titanium–SiO2 nanocomposites and their scaffolds for dental applications

There have been a number of attempts to modify the properties of titanium implants to improve osseointegration. These modifications include alterations of the chemistry and roughness of the surface of the implant. In this work, Ti–10 wt.% SiO₂ nanocomposites and their scaffolds were synthesized using a combination of mechanical alloying and a “space-holder” sintering process. The phase and microstructure analysis was carried out using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and the properties were measured using hardness and corrosion testing equipment. An amorphous structure was obtained at 20 h of milling. The crystallization of the amorphous phase upon annealing led to the formation of a nanostructured Ti–10 wt.% SiO₂ composite with a grain size of approximately 40 nm. The Vickers hardness of the Ti–10 wt.% SiO₂ nanocomposites reached 670 HV_0.2. The in vitro cytocompatibility of these materials was evaluated and compared with conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured. The morphology of the cell cultures obtained on the bulk Ti–10 wt.% SiO₂ nanocomposite was similar to those obtained on the microcrystalline titanium. However, on the porous scaffold, the cells adhered to the insert that penetrated the porous structure with their entire surface, whereas on the polished surface, more spherical cells were observed with a smaller surface of adhesion. Porous Ti–10 wt.% SiO₂ scaffolds have been developed in order to promote bone ingrowth and to induce prosthesis stabilization.     

Alumina–tantalum composite for femoral head applications in total hip arthroplasty

Dense composite laminates of alumina (Al₂O₃) and tantalum (Ta) were fabricated by hot pressing and tested in vitro for potential use as a femoral head material in total hip arthroplasty (THA). Al₂O₃–Ta composite laminates hot pressed at 1450 °C and 1650 °C had flexural strengths of 940 ± 180 MPa and 1090 ± 340 MPa, respectively, which were far larger than the values of 420 ± 140 MPa and 400 ± 130 MPa for Al₂O₃ hot pressed at 1450 °C and 1650 °C, respectively. The interfacial shear strength, determined by a double-notched specimen test, was 310 ± 80 MPa for the composite laminate hot pressed at 1650 °C, indicating strong interfacial bonding between Al₂O₃ and Ta. Scanning electron microscopy (SEM), energy dispersive X-ray (EDS) analysis, and X-ray mapping of polished sections of the hot-pressed laminates showed the presence of an interfacial region formed presumably by diffusion of O (at 1450 °C) or O and Al (1650 °C) from Al₂O₃ into Ta. Composite femoral heads of Al₂O₃ and Ta could combine the low wear of an Al₂O₃ articulating surface with the safety of a ductile metal femoral head.     

Study of the martensitic transformation in NiTi–epoxy smart composite and its effect on the overall behavior

In this work, the effect of wire phase transformation on the overall thermo-mechanical behavior of NiTi–epoxy composites has been investigated. The shape memory wire received in as drawn condition was subjected to three heat treatments which results to different transformation characteristics. Composite specimens were manufactured by casting followed by curing and post curing process. The mechanical behavior of samples has been determined using standard tensile test. The effect of wire volume fraction and test temperature was investigated as well.It is found that the martensitic transformation occurring in the wire affects the mechanical behavior of the composite specimens. In this way, using the wire with higher transformation stress improves the composite tensile strength. This is achieved either by increasing the test temperature or by using the wires heat treated at lower temperatures. From the experimental results, the martensitic transformation can change the debonding mode. It seems that on the constraint of matrix, the transformation occurs simultaneously at several points in wires that result in regular debonded/undebonded pattern.     

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.     

A review of noble metal (Pd,Ag, Pt,Au)–zinc oxide nanocomposites: synthesis,structures and applications

As a promising candidate for future catalytic applications, the noble metal–ZnO nanocomposites are gaining increasing interest due its high catalytic property, and super stability. In this review, the noble metal–ZnO nanocomposites with various composites and structures for catalytic applications will be discussed. We introduce the multi-catalytic properties and design concept of the noble metal–ZnO nanocomposites, and then particular highlight key finding of synthesis method for various noble metal–ZnO nanocomposites. The catalytic activity of noble metal–ZnO nanostructures has been found to rely on not only the species of noble metal but also the architecture of the catalyst material. Moreover, the typical works of modification on noble metal–ZnO nanostructures have been introduced. Critically, the challenges for future research development and our future perspectives are presented.     

A comparative study on erosion characteristics of red mud filled bamboo–epoxy and glass–epoxy composites

Bamboo fiber reinforced epoxy matrix composites filled with different weight proportions of red mud (a solid waste generated in alumina plants) are fabricated. The mechanical properties of these composites are evaluated and are then compared with those of a similar set of glass–epoxy composites. The solid particle erosion characteristics of the bamboo–epoxy composites have been studied and the experimental results are compared with those for glass–epoxy composites under similar test conditions available in the published literature. For this, an air jet type erosion test rig and Taguchi orthogonal arrays have been used. The methodology based on Taguchi’s experimental design approach is employed to make a parametric analysis of erosion wear process. This systematic experimentation has led to determination of significant process parameters and material variables that predominantly influence the wear rate of the particulate filled composites reinforced with bamboo and glass fiber, respectively. The comparative study indicates that although the bamboo based composites exhibit relatively inferior mechanical properties, their erosion wear performance is better than that of the glass fiber reinforced composites. It further indicates that the incorporation of red mud particulates results in improvement of erosion wear resistance of both the bamboo and glass fiber composites.