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In recent years, graphene has attracted a great research interest in all fields of sciences due to its unique properties. Its excellent mechanical properties lead it to be used in nanocomposites for strength enhancement. In current work, a new magnesium-graphene nanoplatelets composite is fabricated for the first time using semi-powder metallurgy method. The effect of graphene nanoplatelets addition on the mechanical behaviour of pure magnesium under both tension and hardness is investigated. The results demonstrate that graphene nanoplatelets are distributed homogeneously in the magnesium matrix, therefore act as an effective reinforcing filler to prevent the deformation. Compared to monolithic magnesium, the magnesium/0.3 wt% graphene nanoplatelets composite exhibited improved elastic modulus, yield strength, ultimate tensile strength and Vickers hardness. The improvement in elastic modulus, yield strength (0.2%), ultimate tensile strength and Vickers hardness for magnesium/0.3 wt% graphene nanoplatelets composite relative to pure magnesium are up to +10.6%, +5%, +8% and +19.3%, respectively. In addition to tensile and hardness tests for the analysis of mechanical properties of as synthesized composite, scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction are used to investigate the surface morphology, elemental percentage composition and phase analysis, respectively. [ABSTRACT FROM AUTHOR]

The structural performance improvement of concrete members is by far a crucial theoretical issue for engineers, and the development of modern smart and composite materials makes it possible to gradually enhance the durability design of the concrete structure. In this study, six beams of the same size and reinforcement ratio, the proposed composite beam (SMA-GFRP-ECC) and five comparative beams (RC, R-ECC, SS-ECC, GFRP-ECC, SMA-ECC), were designed and tested under low-cycle unidirectional cyclic loading and unloading conditions. The energy dissipation capacity, displacement ductility, residual deformation, and self-repairing performance of each concrete beam were evaluated. Afterward, a concise calculation model for the studied composite beam is deduced and developed based on the existing relevant constitutive models and concrete assumptions. The test results indicate that compared with RC beams, the composite reinforced ECC beams show obvious multi-cracking and smaller crack width during the loading process and have good bending ductility. The innovative SMA-GFRP-ECC beam is capable of a high bearing capacity, ductility, and damage self-repairing. The new proposed beam has more than 80% of the maximum crack width recovery capacity during unloading. Hence, the proposed SMA-GFRP-ECC beam is a rather good first attempt of strengthened beams, combining the advantages of SMA, GFRP, and ECC. [ABSTRACT FROM AUTHOR]

Many interesting studies on composites with nano or submicron SiCp have been performed since the size advantages of fine SiC particles. However, it is extremely hard to disperse fine particles in metal melts due to their poor wettability and large surface-to-volume ratio, especially the fabrication of composites with multisized SiCp (5 µm, 0.5 µm, and ∼60 nm) is very difficult. The use of multisized reinforcements is required to solve the dispersion problem. The stir casting technology and hot extrusion method could be used to disperse the multisized SiCp in the matrix. The effects of multisized SiCp on the dynamic recrystallization behavior of the composites are discussed. The large-scale dynamic recrystallization caused by adding multisized SiCp results in a fine matrix microstructure. Compared with the as-accepted AZ31B alloy (YS: 195 MPa, UTS: 277 MPa), the yield strength and ultimate tensile strength of the AZ31B/SiCp/n-1 + S-4 + 5-10 composite were enhanced to 73.8 and 44.8%, respectively. The better tensile properties were attributed to the uniform distribution of reinforcement, strengthening effect of multisized SiCp, and grain refinement of magnesium matrix. [ABSTRACT FROM AUTHOR]

Polystyrene matrixes containing cellulose nanofibril (CNF) with fiber content of 0.5, 1, 5, and 10 wt% were successfully hydrophobized by silylation and extruded into single filaments using both single and dual heat extrusion processing. The fiber–matrix bonding was examined using a scanning electron microscope. With further characterization, Fourier transform infrared spectroscopy showed a formation of Si-O-C bonds, indicating better fiber–matrix adhesion. Raman spectroscopy showed disruption of hydrogen bonding, which indicates interference of parallel nanocellulose fiber adhesion to neighboring fibrils. Thermogravimetric analysis suggests that the thermal stability of the functionalized CNF is higher than that of the corresponding neat sample, which is resultant of stable Si bond formation. Results from dynamic mechanical analysis showed an increasing ultimate tensile strength (UTS) and elastic modulus, with peak values attributed to the dual heat processing with up 112 MPa and 10.8 GPa for the UTS and modulus, respectively. The increase is assumed to be as a result of the linear arrangement of the CNF in the Polystyrene (PS) matrix during the extrusion process. Micromechanics modeling calculations suggest the increase is moving towards the fiber properties. The results revealed the strong reinforcing ability of CNFs and their compatibility with the thermoplastic matrix if functionalized. [ABSTRACT FROM AUTHOR]

In this study, the dispersion of reclaimed carbon fibres following cost-effective surface treatment is explored with a hydrodynamic fibre moving model, and a practical fibre dispersion effect is investigated through various physical dispersion methods. To utilise reclaimed carbon fibres for a desired composite product, our proposed low-cost surface treatment is shown to be beneficial to the physical and chemical properties of the reclaimed carbon fibres and to yield polar-hydrophilic characteristics. Single fibre tensile testing is performed to explore the effect of surface treatment on the reclaimed carbon fibres (a higher tensile strength was observed). A computational hydrodynamic fibre moving model based on a moving particle semi-implicit method is newly designed to perform hydrodynamic simulation to determine aqueous dispersion of discontinuous reclaimed carbon fibres. This simulation helps understanding fibre flocculation phenomena from the perspective of fibre stiffness, which should not be disregarded for the fibre dispersion. Fibre surface analyses including morphology and functional groups are carried out to investigate the effect of surface treatment. The hydrodynamic simulation and proposed fibre dispersion methods with a cost-effective surface treatment approach can be widely applicable to any type of reclaimed carbon fibres to produce recycled fibre reinforced polymer composite materials. [ABSTRACT FROM AUTHOR]

The microstructure, mechanical properties, thermal stability and tensile fracture of two hot-rolled Al-15 vol.% B4C composite sheets (S40 with 0.4 wt.% Sc and SZ40 with 0.4 wt.% Sc and 0.24 wt.% Zr) were investigated. During multi-pass hot rolling, coarse Al3Sc or Al3(Sc, Zr) precipitations appeared and resulted in the loss of most of their hardening effect. In an appropriate post-rolling heat treatment, the hot-rolled sheets regained a significant precipitation hardening because of the precipitation of fine nanoscale Al3Sc and Al3(Sc,Zr) that uniformly distributed in the aluminum matrix. After the peak aging, the ultimate tensile strength at ambient temperature of the S40 and SZ40 sheets can reach 198 MPa and 215 MPa, respectively. During 2000 h of annealing at 300℃, the strengths at ambient temperature of both S40 and SZ40 composite sheets slowly decreased with increasing annealing time. However, the tensile strengths at 300℃ of both S40 and SZ40 composite sheets remained nearly unchanged and were less sensitive to the annealing time and more tolerable for precipitate coarsening, which demonstrated an excellent long-term thermal stability of both materials at elevated temperature. The tensile fracture at ambient temperature of both S40 and SZ40 composite sheets was dominated by the brittle B4C particle fracture, whereas the interfacial decohesion of B4C particles became the prominent characteristic of the fracture at 300℃. [ABSTRACT FROM AUTHOR]

In an attempt to develop new materials that combine structural (mechanical) and functional (electrical and magnetic) properties, a copper composite alloy reinforced through the dispersion of fine Nd2Fe14B intermetallic particles has been synthesized by the powder metallurgy route. Composite master alloy was prepared by blending copper and 8 wt% of intermetallic NdFeB in a planetary ball mill working at 250 r/min under argon atmosphere for 10 h. Resulting composite powders were encapsulated in Cu cans and then consolidated by extrusion at 1023 K. Microstructure features of blended powders and consolidated materials were characterized by means of X-ray diffraction, scanning electron microscopy, and electron probe micro analysis. Fitting of the X-ray diffraction patterns with the Rietveld method revealed that during processing, some NdFeB particles reacted with copper and oxygen to form Nd2CuO4. The lower Nb content on the Nd2Fe14B intermetallic phase due to this oxidation causes the dispersion of Fe and Fe2B particles, which also have soft magnetic properties but a higher moment compared to Nd2Fe14B. The extruded alloys showed enhanced mechanical properties (with yield strength ≥ 600 MPa, ultimate tensile strength ≥700 MPa, and 5% elongation to failure) with satisfactory electrical conductivity (46% IACS) and high values of the coercive field (≥30,000 A/m). [ABSTRACT FROM AUTHOR]

Helical Auxetic Yarn (HAY) possesses negative Poisson's ratio. These yarns can be successfully used as reinforcing elements in composite materials. This paper proposes a novel tri-component helical auxetic structure capable of enhancing the initial modulus of HAY. The novel structure comprises a high modulus thin secondary core II positioned along the first low modulus thick primary core I. An additional stiff strand wraps the cores I and II. Using statistical techniques, evaluation of the secant modulus and not Young's modulus was carried out and validated. The resultant structure was found to possess a relatively high elastic modulus in the range of 11–15 GPa. The structure exhibited an auxetic phenomenon of −62. It was revealed that such high stiffness auxetic yarn could successfully be utilized as reinforcing elements in high stiffness cost-effective auxetic composite structures. [ABSTRACT FROM AUTHOR]

Owing to the unique properties of 2D graphene derivatives (2D GDs), their composites with other materials possess superior characteristics over other existing materials in the universe. Accordingly, 2D GDs-based composites have emerged as leading materials for substantial advancements of various technological industries such as energy, electronics, sensors, catalysis, environmental remediation, biomedical and structural sectors. Recently, numerous research innovations, have been developed for reliable production of 2D GDs-based composites with high quality, plentiful availability and competitive costs. The overall performance of 2D GDs-based composites is controlled by three main issues. First, the synthesis strategy of GD sheets, which determines the characteristic properties, quantity and cost of the 2D GD product. Second, the surface functionalization of GD sheets, which enhances the compatibility and chemical affinity between GD sheets and other materials within the composites. Finally, the processing method of the composite that strongly affects its microstructure, properties, productivity and cost. This makes such three processes, matters of great concern when designing 2D GDs-based composites for specific application. In this article, the structure, properties, synthesis and surface functionalization of 2D GDs are reviewed. Then, the review article discusses the research developments of 2D GDs-based composites with inorganic materials and polymers, in terms of preparation, properties and applications. Particular focus is placed on Green and/or clean production technologies. The recent research interest in the 2D GDs/multicomponent hybrid composites, with their distinctive multifunctional properties, is highlighted. Also, the new implemented applications of 2D GDs-based composites from 2021, are pointed out, as well as the currently running practical projects, which are proposing innovative futural applications prospects. Graphical Abstract [ABSTRACT FROM AUTHOR]

Fibre-reinforced composite materials are extensively used for manufacturing critical engineering components in diverse applications, which demands intelligent and reliable structural health monitoring (SHM) schemes to prevent catastrophic failures associated with composite structures. Composite materials have complex failure mechanisms, and it is essential to employ reliable SHM methods with high accuracy to detect damages at the incipient stage. Although there are several SHM technologies available, no single strategy is impeccable for tackling all damage types due to the incredibly complex failure mechanisms of the composite materials. Machine learning (ML) methods are frequently integrated to compensate for the limitations of the traditional SHM methods. This paper presents the state-of-the-art sensory methods and deep learning (DL) techniques while emphasizing the future directions for the engineering and scientific community interested in developing novel SHM systems for fibre-reinforced polymer composite structures intended for civil, aerospace, automotive, marine, oil and gas exploration industries. [ABSTRACT FROM AUTHOR]

In this study, bovine bone was burnt at 400°C and the resulting ash was heat-treated at 900°C for 90 min to get a white powder. Chemical analysis showed that this white powder was mainly hydroxyapatite (HA). Three different average particle sizes of this powder were produced by milling at three different times. The produced HA was surface treated with a silane coupling agent. Composite samples with 40 vol.% of HA were produced by hot press molding and so mechanical testing was done on the specimens in air and Ringer’s solution. The results of these tests showed that on increasing the molecular weight of polypropylene (PP), creep strain of composites decreases proportionally, and ultimate tensile strength (UTS) and impact resistance increase dramatically. In addition, result of mechanical tests on the soaking specimens in Ringer’s solution showed that Ringer’s solution intensively decreases UTS, creep, and impact properties of PP—HA composite. Furthermore, decreasing HA particle size caused UTS rise, creep strain fall, and impact resistance rise for composites in air condition. Vice versa, in wet condition, decreasing HA particle size caused UTS, creep, and impact resistance to fall. Fracture surfaces of impact samples tests were analyzed by a scanning electron microscope. [ABSTRACT FROM PUBLISHER]

Seawater aging response was investigated in marine-grade glass/epoxy, glass/vinyl ester, carbon/epoxy and carbon/vinyl ester composites with respect to water uptake, interlaminar shear strength, flexural strength, tensile strength, and tensile fracture surface observations. The reduction of mechanical properties was found to be higher in the initial stages which showed saturation in the longer durations of seawater immersion. The flexural strength and ultimate tensile strength (UTS) dropped by about 35% and 27% for glass/epoxy, 22% and 15% for glass/vinyl ester, 48% and 34% for carbon/epoxy 28%, and 21% carbon/vinyl ester composites respectively. The water uptake behavior of epoxy-based composites was inferior to that of the vinyl system. [ABSTRACT FROM AUTHOR]

The influence of Kevlar stitches on delaminations, ultimate tensile strength, and tension--tension fatigue life were examined on carbon/bismaleimide laminates of two stacking sequences ([±45/0/90]2S and [±30/±30/90/90]S), as representative of two classes of fiber-dominated and matrix dominated laminates. Through-thickness stitching offered a significant improvement in the static delamination resistance of laminated composites, but had varying effects on the ultimate tensile stress of the laminates under study, with an increase in strength of [±30/±30/90/̄90]S laminates and a decrease in strength of [±45/0/90]2S laminates. But the fatigue life of matrix dominated specimens and fiber dominated specimens were all reduced. The radiographs indicated that stitching appeared efficient in arresting delamination in [±30/±30/90/̄90]S specimens for both static and fatigue loads, but did not prove to be as efficient in extending fatigue life. since Kevlar threads were prone to breakage under cyclic loading. As a conclusion, while the static strength and delamination resistance of matrix dominated composites is improved by stitching, the static tensile strength of fiber dominated composites and the tension--tension fatigue performance for all lamination sequences is proved to be reduced. [ABSTRACT FROM AUTHOR]

Granite powder-reinforced epoxy composites have been developed with varying granite powder content by weight percentage. The variation of tensile strength and impact strength has been studied and the tensile strength and impact strength were found to be at a maximum for the 50% granite powder-reinforced epoxy composite. The chemical resistance test indicates that the composite materials are resistant to acetic acid, concentrated hydrochloric acid, sodium hydroxide, benzene, carbon tetrachloride, and n-hexane. [ABSTRACT FROM AUTHOR]

Presents a study which examined the mechanical properties of the SiCw/aluminum composite degraded by thermal cycling using tensile tests and hardness measurements. Experimental design; Results and discussion; Conclusion.

A three-dimensional woven composite strength model is presented for predicting the failure behavior of three-dimensional angle interlock woven composites under on-axis uniaxial static tensile loading and shear loading. TheThe model is based on two-level discretization of the repeating unit cell. The repeating unit cell is discretized into sections, elements, subsections and subelements. The model predicts the stress levels at which the secondary failures take place at subelement level. The effect of secondary failure is considered for further analysis and the ultimate tensile strength and shear strength and the corresponding strains are provided. A parametric study has been carried out for different 3D angle interlock woven composite configurations. [ABSTRACT FROM AUTHOR]

The homogeneous dispersion of fine graphite nanoplatelets throughout the epoxy matrix with different mass fraction is prepared. Influence of graphite nanoplatelets of varied mass fraction in the mechanical reinforcement and shape memory effect of graphite nanoplatelets/epoxy composite is investigated. The morphology and crystal structure of graphite nanoplatelets are confirmed with the scanning electron microscope and X-ray diffraction, respectively. The shape memory effects and thermo-mechanical properties of graphite nanoplatelets/epoxy composite are studied using dynamic mechanical analysis. It is found that the storage elastic modulus increases with the mass fraction increase in graphite nanoplatelets in the graphite nanoplatelets/epoxy composite, which is the indication of greater recovery stress of graphite nanoplatelets/epoxy composite compared to that of the primitive epoxy material without graphite nanoplatelets. We had showed that the graphite nanoplatelets/epoxy composite is superior to primitive epoxy in shape memory effect and recovery speed. [ABSTRACT FROM AUTHOR]

This paper investigates the fatigue failure and electrical resistance behaviors of carbon nanotube-based polymer composites at cryogenic temperatures. Tension–tension fatigue tests were performed on carbon nanotube /polycarbonate composites at room temperature and liquid nitrogen temperature (77 K), and the electrical resistance of the specimens was monitored during the tests. Based on the obtained results, the dependence of the mechanical and electrical responses of the nanocomposites on the temperature and the nanotube content was studied. Microscopic examinations were also carried out on the specimen fracture surfaces, and the failure mechanisms of the nanocomposites were discussed. [ABSTRACT FROM AUTHOR]

The reinforcement of composite aluminium extrusions offers a high potential regarding weight reduction and improvement of mechanical properties, which is essential for components in lightweight constructions. The current work gives an overview of the quasi-static properties of spring steel wire reinforced EN AW-6082 with varying reinforcing ratio. The deformation and damage behaviour is investigated in detail for a reinforcing ratio of 11.1 vol.%. It is shown that the relatively ductile behaviour of the spring steel wire leads to multiple necking resulting in higher strains than expected. Current models are expanded and modified for a proper adaptation to the material system. [ABSTRACT FROM AUTHOR]

The main motive of this paper is to prepare a newer composite material using non-conventional reinforcement (industrial waste) for various industrial applications. The aluminium alloy (Al-4032) matrix based composites (AMCs) have been fabricated through bottom pouring stir casting method. The granite powder (GP, ceramic particles) obtained from waste (normally available from construction site) has been used as reinforcement, at 0, 3, 6, 9 % by weight. The particle size of the reinforcement has been up to 54μm. The morphological (microstructure, SEM, XRD) and mechanical (tensile strength, micro-hardness, impact strength) characterization of the AMCs have been carried out. The morphological study reveals that the reinforcement particles (GP) are almost uniformly distributed throughout the matrix phase. The mechanical properties of the AMCs have been observed to be better than the unreinforced alloy. It is expected that the fabricated Al-4032-GP composites will be useful for the automobile parts like piston, disc brakes, high speed machinery and high-speed rotating parts etc. [ABSTRACT FROM AUTHOR]

This work dealt with the fabrication of novel long glass fibre reinforced aluminum metal matrix composite (LGFRAMMC) material for automotive applications. The composite specimens were prepared by incorporating long glass fibre with different fibre volume percentage (50, 66, 80, and 100 vol.%) as reinforcement in aluminium alloy (Al6061) using the friction stir processing (FSP) method. The mechanical behaviour of the composite materials was investigated for their primary loading conditions such as tensile and Izod impact stress. Microstructural characterization and fractured mechanism of the fabricated composites were carried out by scanning electron microscope (SEM) analysis. The tensile strength and elongation of the developed composite specimens decreased with the incorporation of long glass fibre, whereas the Izod impact strength of the developed composite specimens was significantly improved as compared to the conventional base metal (Al6061) body panels used in automobiles. The low tensile strength of LGFRAMMC specimens compared to base metal was because of tunnel defect, brittle fracture and extreme plastic deformation (EPD) as characterized by fibre pull-out, pits, and micro cracks. The synergetic effects of EPD and reinforcing by long glass fibres lead to a remarkable improvement in the impact strength. [ABSTRACT FROM AUTHOR]

This research provides an experimental investigation on the properties of fiber reinforced composite materials consisting of lightweight expanded clay aggregates (LECA) and polyvinyl alcohol (PVA) fibers. The influence of temperature (room temperature, 250°C, and 500°C) on the lightweight geopolymer mortar (LWGM) composite materials is also explored. LECA is used as a partial replacement to river sand with 60% and 80%. The base material utilized for LWGM is slag activated by a mixture of sodium silicate and sodium hydroxide solutions. The fresh properties in terms of workability and density were performed. A series of experiments, such as compression, flexural and uniaxial tensile strength tests, were executed to assess the mechanical properties of LWGM composite materials. In addition, the microscopic variations due to the elevated temperature were also evaluated by scanning electron microscopy (SEM) to understand the macro-scale behavior of the samples. The results indicated that increasing the level of LECA replacement caused a reduction in the density and compressive strength of the LWGM. Also, incorporating a 1% PVA fiber volume fraction significantly enhanced the flexural and uniaxial tensile behavior of LWGM composite materials. The compressive strength enhancements were observed at 250°C due to further geopolymerization, while compressive strength reductions were obtained at 500°C due to the vapor impact and difference in thermal expansion. In addition, the load-carrying capacity of all samples increased, and displacement capacity decreased under flexural tests at 250°C. However, the ductile behavior of the PVA incorporating specimens changed to brittle due to the melting of PVA fibers. [ABSTRACT FROM AUTHOR]

Aluminum metal matrix composites are a new class of materials that have gathered more attention from many materialists. Especially, the automotive components like a piston, cylinder block, brake drum, etc., fabricated by different reinforcement, which has exposed better performance over conventional engineering materials. Aluminum composites are generally fabricated by stir casting technique due to simplicity in operation and adaptive to mass or job order production. The paper provides a background for the readers interested in the production of metal matrix composites through stir casting. Based on the literature assessment, the special attentions taken by the researchers to enhance the uniform distribution of particle to avoid agglomeration are discussed. The composite performances mainly depend on the aluminum matrix, particle size, the quantity of reinforcement, preheating temperature of reinforcement, and processing parameters such as stirring speed, stirring time, and wetting agents. The selection of two reinforcements and their suitable parameters for wetting are attaining interest by many researchers and maybe opted as future scope. [ABSTRACT FROM AUTHOR]

In this study aluminum (Al-6070)/alumina (Al2O3), and Al-6070/ graphite (Gr) reinforced particles metal-matrix composites (MMCs) are fabricated by melt-stirring technique. The MMCs bars and plates are prepared with varying the reinforced particles volume fraction ranging from 5% to 15%. The average reinforced particles size of alumina (Al2O 3) and graphite (Grp) are 23 μm and 53 μm, respectively. The stirring process was carried out at 200 rev/min rotating speed by graphite impeller for 15 min. The microstructure and mechanical properties are investigated on prepared MMCs. It was observed that the hardness of the composite is increased with increasing of reinforced particle volume fraction. The tensile strength and impact strength both are decreased with rising of reinforced volume fraction. The prepared composite plates are welded by gas welding with Al-Si-base filler metal. Rockwell hardness test was conducted and presented the test result for un-welded and welded zone. [ABSTRACT FROM AUTHOR]

An investigation was carried out on SnO2 coating of SiC particles by sol-gel technique and the production of SnO2 coated 20 vol% SiC particle reinforced composite and unreinforced matrix alloy by squeeze casting. The morphology of the coating and microstructural, interfacial and mechanical properties of the composite were characterized by using an optical microscope, image analyzer, scanning electron microscope (SEM), energy dispersion spectroscopy (EDS), and X-ray diffraction (XRD). It has been found that the coating is not degraded during the fabrication process; in other words, SnO2 coating by sol-gel technique is an effective way to improve the matrix/reinforcement interfacial properties. [ABSTRACT FROM AUTHOR]

Presents a study which examined the influences of thermal cycling and isothermal exposure on tensile strength, micro Vickers hardness and fracture mechanism of T6-SiCp/Al6061 composites and base metal of T6-Al6061 under the condition of the same hardness of the base metal for isothermal exposure and thermal cycling. Application of the ceramic particle reinforced metal matrix composites to industrial products; Experimental procedures used; Results and discussion.

This articles reviews till-date available literature on metal matrix composites reinforced with graphene, CNT and other carbonaceous materials. The article has a special focus on the mechanical, tribological and challenges associated with the fabrication of nanocomposites. Simultaneously, it reviews the synthesis, strengthening mechanism and applications of graphene along with research gap associated with graphene metal matrix nanocomposites (GMMNC). Carbonaceous nanofillers, e.g. Graphene, are known to have extraordinary mechanical, thermal and electrical properties along with multifaceted characteristics. These materials have the potential to become an ideal material in numerous application which requires reinforcement. Graphene nanoplatelets (GNP) suffers various challenges starting from its synthesis to the uniform distribution within the matrix material. Our concern is to give details on the challenges associated with graphene and metal matrix composites along with the solution so that new research can be done at its ease. Section 1 of the article gives a detailed analysis of various carbonaceous reinforcement materials. Preparation, processing and dispersion technique for graphene and composite material is given in section 2. Section 3 of the article deals with different matrix material used in MMNC along with the properties and challenges associated with it in tabulated form. Strengthening mechanism used for the enhancement of mechanical properties of composites is described in section 4, whereas, Section 5 deals with the applications and Research gap. [ABSTRACT FROM AUTHOR]

Ecological composites materials have become a topic of interest in materials science and engineering in recent years because of the growing need for environment-friendly composites that maintain properties like light weight, but gain biodegradability and renewability. Bio-composites of kenaf fiber-reinforced bio-based epoxy resin filled with different kind of nanoparticles were prepared in this work using a hybrid manufacturing process combining vacuum-assisted resin infusion and an autoclave. Nanoparticles of carbon, metal oxides and layered silicates were employed in this work to analyze their effect on the mechanical properties of bio-kenaf composites. Nanoparticles were synthesized and heat-treated according to their nature, and Fourier transform infrared spectra confirmed the presence of functional groups. Laminar structures, such as graphene or layered silicates, had more influence on the bio-kenaf composite toughness than the particle-like morphology of metal oxides. However, the nanoparticles influenced the strength because of their effective stress transfer mechanism. Despite voids of different sizes, which were detected using scanning tomography, they did not influence the mechanical properties of the bio-kenaf composites, showing that the filler effect of the nanoparticles is the dominant mechanism. [ABSTRACT FROM AUTHOR]

Reactive hot-melt resin can form joints with a certain flexibility, high processing speed, high initial rigidity, and high temperature. Such resins can be used to manufacture fiberglass composites because they support a high tensile stress, allow for large strains at low stresses, and have a low density and a working temperature range of −40–110°C. Furthermore, when the mechanical stress is removed, the material returns to its initial condition, as observed in the flexural tests. A polyurethane-based reactive hot-melt resin was characterized by tensile shear tests, Shore hardness tests, differential scanning calorimetry, and thermogravimetry. The contact angles at different temperatures were measured to evaluate the adhesive wettability and to select the best application temperature range of the adhesive, finding the best result at 140 °C. The matrix was characterized at different curing times, and matrix bonding with different adhesive materials was evaluated to provide a greater versatility of applications, to explore new fields of use of this resin as in the matrix of a composite with fiberglass. [ABSTRACT FROM AUTHOR]

Growing global environmental threats have attracted researchers and engineers toward design and manufacture of green materials. In this regard, natural filler reinforced composites are environmentally friendly, cost-effective materials with a lot of advantages over conventional carbon/glass fiber reinforced composites. Hence, in this study, the drilling performance of walnut shell powder reinforced composite material was experimentally investigated. For this purpose, the composite specimens were first fabricated by injection molding process, followed by further drilling tests, which were performed with and without ultrasonic vibration. The effect of drilling parameters and ultrasonic vibration was investigated on surface roughness, thrust force and geometrical tolerances (circularity and cylindricity), as the process performance parameters. The obtained results demonstrated that by increase of the spindle rotational speed and decrease of feed rate, the thrust force, surface roughness and geometrical tolerances were reduced. Also, it was seen that ultrasonic vibration could effectively enhance the performance parameters, which was attributed to the intermittent cutting process and impact action of ultrasonic vibration, leading to reduced friction, improved material removal, reduced cutting forces, and better surface quality. [ABSTRACT FROM AUTHOR]

A novel eco-friendly composite material made of polyurethane derived from castor oil reinforced with long cotton fibers was developed. A set of comparative analyses comprising static and dynamic tests was established using specimens made of castor oil-based polyurethane reinforced by glass fibers, and epoxy reinforced by glass and cotton fibers. The manufacturing method and estimation of fiber volume fraction of the specimens were described in detail. Tensile and flexural tests were performed to evaluate the mechanical performance of the novel laminate. Fractographic post-mortem examinations assessed the quality of the fiber–matrix interaction and allowed direct observation of the failure modes. Surface treatment of natural fibers appears necessary to improve the adhesion of the natural fibers to the matrix. Dynamic responses are discussed, considering natural frequencies and modal damping coefficients. In this context, the potentialities and the limitations of using the novel eco-friendly composite material as structural parts are discussed. [ABSTRACT FROM AUTHOR]

In the search for high-performance parts and structures, especially for the aviation and aerospace industry, metal matrix composites appear with prominence. However, despite exhibiting high levels of mechanical properties and low densities, these materials are still very expensive, mainly due to complex production. Thus, this work aims to present and evaluate a novel way of manufacturing metal matrix composites, with relative low cost and complexity: by using low-energy fusion welding to deposit the matrix material on top of continuous metal wire reinforcement. For proof of concept, Al alloy was used as matrix material, a single Ti alloy wire as reinforcement, and gas metal arc welding CMT-Pulse® as the process for material deposition. The simplified Al–Ti composite was evaluated in terms of impact resistance and tensile strength and stiffness. Overall, the mechanical performance of the composite was around 23% higher than that of the matrix material itself (Al), this with only about 2% of reinforcement volume and just over 3% of increase in weight. Analyses of the Al–Ti composite fractures and cross-sections and of chemical composition and hardness of the matrix–reinforcement transition interface indicated the preservation (no melting) of the Ti wire and the existence of a fine contour of bonding between matrix and reinforcement. At the end, a brief discussion on the dynamics of the wire reinforcement preservation is carried out based on high-speed filming. [ABSTRACT FROM AUTHOR]

The mechanical performance of a silica-based mineral nano-coating applied to alkali-resistant glass textile-reinforced composite materials aimed at structural strengthening is investigated experimentally. The silica nano-film is directly applied to the alkali-resistant glass fabric by sol–gel deposition. Two lime mortars are adopted as embedding matrix, which differ by the ultimate compressive strength and elongation. Uni-axial tensile tests of prismatic coupons are carried out according to the ICC AC434 guidelines. Remarkable strength and ductility enhancements could be observed in the silica-coated group, as compared to the uncoated group, for both mortar types. Digital image correlation, electron scanning and optical microscopy provide evidence of improved interphase strength. X-ray diffraction of the anhydrous mortars brings out the role of the mineralogical composition of the embedding media on the overall bonding properties of the composites. Consideration of design limits and energy dissipation capabilities reveals the crucial role of matrix ductility in bringing the contribution of interphase enhancement to full effect. We conclude that best performance requires optimizing the pairing between fabric-to-matrix adhesion and matrix ductility. [ABSTRACT FROM AUTHOR]

The present work deals with the hygrothermal aging of the bolt joints prepared from glass fiber reinforced plastics. To investigate the effect of nanoclay on joint performance, nanoclay content was varied from 0 to 5 wt%, with laminates prepared from 3 wt% of nanoclay content demonstrating the best mechanical properties. Nanoclay acts as a mechanical interlock between the fiber and the epoxy and thus improves the interfacial bonding. A good dispersion of nanoclay also improves moisture barrier properties which in turn reduces the degradation of the composite material hygrothermal conditions. Bolt joints were prepared from woven glass fiber reinforced laminates incorporating 3 wt% of nanoclay content. To design the bolt joint, ASTM D5961 was used and the geometric parameters, i.e. edge distance to hole diameter (E/D) ratio and width to hole diameter (W/D) ratio were fixed to 5 and 6, respectively. Three different temperatures, i.e. 25℃, 50℃ and 75℃ were considered for the aging to three different duration of exposure, i.e. 1, 2 and 3 weeks. The effect of different levels of bolt torque, i.e. 0, 2 and 4 Nm were considered for the failure analysis of the joint. A full factorial design of experiment was conducted on important control factors, i.e. water temperature, exposure time, bolt torque and material variation. It was found that the hygrothermal conditions degraded the material with temperature as the most contributing factor. [ABSTRACT FROM AUTHOR]

The composite material was obtained by chemical vapor deposition growth of carbon nanotubes on the surface of aluminum particles followed by high-temperature compaction under pressure. The content of carbon nanotubes was 1 wt.%. A composite material with a hardness of 58–60 HB, which is two times higher than the hardness of original aluminum with an adjustable thermal conductivity of 50–150 W/(m × K) and with a low density of 2.7 g/cm3 have been obtained. It was found that the hardness and thermal properties could be adjusted depending on the temperature during hot pressing by controlling the formation of Al3C4 carbide. [ABSTRACT FROM AUTHOR]

A comprehensive experimental parametric study is performed to investigate the electro-mechanical response of novel three-dimensional conductive multi-functional carbon/epoxy composite materials. Three-dimensional conductive network is generated by embedding multi-wall carbon nanotubes in the epoxy matrix and reinforcing short carbon fibers between the carbon fabric laminates. An open mold compression method is utilized to fabricate the composite materials. Wet electro-up-flocking technology is employed to reinforce 150-µm and 350-µm length carbon fibers vertically at varying densities (500, 1000, 1500, 2000 fibers/mm2) between each laminate to analyze the effects these parameters have on electrical resistivity, tensile properties, and electro-mechanical response to quasi-static tensile loading. A high-resolution four-point circumferential ring probe is used to obtain electrical measurements. The resistivity of the composites having 150 µm flocked carbon fibers did not show significant change with increase in flock density; however, composites of 350-µm length carbon fibers showed a clear decrease in resistivity by a factor of 10 when the flock density increased from 500 to 2000 fibers/mm2. The electro-mechanical response of composites without short carbon fibers is inconsistent and jagged compared to that of flocked composites. The composites having 350-µm long carbon fibers showed a longer duration of initially decreasing resistance due to the applied tensile load when compared to that of 150 µm flocked carbon fibers. However, composites with no short carbon fibers registered maximum value of percentage change in resistance at the break point of tensile loading. [ABSTRACT FROM AUTHOR]

The textile industry generates a large amount of byproducts that must be treated before being recycled or disposed of. The treatments to extract the dyeing agents are mandatory, and involve costs and interaction with toxic reagents. A relevant amount of such byproducts are short cotton dyed fibers. Cotton fibers are high-quality cellulosic fibers and can be used as composite reinforcement. In this paper, dyed cotton fibers were used to formulate, obtain and tensile test composite materials. The impact of the presence of dyes was studied and such dyes enhanced the interphase between the matrix and the reinforcement. On the other hand, when a coupling agent was incorporated to the formulation of the composites, the dyes hindered the chemical interactions between the maleic acid and the OH groups of the cellulosic fibers. Nonetheless, the composite materials showed competitive mechanical properties that were better than other natural fiber-reinforced composites and comparable to some glass fiber-based ones. Dyed cotton fibers can be used as reinforcement without further treatment, increasing the value chain of the textile industry and decreasing the chemical treatments necessary to recycle or dispose of dyed textile fibers. [ABSTRACT FROM AUTHOR]

Voids, the most studied type of manufacturing defects, form very often in processing of fiber-reinforced composites. Due to their considerable influence on physical and thermomechanical properties of composites, they have been extensively studied, with the focus on three research tracks: void formation, characteristics, and mechanical effects. Investigation of voids in composites started around half a century ago and is still an active research field in composites community. This is because of remaining unknowns and uncertainties about voids as well as difficulties in their suppression in modern manufacturing techniques like out-of-autoclave curing and parts with high complexity, further complicated by increased viscosity of modified resins. Finally, this is because of the increasing interest in realization of more accurate void rejection limits that would tolerate some voidage. The current study reviews the research on formation, characterization, and mechanical effects of voids, which has been conducted over the past five decades. Investigation and control of void formation, using experimental and modeling approaches, in liquid composite molding as well as in prepreg composite processing are surveyed. Techniques for void characterization with their advantages and disadvantages are described. Finally, the effect of voids on a broad range of mechanical properties, including inter-laminar shear, tensile, compressive, and flexural strength as well as fracture toughness and fatigue life, is appraised. Both experimental and simulation approaches and results, concerning voids' effects, are reviewed. [ABSTRACT FROM AUTHOR]

The paper presents an experimental analysis of the anisotropic effects of the structural advanced carbon fiber sheet molding compound composites (AC-SMCs) subjected to quasi-static and fatigue loading. Two configurations of AC-SMC composites (randomly oriented and highly oriented) considering three different orientations (0°, 45°, 90°) with respect to the material thermo-compression flow direction are investigated under quasi-static and fatigue tensile loading. The effects of fibers orientation induced by the thermo-compression process are analyzed in terms of ultimate strength, elastic modulus, and macroscopic damage corresponding to the stiffness reduction, and related to the quasi-static and fatigue behavior. For both loading conditions, the macroscopic damage of AC-SMC randomly oriented exhibits a two-stage evolution without any damage saturation prior to the samples' failure. In addition, the difference between the highly oriented and randomly oriented configurations is pronounced especially for the 45° and 90° orientations. Post-mortem X-ray radiography and SEM observations show that damage mechanisms such as microcracks appear between and inside bundles, and their occurrence depends on the sample orientation. Experimental findings are compared with those of an equivalent advanced glass fiber reinforced sheet molding compounds composite. The degree of anisotropy is more pronounced for AC-SMC. Indeed, the dependency of the behavior during the manufacturing process induces orientation. Furthermore, the damage evolutions of the two types of SMCs have displayed different kinetics, especially for the saturation stage which is not observed for the AC-SMC composite. [ABSTRACT FROM AUTHOR]

Punch shear in unidirectional composites is induced by transverse shear loading that progressively perforates the laminate within a narrow shear annulus. At lower micromechanical length scales, punch shear loading creates unique micromechanical damage mechanisms dominated by transverse fiber shear failure, fiber–matrix interphase debonding and large inelastic deformation and cracking of the matrix. A new punch shear experimental method has been developed to test unidirectional S glass/DER353 epoxy composite ribbons at sub-millimeter length scale. The experimental data consist of a statistical measurement of the continuum response (load-deformation and punch shear strength) and the characterization of micromechanical damage modes. A simplified 2D micromechanical finite element model incorporating Weibull fiber strength distribution has been developed and correlated with the experimental data. The 2D micromechanical finite element model can simulate the punch shear failure of the ribbon incorporating mixed mode fiber fracture, and fiber–matrix debonding mechanisms using zero thickness cohesive elements. Results from stochastic simulations of punch shear experiments show that an equivalent 2D micromechanical finite element model can predict the micromechanical damage mechanisms and the statistical distribution of punch shear strength of the continuum with favorable correlation with the experiments. This paper presents a combined experimental and computational approach in simulating the stochastic non-linear progressive punch shear behavior of unidirectional composites for the first time in the literature. [ABSTRACT FROM AUTHOR]

Punch shear in unidirectional composites is induced by transverse shear loading that progressively perforates the laminate within a narrow shear annulus. At lower micromechanical length scales, punch shear loading creates unique micromechanical damage mechanisms dominated by transverse fiber shear failure, fiber–matrix interphase debonding and large inelastic deformation and cracking of the matrix. A new punch shear experimental method has been developed to test unidirectional S glass/DER353 epoxy composite ribbons at sub-millimeter length scale. The experimental data consist of a statistical measurement of the continuum response (load-deformation and punch shear strength) and the characterization of micromechanical damage modes. A simplified 2D micromechanical finite element model incorporating Weibull fiber strength distribution has been developed and correlated with the experimental data. The 2D micromechanical finite element model can simulate the punch shear failure of the ribbon incorporating mixed mode fiber fracture, and fiber–matrix debonding mechanisms using zero thickness cohesive elements. Results from stochastic simulations of punch shear experiments show that an equivalent 2D micromechanical finite element model can predict the micromechanical damage mechanisms and the statistical distribution of punch shear strength of the continuum with favorable correlation with the experiments. This paper presents a combined experimental and computational approach in simulating the stochastic non-linear progressive punch shear behavior of unidirectional composites for the first time in the literature. [ABSTRACT FROM AUTHOR]

The research work reported in this paper involves investigation of the mechanical and durability performance of unstressed and stressed Tokyo Rope carbon-fiber composite cables for prestressing applications. This research is critical in order to establish the critical (allowable) stress and safety factors for the use of carbon-fiber composite cable tendons for prestressed precast-concrete members. The carbon-fiber composite cable specimens were exposed to simultaneous high alkali environment and sustained loading at different elevated exposure temperatures (22℃ and 60℃) for 3000, 5000, and 7000 h. The high alkali environment (12.8 pH) simulated the concrete pore solution and the elevated temperature was used to accelerate the aging process. The applied sustained stress on the carbon-fiber composite cable strands was equivalent to 40% and 65% of their guaranteed tensile strength. This was achieved through testing 171 carbon-fiber composite cable specimens subjected to stress levels of 0%, 40%, and 65% of their guaranteed strength, under tensile load. Also, 136 carbon-fiber composite cable specimens were tested to investigate the transverse shear strength. In addition, the durability characteristics of the constituent materials of the carbon-fiber composite cable strands were assessed to understand the long-term behavior of these materials. The results showed the effect of sustained stress on the degradation of carbon-fiber composite cable strands. Under sustained stress of 40% and 65%, the reductions in tensile strength were 10.6% and 12.3%, respectively. Scanning electron microscope results on epoxy resin indicated that no degradation is detected since the surface remains smooth without any pitting or loose material. [ABSTRACT FROM AUTHOR]

The present paper explores different techniques for increasing flexural performance of composite sandwich panels made of hand-layup glass fiber reinforced polymer skins and low density closed cell polyurethane foam core. An experimental program compares the performance of simple panels face to the use of transversal and longitudinal internal glass fiber reinforced polymer ribs and the installation of a strain hardening cementitious base composite top layer over the panels. Based on the experimental results, finite element models are also developed to simulate the flexural behavior of tested panels and conducted an in depth analysis of the techniques studied. Obtained experimental and numerical results show that the use of internal glass fiber reinforced polymer ribs (especially in longitudinal direction) along with the use of strain hardening cementitious base composite significantly and effectively increases the flexural performance of sandwich panels. The high stiffness to weight ratio capacity of the panels attained by applying the proposed method enables its use in rehabilitation of historical places. Furthermore, the proposed techniques could be helpful for strengthening available composite sandwich panels. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the hygrothermal effect on fatigue behavior of quasi-isotropic carbon/epoxy plain weave aerospace laminates containing artificial flaw under axial tension–tension loading. Dry and wet specimens were tested at tensile load-controlled cyclic loading with a stress ratio R = 0.1 and a load frequency of 7 Hz at room temperature (RT) and at 82℃ under different stress levels. Allowable stiffness change as a failure criterion was used to determine the delamination propagation onset threshold under cyclic tensile loading at each environmental condition. The delamination propagation onset was verified using the ultrasonic imaging (C-Scan) technique. The experimental results show that (1) fatigue life of CFRP specimens was more individually affected by moisture than by temperature and (2) combined moisture and temperature cause a drastic decrease in fatigue life. Finally, an investigation of the effect of hygrothermal conditions on stiffness degradation and damage of composite laminates subjected to tensile fatigue loading has been also carried. On the basis of the residual stiffness degradation, a damage variable was presented and phenomenological damage models were proposed by employing fatigue modulus and secant modulus concepts as measure of material damage. [ABSTRACT FROM AUTHOR]

The effect of a thermal treatment, i.e. annealing, on the adhesion of a thermoplastic polyurethane overmolded on a precoated steel substrate was evaluated. The hybrid part was subjected to three different annealing temperatures after the overmolding process. Adhesion of the thermoplastic elastomer was achieved by using an in-house-developed, two-step curable organic powder coating, which was selectively crosslinked to a polyallophanate state. The powder material was applied to the steel substrate by electrostatic charging followed by molecular crosslinking in an oven. The influence of the metal surface pretreatment was also evaluated regarding adhesion. The effects of the postthermal treatment were assessed through mechanical peel test, differential scanning calorimetry, atomic force microscopy, and scanning electron microscopy. Interesting results were obtained regarding strong adhesion between the precoated metal sheets and thermoplastic polyurethane after injection molding, especially in hybrids that were annealed at higher temperatures with the in-house adhesive coating. [ABSTRACT FROM AUTHOR]

A single-ply unidirectional IM7/8552 carbon fiber reinforced plastic composite with artificially introduced circular defects is subjected to dynamic tensile loading using a modified Kolsky tension bar. A high-speed X-ray phase contrast imaging method is integrated with the Kolsky bar setup to record the crack initiation from the defects and subsequent propagation in the material in real time during the tensile loading. The tensile loading was applied either in longitudinal (0° to fibers) or transverse (90° to fibers) direction of the specimens. Shear failure of the matrix and axial splitting along the loading/fiber direction were observed in longitudinal specimens to initiate from the edge of the artificial circular defects. Debonding of fiber and matrix was observed in transverse specimens, which initiated from the top and bottom edge of the hole. The dynamic tensile loading history during the crack propagation was recorded using a piezoelectric load cell and synchronized with the observed damage and failure processes. [ABSTRACT FROM AUTHOR]

Three-dimensional fiber-reinforced foam cores may have improved mechanical properties under specific strain rates and fiber volumes. But its performance as a core in a composite sandwich structure has not been fully investigated. This study explored different manufacturing techniques for the three-dimensional fiber-reinforced foam core using existing literature as a guideline to provide a proof of concept for a low-cost and easily repeatable method comprised of readily available materials. The mechanical properties of the fiber-reinforced foam were determined using a three-point bend test and compared to unreinforced polyurethane foam. The foam was then used in a sandwich panel and subjected to dynamic loading by means of a gas gun (103 s−1). High-strain impact tests validated previously published studies by showing, qualitatively and quantitatively, an 18–20% reduction in the maximum force experienced by the fiber-reinforced core and its ability to dissipate the impact force in the foam core sandwich panel. The results show potential for this cost-effective manufacturing method to produce an improved composite foam core sandwich panel for applications where high-velocity impacts are probable. This has the potential to reduce manufacturing and operating costs while improving performance. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymer composites have been around for many decades but recently their use has started to increase in multiple industries such as automotive, aerospace, and construction. The conventional composite manufacturing processes such as wet lay-up, resin transfer molding, automatic lay ups etc. suffer from a lot of practical and material issues which have limited their use. The mechanical properties of the parts produced by such processes also suffer from variation that causes problems downstream. Composites based additive manufacturing processes such as Fused Deposition Modeling and Composite Filament Fabrication are trying to remove some of the barriers to the use of composites. Additive manufacturing processes offer more design and material freedom than conventional composite manufacturing processes. This paper compares conventional composite processes for the manufacturing of Epoxy-Fiberglass fiber reinforced polymers with composite filament fabrication based Nylon-Fiberglass fiber reinforced polymers. Mechanical properties such as tensile strength, elastic modulus, and fatigue life are compared for the different processes. The effect of process parameters on these mechanical properties for the composite filament fabrication based process is also examined in this work. It is found that the composite filament fabrication based process is very versatile and the parts manufactured by this process can be used in various applications. [ABSTRACT FROM AUTHOR]

The one-dimensional structure of carbon nanotubes makes them highly anisotropic, making them to possess unusual mechanical properties, and hence employed as promising nanofiller for the composite structures. However, various carbon nanotube properties are not completely utilized when they are used as reinforcement in composites due to inadequate and immature processing techniques. In the present work, an attempt has been made to utilize the strong anisotropic nature of multi-walled carbon nanotubes (MWCNTs) for improving the fatigue life of nanocomposites only by considering a very low weight percentage (<0.5 wt%). The anisotropy of MWCNTs was imparted into the nanocomposites by aligning them in the epoxy matrix with DC electric field during composite curing. Nanocomposites were made for three MWCNT loadings (0.1, 0.2, and 0.3 wt%). The tensile fatigue behavior was investigated under stress control by applying cyclic sinusoidal load with the frequency range of 1-3 Hz and stress ratio, R=0.1. The specimens were tested for the fatigue load until the failure or 1E+05 cycles. The fractured surfaces were examined through scanning electron microscope to analyze the fatigue fracture behavior. A small weight percentage of MWCNT loading (0.2 wt%) into the polymer composite has enhanced on an average 13% to 15% fatigue life, which is encouraging to develop the low cost, improved fatigue life composite structures. Also, the energy dissipation mechanism in MWCNT dispersed nanocomposites has shown a reduced crack propagation rate. [ABSTRACT FROM AUTHOR]

The present paper explores a new modular floor prototype to be used in emergency houses. The prototype is composed of a frame structure made of glass-fibre-reinforced polymer tubular pultruded profiles, a slab made of sandwich panels with a polyurethane foam core and glass-fibre-reinforced polymer skins, and a tailored connection system that provides integrity between assembled components. A series of experimental tests are carried out including flexural tests on a single panel, on two and three connected panels, and on the assembled floor prototype. The behaviour of the panels is analysed when they are not considered part of the glass-fibre-reinforced polymer framed structure, namely the failure mechanisms and the efficiency of the proposed connection system between the panels. The performance of the floor prototype to support typical load conditions of residential houses is also assessed. Additionally, an analytical model was used to deeper study the behaviour of the developed sandwich panels, connection system and the modular floor prototype. [ABSTRACT FROM AUTHOR]