Search Results (1,441)

Multiwalled carbon nanotube (MWCNT) nanopaper (NP)-reinforced in-mold coating (IMC) nanocomposites were fabricated by dip soaking without organic solvent. The thermally activated IMC resin was selected to provide electromagnetic interference shielding protection for sheet molding compound (SMC) material as well as other plastic materials due to the proven good adhesion of IMC resin to the substrate. In this work, the technical feasibility of a continuous fabrication process was evaluated for a nanopaper/IMC (NP/IMC) composite. The curing behavior of the candidate IMC resin was studied for a better understanding of the fabrication of NP/IMC nanotape as a prepreg (with 10% polymerization), as well as the final curing once the nanotape was applied to the substrate. The required limiting maximum temperature to prevent curing during infiltration was established. This allows the fabrication of multilayer nanotape or coatings by stacking several layers of tape to improve the EMI shielding protection. To be specific, the average EMI shielding effectiveness for a one-layer composite was 21 dB, while it increased to 48 dB on average for a six-layer composite. Full article

This study used a hybrid combination of kenaf and hemp fibers and the multi-walled carbon nanotube (MWCNT) reinforcements in the matrix phase to synthesize the composites. A kenaf/hemp fiber blend with MWCNTs in epoxy was used for the specific concentration. The procedure used three composite materials chosen from pilot trials. The ratio of MWCNT filler particles was altered up to the agglomeration limit based on initial trials. Two specimens (2 and 3) were supplemented with MWCNTs in a concentration range of 0.5 wt. % to 1 wt. %, with the fiber concentration being maintained in equilibrium with the epoxy resin, all of the materials were tested under the same conditions. The hybrid nanocomposite was characterized for its morphological and mechanical properties; the tensile properties were higher for 1% MWCNTs concentration (specimen 2), while the flexural properties were higher for 0.5% MWCNTs, with values of 43.24 MPa and 55.63 MPa, correspondingly. Once the MWCNT concentration was increased to 1 wt. %, the maximum impact strength was achieved (specimen 3). In the limits of the Shore-D scale, the kenaf fiber and hemp fiber matrix composite (specimen 1) gained a hardness index of 84. Scanning electron microscopy was carried out to analyze the morphological features of the fractured samples and to assess the adhesion between the fiber, matrix, and surface. Among the various fillers tested, the kenaf fiber/hemp/MWCNT composite (specimen 3) demonstrated superior binding and reduced the incidence of fiber pull-out, breakage, and voids. In addition to the comparative analysis, the addition of 0.5 wt. % MWCNTs resulted in better mechanical properties compared to the other two combinations. Full article

Research on polymer nanocomposite nanofibers has seen remarkable growth over the past several years. One of the main driving forces for this progress is the increasing applicability of polymer nanocomposite nanofibers for technological applications. This review basically aims to present the current state of manufacturing polymer/graphene nanofiber nanocomposites, using appropriate techniques. Consequently, various conducting and thermoplastic polymers have been processed with graphene nano-reinforcement to fabricate the nanocomposite nanofibers. Moreover, numerous methods have been adopted for the fabrication of polymer/graphene nanocomposites and nanofibers including interfacial polymerization, phase separation, freeze drying, template synthesis, drawing techniques, etc. For the formation of polymer/graphene nanocomposite nanofibers, electrospinning can be preferable due to various advantages such as the need for simple equipment, control over morphology, and superior properties of the obtained material. The techniques such as solution processing, melt spinning, and spin coating have also been used to manufacture nanofibers. Here, the choice of manufacturing techniques and parameters affects the final nanofiber morphology, texture, and properties. The manufactured nanocomposite nanofibers have been examined for exceptional structural, microstructure, thermal, and other physical properties. Moreover, the properties of polymer/graphene nanofiber rely on the graphene content, dispersion, and matrix–nanofiller interactions. The potential of polymer/graphene nanocomposite nanofibers has been investigated for radiation shielding, supercapacitors, membranes, and the biomedical field. Hence, this review explains the literature-driven significance of incorporating graphene in polymeric nanofibers. Conclusively, most of the studies focused on the electrospinning technique to design polymer/graphene nanofibers. Future research in this field may lead to advanced innovations in the design and technical applications of nanocomposite nanofibers. To the best of our knowledge, research reports are available on this topic; however, the stated literature is not in a compiled and updated form. Therefore, field researchers may encounter challenges in achieving future advancements in the area of graphene-based nanocomposite nanofibers without first consulting the recent literature, such as an assembled review, to gain necessary insights, etc. Consequently, this state-of-the-art review explores the manufacturing, properties, and potential of polymer/graphene nanocomposite nanofibers. Full article

This research attempts to investigate the thermal performance of solar air collectors with pin fins and turbulators. Incorporating carbon-nanotube-based fins and turbulators in solar collectors can enhance their performance due to their high thermal conductivity, low weight, and high aspect ratio. In the present study, numerical analyses of a solar collector with pin fins and turbulators are carried out to investigate its effect on the Nusselt number. The paper begins with the numerical analysis of conventional air collectors and compares them with theoretical results. This is followed by numerical analyses, which are carried out to examine different configurations of the absorber plate with pin fins of varying diameters (10 mm, 20 mm, and 30 mm) and turbulators of varying heights (20 mm, 40 mm, and 60 mm) in the base plate. The analyses include variations in the Reynolds number ranging from 3000 to 15,000. Subsequently, after the performance of the solar collector with pin fins is evaluated, the effect of turbulators of varying heights on the Nusselt number is analyzed, followed by the analysis of the combined effect of pin fins and turbulators. The results are compared with traditional solar collectors and show that the combined effect of pin fins and turbulators can significantly improve the thermal performance of solar air collectors. The findings of this study can contribute to the development of renewable energy-based air conditioning, ventilation, and heating systems. Full article

Statistical based reconstruction methods and signal processing tooling techniques are implemented and used to detect delaminations or debondings within composite complex items with very high precision. From the literature, it appears that although a single procedure for the estimation of structural health is a fast solution, multiple analyses based on different reconstruction methods or different damage parameters are the way to achieve maturation assessments of the methodology. This highlights the fact that the hardware and software parts of an SHM system need two different assessment and maturation ways. This work focuses on the software part by proposing a way to start assessing the outcomes. In this paper, the damage detection and localization strategy in CFRP plate-like structures with elastic guided waves excited and acquired with a circular array PWAS network is considered. Previous outcomes are compared by new analyses using a new post-processing approach based on a cross-correlation-based technique in terms of the BVID (Barely Visible Impact Damage) surface position and its center of mass. The advantage of this specific study is hopefully to enable confidence in the transition from R&D to field implementation. In addition, this work tries to evidence an improvement in terms of cost efficiency and reduced complexity while maintaining the same accuracy. Full article

High-density polyethylene (HDPE) is a highly versatile plastic utilized in various applicative fields such as packaging, agriculture, construction, and consumer goods. Unfortunately, the extensive use of polyethylene has resulted in a substantial accumulation of plastic waste, creating environmental and economic challenges. Consequently, the recycling of polyethylene has become a critical concern in recent times. This work focuses on the recycling of HDPE parts recovered from end-of-life boats into materials suitable for the marine environment with additive manufacturing technology via screw-assisted extrusion 3D printing. In particular, rigid materials are obtained by adding glass fibers to HDPE to mitigate the loss of mechanical performance upon recycling. Eventually, the properties obtained with two different production methods were compared, namely compression molding and screw-assisted extrusion 3D printing. Since the developed materials will be exposed to an aggressive environment, an extended thermos-mechanical characterization (including fatigue resistance) and investigation of the stability to UV exposure were performed. Full article

Among conducting polymers, polythiophene has gained an important stance due to its remarkable physical features. Graphene is a unique, two-dimensional, nanocarbon nanomaterial. As in other polymers, graphene has been reinforced in polythiophene to form advanced nanocomposites. This comprehensive review covers the design, essential features, and methodological potential of significant polythiophene and graphene-derived nanocomposites. In this context, various facile approaches, such as in situ processing, the solution method, and analogous simplistic means, have been applied. Consequently, polythiophene/graphene nanocomposites have been investigated for their notable electron conductivity, heat conduction, mechanical robustness, morphological profile, and other outstanding properties. Studies have revealed that graphene dispersion and interactions with the polythiophene matrix are responsible for enhancing the overall characteristics of nanocomposites. Fine graphene nanoparticle dispersal and linking with the matrix have led to several indispensable technical applications of these nanocomposites, such as supercapacitors, solar cells, sensors, and related devices. Further research on graphene nanocomposites with polythiophene may lead to remarkable achievements for advanced engineering and device-related materials. Full article

Polymeric floating photocatalysts based on polyethylene (PE)/TiO₂ compositions were synthesized by in situ ethylene polymerization in the presence of a titanium–magnesium catalyst synthesized by the sequential deposition of a magnesium–aluminum complex and TiCl₄ on commercial TiO₂ P25. The optical band gap of the synthesized PE/TiO₂ composites was shown to be 3.1–3.3 eV, which allowed for their use as photocatalysts for the utilization of solar light. The photocatalytic activity of the PE/TiO₂ composites was studied for the degradation of methyl orange (MO) under irradiation with UV light (λ_max = 384 nm). The composites containing 20–50 wt.% of PE were found to have an optimum combination between floatability and photocatalytic activity. The maximum photodegradation rate was observed at an MO concentration below 5 ppm. The polymeric PE/TiO₂ floating photocatalysts could be used repeatedly, but the long-term exposure of the composites to UV radiation was accompanied by oxidation of the polymer. Full article

Coupled shear walls (CSWs) are structural elements used in reinforced concrete (RC) buildings to provide lateral stability and resistance against seismic and wind forces. When subjected to high levels of seismic loading, CSWs exhibit nonlinear deformation through cracking and crushing in concrete and yielding in reinforcements, thereby dissipating a significant amount of energy, leading to their permanent deformation. Externally bonded fiber-reinforced polymer (EB-FRP) sheets have proven to be effective in strengthening RC structures against various loading and environmental conditions. In addition, their high strength-to-weight ratio makes them an attractive solution as they can be easily applied without significantly increasing the structure’s weight. This study investigates the effectiveness of using EB-FRP sheets to reduce residual displacement in CSWs during severe earthquake loadings. Two series of 15-story and 20-story CSWs in Western and Eastern Canadian seismic zones, which serve as representative models for medium- and high-rise structures, were evaluated through nonlinear time history analysis. The numerical simulation of all CSWs and strengthened elements was carried out using the RUAUMOKO 2D software. The findings of this study provided evidence of the effectiveness of EB-FRP sheets in reducing residual deformation in CSWs. Additionally, significant reductions in the rotation of the coupling beams (CBs) and the inter-story drift ratio were observed. The results also revealed that bonding vertical FRP sheets to boundary elements and confining enhancement by wrapping CBs and wall piers is a very effective configuration in mitigating residual deformations. Full article

The purpose of this study was to reveal the effect of printing direction and post-printing conditions on static and fatigue bending characteristics of Ultem 9085 at two stress levels. Right after the printing, the Ultem samples were subjected to three cooling conditions: cooling in the printer from 180 to 45 °C for 4 h, rapid removal from the printer and cooling in the oven from 200 to 45 °C during 4 h, and removal from the printer and cooling at room temperature. Static 3-point bending tests were performed to estimate the flexural characteristics of Ultem 9085 samples after subjecting them to different post-printing conditions. The flexural strain was evaluated and applied for the stress ratios such as 75% and 50% of σ_max. Thus, displacement-controlled fatigue tests were carried out to reveal the effect of post-printing conditions on fatigue bending characteristics. The results obtained for the X and Y printing directions proved that the Ultem samples subjected to the cooling conditions in the printer and the oven had a similar static and fatigue behavior, while a lower performance was obtained for the samples cooled at room temperature. Regardless of the cooling regime, significantly lower bending performance was revealed for the samples printed in the Z-direction since they have intra-layer filaments parallel to the stress plane, and, accordingly, intra-layer adhesion has a crucial influence on mechanical performance. Full article

In the context of energy efficiency and resource scarcity, lightweight construction has gained significant importance. Composite materials, particularly sandwich structures, have emerged as a key area within this field, finding numerous applications in various industries. The exceptional strength-to-weight ratio and the stiffness-to-weight ratio of sandwich structures allow the reduction in mass in components and structures without compromising strength. Among the widely used core designs, the honeycomb pattern, inspired by bee nests, has been extensively employed in the aviation and aerospace industry due to its lightweight and high resistance. The hexagonal cells of the honeycomb structure provide a dense arrangement, enhancing stiffness while reducing weight. However, nature offers a multitude of other structures that have evolved over time and hold great potential for lightweight construction. This paper focuses on the development, modeling, simulation, and testing of lightweight sandwich composites inspired by biological models, following the principles of biomimetics. Initially, natural and resilient design templates are researched and abstracted to create finished core structures. Numerical analysis is then employed to evaluate the structural and mechanical performance of these structures. The most promising designs are subsequently fabricated using 3D printing technology and subjected to three-point bending tests. Carbon-fiber-reinforced nylon filament was used for printing the face sheets, while polylactic acid (PLA+) was used as the core material. A honeycomb-core composite is also simulated and tested for comparative purposes, as it represents an established design in the market. Key properties such as stiffness, load-bearing capacity, and flexibility are assessed to determine the potential of the new core geometries. Several designs demonstrated improved characteristics compared to the honeycomb design, with the developed structures exhibiting a 38% increase in stiffness and an 18% enhancement in maximum load-bearing capacity. Full article

Polymer-based composites represent a special class of materials in demand by the industry. In comparison with other polymers, ultra-high molecular weight polyethylene (UHMWPE) is characterized by exceptionally high wear and impact resistance. There are different technologies for producing bulk material from UHMWPE powder and from its mixtures with various reinforcing additives. In this work, samples for research were made by cyclic impact compaction (CIC), graphene nanoplatelets and single-walled carbon nanotubes (SWCNTs) were the reinforcing nanofillers. Nanoscale detonation carbon (NDC) produced by the detonation decomposition of acetylene was employed as a graphene nanofiller. The obtained samples were subjected to a wear test, and their hardness and tensile strength were measured. Studies have shown that the reinforcement of UHMWPE with NDC and SWCNTs leads to an increase in its hardness by 6.4% and 19.6%, respectively. With the same nanofillers, the wear resistance when rubbing against a steel ball rises by 1.13 and 1.63 times, and the coefficient of friction drops by 10% and 20%, respectively. Meanwhile, the tensile strength of UHMWPE drops by 11.7% and 40.4%, and the elongation by 11.9% and 30.1% when reinforcing UHMWPE with NDC and SWCNTs, respectively. Full article

Human society’s need to build low-weight, high-strength and durable structures has increased the demand for composite materials. In this case, composites are used where high mechanical strength, low weight, sound and thermal insulation properties are required. One of the most important issues now is designing materials and coatings aimed at reducing heat loss and resisting high temperatures. One way to address this problem is to develop a technique for preparing and applying composite materials that slow down their heating applied to a surface. In this study, carbon nanotubes (CNTs) reinforced composites were fabricated using silicone molding to be applied to honeycomb sandwich structures. To determine the effect of CNTs on the thermal behavior of the sandwich panels, different weight percentages of this material (0.025, 0.05. 0.075 wt.%) were added to the epoxy resin. The results showed that the thermal stability of the epoxy composites was directly related to the increase in the percentage of CNTs as the CNT content increased to 0.075 wt.%, and the thermal degradation temperature of the epoxy composites increased by 14 °C. In addition, the energy absorption increased by 4.6% with an increase in CNTs up to 0.075 wt.%. Density measurements showed that the density of the nanocomposite samples increased by adding CNTs to pure epoxy resin. The actual densities of the samples reinforced with 0.025, 0.05, and 0.075 wt.% CNTs are 0.925, 0.926, and 0.927 of the theoretical density, respectively. Since the CNT dispersion uniformity in the epoxy matrix can significantly affect the properties of the composites, in this study, a new method of dispersing CNTs in the epoxy resin matrix resulted in higher thermal conductivity while using lower amounts of CNTs compared to other studies. The storage modulus of the epoxy matrix composites reinforced with 0.05 wt.% in this study was 25.9% and 6.9% higher than that from the previous study reinforced with 0.1 wt.% and 0.25 wt.% CNTs, respectively. Furthermore, the tanδ and loss modulus of the composite reinforced with 0.05 wt.% CNTs in this study were 52% and 54.5% higher than that from the previous study with 0.1 wt.% CNTs, respectively. This study provided an optimal approach for designers and engineers who want to effectively design their composite honeycomb sandwich structure with better thermal properties. Full article

This paper presents an experimental analysis of the tensile behavior of unidirectional carbon/epoxy prepreg, focusing on the nonlinearity observed at the beginning of the stress–strain curve. Due to the material’s high viscosity, securely holding specimens during testing was challenging, prompting modifications in the gripping method to ensure reliable data. By using a longer gauge length, the slippage impact on elastic modulus measurement was minimized, resulting in good repeatability among the test samples. Experimental findings highlighted the significant interaction between fiber waviness and the viscous matrix, leading to stiffness reduction. The linear stiffness of the samples closely matched that of the fibers and remained unaffected by temperature variations. However, at higher temperatures, the epoxy matrix’s decreased viscosity caused an upward shift in the stiffness plot within the non-linear region. To support the experimental findings, a micromechanical model of prepreg tow with fiber waviness was proposed. An RVE model of periodically distributed unidirectional waved cylindrical fibers embedded within the matrix was developed to predict effective material stiffness parameters. The simulation outcomes aligned well with the uniaxial tensile test of the prepreg tow, demonstrating the proposed RVE model’s capability to accurately predict elastic properties, considering factors like fiber arrangement, waviness, and temperature. Full article

Stress evaluation plays a pivotal role in the design of material systems, often accomplished through the finite element method (FEM) for intricate structures. However, the substantial costs and time requirements associated with multi-scale FEM analyses have prompted a growing interest in adopting more efficient, machine-learning-driven strategies. This study investigates the utilization of advanced machine learning techniques for predicting local stress fields in composite materials, presenting it as a superior alternative to traditional FEM approaches. The primary objective of this research is to develop a predictive model for stress field maps in composite components featuring diverse configurations of fibers distributed within the matrix. To achieve this, we employ a Convolutional Neural Network (CNN) with a specialized U-Net architecture, enabling the correlation of spatial fiber organization with the resultant von Mises stress field. The CNN model was extensively trained using four distinct data sets, encompassing uniform fibrous structures, non-uniform fibrous structures, irregularly shaped fibrous structures, and a comprehensive combination of these data sets. The trained U-Net models demonstrate exceptional proficiency in predicting von Mises stress fields, yielding impressive structural similarity index scores (SSIM) of 0.977 and mean squared errors (MSE) of 0.0009 on a dedicated test set. This research harnesses 2D cross-sectional imagery to establish a surrogate model for finite element analysis, offering an accurate and efficient approach for predicting stress fields in composite material design, irrespective of geometric complexity or boundary conditions. Full article