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In the study, acoustic emission (AE) technique was applied to monitor polymer failures. Specimens produced of two aluminum flat bars bonded together with a thick layer of cured epoxy resin were subjected to double cantilever beam (DCB) test. Epidian 5 epoxy resin cured with PAC curing agent as well as Epidian 53 epoxy resin cured with Z1 curing agent were used as adhesives. However, a special procedure of specimens preparation was needed which was elaborated by authors after preliminary research including aditional analysis of surface roughness parameters and surface free energy of aluminum flat bars. Acoustic emission system was then used to register AE signal parameters during fracture test: frequency of elastic waves emitted inside the material, number of hits (event), number of counts, energy and amplitude. Next, the obtained AE parameters were deeply analyzed and compared to the results of mechanical test and authors' previously conducted examinations. Moreover, a special emphasis was put on applicability of wawelet transform (WT) as well as numerical simulation for fracture analysis was conducted. [ABSTRACT FROM AUTHOR]

This article aims to assess the suitability of natural neem gum in various composite material applications in place of epoxy resin. The assessment was done by thermal characterisation, experimental study and comparative analysis of thermal behaviour, Fourier transform IR spectroscopy (FTIR) characterisation and comparison of functional groups and mechanical properties of neat epoxy and neat neem resins. To study and compare thermal behaviour differential scanning calorimetry (DSC), thermogravimetric (TG) and relative derivative TG (DTG) analysis were conducted. The glass transition temperatures, exothermic and endothermic peaks, curing of thermosetting epoxy and crystallisation of polymeric neem, value of % cure and mass change or mass loss concerning temperature of both the resins were experimentally determined and comparative analysis was conducted to find the suitability of neem resin in composite material applications in place of epoxy resin. Functional groups of neem gum were identified and mechanical properties such as bond strength, toughness, rigidity and ductility were characterised and compared with that of epoxy resin by conducting FTIR. [ABSTRACT FROM AUTHOR]

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Summary: This research proposes a novel low‐cost aperture coupled elliptic patch nanoantenna which works best when it has a stable radiation pattern and good gain. On the upper portion of the substratum, a cross‐shaped hole was additionally engraved from a metallic strip with a silver composition. Elliptical‐shaped silicon material is employed as a patch in this antenna design which is made on a substrate made of inexpensive glass epoxy. The silver substance makes up the nanometallic strip line at the substrate's base. A cross‐shaped hole has also been etched from a metallic strip with a silver composition on the upper section of the substrate. As the foam substrate to be used in between the feed and antenna substrates, Rohacell was adopted. A proposed simple cross‐shaped aperture enhanced the bandwidth of the planned antenna without degrading its radiation performance and is loaded on a proximity‐linked elliptical microstrip antenna. To achieve the highest coupling, the lowest back radiation, the least amount of spurious radiation, and good efficiency, the patch and feed line are positioned in the middle, at a right angle over the slot. The proposed antenna was simulated in HFSS, and optimum results were observed from the output. The results were evaluated based on radiation pattern, return loss, smith chart, radiation efficiency, and 3D polar plot for 300, 500, and 800 THz frequencies. Also, the impedance bandwidth, gain, and a number of bands were compared with other conventional methods and our proposed method proved to outperform the existing method in all aspects. [ABSTRACT FROM AUTHOR]

Conventional pressure-type anchoring systems face challenges such as difficulty in recovery, low recovery efficiency, and insufficient durability over long-term use. Although the single-use cost of Carbon Fibre Reinforced Polymer (CFRP) strand anchors is higher than that of conventional steel strands, recovery and reuse can significantly reduce costs. Therefore, this study aims to investigate the bonded anchoring method of CFRP and proposes an innovative thermoplastic CFRP prestressed strand design that combines both anchoring strength and recoverability to address the shortcomings of existing anchoring systems. Two bonding materials, thermosetting resin and thermoplastic resin, were selected for bond strength tests under different conditions. The results indicated that epoxy resin had a bonding force of 280 kN and an anchoring efficiency of approximately 70%, making it the most suitable material. However, the anchoring efficiency still needs improvement. Based on this, an improved design scheme was proposed, which can increase anchoring efficiency to over 95%. Additionally, based on the dispersed bonding anchor system, this study explored a solution that involves adding a positioning plate at the end of the anchor strand and using epoxy resin for anchoring. The anchoring performance tests showed that the tensile strength of the CFRP strand ranged from 2.7–2.8 GPa, with an average anchoring efficiency of 100.5%, demonstrating excellent anchoring performance. Further thermoplastic recovery tests showed that when the temperature increased to 90°C, the maximum recovery force of the strand was 17.2 kN, about 4.4% of the ultimate load. When the temperature increased to 150°C, the maximum recovery force was 7.5 kN. The recovered CFRP strands were clean, with no resin residue, and had no damage, maintaining an intact structure. The proposed thermoplastic CFRP prestressed strand design demonstrates significant advantages in anchoring strength and recoverability. With the improved design, anchoring efficiency can be increased to over 95%, and the high-temperature recovery process shows good feasibility. Compared with traditional anchoring systems, CFRP strands offer higher anchoring efficiency, lower recovery force requirements, better economics, and sustainability, making them a promising solution for engineering applications. [ABSTRACT FROM AUTHOR]

Braided composites are gaining attention in the most industrial applications. To design rods with optimal tensile properties against combined loads, experimental studies were conducted to investigate the effect of using axial yarn and core in different categories on the tensile properties of braided reinforced composite rods. In this study, six types of braided composite rods with different arrangements of braid components (axial yarn or core type) were produced using glass and polyester fibers with epoxy resin as the matrix. The elastic modulus, ultimate tensile strength, and work of fracture of these rods were tested, and the experimental elastic modulus of samples were compared with previously developed models. Moreover, comparing the stress-strain results of the samples revealed that the produced hybrid samples demonstrate pseudo-ductile tensile behavior, showing varying trends as the type of reinforcement is altered. The results indicate that using a double-layer triaxial braid as reinforcement for the composite can increase the elastic modulus up to 13% compared to the similar single-layer sample. Additionally, employing a double-layer triaxial braid as reinforcement for the composite leads to a greater work of fracture. However, in terms of ultimate tensile strength, biaxial braid reinforcement demonstrates better performance in reinforcing the composite rods. [ABSTRACT FROM AUTHOR]

[Display omitted] Thermoset epoxy resin-based materials are widely used, but their permanent cross-linked network limits their processability and reusability, which can lead to environmental burdens. In this work, by exploiting the weak reactivity of aniline to design appropriate reaction ratios, we achieved a linear link between the epoxy resin and the curing agent. This linear link, along with the crosslinking points provided by the flexibly branched polyurethanes, avoids the inherent brittleness associated with the highly crosslinked network of conventional epoxy resins. As a result, the adhesive exhibits extraordinary improvements in extensibility and toughness. The lap shear strength, tensile strength and elongation at break reach 11.9 MPa, 14.4 MPa and 607 %, respectively. The fracture toughness is as high as 109.6 kJ/m2, far beyond the existing epoxy adhesives. The synergistic effect of disulfide bonds and hydrogen bonds confers the adhesive with self-healing and repeatable bonding characteristics. The multi-level hydrogen bonding and appropriate phase separation structure are key to optimizing toughness, resulting in excellent comprehensive performance. The introduction of polyurethane not only improves toughness but also enhances the interfacial bonding force between the adhesive and the substrate, broadening the scope of applications. The prepared high-performance polymers provide new insights into reusable epoxy adhesives. [ABSTRACT FROM AUTHOR]

Establishment of high‐performance epoxy resin with satisfactory fire safety, mechanical properties, and excellent transparency is urgently desirable, but still remains significant challenges. Herein, a super‐tough yet high flame retardant epoxy resin (EP/BTD) was designed and prepared by incorporating bi‐DOPO structure and hydrogen‐bonding networks. Although the phosphorus content was only 0.69 wt% (10 wt% of bi‐DOPO flame retardant [BTD]), EP/BTD‐10 showed a high limiting oxygen index value (33.4%), satisfactory UL‐94 rating (V‐0), and good heat suppression ability (total heat release [THR] and peak heat release rate [PHRR] reduced to 29.0% and 42.2%, respectively). Furthermore, the flame retardant mechanism of EP/BTD was illustrated and attributed to dual‐phase fire‐retardant effect. Additionally, EP/BTD‐7.5 featured notably mechanical properties, of which the tensile strength, elongation at break and impact strength increased by 44.6%, 40.0%, and 232.6%, respectively, due to hydrogen‐bonding network and π–π interaction. More importantly, EP/BTD maintained high visible light transmittance and excellent UV‐blocking properties. In summary, this work provided a guidance for the development of high‐performance epoxy resin and was expected to expand the practical applications. [ABSTRACT FROM AUTHOR]

In the research on amino acids as bio‐based curing agents for epoxy resins, L‐tryptophan and L‐tyrosine have emerged as promising alternatives. Understanding the curing reactions and reaction kinetics is crucial for designing an appropriate curing regime to tailor the mechanical properties of thermosets. This study provides a comprehensive analysis of the curing reactions, curing kinetics, and latency of epoxy resin cured with L‐tryptophan or L‐tyrosine in the presence of urea‐based accelerators. L‐tryptophan involves three distinct curing reactions, corresponding to its three functional groups, while data on L‐tyrosine as a curing agent is less definitive. The degree of cure can be reliably predicted using model‐free kinetics for all resin systems studied. Overall, the inclusion of accelerators facilitates rapid curing at elevated temperatures while maintaining adequate processability for up to four weeks of storage at room temperature. [ABSTRACT FROM AUTHOR]

Low toughness and brittleness limit its application range of thermosetting epoxy resin (EP) based foams. In current research, inorganic particles are commonly utilized as heterogeneous nucleating agents to enhance foaming quality and EP toughness. However, the increasing inorganic particle content usually leads to particle agglomeration, which negatively impacts foaming quality and reduces EP performance. Block copolymers, which appear as liquid to effectively mitigate agglomeration, are employed as toughening materials for EP. In this study, a small number of modified calcium silicate particles (MCS) were used as anchor points to induce the distribution of block copolymers (P‐F68) to improve EP toughness and effectively enhance cell nucleation, thus, EP/MCS/P‐F68 foams performance was improved. The research results showed that EP foams obtained excellent cell structure and very small foam density (0.256 g/cm3) at the P‐F68 content of 10 wt%. The continuous increase of P‐F68 content would lead to the thickening of cell wall and the increase of cell size. Simultaneously, the core‐shell structure formed by P‐F68 in EP effectively enhanced the toughness of EP foams and mitigated its brittleness, offering crucial theoretical guidance for toughening and regulating the cell structure of EP foams. [ABSTRACT FROM AUTHOR]

In order to enhance the flame retardancy of epoxy resin (EP) without affecting its mechanical properties, a phosphorus‐nitrogen synergistic flame retardant (MPCD) was synthesized in this paper by using melamine, paraformaldehyde, 9,10‐dihydro‐9‐oxa‐10‐phospha‐phenanthrene‐10‐oxide (DOPO) and cashew phenol as the raw materials, which was applied to the Ep in order to improve its flame retardancy and toughness. Experiments have shown that only 5% content of MPCD added into the EPs could achieve a significant LOI of 35.8% and successfully obtained a V‐0 rating in UL‐94 testing. In contrast, the PHRR with 5% additional MPCD was 456.4 kW/m2 and the THR was 80.2 MJ/m2, which were 52.6% and 29.4% lower than that of pure EPs, respectively. The PHRR of pure EPs was 963.1 kW/m2 and THR was 113.6 MJ/m2, which indicated that the addition of MPCD improved the EP system's flame retardant performance. The impact strength of pure EPs was 13.5 KJ/m2, and 5% addition of MPCD resulted in a 99% increase in the impact strength of EP/MPCD cured samples up to 26.9 KJ/m2, which was explained by the cashew phenol moiety's flexible chain segments. Furthermore, it is discovered by researching its flame‐retardant mechanism that the addition of MPCD may significantly improve the carbon layer's capacity to form char and maintain thermal stability. It can also efficiently trap free radicals and dilute the combustible gases produced during combustion. The flame retardant can increase the overall safety of the EP system by acting as a biphasic flame retardant in both the gas and the solidified phases at the same time. [ABSTRACT FROM AUTHOR]

Epoxy resin (EP), as a widely used polymer material, is inherently flammable. Imparting it with high-efficiency flame-retardant properties has always been the focus of attention. In this work, using triallyl isocyanurate (TAIC) and 9,10-dihydro-9-oxa-10-phospha phenanthrene-10-sulfide (DOPS) as raw materials, a novel double-group flame retardant, tris(3-(9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-sulfide)-propyl)triazine-2,4,6-trione(DOPS-TAIC), has been synthesized via a one-step method. Before curing, the structure was characterized by FT-IR, 1H NMR, and 31P NMR. Subsequently, the flame retardant DOPS-TAIC was applied to EP, and a series of testing methods were employed to investigate the effects of DOPS-TAIC on the thermal stability, flame retardancy, and mechanical properties of EP. Furthermore, the flame retardant mechanism of DOPS-TAIC in the gas phase and condensed phase was further explored. The results showed that EP/DOPS-TAIC achieved a UL-94 V-0 rating with an LOI value of 31.6% when added at 12.5 wt%. In addition, the total heat release, peak heat release rate, and average heat release rate (av-HRR) of EP/DOPS-TAIC-12.5 wt% were significantly reduced by 35.05%, 61.83%, and 51.68%, respectively. SEM-EDS results showed that DOPS-TAIC can effectively promote the generation of expanded dense char layers and retain flame retardant elements (P and S) in the char layer. Meanwhile, TG-IR and Py-GC/MS demonstrate their radical quenching effect in the gas phase, indicating that DOPS-TAIC possesses both condensed-phase and gas-phase flame-retardant mechanisms. Therefore, this study provides a simple and effective method for developing flame-retardant epoxy resins. [ABSTRACT FROM AUTHOR]

The objective of the present work was to prepare hybrid epoxy composites with improved mechanical and thermal properties. The simultaneous use of two different modifiers in an epoxy resin was motivated by the expected occurrence of synergistic effects on the performance properties of the matrix. Such a hybrid composite can be used in more severe conditions and/or in broader application areas. Hybrid epoxy composites were prepared with polyurethane (PUR), Nanomer nanoclay and carbon nanotubes (CNT), followed by the evaluation of their mechanical and thermal properties. Synergistic improvements in mechanical properties of hybrid composites were observed for 0.5 wt% Nanomer and 1 wt% carbon nanotubes (CNT), 7.5 wt% PUR and 1 wt% CNT, and 5 wt% PUR and 1 wt% CNT, confirming the occurrence of synergistic effects as to the impact strength (IS) of the matrices, compared to binary systems. The toughening induced by CNT/Nanomer modifiers can be attributed to the specific interfacial interactions between the two nanoparticles, while in the case of CNT/PUR, it can be explained by the combined effects of flexible polymer chains and the specific arrangement of nanoparticles in epoxy systems. Spectroscopy analysis confirmed the occurrence of interaction between OH groups in the epoxy matrix with CNT and reactive groups of PUR. The fracture surface showed plastic deformations, with good dispersion of CNT, explaining the improved mechanical properties of the matrix composites. [ABSTRACT FROM AUTHOR]

This paper deals with the design of novel epoxy adhesives by incorporating thermoplastic polymers such as polyetherimide (PEI) and poly(ε-caprolactone) (PCL) into a bio-based and recyclable epoxy resin, known as Polar Bear. The adhesives were characterized by their mechanical (quasi-static and dynamic) and rheological properties, thermal stability, and adhesion properties in single-lap joints tested at three different temperatures (i.e., −55 °C, 23 °C, 80 °C). The experimental results indicated that low PEI content substantially improved the mechanical performance and toughness of the adhesive, while preserving good processability. Nonetheless, exceeding 3% weight percentage adversely affected the adhesives' mechanical resistance and workability. Conversely, while PCL addition enhanced the adhesives' viscosity, it also decreased mechanical performance. However, its eco-friendliness offers potential for sustainable adhesive applications. It is worth noting that regardless of temperature, the modified adhesives consistently outperformed the commercial epoxy adhesive (DP-460), used as reference, in single-lap shear joint tests. Additionally, both PEI- and PCL-modified epoxy adhesives have demonstrated recyclability through a simple acid-based process, enabling joint disassembly and recycling of the adhesive into a thermoplastic polymer. Overall, the modified adhesives represent a promising eco-friendly, high-performance alternative for structural applications, aligning with sustainable and circular practices. [ABSTRACT FROM AUTHOR]

Multifunctional polymer composites containing micro/nano hybrid reinforcements have attracted intensive attention in the field of materials science and engineering. This paper develops a multi-phase analytical model for investigating the effective electrical conductivity of micro-silicon carbide (SiC) whisker/nano-carbon black (CB) polymer composites. First, CB nanoparticles are dispersed within the non-conducting epoxy to achieve a conductive CB-filled nanocomposite and its electrical conductivity is predicted. Some critical microstructures such as volume percentage and size of nanoparticles, and interphase characteristics surrounding the CB are micromechanically captured. Next, the electrical conductivity of randomly oriented SiC-containing composites in which the nanocomposite and whisker are considered as the matrix and reinforcement phases, respectively, is estimated. Influences of whisker aspect ratio and volume fraction on the effective electrical conductivity of the SiC/CB-containing polymer composites are explored. Some comparison studies are performed to validate the accuracy of the model. It is observed before the percolation threshold that the addition of nanoparticles with a uniform dispersion can improve the electrical conductivity of the polymer composites containing SiC/CB hybrids. Moreover, the results show that the electrical conductivity is more enhanced by the decrease in nanoparticle size. Interestingly, the composite percolation threshold is significantly reduced when SiC whiskers with a higher aspect ratio are added. This work will be favorable for the design of electro-conductive polymer composites with high performances. [ABSTRACT FROM AUTHOR]

Recycling end-of-life wind turbines poses a significant challenge due to the increasing number of turbines going out of use. After many years of operation, turbines lose their functional properties, generating a substantial amount of composite waste that requires efficient and environmentally friendly processing methods. Wind turbine blades, in particular, are a problematic component in the recycling process due to their complex material composition. They are primarily made of composites containing glass and carbon fibers embedded in polymer matrices such as epoxies and polyester resins. This study presents an innovative approach to analyzing and valorizing these composite wastes. The research methodology incorporates integrated processing and analysis techniques, including mechanical waste treatment using a novel compression milling process, instead of traditional knife mills, which reduces wear on the milling tools. Based on the differences in the structure and colors of the materials, 15 different kinds of samples named WT1-WT15 were distinguished from crushed wind turbines, enabling a detailed analysis of their physicochemical properties and the identification of the constituent components. Fourier transform infrared spectroscopy (FTIR) identified key functional groups, confirming the presence of thermoplastic polymers (PET, PE, and PP), epoxy and polyester resins, wood, and fillers such as glass fibers. Thermogravimetric analysis (TGA) provided insights into thermal stability, degradation behavior, and the heterogeneity of the samples, indicating a mix of organic and inorganic constituents. Differential scanning calorimetry (DSC) further characterized phase transitions in polymers, revealing variations in thermal properties among samples. The fractionation process was carried out using both wet and dry methods, allowing for a more effective separation of components. Based on the wet separation process, three fractions—GF1, GF2, and GF3—along with other components were obtained. For instance, in the case of the GF1 < 40 µm fraction, thermogravimetric analysis (TGA) revealed that the residual mass is as high as 89.7%, indicating a predominance of glass fibers. This result highlights the effectiveness of the proposed methods in facilitating the efficient recovery of high-value materials. [ABSTRACT FROM AUTHOR]

Epoxy resins are extensively employed as adhesives and matrices in fibre-reinforced composites. As polymers, they possess a viscoelastic nature and are prone to creep and stress relaxation even at room temperature. This phenomenon is also responsible for time-dependent failure or creep fracture due to cumulative strain. Several constitutive equations have been used to describe the mechanical time-dependent response of polymers. These models have been proposed over the past six decades, with minimal direct and practical confrontation. Each model is associated with a specific application or research group. This work assesses the predictive performance of four distinct time-dependent constitutive models based on experimental data. The models were deemed sufficiently straightforward to be readily integrated into practical engineering analyses. A range of loading cases, encompassing constant strain rate, creep, and relaxation tests, were conducted on a commercial epoxy resin. Model parameter calibration was conducted with a minimum data set. The extrapolative predictive capacity of the models was evaluated for creep loading by extending the tests to five decades. The selected rheological models comprise two viscoelastic models based on Volterra-type integrals, as originally proposed by Schapery and Rabotnov; one viscoplastic model, as originally proposed by Norton and Bailey; and the Burger model, in which two springs and two dashpots are combined in a serial and parallel configuration. The number of model parameters does not correlate positively to superior performance, even if it is high. Overall, the models exhibited satisfactory predictive performance, displaying similar outcomes with some relevant differences during the unloading phases. [ABSTRACT FROM AUTHOR]

Carbon-fiber-reinforced polymers (CFRPs) with epoxy matrices are widely applied in high-performance structural applications and represent one of the biggest classes of materials with urgent need for end-of-life management. Available waste management methodologies for conventional thermoset composites with a focus on CFRPs are briefly reviewed and their limitations are highlighted. In the quest to obtain materials with mechanical performance, thermal stability, and sustainability, the research community has turned its interest to develop polymer composites with adaptable and dynamic networks in their matrix, and lately also at an interface/interphase level. The current review focuses on the life extension/waste management options that are opened through the introduction of covalent adaptable networks in the epoxy matrix of CFRPs. The processing conditions that are applied for the healing/repairing, welding/reshaping, and/or recycling of CFRPs are presented in detail, and compared based on the most common dynamic exchange reactions. [ABSTRACT FROM AUTHOR]

Epoxy nanocomposites are widely used in various applications because of their excellent properties. Different types of manufacturing techniques are used to produce epoxy composites based on various fillers, molecular weight, and applications required. The physical properties and chemical structure of epoxy resin help in determining the method for its manufacturing. Coatings and adhesive formulations are prepared using high- molecular-weight epoxies, whereas epoxy nanocomposites require low-molecular-weight epoxies due to ease of manufacturing. A low-molecular-weight epoxy can provide high crosslink density to the epoxy but may also cause inherent brittleness in epoxy nanocomposites. Further, the addition of CNTs may also cause more brittleness in the final product. In this work, the authors have developed a method to process composites based on high-molecular-weight epoxy reinforced with high loading of CNTs (15 wt.%). The high molecular weight will bring lots of challenges during manufacturing. In this paper, a novel manufacturing technique based on separate molding and curing conditions to produce highly concentrated CNT-filled epoxy with high-molecular-weight epoxy resin is described, achieving excellent mechanical properties, good toughness, and high electrical conductivity in an efficient, low-cost, environmentally friendly, and high-volume way. The findings demonstrated improvements in these mechanical properties compared to conventional systems. They also highlight the potential of the novel method to develop advanced composite materials which can revolutionize industrial sectors such as aerospace, automotives, and electronics where structural integrity and thermal stability are important. [ABSTRACT FROM AUTHOR]

The range of sensor technologies for structural health monitoring (SHM) systems is expanding as the need for ongoing structural monitoring increases. In such a case, damage to the monitored structure elements is detected using an integrated network of sensors operating in real-time or periodically in frequent time stamps. This paper briefly introduces a new type of sensor, called a Customized Crack Propagation Sensor (CCPS), which is an alternative for crack gauges, but with enhanced functional features and customizability. Due to those characteristics, it is necessary to develop a family of computer-aided supporting models for rapid prototyping and analysis of the new designs of sensors of various shapes and configurations, which this paper presents by use of simulation tools. For a prototyping of the sensor lay out, an algorithm is elaborated, based on an application created in LabVIEW 2022 software, which generates two spreadsheets formatted by the requirements of Autodesk Inventor 2014 and COMSOL Multiphysics 5.6 software, based on data entered by the user. As a result, a tailored-in-shape CCPS layout is prepared. A parametric model of the sensor is prepared in Autodesk Inventor software, which automatically changes its geometric dimensions after changing data in an MS Excel spreadsheet. Then, the generated layout is analyzed to obtain electromechanical characteristics for defined CCPS geometry and materials used in the COMSOL Multiphysics software. Another application is devoted to purely mechanical analysis. The graphical user interface (GUI) add-on based on the Abaqus 2018 software engine is prepared for advanced mechanical analysis simulations of sensor materials in selected loading scenarios. The GUI is used for entering material libraries and the selection of loading conditions and a type of specimen, while the results of the numerical analysis are delivered through Abaqus. The main advantage of the developed GUI is the capacity for personnel inexperienced in using the Abaqus environment to perform analysis. Some results of simulation tests carried out in both COMSOL Multiphysics as well as Abaqus software are delivered in this paper, using a predefined parametric sensor model. For example, using a rigid epoxy resin for an insulating layer shows a negligible difference in the level of strain compared to the structure during a simulated tensile test, specifically in the tested layer thickness range of up to 0.3 mm. However, during bending tests, an approx. 17% change in principal strain level can be observed through the top to bottom edge of the epoxy resin layer. The adopted methodology for carrying out simulation studies assumes the parallel use of a set of various computer-aided tools. This approach allows for taking advantage of individual software environments, which allows for expanding the scope of analyses and using the developed models and applications in further research activities. [ABSTRACT FROM AUTHOR]

[Display omitted] • UIO-66-NH 2 /Ti 3 C 2 Tx was synthesized in one step, and UIO-66-NH 2 was used as a tannic acid inhibitor in nanocontainer. • TU-T material has high dispersion in epoxy resin, while giving epoxy coating long-term corrosion resistance and self-healing function. • The TU-T has an intelligent pH response to give the coating a slow release function. In this study, we developed a composite material comprising UIO-66-NH 2 encapsulated tannic acid (TA) loaded on Ti 3 C 2 Tx to improve the corrosion resistance of water borne epoxy (WEP) coatings. The successful synthesis of the material was determined by FT-IR, XRD, XPS, EDS, TGA, SEM and TEM characterization. Furthermore, ultraviolet (UV)tests were conducted to evaluate the release rate of TA at varying pH levels, revealing a release rate of approximately 95 % at pH 2. Electrochemical impedance spectroscopy (EIS) results over 60 d indicated that the R c value of TU-T/WEP remained unchanged at 3.934 × 108, demonstrating a two-order magnitude increase compared to those of pure epoxy coatings, attributed to the synergistic active and passive protection of TU-T materials. The self-healing ability of the TU-T/WEP coating was validated through manual scratch experiments. Additionally, the EIS test showed that the R c value of TU-T/WEP coating increased to 3.5 × 105 after 72 h, representing a two-order magnitude increase over that of the WEP coating alone. This study introduces a novel approach using green tannic acid as a corrosion inhibitor and amino-functionalized Ti 3 C 2 Tx with UIO-66-NH 2 to enhance corrosion resistance and self-healing aproperties of coatings. [ABSTRACT FROM AUTHOR]

There is a demand to ramp up the rate of production of primary aerostructures and as such new processing methods are required. This study investigates a two-stage process for integrating composite structures. In Stage 1, a series of doublers are infused and semi-cured to a target degree of cure (α). In Stage 2, these doublers are integrated into a preformed stiffened panel, to increase thickness locally, followed by infusion. The impact of this integration on quality in terms of thickness and void content of the semi-cured doublers is assessed through the processing stages. The results indicate that semi-curing elements to a higher degree of cure (α = 0.74) around the gel point (α = 0.70) of the epoxy matrix have minimal impact on the relative quality of the final structure. However, at a lower semi-cure (α = 0.47), the void (> 100 µm) content increased from 0.8 to 1.92% during the secondary stage. Tracking the thermal profile of the semi-cured elements through the stages combined with a Cure-Temperature-Transition diagram shows that at a lower degree of cure, the resin in the semi-cured doublers will be in a liquid phase during Stage 2 leading to the potential for resin reflow. [ABSTRACT FROM AUTHOR]

AbstractFibre-reinforced polymer (FRP) composites are increasingly favoured for strengthening existing structures due to their numerous structural benefits. Nevertheless, the performance of such technology is strongly affected by the behaviour of the epoxy resin adhesive layer, which is largely dependent on its curing conditions. This study introduces a deep learning (DL) framework that leverages eXtreme Gradient Boosting (XGBoost) and genetic programming (GP) to comprehensively study the influence of curing scenarios on the vitreous transition of the adhesive. An experimental dataset comprising 160 data points was used to develop predictive models. The XGBoost models exhibited high predictive accuracy for both the onset vitreous transition temperature and the peak tan δ vitreous transition temperature, achieving R2 values of 0.982 and 0.993 for the unseen test set, respectively. While the GP models exhibited lower predictive accuracy with R2 values of 0.834 and 0.842, they provided explicit equations that enhance the interpretability of the DL model and facilitate practical application. To make these insights accessible to engineers without programming expertise, a web-based graphical user interface software was developed, incorporating all DL models. Additionally, a feature influence assessment was conducted, providing visual representations of the impact of each feature on the output results, thus enhancing interpretability for engineering applications. [ABSTRACT FROM AUTHOR]

In ultra–high voltage converter stations, the phenomenon of flashover along the outer insulation of dry hollow reactors made of epoxy (EP) /glass fiber (GF) composites poses a potential threat to the stability of the power system. To enhance its flashover performance under varying complex conditions, it is necessary to conduct in–depth research on the flashover mechanism of this material under different voltage forms. This study conducted tests on the flashover voltage, surface space charge distribution, and partial discharge (PD) parameters under varying AC–DC ratios and AC frequencies, and exploring their relationships. The results show that the DC content in the AC–DC ratio decreases, the flashover voltage decreases, the apparent total discharge of PDs increases, and the maximum surface space charge density decreases. The main influencing factor is the increase in the number of seed charges involved in gas ionization. Increasing the AC frequency, the flashover voltage decreases, the apparent total discharge increases significantly, and the surface charge density remains basically unchanged. The main reason is that the change in the number of alternating cycles further increases the number of seed charges. This study reveals the flashover mechanism of EP/GF composites under different voltage forms, which provides theoretical support for subsequent material modification. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of fibre-reinforced epoxy composites is strongly influenced by the orientation of reinforcing fibres within the epoxy matrix. Understanding the relationship between fibre orientation, void formation, density, and mechanical properties in fibre-reinforced polymer (FRP) composites is crucial for optimizing their performance. Basalt fibres, known for their superior properties, were integrated into epoxy resin to create composite materials with varied fibre orientations via the hand lay-up method. The composites were fabricated into oneply ((0/90) and (±45)), two-plies (0/90)(±45)) and three-plies ((0/90)(±45)(0/90) and (±45)(0/90)(±45). The addition of basalt fibres increased the composite density, owing to the inherently denser nature of basalt compared to epoxy. When the number of basalt fibre plies is increased to two and three, the density of the composites decreases due to the presence of voids and the trapping of air between the layers of fibres during the process of layering and impregnation. One-ply composites with (0/90) orientation exhibited higher tensile strength and Young's modulus due to fibre alignment with the loading axis, enhancing load resistance. Conversely, (±45) orientation resulted in higher tensile strain, promoting deformation and load distribution in shear. Tensile strength and Young's modulus of two plies of basalt fibre composites lie between those of one-ply composites with (0/90) and (±45) orientations since the (0/90) fibres efficiently resist the applied load along their aligned directions, while the (±45) fibres aid in distributing and absorbing the load in shear, which enhances overall tensile strength and modulus compared to one-ply (±45) composites. In the case of three-plies composites, the composites with two plies oriented in (0,90) demonstrated higher tensile strength and Young's modulus when compared to those with two plies of fibres oriented in (±45). [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review of the published literature on bamboo natural fiber, focusing on its potential as a viable reinforcement for bio-composites. Bio-composites, which incorporate lignocellulosic fibers as reinforcement within a polymer matrix, are emerging both as an effective and sustainable solution to address the growing issue of plastic waste. With an increase in global environmental concerns, there is now an increasing demand for eco-friendly and sustainable materials. Numerous researchers have systematically investigated the use of bamboo fiber, derived from bamboo plants, as a promising reinforcement material. However, there does exist variations in extraction methods, choice of polymer matrices, processing routes, and material characterization techniques. This paper synthesizes the available information on several key aspects to include the following: (i) bamboo fiber extraction methods, (ii) bio-composite processing routes, and (iii) bio-composite characterization techniques. The collection of information does aim at enhancing the prevailing understanding of bamboo fiber-reinforced bio-composites while concurrently highlighting their potential applications. [ABSTRACT FROM AUTHOR]

Replacing thermoset insulation by healable and recyclable covalent adaptable networks is a promising approach to the sustainable development of electrical and electronic devices. However, the repair performance gifted by dynamic covalent bonds always conflicts with the excellent mechanical properties gifted by stiff cross‐linked networks. In this paper, by introducing dynamic thiocarbamate bonds, polythiourethane (PTU) with excellent mechanical properties and electrical insulation comparable to commercial epoxy resins are successfully developed, which exhibit superior healability and recyclability properties. Sub‐centimeter scale electrical breakdown failures of the PTU samples could be efficiently self‐healed with a healing efficiency up to 90%, while the storage modulus and volume resistivity exceeded 2 GPa and 1016 Ω cm, respectively. Even though the electrical breakdown strength inevitably declined after multiple repair processes, PTU samples could restore their initial excellent insulation performance by simply reprocessing with the efficiency above 95%. Moreover, the efficient healability performance of large‐sized electrical breakdown failures remained after the reprocessing. These outstanding characteristics underscore the tremendous potential of PTU materials as a new generation of sustainable high voltage insulation. [ABSTRACT FROM AUTHOR]

Lignin, as an industrial by‐product, can be used as a phenolic substancen. In this study, enzymatic hydrolysis lignin (L) was treated with potassium ferrate and phenol respectively to obtain oxidized lignin (OL) and phenolated lignin (PL). Their phenolic hydroxyl content (PhOH) increased by 29.1% and 40.5%, respectively. Then four kinds of epoxy resins were prepared, namely lignin‐free epoxy resin (LFER), L epoxy resin (LER), PL epoxy resin (PLER), and OL epoxy resin (OLER). Gel permeation chromatography (GPC) and Fourier transform infrared analyses indicated that potassium ferrate oxidation could decline the molecular weight (Mw) and increase the PhOH of L. Mechanical properties test and dynamic mechanical analysis (DMA) results show that cured OLER (OLEN) has higher crosslinking density and better mechanical properties (shear strength increased by 14%, tensile strength increased by 15%) than cured LER (LEN). Thermogravimetric analysis results show that OLEN has better thermal stability than cured LFER (LFEN) and LEN. In addition, scanning electron microscopy images showed that the modified L had better compatibility. This study presents a novel approach for lignin oxidation. [ABSTRACT FROM AUTHOR]

In order to provide long-term anti-corrosion properties of the coatings on the substrate, a microcapsule self-healing coatings system was designed in this paper. Microcapsules were synthesized with ethyl cellulose and octadecyl amine, which were added to epoxy resin to prepare self-healing coatings. The shape of microcapsules was spherical, the average particle size of microcapsules was about 100–120 μm, and the average thickness of microcapsules was 4.43 μm, which was conducive to the preparation of the coatings. The initial evaporation temperature of the microcapsules was 165℃. The ethyl cellulose organic crosslinked shell enhances the strength of the microcapsules and improves the thermal stability of the microcapsules. Electrochemical impedance spectroscopy showed that the impedance of the coatings with 6 wt% microcapsules was about 2.68 × 106 Ω/cm2, which was 2 orders of magnitude higher than that of the coatings without microcapsules (5.23 × 104 Ω/cm2). Scanning electron microscope was used to observe the artificial scratches of the coatings for 24 h, and it was found that the microcapsule could repair the artificial scratches of the coatings well. The results showed that the addition of microcapsules can improve the anti-corrosion properties of the coatings. [ABSTRACT FROM AUTHOR]

Ultrasonic methods are more sensitive to defects such as voids, pores, and discontinuities that can diminish the true elastic and acoustic properties of materials compared to destructive testing. Therefore, the elastic properties and some acoustic properties of the epoxy phenol novolac modified with polystyrene (EPN‐PS) matrix‐based nano‐ and hybrid composites were determined for the first time using ultrasonic method. Montmorillonite‐type nanoclay (NC) and industrial red mud waste (RMW) at a rate of 1–4 and 15–35 wt% respectively, were used as fillers in the composite preparation. According to the results, the highest elastic coefficient values (L = 8.14 GPa, G = 1.76 GPa, K = 5.79 GPa and E = 4.80 GPa) were obtained in the EPN‐PS/NC1 (with 1 wt% NC) nanocomposite sample compared to the elastic properties of pure EPN and EPN‐PS, while the highest elastic coefficient values (L = 8.97 GPa, G = 2.19 GPa, K = 6.06 GPa, and E = 5.86 GPa) among hybrid composites (HC) were obtained for the HC35 containing 2 wt. % NC and 35 wt% RMW. Due to both its high elastic and good acoustic properties, wall panels and floors produced using HC35 hybrid composite can be used for sound insulation in noisy environments. Highlights: First evaluation of the acoustic characteristics of epoxy phenol novolac modified with polystyrene‐nanoclay/red mud waste (EPN‐PS‐NC/RMW) composites.NC4 with 4 wt% nanoclay showed the lowest elastic and acoustic properties.Nanoclay ratio above 1 wt% reduces elastic and acoustic properties.The increasing RMW ratio in hybrid composites increases elastic properties.High elastic and acoustic properties make HC35 ideal for sound insulation. [ABSTRACT FROM AUTHOR]

To improve the subpar lubricating performance of epoxy resin, this paper presents the preparation of a novel bimetallic phyllosilicate featuring a distinctive rice‐granular morphology, which incorporates nickel and iron metal cations through a facile hydrothermal process. These phyllosilicates were then integrated into the epoxy matrix to form composites. A comprehensive analysis of the target product validates the rationality of the synthesis strategy for the as‐prepared rice‐granular bimetallic nickel/iron phyllosilicate, demonstrating a homogeneous hierarchical structure with numerous tiny nanosheets of nickel/iron phyllosilicate grown in situ on the flat surfaces of the rice‐granular metal–organic frameworks. An adequate addition of nickel/iron phyllosilicates allows for excellent dispersion within the matrix and establishes strongly bonded interfaces, steadily increasing the elastic modulus and hardness. Notably, the average friction coefficients decrease from 0.515 for the pure resin to 0.450 for the composites when the filler content reaches 7%, indicating a significant solid lubrication effect. In contrast, adding just 1% nickel/iron phyllosilicate moderately improves wear resistance, elongation at break, and tensile strength. Furthermore, it was found that as the filler content increased, the weight loss rate was reduced by approximately 43.8%, while the residual char increased by 74.2%, significantly enhancing the thermal stability of epoxy composites at high temperatures. This study offers a promising approach to preparing self‐lubricated epoxy composites with favorable mechanical and thermal properties. Highlights: NiFePS was successfully synthesized via a facile two‐step self‐polymerization.Excellent mechanical properties of composites could be achieved with low content of NiFePS.The friction coefficient and wear rate were lowered remarkably.The friction mechanism was solid lubrication. [ABSTRACT FROM AUTHOR]

The interest in natural fiber reinforced polymer composites is rapidly growing in terms of both industrial and domestic applications. The present study is an attempt to improve the mechanical properties of composites made of areca fiber and epoxy resin with the incorporation of alumina filler. The filler was added in various percentages (0wt%, 2wt%, 4wt%, 6wt%, 8wt %) and the composite fabrication was done by compression molding technique. The fabricated composites were tested for tensile, hardness and impact properties. The results demonstrate that 8wt%Al2O3-A-E composite shows superior (tensile, impact, Hardness) mechanical composites. For improvement of hardness and strength main contributing factors were uniform dispersion of Al2O3 (Aluminum oxide) particles and better load transfer between Al2O3 (Aluminum oxide) particles and epoxy matrix. The effect of alkaline treatment of areca of fibers was verified by FTIR analysis. The experimental investigation attempt to improve the Areca epoxy composites by loading fillers and for the applications of light weight and high strength components in different sectors like aerospace and automobiles. Fracture surfaces were analyzed using Scanning Electron micrograph (SEM). [ABSTRACT FROM AUTHOR]

A low-cost fully dicyclopentadiene (DCPD)-networked epoxy system was designed. Compared to commercial diglycidyl ether of bisphenol-A epoxy resin counterparts, the cured DCPD-based resin demonstrates excellent thermal properties (Tg > 250 °C) and a low dissipation factor (0.0065 at 10 GHz), indicating its potential as a promising thermoset for high-performance electronic applications. [ABSTRACT FROM AUTHOR]

Highlights The self‐healing process in PCL (polycaprolactone)/epoxy blends is studied in order to optimize the healing process and understand its underlying mechanism. For this purpose, PCL/epoxy blends are prepared with and without multiwall carbon nanotubes (MWCNTs) addition. Three different self‐healing heat‐inducement techniques are used (an oven, Joule effect, and infrared (IR) lamp) as a function of healing time (2, 5, 10, and 15 min) and PCL concentration (5, 10, and 15 wt%). The results obtained demonstrate that the addition of MWCNTs to the polymer matrix in PCL/epoxy blends accelerates the self‐healing process, attributed to an improved heat diffusion in MWCNTs/PCL/epoxy blends. The best self‐healing results were obtained with the highest self‐healing time and concentration of PCL, caused by the higher probability of the crack formation over a PCL reservoir. The most efficient techniques to induce the self‐healing process in PCL/epoxy blends with and without MWCNTs are the conventional oven and the Joule Effect, respectively, being faster the latter method, as it induces a homogeneous internal heating of the material. Moreover, Joule effect can be controlled remotely, while IR radiation is a noncontact technique, which can be applied in situ. The three heating methods are evaluated considering these factors alongside their energy efficiency, establishing a method to choose a specific heating source for similar systems. PCL/epoxy blends reinforced with MWCNTs have been manufactured. Variable heating sources have been analyzed. The influence of the heating source on the self‐healing is studied. Joule constitutes the faster heating for MWCNTs/PCL/epoxy system. [ABSTRACT FROM AUTHOR]

Piezocomposite ultrasonic transducers (PUTs) are extensively used in diverse technological fields, however, PUTs based on conventional 1–3 piezocomposite containing only one type of piezo pillars have met a bottleneck in further performance enhancement. Herein, based on the [011]‐oriented relaxor ferroelectric Pb(In1/3Nb2/3)O3‐Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PIN‐PMN‐PT) crystal, a novel (1A,1B)‐3 piezocomposite structure containing two types of single‐crystal pillars‐ high d33, kt pillars with square cross‐section (termed as 1A) and high dhgh pillars with rectangular cross‐section (termed as 1B), alternately arranging in epoxy resin and forming a 5 × 9 array are reported. The combination effect and synergistic action of two different piezo‐pillars in the piezocomposite notably broaden the working bandwidth, improve the sound sensitivity, and also produce a suppression effect to undesirable transverse vibration modes. Experimental results validate the performance enhancements of (1A,1B)‐3 composite‐based PUT: the increases in –3 dB transmitting, receiving bandwidth, and receiving sensitivity are 71.4%, 28.6%, and 26.6%, respectively, in comparison to conventional 13 single‐crystal composite‐based PUT. Moreover, its hydrostatic figure of merit (HFOM) dhgh (=4084.9 × 10−15 m2 N−1) is 177.3% higher than that of commercial single crystal 13 piezocomposites. The proposed design strategy represents a promising development direction of next‐generation bandwidth and high‐sensitivity ultrasonic transducers. [ABSTRACT FROM AUTHOR]

Thermal interface materials (TIMs), which consist of polymers and thermally conductive fillers, are crucial for improving heat dissipation. This study examines the impact of surface functionalization of Si₃N₄ thermal conductive fillers on the performance of TIMs. Si₃N₄ fillers are modified with silane coupling agents of varying alkyl chain lengths, producing fillers with contact angles ranging from 25° to 151.2°, thereby ensuring enhanced interfacial compatibility with various polymers. The modified fillers are incorporated into three common polymers—silica gel (SG), epoxy resin (EP), and polyurethane (PU)—to fabricate TIMs. When the contact angle of Si₃N₄ fillers is 73.3°, they demonstrate excellent interfacial compatibility with EP, leading to a 54.37% increase in thermal conductivity and a 162.75% enhancement in elongation at break for the TIM. At a contact angle of 132.7°, the TIMs prepared with SG exhibit an 86.36% increase in thermal conductivity and a 23.88% increase in elongation at break. Given that the original Si₃N₄ already possesses adequate interfacial compatibility with PU, no further modification is required. These findings offer valuable insights for future research aimed at optimizing Si₃N₄ fillers and TIMs to achieve enhanced thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, a novel kind of core–shell microsphere for toughening epoxy resin was developed and investigated. Polyurethane/polythiourethane (PU/PSU)-based core–shell microspheres with polyurethane as the core and polythiourethane as the shell were prepared by dispersion polymerization method via thiol-isocyanate click chemistry. The structure, morphology and particle sizes of PU/PSU core–shell microspheres were investigated by infrared spectroscopy, transmission electron microscopy and scanning electron microscopy. Results showed that the PU/PSU microspheres were successfully fabricated and had a core–shell structure with the particle size of about 0.5–1.5 µm. The PU/PSU core–shell microspheres can be uniformly dispersed in epoxy resin matrix, and the factors which affected the toughening performance of PU/PSU microspheres on the epoxy resin were investigated in detail. When they were used to toughen the epoxy resin, both the tensile strength and impact strength of the epoxy resin can be enhanced simultaneously. When the PU/PSU core–shell ratio was 1:8 and the amount of PU/PSU core–shell microspheres was 8 wt% of epoxy resin, the tensile strength of the epoxy resin toughened by PU/PSU microspheres was 62.5 MPa, which was 1.27 times that of pristine epoxy resin, and the impact strength reached the value of 13.1 kJ/m2, which was 2.47 times that of pristine epoxy resin. This study indicates that PU/PSU core–shell microspheres are a kind of novel toughening agent which may find potential applications in toughening thermosetting resins, such as epoxy resin. [ABSTRACT FROM AUTHOR]

This study reveals that incorporating silane-coupling agents such as KH560, KH590, KH570, and KH550 into the resin matrix can improve the epoxy mechanical performance as well as the interfacial interaction between basalt fibers and modified epoxy. The increasing silane contents slightly increased thermal stability and char yields. The study also found that amino-silane coupling agents, particularly KH550, demonstrated better thermal stability enhancement. Pure epoxy had a Tg of 91.4 °C, while epoxy had modified with 9wt% KH550 exhibited the highest Tg of 98.7 °C. For instance, at 6 wt% concentration of KH560, KH590, KH570, and KH550, the flexural strength of the epoxy matrix increased by 69.4%, 57.6%, 83.4%, and 84.7%, respectively. When the content of KH590, KH570, and KH550 is 9 wt%, the tensile increases by 77.6, 49.0, and 79.6%, respectively. The W-BFs/epoxy composite flexural strength enhanced by 65.3, 81.5, and 74.5%, respectively. The compatibilizing agent would react with the silicon hydroxyl groups on the surface of the basalt fibers, as well as with the epoxide in the resin. This would create a Si-O-Si new bond, which would make the connection between the modified epoxy and the basalt fibers stronger. This process is favored for its cost-effectiveness and user-friendly operation. [ABSTRACT FROM AUTHOR]

Epoxy resins are susceptible to condensation in high humidity environments, leading to flashover discharges that compromise their insulation properties. Hence, investigating the electrohydrodynamic behaviors of droplets on epoxy resin surfaces is crucial for understanding and mitigating such phenomena. By analyzing the droplet dynamics through experiments, this study thoroughly explores the spreading and migration characteristics of droplets under the influence of varying AC voltages. Simulation and numerical models are developed to depict droplet motion and force dynamics, integrating principles of hydrodynamics and electrodynamics. The findings reveal that droplets spread in the direction of the electric field, with the extent of spreading increasing with the increase in voltage. This spreading is influenced by various factors, including the droplet's position, volume, and surface tension. Primarily, the electric field at the droplet's base generates a tangential force that determines its spreading. Furthermore, the droplet tends to move toward the nearer electrode, especially when a tip structure emerges on its surface, facilitating more rapid deformation in that direction. [ABSTRACT FROM AUTHOR]

Atom interferometry shows high sensitivity for inertial measurements in the laboratory, but it faces difficulties in field applications because of a trade-off between sensitivity and size. Therefore, there is an urgent need to develop a small sensor with high resolution for measuring acceleration and rotation in inertial navigation applications. Presented here is a miniaturized inertial sensor capable of measuring acceleration and rotation simultaneously based on high-resolution dual atom interferometers. A sensor head is integrated within a volume of 100 l, in which the vacuum chambers are fabricated by bonding quartz-glass windows with epoxy resin. A photoelectric cabinet is composed of four 3U rack units by integrating optical modules and electronic units. Dual atom interference fringes with a contrast of 29% are observed, and the acceleration and rotation are measured simultaneously by extracting their phase shifts. By developing a temperature compensation method to eliminate phase drifts caused by the thermal deformation of the Raman mirrors and using wave vector reversal to eliminate the phase drifts independent of the direction of the wave vector, measurement resolutions of 40 ng at 518 s and 6.1 nrad/s at 10 880 s are achieved for acceleration and rotation, respectively, from Allan deviations. [ABSTRACT FROM AUTHOR]

There are a large number of steel components in substations/converter stations whose performance is seriously affected by being exposed to environmental corrosion and fire, endangering the operation of the substation/converter station. The current protective measures for steel components in substations/converter stations primarily involve the application of anti-corrosion and fireproof coatings. However, these coatings can easily peel off, resulting in a significant loss of their protective effectiveness. In response to this challenge, a new type of silicone-modified epoxy resin substrate has been synthesized by chemically grafting silicone resin onto epoxy resin segments, which retains the high adhesion of epoxy resin while enhancing its weather resistance. The use of synthesized nano zinc oxide-modified graphene oxide as a fireproof filler significantly improves the physical barrier effect and corrosion resistance of the coating. Additionally, the innovative addition of new metal anti-corrosion active pigments improves the adhesion and impermeability of the coating. Therefore, a steel structure coating for substations/converter stations with both fire and corrosion prevention functions has been developed. Standard tests conducted by national institutions have shown that the coating meets the performance requirements. [ABSTRACT FROM AUTHOR]

In order to increase the thermal conductivity of neat epoxy resin and broaden its practical application in high-voltage insulation systems, we have constructed four kinds of epoxy resin nanocomposite models (a neat epoxy resin (EP), a graphene-doped epoxy resin nanocomposite (EP/GR) and hydroxyl- or carboxyl-functionalized graphene-doped epoxy resin nanocomposites (EP/GR-OH or EP/GR-COOH)) to systematically investigate their thermodynamic and electrical properties using molecular dynamics (MD) simulations. Compared with the EP model, carboxyl-functionalized graphene particles enhanced the thermal conductivity of the EP/GR-COOH model by 66.5% and increased its Tg by 26.6 K. Furthermore, the dielectric constant of the EP/GR-COOH model was significantly reduced. To investigate the intrinsic mechanism, the lowest fraction of free volume (13.22%) and the largest number of hydrogen bonds (102.2) in the EP/GR-COOH model were identified as playing essential roles for its excellent thermodynamic properties and favorable electrical performance. The present study provides a molecular-level understanding of the satisfactory thermodynamic and electrical properties of the EP/GR-COOH nanocomposite, which will aid in designing novel epoxy resin nanocomposite materials with high thermal conductivity. [ABSTRACT FROM AUTHOR]

Cleavable bio-based epoxy resin systems are emerging, eco-friendly, and promising alternatives to the common thermoset ones, providing quite comparable thermo-mechanical properties while enabling a circular and green end-of-life scenario of the composite materials. In addition to being designed to incorporate a bio-based resin greener than the conventional fully fossil-based epoxies, these formulations involve cleaving hardeners that enable, under mild thermo-chemical conditions, the total recycling of the composite material through the recovery of the fiber and matrix as a thermoplastic. This research addressed the characterization, processability, and recyclability of a new commercial cleavable bio-resin formulation (designed by the R-Concept company) that can be used in the fabrication of fully recyclable polymer composites. The resin was first studied to investigate the influence of the different post-curing regimes (room temperature, 100 °C, and 140 °C) on its thermal stability and glass transition temperature. According to the results obtained, the non-post-cured resin displayed the highest Tg (i.e., 76.6 °C). The same post-curing treatments were also probed on the composite laminates (glass and carbon) produced via a lab-scale vacuum-assisted resin transfer molding system, evaluating flexural behavior, microstructure, and dynamic-mechanical characteristics. The post-curing at 100 °C would enhance the crosslinking of polymer chains, improving the mechanical strength of composites. With respect to the non-post-cured laminates, the flexural strength improved by 3% and 12% in carbon and glass-based composites, respectively. The post-curing at 140 °C was instead detrimental to the mechanical performance. Finally, on the laminates produced, a chemical recycling procedure was implemented, demonstrating the feasibility of recovering both thermoplastic-based resin and fibers. [ABSTRACT FROM AUTHOR]

During the thermal aging process of epoxy resin, microcracks, interfacial delamination, and warpage are the key factors leading to semiconductor device damage. Here, epoxy-resin specimens (EP-Ss) and epoxy-resin/silicon-wafer composites (EP-SWs) were prepared to analyze the distribution of residual stress (RS) in epoxy resin and its thermal aging process changes. The uniaxial tensile approach and Raman spectroscopy (RAS) showed that the peak shift of aliphatic C-O in EP-Ss was negatively correlated with the external stress, and that the stress correlation coefficient was −2.76 × 10−2 cm−1/MPa. Then, RAS was used to evaluate the RS distribution of EP-SWs, obtaining a high-resolution stress-distribution image of 50 × 50 pixels and revealing a strong stress concentration at the interface between the epoxy resin and the silicon wafer. Additionally, Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), Field-emission scanning electron microscopy (FE-SEM), and RAS were used to analyze the chemical composition, molecular structure, interfacial microstructure, and RS of the epoxy resin during the thermal aging process. With the increase in the thermal aging time, the epoxy resin underwent secondary curing, the RS at the interface changed from tensile stress to compressive stress, and cracks were formed. The results illuminate the effect of the thermal aging process on the interface-failure mechanism of composite materials, aiding in the reliability evaluation and safety design of semiconductor devices. [ABSTRACT FROM AUTHOR]

In accordance with German guideline ZTV-ING Part 4, full-locked coil ropes are provided with a three-layer corrosion protection coating based on epoxy resin and polyurethane, which must be renewed regularly. An alternative method is to use a coating of high-density polyethylene (HDPE), which is extruded onto the rope. In this article, the mechanical behavior of the thermoplastic material is studied, taking into account various accelerated aging processes, which are derived from the climatic boundary conditions of a real bridge structure and implemented in tests. In addition to the quasi-static material behavior, which is described using the uniaxial tensile test, the cyclic conditioning, relaxation, type of production and oxidation stability are also investigated. Finally, the results obtained are evaluated with regard to the applicability of the material as corrosion protection for full-locked coil ropes. [ABSTRACT FROM AUTHOR]

This study investigates the effect of stress amplitude on the damage sensing characteristic of glass fibre reinforced (GFRP) composites under fatigue loading using the electrical resistance change (ERC) method. The electrical conductivity of GFRP composites was achieved by incorporating 0.3 wt.% multi-walled carbon nanotubes (MWCNTs) into epoxy resin by ultrasonication method. In-situ electrical resistance measurements during fatigue tests of MWCNT-filled GFRP (MWNCT/GFRP) composites were conducted at two different stress amplitudes, S = 0.6 and S = 0.5. The average stiffness losses at failure were observed as 28% and 25% for S = 0.6 and S = 0.5 respectively. The corresponding ERC ratios at failure were found as 153% and 59% for S = 0.6 and S = 0.5, respectively. A two-parameter Weibull analysis, based on the ERC ratios corresponding to 40%, 60%, 80%, and 100% (failure) fatigue life, was implemented to establish reliability curves at the two stress amplitudes. The ERC ratios at failure with a 95% reliability for S = 0.6 and S = 0.5 were determined as 64% and 23%, respectively. Finally, the remaining fatigue life and the stiffness loss of composite specimens at the ERC ratios corresponding to various Weibull reliability were found for both stress amplitudes. [ABSTRACT FROM AUTHOR]

New reaction systems "oxirane – nucleophile X– – proton‐donor reagent AH – solvent" have been proposed for the detection of epoxides in which nucleophilic opening of the oxirane ring occurs accompanied by the formation of a colored product. The kinetic and mechanistic regularities of reactions in the proposed systems were investigated. Reaction orders with respect to the components of the systems have been determined: close to 1 – for oxirane and X−, close to 0 – for AH. It was shown that the proposed chromogenic reactions represent nucleophilic substitution of SN2‐type and allow the detection of epoxides containing both a terminal and internal epoxy group, which can be used to monitor processes in systems where epoxides are either the initial compounds or the synthesis products. Based on the conducted studies, it is possible to develop methods for the quantitative determination of epoxides using kinetic methods of analysis and UV–visible spectroscopy. [ABSTRACT FROM AUTHOR]

Several studies indicate that epoxy resin exhibits a very wide range of mechanical behavior, in particular its strength, as a function of stress state. Especially when epoxy resin is used as matrix material for fiber reinforced composites (FRC), this becomes relevant due to complex stress conditions in the matrix. However, the knowledge about the behavior of epoxy resin under uni, bi, and triaxial stress conditions is lacking. Therefore, the mechanical properties of a typical epoxy resin for the production of FRC were investigated given such load conditions. The determined strengths were compared with the predictions of the extended paraboloid criterion. Uniaxial tension and compression tests, torsion tests with overlaid tension and compression, and triaxial tension tests were performed. An elastoplastic material model and a nonlocal damage model were formulated to demonstrate the application of the extended paraboloid strength criterion. In particular, large plastic strains under shear stress conditions, as well as a perfectly brittle material behavior with significantly reduced strength under triaxial tension, could be shown. [ABSTRACT FROM AUTHOR]

Tissue slices can undergo distortions during processing into resin for light and electron microscopy as a result of differential shrinkage of the various tissue components, and this may necessitate removal of a considerable amount of material from the final resin‐embedded tissue block to ensure production of complete sections of the sample. To mitigate this problem, a number of techniques have been devised that ensure the sample is held flat during the final curing/polymerisation of the resin. For embedding in acrylic resins, oxygen must be excluded as it inhibits polymerisation, and methods devised for epoxy resin embedding are generally unsuitable. The method describes the preparation and use of air‐tight flat‐embedding chambers prepared from Melinex film and provides an inexpensive, technically simpler, and versatile alternative to chambers formed from either Thermanox coverslips or Aclar films that have previously been advocated for such purposes. Lay description: Tissue slices can undergo distortions during processing into resin for light and electron microscopy as a result of differential shrinkage of the various tissue components. Such distortions may necessitate removal of a considerable amount of material to ensure production of complete sections of the sample. For embedding in acrylic resins, oxygen must be excluded as it inhibits polymerisation, and methods devised for epoxy resin flat‐embedding are generally unsuitable. Air‐tight flat‐embedding chambers prepared from either Thermanox coverslips, or a combination of PTFE‐coated glass slides, polycarbonate film gaskets, and Aclar film have been advocated for such purposes. Thermanox coverslips are expensive and limited in size to 22 mm × 60 mm, and the alternative method is technically complicated. Melinex film is commercially available as 210 mm × 297 mm sheets and is approximately 1/20th the price of Thermanox and less than half the price of Aclar film. The method describes the preparation and use of embedding chambers made from Melinex film, glass slides and double‐sided adhesive tape as a technically simpler, inexpensive and versatile alternative to both Thermanox coverslips and the Aclar film method. [ABSTRACT FROM AUTHOR]

To improve the poor tribological performances of the copper alloy used in engine bearings under boundary lubrication and dry sliding wear, a new polymer coating consisting of polyimide/polyamide imide/epoxy resin (PI/PAI/EP), polytetrafluoroethylene (PTFE) and ZrO2 has been designed. The tribological and mechanical characteristics of the coatings at various thicknesses were studied by friction and wear experiments, nanoindentation experiments, simulation experiments of the stress and deformation and fluid-structure coupling simulation tests. The results showed that when the thickness of the coating was 20 μm, the deformation of the coating was the lowest and the friction coefficient of the coating was 0.167. As the thickness of the coating was increased, the support effect of the substrate on the coating decreased, and the thickness of the coating increased under positive pressure. Compared with the substrate, the friction coefficient of the coating under boundary oil lubrication conditions was reduced by 53.85%. The fluid-structure coupling calculation showed that the boundary lubrication and dry sliding wear of the copper alloy were improved by the designed coating. The fluid-structure coupling calculation showed that the peak variation rates of the coating bearing pressure was 0.02%. The coating on the surface of the bearing had little influence on the oil pressure, but at the same time, improved the tribological properties of the engine bearing. [ABSTRACT FROM AUTHOR]