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The bonding performance and formation of the interphase region between fiber and matrix have significant effects on the strength and durability of composites. A new approach, involving combined experimental and numerical analyses, has been developed to avoid the shortcomings and scattering associated with local experimental methods. For this purpose, tensile tests are performed on specimens fabricated from a single glass fiber and epoxy resin. The elongations for specified lengths are measured using the digital image correlation (DIC) technic. The size of the fiber diameter and specimen section are also measured from SEM images. The obtained experimental displacements for micro tensile tests are used in an inverse elastic finite element solution to obtain the interphase elastic modulus. It is shown that, considering the interphase thickness of 1.0 μm that is more realistic, the interphase elastic modulus is in the range of 12 ∼ 19 GPa. However, the performed sensitivity analysis shown that considering interphase thickness ranging from zero to 2.0 μm the interphase elastic modulus varies between 9 and 46 GPa. It is shown that the proposed procedure can be used to obtain the overall mechanical properties of the matrix/fiber interphase in long fiber composites. [ABSTRACT FROM AUTHOR]

Epoxy resin is a thermosetting resin with excellent mechanical properties. It has been pointed out that there are problems on its mechanical properties due to poor polymerization of the epoxy ring caused by water and chlorine impurities during resin production. In this study, we focused on the electrochemical behavior during curing reaction of epoxy resin. To investigate the electrochemical reaction, galvanostat meter was used to measure the voltage behavior during chemical reaction. Molecular Orbital (MO) method was used to understand the mechanisms of voltage behavior during curing reaction. Furthermore, the effect of water existence during curing reaction was investigated by experimentally and analytically. As a result of experimental electrochemical reaction, we successfully measured the voltage behavior associated with the curing reaction. In the case of MO analysis, the epoxy and curing agent models were prepared. Before the reaction, each molecule had zero charge, but after the reaction, it was confirmed that the epoxy had a positive charged and the amine had a negative charged. It is thought that the voltage could be observed due to the movement of this charge during curing reaction. It has been also demonstrated through experimentation and analysis that water accelerates the curing reaction. It was observed that the accelerating effect amplifies as the quantity of water increases. Building upon these results, it was confirmed that the factor leading to the increase in voltage is due to the amount of water. To examine the presence of chlorine impurities during the production of epoxy resin, MO analysis was conducted on the production reaction of epoxy prepolymers. The findings indicated that as the water content increases, the reaction that results in the production of by-products is amplified. This outcome suggested that by-products were already incorporated during the formation of the epoxy. In conclusion, this study provides significant insights into the electrochemical behavior during the curing reaction of epoxy resin, the role of water in accelerating the reaction, and the impact of chlorine impurities during resin production. The findings pave the way for further research to optimize the production process and enhance the mechanical properties of epoxy resin. [ABSTRACT FROM AUTHOR]

The thermoplastic high-ortho phenolic resins (HPRs) were synthesized by a one-step synthesis using phenol, formaldehyde, zinc acetate, sulfuric acid, and small amounts of ethanol. It was then blended with epoxy resins, and a small amount of ethylenediamine (EDA) was added as a curing agent for dry spinning to produce the as-spun fibers. Heat curing and microwave curing treatments were performed to obtain phenolic epoxy fibers. Using Fourier transform infrared spectroscopy to study the structural changes during the fiber curing process revealed that the amino groups in EDA opened the epoxy groups to generate the hydroxyl groups. The hydroxyl groups can further react with the epoxy groups, which accelerate the curing reaction. Thermogravimetric analysis (TGA) results showed a higher residual carbon degree in the fibers after curing. Mechanical property testing demonstrated a significant improvement in the mechanical properties of the fibers. By modifying the blending and optimizing the curing process, the heat resistance of the fibers was successfully improved, resolving the issue of poor mechanical properties in the high-ortho phenolic epoxy fibers (HPEFs). [ABSTRACT FROM AUTHOR]

The resin film infusion (RFI) process is a novel composite molding method for high-fiber content, excellent mechanical properties, low porosity, and adjustable thickness. This review examines two common resin materials used in the RFI process: bismaleimide resin (BMI) and epoxy resin. Furthermore, numerical simulation methods for isothermal and non-isothermal processes in the RFI process are described, focusing on the analysis of the mathematical model of resin flow. Finally, it covers the unique properties of RFI composites and showcases the RFI process's cost-effectiveness and functionality in fabricating composite structures for various applications. The limitations and potential future developments of RFI process molding technology are also summarized. [ABSTRACT FROM AUTHOR]

Bisphenol-A resin epoxy resin composites doped with various concentrations of inorganic hybrid nanofillers, TiO2 + ZnO, were thoroughly examined in the research described in this report for their microwave dielectric relaxation spectroscopy. Ultrasonic dispersion techniques were used to disperse the TiO2 + ZnO hybrid nanofiller into the Bisphenol-A resin. X-ray diffraction (XRD) was employed to ascertain the structural characteristics of the TiO2 and ZnO nanoparticles (NPs) and TiO2 + ZnO hybrid NPs doped neat epoxy (epoxy + hardener). A Vector network analyzer was used to measure the dielectric properties of the hybrid NPs doped neat epoxy in the frequency range from 200 MHz to 20 GHz. Our findings offer important new perspectives on the polarization mechanisms and structural properties of these composite materials. The complex relationship between frequency and dielectric characterization led to measurement complexities that often come with extensive time and cost requirements. This paper presents the random forest regression model as an effective method for predicting the frequency-dependent dielectric constants in composite materials. The main objective of this study was to examine the performance metrics, such as the adjusted R-squared score, root mean squared error (RMSE), and mean absolute error (MAE), across various values of the minimum node size parameter (nmin). This study showcases the effectiveness of the RF regression model to accurately and efficiently predict the frequency-dependent dielectric constants in composites. As a result, it eliminates the requirement for laborious and expensive laboratory testing. [ABSTRACT FROM AUTHOR]

Crack localisation is a fundamental step of damage identification. Most of the published research on crack localisation based on natural frequency consists in model updating which requires a great deal of calculation. This paper presents a simple method of crack localisation in composite cantilever beam-type structures. The proposed method consists of classifying the reduction of the first four measured natural frequencies and deducing the damage position from a table. For these purposes, a finite element model is first used to study the direct problem: the vibration behaviour of an intact beam and the changes caused in the damaged state. Then it is shown that the classification of the frequency reduction ratio is different for each damaged zone. Consequently, the beam is discretized into several areas according to the classifications of the first four frequency ratios. Therefore, this discretization is represented in a table to be used in damage localisation. The robustness of the suggested technique is first tested numerically by using the Abaqus/CAE finite element software environment. Then, the applicability of the localisation method is validated experimentally on a cracked glass fibre-reinforced epoxy beam. The results show that the proposed method can successfully localise damage in composite beams. [ABSTRACT FROM AUTHOR]

This work controlled the polymerization reaction, melting, and mixing processing of a mixture including epoxy resin and polyethylene glycol (PEG) by a pulverizer, to effectively develop high-performance shape memory epoxy/PEG (EPP) filaments. The process parameters of polymerization-melting-mixing-drawing were determined through the extrusion force investigation. The results showed that EPP mixtures could be developed into filaments through polymerization-melting-mixing-drawing process, reducing the spinning temperature and filament diameter from 300°C and 31 mm to 235°C and 13 mm, respectively. The Fourier transform infrared spectra confirmed the complete polymerization of epoxy resin and the stable existence of PEG. EPP filaments developed through the polymerization-melting-mixing-drawing process have exhibited controllable dynamic thermal mechanical properties and Tg, excellent shape recovery effects, and adjustable stimulus temperature. This work developed shape memory EPP filaments through a polymerization-melting-mixing-drawing process, with controllable spinnability and adjustable stimulus temperature, providing a reference for high-performance filament fabrication and process optimization. [ABSTRACT FROM AUTHOR]

AbstractBisphenol A (BPA), a synthetic chemical widely used in the production of polycarbonate plastic and epoxy resins, has been associated with a variety of adverse effects in humans including metabolic, immunological, reproductive, and neurodevelopmental effects, raising concern about its health impact. In the EU, it has been classified as toxic to reproduction and as an endocrine disruptor and was thus included in the candidate list of substances of very high concern (SVHC). On this basis, its use has been banned or restricted in some products. As a consequence, industries turned to bisphenol alternatives, such as bisphenol S (BPS) and bisphenol F (BPF), which are now found in various consumer products, as well as in human matrices at a global scale. However, due to their toxicity, these two bisphenols are in the process of being regulated. Other BPA alternatives, whose potential toxicity remains largely unknown due to a knowledge gap, have also started to be used in manufacturing processes. The gradual restriction of the use of BPA underscores the importance of understanding the potential risks associated with its alternatives to avoid regrettable substitutions. This review aims to summarize the current knowledge on the potential hazards related to BPA alternatives prioritized by European Regulatory Agencies based on their regulatory relevance and selected to be studied under the European Partnership for the Assessment of Risks from Chemicals (PARC): BPE, BPAP, BPP, BPZ, BPS-MAE, and TCBPA. The focus is on data related to toxicokinetic, endocrine disruption, immunotoxicity, developmental neurotoxicity, and genotoxicity/carcinogenicity, which were considered the most relevant endpoints to assess the hazard related to those substances. The goal here is to identify the data gaps in BPA alternatives toxicology and hence formulate the future directions that will be taken in the frame of the PARC project, which seeks also to enhance chemical risk assessment methodologies using new approach methodologies (NAMs). [ABSTRACT FROM AUTHOR]

In this study, the shear strength and thermal properties of the adhesively bonded joints were investigated of adhesives reinforced with nanoparticles using carbon fiber-reinforced composite materials. The diglycidyl ether bisphenol A (DGEBA) was used as the epoxy resin. Single lap joint tests of 1% wt. Multi-walled carbon nanotubes (MWCNT) and 3, 5, and 7% wt. silicon dioxide (SiO2) nanoparticle-reinforced mixed adhesives were performed according to ASTM D5868 standards. The shear strengths of the mixed adhesives obtained by mixing at different ratios were compared with the epoxy resin. Upon conducting an analysis of the shear strengths of nanomaterials, results indicate that the incorporation of 1CNT + 3SiO2 in the nanomaterials showed the greatest improvement, with a 46% increase in shear strength. 1CNT + 5SiO2, 1CNT, and 1CNT + 7SiO2 showed increases of 32%, 14%, and 5%, respectively. The results of a tensile test indicate that pure epoxy exhibited a tensile strength of 5953 N, 1CNT, and 3SiO2, while the epoxy composite demonstrated a significantly higher tensile strength of 8738 N, along with an elongation of 0.72 mm. In addition, the morphology of fractured surfaces was examined by scanning electron microscopy (SEM). To investigate damage mechanisms, such as bridging, crack blunting, and branching of nanoparticles were observed. Characterization of epoxy resin and mixed MWCNT + SiO2 nanoparticles reinforced adhesives were also performed using Fourier infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and differential thermal analysis (DTA). Nanoparticles are settled between polymer chains, improving polymer chains' motion and thermal properties. [ABSTRACT FROM AUTHOR]

The kinetics of the curing reactions of two epoxy resin types, aliphatic epoxy resin (ALER) and aromatic epoxy resin (ARER), were evaluated by FTIR, TGA, DSC, SEM, and XRD characterization techniques. Increased curing times improved the mechanical properties of cured ALER epoxy and improved durability compared to that of cured ARER epoxy resin. Flexural stress and modulus of cured ARER epoxy resin were significantly improved after an increase in the curing time. The flexural strength of ARER epoxy increased by 27.2%, while the ALER epoxy flexural strength increased by 10.1% after 840 h curing time. The glass transition temperature at maximum curing was higher for ARER epoxy (76 °C) than for ALER epoxy (65 °C). The XRD results of epoxy resins showed that crystallinity increased as curing times were increased. The kinetic parameters calculated from the maximum rate of TGA mass losses for both ARER and ALER cured for 840 h were equivalent with rate coefficients, ${10^{11 \pm 2}}{{\rm{s}}^{ - 1 }}\exp \left({ - 164 \pm 2 {\rm{kJ\ mo}}{{\rm{l}}^{{\rm{ - 1}}}}/RT} \right)$ 10 11 ± 2 s − 1 exp − 164 ± 2 kJ mo l − 1 / RT . This indicated that first-order decomposition is rate-determining. Afte curing for 168 h the kinetic parameters were significantly smaller indicating that the epoxy resins are more volatile and the maximum mass-loss rate is both reaction and diffusion rate limiting. [ABSTRACT FROM AUTHOR]

Nanodiamond has been categorized among remarkable zero dimensional nanocarbon. This carbon nanoparticle has been applied as important nanofiller in the polymeric matrices. This state-of-the-art review article portrays fundamentals, physical properties, and prospects of nanodiamond filled thermosetting matrices. Among thermosets, most research efforts have been reported on the nanodiamond filled epoxy and polyurethane matrices. Consequently, the epoxy/nanodiamond and polyurethane/nanodiamond nanocomposites have been designed. The nanodiamond nanoparticle addition in polymers caused microstructural variations and enhancements in mechanical, thermal, wear, adhesion, and related advanced features. The property improvement was observed due to the nanofiller dispersion, matrix-nanofiller interactions, and interface formation. Type of thermosetting polymer, curing agent, nanodiamond content, nanodiamond functionalities, and processing method define the final nanocomposite architecture, morphology, and ensuing characteristics. Consequently, the high-tech epoxy/nanodiamond nanocomposites and polyurethane/nanodiamond nanocomposites exposed capability toward technological relevance like coatings, microwave absorption, and biomedical. As few thermosetting matrices have been used with the nanodiamond nanofillers so far, more comprehensive future efforts are needed to disclose the actual potential of thermosetting polymer/nanodiamond nanocomposites. [ABSTRACT FROM AUTHOR]

Finite element (FE) simulations of adhesively bonded composite joints were conducted using the cohesive zone model (CZM). To clarify the effect of fracture criteria on the accuracy of the CZM simulation, two types of mixed-mode criteria including the -linear summation model of Modes I and II energy release rates, G I / G IC + G II / G IIC = 1 , and the nonlinear power-law, ( G I / G IC ) n + ( G II / G IIC ) n = 1 , were employed. A CZM formulation using the power-law fracture criterion was developed in this study. The load–displacement curves calculated by the two models were compared with the experimental results obtained from mixed-mode Fernlund–Spelt-type double cantilever beam tests, and the Mode II end-notched flexure (ENF) tests. Calculations using the nonlinear fracture criterion were closer to the experimental results. Consequently, it is concluded that nonlinear fracture modeling is of vital importance for accurate strength analysis of mixed-mode adhesive joints. [ABSTRACT FROM AUTHOR]

Users of the microbond test assume that a microbond resin droplet's properties are equivalent to a macroscale specimen. However, there is currently no standardised methodology for determining the cure state of droplet specimens used in the microbond test. In this paper, we present a technique for microbond test users to better understand the properties of thermoset droplet specimens. Utilising a conventional benchtop spectrometer, a novel sample preparation technique involving curing epoxy droplets on thin-steel filaments allowed for high-throughput determination of the microbond droplet cure state. The parity between steel filament and glass fibre microbond samples was confirmed by infrared microspectroscopy. It is shown that cure schedules used in manufacturing composite parts produced microbond droplets with degrees of cure lower than that of bulk matrix specimens subjected to an identical thermal history. Testable microbond droplets could only be prepared for commercial resin systems when introducing a room temperature pre-curing time of at least 2 h. It is concluded that microbond testing should be supported by some droplet cure state characterisation methods to ensure that interfacial effects are not artefacts of droplet sample preparation. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced epoxy resin composite (CF/EP) is widely used in aerospace applications, automotive industry, construction engineering and many other important sectors, for it has excellent mechanical properties and corrosion resistance. However, the three-dimensional cross-linked structure of the cured epoxy resin determines its insolubility and non-melting characteristics, which makes it challenging to efficiently degrade CF/EP waste and recycle the high-value carbon fibers. In this study we propose a strategy that degrades the CF/EP waste via a facile and efficient solvothermal degradation route. The results showed that the degradation ratio of the resin increased significantly with the rise in reaction temperature. When the reaction temperature reached 180 °C there were no obvious resin residues on the surface of the recycled carbon fibers. It was found that the recycled carbon fibers were not obviously damaged during the solvothermal degradation process, as shown by the scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman analyses. [ABSTRACT FROM AUTHOR]

A study was conducted on the tensile stress of an epoxy resin (Resoltech® 1050/1056). This was done by gathering a sample of 39 tensile strength data under consistent levels of stress. The tensile stress resistance is often characterized using a three-parameter Weibull distribution and the reliability of this characterization, given by confidence intervals (CIs). This approach commonly utilizes data-resampling techniques to estimate the CI of its parameters. CIs are constructed from six existing point-estimation methods. Herein, the jackknife was carried out to calculate the CIs using 39 subsamples and bootstrap methods using 100 or 200 subsamples. To date, there have been no studies exploring the effectiveness of subsampling methods for constructing CIs related to tensile strength. In this study, jackknifed and bootstrapped samples are used to implement the percentile method and three variations of the bias correction methods. We then performed simulations to evaluate the reliability of these methods using a Weibull random number generator. Our results showed that while the bias-corrected approach generated the most stable CIs from replicate samples, its accuracy was contingent on the point-estimation method employed. We also found that the different methods for calculating CIs resulted in significantly varying widths of the CIs. [ABSTRACT FROM AUTHOR]

This research focuses on the mechanical characterization of FG material graded with Graphene nano-platelets (GPLs) in the transverse direction. Different weight percentages of GPL (0–2 wt. %) were incorporated into epoxy resin for manufacturing the FGM using a simple casting method and the effects were analyzed. This paper aims to enhance the material’s performance, especially focusing on its potential use in biomedical tools. Mechanical tests including assessment on tensile, flexural, impact strength, and microhardness demonstrated substantial improvement in strength and stiffness as compared to other nanocomposite structures. Microstructural analysis using scanning electron microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) analysis which hint at the strong chemical interaction and physical association of GPL nanofiller with the epoxy resin. Thermal analysis was conducted using the Dynamic Mechanical Analysis (DMA) test, which revealed enhanced thermal stability of the FG specimen with a higher glass transition temperature than other carbon nanofillers mixed in epoxy resin. This is advantageous for the FG material to maintain its glassy state, maintaining safety and reliability during high-temperature medical applications. All these findings indicate that the proposed FG-GPL material possesses the necessary mechanical properties, suggesting that customized nanofiller integration could lead to significant advancements in medical procedures, such as in vivo stomach biopsy treatments, drug delivery systems, etc. The material also meets specific anatomical requirements and reduces the risk of malfunction, thereby ensuring patient safety as justified by current experimental investigations. [ABSTRACT FROM AUTHOR]

AbstractDual-curing Epoxy thermosets has found widespread use in polymer materials in recent years. Dual-curing system is one of the ways used to control the curing rate of epoxy resin to design the final product through two different curing systems with different reaction conditions. This review begins with an introduction to dual-curing systems based on epoxy and relevant reaction mechanisms. It then provides an overview of the types of dual-curing epoxy resin such as epoxy-acrylate, epoxy-amine, epoxy-thiol, epoxy-siloxane and epoxy-allyl phenol that can be encountered in these systems. Due to the variety of dual-curing models of epoxy resin, different dual-curing models and systems can be used to control the properties of the materials. The review concludes with a review of recent and successful research on dual-cured materials for shape memory polymers, adhesive materials, 3D printed materials, structured surface topologies, and holographic materials. [ABSTRACT FROM AUTHOR]

Poly-ether-ether-ketone (PEEK) and carbon-fiber-reinforced PEEK (PEEK-CF) are examples of engineering thermoplastics with exceptional mechanical properties. In the context of Fused Filament Fabrication (FFF), the interlayer bonding between PEEK and PEEK-CF has a significant impact on the mechanical properties of printed components. Epoxy resin is used to enhance the interfacial bonding between PEEK and PEEK-CF due to its remarkable adhesive properties, while preserving the dimensional and weight attributes of the bonded sandwich structure. The application of epoxy resin as a post-processing technique enables the creation of intricate geometric designs within the bonded sandwich structures. This study presents a straightforward technique for producing sandwich structures using PEEK and PEEK-CF, followed by improving their mechanical properties through isothermal annealing. We conduct systematic single-factor experiments to explore the mechanical advantages of FFF-printed PEEK and PEEK-CF via three-point bending tests on individually printed monolithic specimens. Furthermore, mono-material specimens are bonded using epoxy resin to form dual-material bending specimens. Our findings reveal an optimal sequence: after isothermal annealing, mono-material specimens bonded with epoxy resin exhibit superior flexural strength and modulus. In addition, an in-depth examination of the meso-structure and fracture morphology of FFF-printed sandwich structures after bonding and heat treatment reveals insights into toughening and reinforcement mechanisms. This analysis is complemented by corresponding finite element simulations to validate the results. Notably, our research highlights the successful optimization of interlayer structures, facilitating the creation of sandwich structures with superior mechanical performance. [ABSTRACT FROM AUTHOR]

The elastic, plastic, and in-plane damage evolutions of a carbon-fiber-reinforced epoxy composite fabricated via filament winding were studied based on continuum damage mechanics. The specific voids and resin-rich region distributions depended on the material and manufacturing conditions. The damage evolutions were expressed by a unified curve, indicating that the continuum damage mechanics approach gave a robust prediction of the damage evolution, although the critical damage at the ultimate failure depended on the material and manufacturing conditions. The damage coupling parameters were also affected by these conditions, which changed the damage evolution behavior under simultaneous shear and transverse damage development situations. [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]

The adhesive bonding approach is widely used in assembling of spars, stringers, ailerons, flaps, and rudders in aircraft. The present research investigated the impact of silicon carbide (SiC) nanoparticle inclusion on the shear and free vibrational behaviour of adhesively bonded single lap joints (SLJ). The shear test results showed that the inclusion of 1.5 wt.% SiC in the epoxy resin enhanced the shear behaviour of adhesively bonded SLJ. Furthermore, the failure surfaces of adhesively bonded SiC-reinforced SLJ were examined using a field emission scanning electron microscope (FESEM). The microstructural investigation of the failure surface demonstrated that the development of rougher surfaces, plastic void enlargement, and formation of shear bands in the joint region had improved adhesion among GFRP adherends. Thus, the SiC-incorporated adhesively bonded SLJ had predominant cohesive failures. Meanwhile, the SiC-free lap joint had an adhesive failure due to lower adhesion. The vibrational results avowed that 1.5 wt.% SiC-incorporated adhesively bonded SLJ has higher natural frequencies. Results also affirmed that higher wt.% SiC-incorporated joint had better modal damping values due to nanoparticle accumulation, which increased the interaction between glass fiber reinforced polymer (GFRP) adherends. [ABSTRACT FROM AUTHOR]

Due to the high strength, high modulus, lightweight and other characteristics, carbon fiber reinforced polymer (CFRP) is widely used in aerospace, high-speed aircraft, and other fields. In this article, a high-damping CFRP reinforced by flake polyurethane fillers is prepared with good mechanical properties, and the effects of flake polyurethane fillers on the mechanical and damping properties of CFRP are studied. The results show that the mechanical and damping properties of CFRP could be significantly improved by the appropriate content of the flake polyurethane fillers. In addition, the optimal content of the flake polyurethane fillers is 3 wt.%, and the flexural strength, interlaminar shear strength, and damping properties of CFRP are increased by 6.19%, 12.07%, and 9.48%, respectively. [ABSTRACT FROM AUTHOR]

Flax and carbon fibers reinforced polymer composites have high potentials to be used as sustainable building materials. To understand the impact resistance of these fiber composites, the present article studied the impact resistance of unidirectional flax fiber and carbon fiber reinforced polymer (FFRP and CFRP) composite plates. The impact response, damage resistance, and impact tolerance were investigated using drop hammer impact and compression after impact (CAI) tests. The internal damage of FFRP and CFRP due to impact loads was studied using acoustic emission technology. In addition, the development process of impact damage was analyzed. CFRP plates show a higher specific energy absorption rate than that of FFRP, because of the more serious internal damage and brittle fracture tendencies. Matrix cracking was the primary damage in FFRP and CFRP under impact load. Compared with CFRP, FFRP possesses a higher CAI due to less damage. Further expansion of the matrix crack caused by the original impact occurs in the impacted fiber-reinforced polymer composites (FRP) under a compressive load. [ABSTRACT FROM AUTHOR]

AbstractPolymer composites containing carbon nanoparticles have attracted considerable attention because of their special functional characteristics. Characterization of optical and dielectric characteristics was done. To comprehend the impact of nanofillers, dielectric characteristics, UV–Vis spectroscopy, XRD, and Fourier transform spectroscopy were employed. The role of carbon fillers on metrics, such as band gap energy, absorption coefficient, and dielectric characteristics of nanocomposites was examined to differentiate between the effects of nanofillers. The AC conductivity is explained following the classical percolation theory. The percolation threshold is discovered to be 1 wt.% of a hybrid system of nanofillers consisting of graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs). The presence of carbon nanofillers significantly enhances the electrical conductivity of the nanocomposites. The optical band gap energy of nanocomposites was obtained from the Tauc method. The study establishes the relationship between band gap energy and AC conductivity using Tauc’s relation and Jonscher’s power law. The results show that the band gap energy of composites decreases with the addition of hybrid nanofillers, with values observed at 2.65 eV and 2.95 eV, while without fillers of 3.1 eV and 3.05 eV attributed to increased localized states within the bandgap. Composites with nanofillers show an AC conductivity of 1.86 S/m at 1 wt% of nanofillers, compared to 1.52 × 10−6 S/m and 1.09 × 10−6 S/m for composites without nanofillers. The UV–Vis spectra reveal a significant blue shift in the absorption peak when the weight percentage of carbon nanoparticles is increased. The findings of this study point toward the possibilities of the development of novel nanocomposites with enhanced performance for electronics and energy storage. [ABSTRACT FROM AUTHOR]

The current research introduces a multilayer functional structure along with its corresponding multi-objective optimization design strategy intended to improve the design efficiency of materials exhibiting remarkable properties in both load-bearing and electromagnetic wave absorption. The composite structure contains several layers of graphite oxide reinforced epoxy resin, each of which has a different thickness and volume fraction of fillers. The proposed strategy employs the volume fraction of fillers and thickness of each layer as the design variables, with the electromagnetic wave absorption bandwidth and bending stiffness of the entire structure serving as objectives. The multi-objective model was derived using the Maxwell-Garnett Model, Halpin-Tsai Model, Transmission Line Theory and Classical Laminate Theory. To efficiently optimize the multilayer structure, the JAYA, an evolutionary algorithm is employed as optimizer. The results indicate that the optimized structure exhibits a considerable increase in electromagnetic wave absorbing capacity and a slight increase in load-bearing performance relative to the original structure, while the total thickness remains constant. In addition, the whole process takes only a few seconds. [ABSTRACT FROM AUTHOR]

Poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) exhibit valuable mechanical properties like high stiffness and tensile strength but are sensitive to processing parameters. The influence of these parameters was evaluated by measuring the variation of melt viscosity during processing. For all experiments, in the absence of chain extenders, the decrease in melt viscosity clearly showed the degradation of polymers during processing. This is more pronounced for PHBV than PLA. In order to compensate for the degradation and, if possible, improve the melt strength of these bio-based polymers, two chain extenders have been evaluated: dicumyl peroxide (DCP) and a polymeric epoxy acrylate chain extender (Joncryl® ADR 4400). DCP reacts quickly with PLA and PHBV, while the epoxy-acrylate chain extender shows slower kinetics. For the PLA, with both investigated chain extenders, an increase in the molecular weight as compared with the virgin polymer and eventually the apparition of an insoluble fraction due to branching and crosslinking are observed. In the case of PHBV, the degradation is compensated by using DCP, requiring short processing times. No significant increase in molecular weight was observed when using the polymeric epoxy acrylate chain extender, requiring longer residence times, although the apparition of a gel fraction suggests the presence of branching and crosslinking. [ABSTRACT FROM AUTHOR]

304 austenitic stainless-steel (SS) strip-based carbon fiber metal laminates (CFMLs) have raised significant concerns, in terms of their mechanical performance. On top of that, the hybrid laminates' interlamination performance is vital in regulating their failure patterns. Along these lines, in this work, SS strips with regulatable micromorphology and composition were obtained by using physical and chemical surface modification strategies, including polishing, acid etching, anodization, and thermal treatment. The shear strength of the treated-SS/epoxy single lap joints (two treated-SS strips bonded by the epoxy resin via hot curing process) was systematically explored, and the origins of the enhancement mechanism were attributed to the resulting surface microstructure, as well as the possible chemical reactions between the treated surface and the curing agent. The etching-anodizing-thermally treated-SS (EAT-SS)/epoxy joint exhibited the maximum shear strength (16.04 MPa) and work of fracture (5.85 kJ·m−2) due to the substantial cohesive failure pattern of the epoxy. The encouraging enhancement was mainly attributed to the synergistic effect of the micro-annular pit and the nanoporous array structure of the EAT-SS surface. These effects induced a significant mechanical interlock and a plausible chemical reaction at the interface, which led to improved bonding strength between the epoxy and treated-SS surface. Overall, in this work, it was demonstrated that the combination of the anodization and thermal treatment can effectively improve the interlamination bonding properties between the SS strip and the epoxy resin due to the combination effect of mechanical interlocking and chemical bonding. [ABSTRACT FROM AUTHOR]

Phenolic epoxy resin (F51) was first reacted with silane coupling agent (3-aminopropyl)triethoxysilane (KH550) to form a silanized phenolic epoxy resin (SPER); then the SPER was copolymerized with methylphenyl silicone resin (MPS) to synthesize phenolic epoxy modified silicone copolymer (PEMSC). The chemical structure of the PEMSC was characterized by FT-IR. The results of tensile strength and shear strength measurements indicated that the successful introduction of F51 significantly improved the mechanical and adhesive properties of the PEMSC; compared with the PEMSC with 10 phr of F51 added, the tensile strength and shear strength of the PEMSC with 40 phr increased by 8.5 and 3.5 times respectively. The TGA and DTGA analysis showed that the initial thermal decomposition temperature and the residual weight of PEMSC at 800 °C decreased compared to MPS, but the temperature corresponding to the maximum thermal decomposition rate in the second stage increased. Qualitative analysis was conducted on the decomposition products of PEMSC using gas chromatography coupled with mass spectrometry (GC-MS). The results showed that the relative content of aromatic hydrocarbons and their derivatives in the decomposition products of PEMSC was 64.11%, and the relative content of cyclic trimers and higher cyclomers was 20.41%. [ABSTRACT FROM AUTHOR]

Epoxy sheet molding compound (ESMC) composites have excellent mechanical properties, dimensional stability and electrical insulation, and are widely used in the automotive industry. In our previous work silane coupling agent modified, hollow glass microspheres (SiHGM) and montmorillonite (MMT) were incorporated to enhance the mechanical properties of the ESMC composites. It was found that the ESMC composites containing MMT (EP/SiHGM/MMT-1) exhibited excellent mechanical strength. However, the flammability of the epoxy resin (EP) limits the use of ESMC composites for applications that require good flame retardancy. In this paper we describe our research in which MMT was used to increase the flame retardancy of ESMC composites. The results showed that the addition of MMT made the ESMC composites have excellent flame retardancy. The limiting oxygen index (LOI) of the ESMC composites containing 1 phr MMT (EP/SiHGM/MMT-1) was 26.8%, which was 8.94% higher than that of the ESMC composites without MMT (EP/SiHGM/MMT-0). In addition, the peak heat release rate (PHRR), average heat release rate (AHRR) and total heat release (THR) of the EP/SiHGM/MMT-1 were 322.8 kW/m2, 95.3 kW/m2 and 38.6 MJ/m2, respectively, which were 22.6%, 8.2% and 8.0% lower than those of EP/SiHGM/MMT-0. The carbon monoxide production (COP) and carbon dioxide production (CO2P) of EP/SiHGM/MMT-1 were 0.0092 g/s and 0.2071 g/s, respectively, which were 34.3% and 22.8% lower than those of EP/SiHGM/MMT-0. The fire growth index (FGI) of EP/SiHGM/MMT-1 was 2.4, which was a decrease by 29.4% compared to EP/SiHGM/MMT-0. In addition, the flame retardant mechanisms were revealed. We suggest that MMT promoted dehydration and charring of the epoxy resin and helped construct an intact physical barrier, which had good blocking effects. The prepared composite has great application prospects for those occasions that require high flame retardancy. Thus, this work provides an innovative strategy for preparing low density epoxy composites with excellent flame retardancy and high mechanical properties. [ABSTRACT FROM AUTHOR]

AbstractTo address the issues of high porosity and low strength in calcium sand of artificial islands, this study focuses on improving the calcium sand’s mechanical properties. The effects of WER curing methods and coconut fiber modification on the UCS and microscopic mechanisms of calcium sand are investigated. The results indicate that both fiber incorporation and the increase in WER ratio can enhance the unconfined compressive strength of calcareous sand, with the addition of a certain amount of coconut coir fiber showing a more significant strength increase. The optimal recommended dosage of WER is 15%, which results in an UCS of 1218 kPa, an increase of nearly 4.27 times compared to 9% WER dosage. Coconut coir fiber has good tensile strength that can improve the compressive strength of calcareous sand after curing. The UCS of calcareous sand cured with a fiber content of 0.3% to 0.5% is increased by 1247 kPa to 1792 kPa compared to cured soil with no fiber. The strong binding nature of WER addresses the issue of large porosity in calcareous sand. Together with the penetrating coconut coir fibers, it forms a three-dimensional reticular framework structure, thereby enhancing the compressive performance of the calcareous sand-cured soil mass. [ABSTRACT FROM AUTHOR]

Since the discovery of gigantic permittivity properties of CaCu3Ti4O12 (CCTO) ceramics, development of its polymer composites application in supercapacitors, varistors and switching devices has been extensively investigated. Here the one-dimensional (1D) nano-sized CCTO nanofibers were prepared and used as fillers to improve the varistor Characteristics of epoxy composite materials. An obvious varistor effect was observed in CCTO_nfs/epoxy composite. The mechanisms of this varistor effect were analyzed by scanning capacitance microscopy technology. The nonlinear coefficient (α) of CCTO_nfs/epoxy composite with 48 wt% filler loading is about 4.65, which is much higher than of 2.42 for a single CCTO nanofiber. The mechanisms for this discrepancy were analyzed by scanning capacitance microscopy technology. The results show that the nonlinear current density-electric filed (J-E) relationship of the epoxy composites is contributed by the synergistic effects of potential barriers established at interfaces, grain boundaries and the participation of oxygen vacancies in CCTO nanofibers. All these results presented here provide a new insight into the electrical properties of CCTO. The CCTO_nfs/epoxy composites should have good application prospects in polymer composite varistor. [ABSTRACT FROM AUTHOR]

The poor interfacial properties of polyvinyl alcohol (PVA) fibers and epoxy resin seriously affect the toughening effect of PVA fibers on epoxy resin. To solve this problem, the surface of PVA fibers was modified with 3-aminopropyltriethoxysilane (KH550) and 3-glycidoxypropyltrimethoxysilane (KH560), as well as the surface of PVA fibers with tannic acid (TA) and KH560. The acid-cured epoxy resin toughening mechanism of the modified PVA fibers was systematically investigated by multiscale analysis. The experimental data showed that the epoxy resin performed best when TA and KH560 synergistically modified PVA fibers. The impact strength of the epoxy resin increased by 76.3% and the tensile strength by 20.3%. The toughening mechanism of modified PVA fibers on the epoxy resin was revealed by a series of characterizations such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA). Because KH560 can participate in the curing reaction of the epoxy resin, it greatly enhances the adhesion between the fiber and the resin. The toughening mechanism of TA and KH560 working together on PVA fibers to strengthen epoxy resin is summarized through the analysis of different scales. This also offers theoretical and experimental support for using PVA fibers in composites. [ABSTRACT FROM AUTHOR]

Aluminium alloys play a crucial role in the aerospace industry due to their lightweight properties and strength. Achieving an acceptable level of corrosion protection of aluminium alloys without chromates remains a challenge. Ongoing research at the author's company focuses on improving corrosion resistance by formulating epoxy systems and exploring additives without the use of Cr. The company's best to-date Cr-free (CF) primer reached 5000 h of salt spray exposure. Additionally, IPTREAT12, a water-based pre-treatment that enhances adhesion and corrosion resistance, was investigated. IPTREAT12, which replaces chromating baths, significantly extended the lifespan of the paint system. When combining Indestructible's surface pre-treatment IPTREAT12 with one of its Cr-free paint formulations, over 6000 h of salt spray resistance were reached. [ABSTRACT FROM AUTHOR]

AbstractThe continuous integration and refinement of electronic equipment results in the more stringent requirements for epoxy resin (EP) based materials, such as excellent heat dissipation and low coefficient of thermal expansion (CTE). In order to improve the dispersion of silica powder (SP) in EP and thus expand the application of EP in the field of electronic packaging, our research described in this paper adopted the KH-550 coupling agent to modify the surface of SP (m-SP). The effects of KH-550 coupling agent on the characteristics of the composites were investigated in terms of thermal, rheological, electrical insulation and mechanical properties. The results showed that when the content of KH-550 was 2 wt% of the fillers, the best modification effect was achieved, and the surface properties of the fillers were changed accordingly. In particular, the materials filled with m-SP exhibited lower viscosity end, better mechanical and electrical insulation properties. It was also found that the adding of the KH-550 had different effects on the thermal degradation, dynamic thermo-mechanical properties and the thermal deformation behavior of the materials. According to our study, the thermal conductivity and the CTE of m-SP/EP filled with 70 wt% of modified fillers were 0.787 W/m.K and 28.3 ppm/°C respectively, corresponding to a significant thermal conductivity improvement and low CTE. [ABSTRACT FROM AUTHOR]

AbstractOur research described in this manuscript investigated the dielectric properties and structural characteristics of Bisphenol-A epoxy resin composites infused with various concentrations (5 wt.%, 10 wt.%, and 15 wt.%) of hybrid nanofillers, namely alumina (Al2O3) and zinc oxide (ZnO). Ultrasonic dispersion was utilized to integrate the nanofillers into the resin matrix. Structural properties were assessed using X-ray diffraction (XRD), which confirmed the presence of the Al2O3 and ZnO nanoparticles within the epoxy matrix. Dielectric properties were measured over a frequency range of 104 Hz to 2 MHz. The results provide new insights into the polarization mechanisms and structural characteristics of these composites, highlighting their potential for enhanced dielectric performance in high-frequency applications. To further understand and predict these dielectric properties, the CatBoost and LightGBM regression models were employed to predict the dielectric constant (ε'), loss tangent (tan δ), and AC conductivity (σac) of these composites. The models demonstrated strong predictive accuracy, with performance metrics, including Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and R-squared (R2), indicating the robustness and accuracy of the models in predicting the dielectric properties of the composites. The study’s findings underscore the significant potential of Bisphenol-A epoxy resin composites with hybrid nanofillers for high-frequency dielectric applications. [ABSTRACT FROM AUTHOR]

Eggshells are daily food waste disposed of in landfills, producing environmental issues and an unpleasant odour. Eggshells powder may be suitably applied as a filler in epoxy resins to improve their mechanical properties. The material properties and fracture energy of toughened epoxy with eggshell powder (TEEP) were measured and investigated. Dog-bone specimens were fabricated to investigate the mechanical properties of TEEP (i.e. elastic modulus, Poisson's ratios and tensile strength) and tested under quasi-static tensile loading. Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests were used to determine the mode I and Mode II fracture energies of TEEP specimens, respectively. For this purpose, oven-dried eggshells were crushed into particles size of 100 µm. The volume fraction of eggshell powder as filler in TEEP is designated as 0%, 2.5%, 5%, and 10%. The epoxy resin system was made by mixing EPIKOTE Resin 828 and Hardener 651 with a mixing ratio of 5:2 by weight. The results showed that the tensile strength, elastic modulus, fracture energy in Mode I and Mode II were optimum at TEEP 5% with an enhancement of 36.8%, 24.9%, 60.3% and 166.3%, respectively compared to that of neat epoxy. This is due to better surface roughness and the ability of eggshell powder as a crack arrestor. However, TEEP with 10% eggshell prone to agglomeration of eggshell powder caused poor bonding with epoxy resin and affect the mechanical properties. [ABSTRACT FROM AUTHOR]

We investigated the debonding on-demand (DoD) of adhesively bonded hybrid dissimilar joints by applying electromagnetic induction heating to the joint overlap section, wherein the epoxy resin is reinforced with iron oxide (Fe3O4) particles. Ti-6Al-4 V adherends were bonded with CFRP or GFRP adherends using neat/modified epoxy adhesive. DoD tests revealed that eddy current heating of Ti-6Al-4 V was a dominant heating mechanism of the joints while both eddy current and magnetic hysteresis of CFRP and Fe3O4 acted as a secondary heating factor. A low content Fe3O4 and thinner composite adherend reduced the time to failure of the joints. Likewise, CFRP required a shorter time for debonding compared to GFRP due to its electromagnetic properties. Modifications with 2 and 5 wt.% Fe3O4 for CFRP and GFRP joints led to 31% and 37% time reduction which will be crucial for energy-saving when debonding large structures. Remarkably, sandblasting improved the electromagnetic induction capabilities of Ti-6Al-4 V, leading to a notable increase in the heating rate, which jumped from around 20°C/s to 80°C/s. Sandblasting enhanced the surface roughness of the adherends but only the water contact angle of GFRP decreased considerably. Fe3O4 modifications increased the epoxy residue on the Ti-6Al-4 V surface from 26% to 99%. DIC revealed the strain distribution of bulk materials to understand the thermomechanical mismatches between the materials and the adhesive joints exhibited high peel stresses at the overlap ends. The low weight content (2 and 5 wt.%) of Fe3O4 exhibited beneficial effects on the mechanical, thermal, thermomechanical, wettability and lap shear strength. [ABSTRACT FROM AUTHOR]

Double epoxy group double quaternary ammonium salts (DEpDQAS) were synthesized by epichlorohydrin (ECH) reacting with N,N,N'N'-tetramethylethylenediamine (TMEDA) and N,N,N'N'-tetramethyl-1,6-hexanediamine (TMHDA), respectively. The results of orthogonal experiments showed that temperature and time were the key factors influencing on epoxy value and quaternarization ratio respectively. The optimal condition for higher epoxy value was the reaction temperature at 15 °C and methanol as solvent. The reaction kinetic process was determined by conductivity, which showed that the reaction had a short induction period and appeared discontinuity in progress that the reaction rate of the first stage was almost constant, while the reaction rate of the second stage decreased gradually. The product was characterized by infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR). The results of surface tension testing showed that DEpDQAS-6 with longer spacer chain had better surface activity and lowered the solution surface tension to 26 mN·m−1 at 25 °C and CMC 0.27 mol·L−1. The thermodynamic parameters of micellization were obtained basing on charged pseudo-phase model. The studies of cytotoxicity in vitro and antibacterial activity showed that DEpDQAS was biocompatible and its antibacterial activity was more effective against Escherichia coli than against Staphylococcus aureus. [ABSTRACT FROM AUTHOR]

On-site construction projects typically employ staggered fastener patterns. This article describes the application of Hollo Bolts (HB). It also highlights the effectiveness of using flexible epoxy adhesive to increase the load-carrying capacity of staggered connections fastened with HB. The distribution of loads between connecting elements largely determines joint performance. Pultruded glass fiber reinforced polymer (PGFRP), bolted (B), and hybrid bolted/bonded (BB) double lap joints were subjected to a typical pulling load and numerically validated in this investigation. To simulate delamination effects, a Cohesive Zone Model with a 3D progressive damage analysis was developed. In addition, a parametric study capturing the influence of various geometrical variables such as e/d, overlap length, bolt size, adherend thickness, and the number of bolts was used to compare both categories of joints in detail. The results indicate that for staggered connections fastened with HB, an efficient load transfer can be obtained in conjunction with flexible epoxy adhesive. It is anticipated that this interaction will be even more effective as the overlap length, adherend thickness, and fastener diameter increase. The present study proves that BB connections are 43.56% stronger than B connections. [ABSTRACT FROM AUTHOR]

Natural composites play a crucial role in industries due to low density, environment friendly and low cost. However, the performance is limited compared to conventional materials. Hence, it is necessary to perform research on the improvement of the strength of natural composites. Peepal fiber is one of the natural fibers noticed by a limited number of researchers. Hence, an attempt has been made to reveal new scientific information of peepal fiber-based composites. In this research, the natural composite was made using peepal fiber and epoxy resin by the hand layup process. Further, nanofillers like silica (SiO2) and silicon carbide (SiC) were used as reinforcing agents. Both reinforcements were added with the epoxy/peepal (70:30) composite as fixed quantity (2 wt%) for comparison purposes. The performance of composites was assessed concerning the reinforcement type. Materials such as epoxy/peepal, epoxy/peepal/2 wt% SiO2, epoxy/peepal/2 wt% SiC and epoxy/peepal/1 wt% SiO2/1 wt% SiC were fabricated. Investigation on mechanical, thermal in addition to water intake characteristics was made. Epoxy/peepal/2 wt% SiO2 composite exhibited maximum tensile, flexural, impact and hardness of 88, 72 MPa, 9.5 kJ/m2 and 77 shore-d respectively. Further, the same composite showed the least thermal conductivity and low water absorption. [ABSTRACT FROM AUTHOR]

There are needs and challenges in using natural resources to produce advanced materials with sustainability. So, in this modern time, natural fibres are used as reinforcement in composites because of their excellent properties, such as lower costs, biodegradability, lightweight, high corrosion resistance, high wear resistance, fewer health hazards and availability. However, greenhouse gases are released by the open burning of crop residues, such as wheat straw, rice straw, barley and many others, which increases global warming and declines air quality. So, in this experimental work, wheat straw fibres (WSFs) were used as natural fibres because of several factors, such as abundant availability, promoting of green composites and keeping rural areas clean (i.e. pollution-free) by reducing open burning. The same weight percentage of WSFs of different uniform mesh sizes was used with epoxy resin to fabricate the specimens for measuring the tensile and flexural properties as per the ASTM D 638 and D 790 standards. The results show that different behaviour of all specimens was observed under tensile and flexural loading. However, a specimen devoid of WSFs has the highest ultimate tensile and flexural strength, which were 25.064 MPa and 70.25 MPa, respectively. [ABSTRACT FROM AUTHOR]

In this research, a comprehensive comparison of the effects of adding nanomaterials on mechanical behavior of structural adhesive was experimentally investigated. The nanomaterials, namely graphene nanoplatelets (GNPs), Multi-Walled Carbon Nanotubes (MWCNTs), and reduced graphene oxide (RGO) were introduced at varying weight fractions of 0.25, 0.5, 0.75, and 1 wt% within the host adhesive. In addition to the parameters of type of nanomaterial and weight fraction, the effect of nanomaterial functionalization was also included. Two types of primary functionalization: carboxyl (COOH) and amine (NH2) along with non-functionalized filler was utilized. The nanomaterials were mixed in a high viscous structural adhesive araldite® 2011 by following a comprehensive mixing method. Flat doge bone specimens were prepared according to ASTM standard and subjected to testing using a universal testing machine (UTM). The results of the experimentation showed that the mechanical behavior of epoxy adhesive is significantly influenced by the addition of any type carbonaceous nanomaterial (GNPs, MWCNTs, and RGO) in the study, however, significant variation in mechanical properties (Elastic Modulus, Tensile Strength, Failure Strain, and Tensile Toughness), as well as their respective trends was observed among these nanomaterials. Overall, the introduction of GNPs was observed to increase the brittleness of the epoxy adhesive, whereas MWCNTs exhibited a contrasting effect by reducing brittleness. Moreover, it was found that the effect of functionalization and filler concentration on resulting properties was independent of each other. [ABSTRACT FROM AUTHOR]

In the manufacturing of optical products, precise adjustments are made to maintain the optical axis alignment of optical components, which are then securely positioned using adhesives. To achieve positional accuracy at the micron level, it is essential to comprehend the deformation of the adhesive joint over time during processing. This study focuses on investigating the displacement of optical components resulting from the deformation of a cationic photopolymerized epoxy adhesive, which cures under ultraviolet (UV) radiation. First, the conversion of the adhesive was formulated based on a curing reaction model. This conversion can be divided into three stages: the initial reaction during UV irradiation, the subsequent dark reaction, and the reaction induced by heating. Moreover, formulations were developed to describe changes in curing shrinkage, thermal expansion, and viscoelasticity in relation to the conversion. These equations, governing the adhesive properties, were then used to perform finite element method (FEM) simulations to analyze the position of the optical component. Experimental tests on adhesively bonded components were conducted under conditions identical to those employed in the simulation. Throughout the curing process of the adhesive, the optical component was continuously imaged using a coherence-scanning interferometer, enabling the quantification of its displacement from the acquired images. The results of the FEM simulation and experimental analysis exhibited a consistent trend, indicating the effectiveness of the modeling and simulation methods employed in this study. The majority of the displacement of the optical component occurred over several hours during the dark reaction stage, rather than during UV irradiation. Notably, the movement of the optical component was not limited solely to the thickness direction of the adhesive layer because of curing shrinkage but also extends to the in-plane direction because of the non-uniform distribution of the UV irradiation intensity. [ABSTRACT FROM AUTHOR]

This study improved laser shock-wave adhesion test (LaSAT) to evaluate the bonding strength of an aluminum alloy/epoxy resin adhesive, since the bonding strength is dependent on loading rate. In this method, strong shock wave due to laser ablation induces interfacial fracture, and the critical stress is computed using numerical simulations of the FEM. To accurately evaluate the bonding strength, the input waveform caused by laser ablation was identified for FEM computation. Such ablation impact (pressure vs. time) and its spatial distribution of ablation impact were experimentally investigated, and this study computed stress-wave propagation in the specimen. It is found that numerical simulation with FEM reproduced well the wave propagation. A wide range of loading rates was achieved by the quasi-static tensile test, split Hopkinson pressure bar (SHPB) test, and LaSAT. As a result, bonding strength exhibited a significant dependence on the strain rate, similar to that of bulk resin materials in general. [ABSTRACT FROM AUTHOR]

Epoxy nano-magnetic composites exhibit remarkable and promising properties by synergistically combining the properties of epoxy resin and magnetic nanofillers. The current study deals with the synthesis of Fe3O4, NiFe2O4, and CoFe2O4 nanoparticles and their respective nanoparticles-doped epoxy composites, as well as the structural, optical, and dielectric characterization of the resultant nano-composites. To investigate the surface morphology of the synthesized nanoparticles, field emission electron microscopy (FESEM) analysis was employed. By measuring electron diffraction spectroscopy (EDS), the presence of various chemicals was verified. X-ray diffraction (XRD) was used to determine the structural details of the synthesized nanoparticles and nanoparticles-doped epoxy composites. The structural chemistry and surface functionality of the nano-epoxy composites were investigated using Fourier transform infrared spectroscopy (FTIR). The magnetic properties of the synthesized nanoparticles and nanoparticles loaded epoxy composites were also studied using a vibrating sample magnetometer (VSM). UV–visible reflection spectroscopy was also carried out to find the optical properties of the synthesized nanoparticles, neat (undoped) epoxy, and nanoparticles-doped epoxy composites. Dielectric spectroscopy measurements of nanoparticles-doped epoxy composites were performed using an Agilent E4980A precision LCR (Inductance Capacitance Resistance) meter with an Agilent 16451B-test fixture LCR and vector network analyzer (VNA) in the frequency span of 10 kHz to 2 MHz and 200 MHz to 20 GHz, respectively. The influence of the synthesized nanoparticles on the neat (undoped) epoxy composites and the results in view of future applications are fully discussed. [ABSTRACT FROM AUTHOR]

Bitumen emulsion faces the major concern of low mechanical strength, especially at high service temperatures. To improve the mechanical performance of bitumen emulsion, waterborne epoxy resin was used as a modifier in this study. The effects of waterborne epoxy resin on the fatigue performance of bitumen emulsion were evaluated in this study using both the stress-controlled time sweep test and linear amplitude (LAS) test. The dissipated energy concept and viscoelastic continuum damage (VECD) theory were adopted to analyze the fatigue testing data obtained from the time sweep test and LAS test, respectively. It is found that the fatigue life of the emulsion residues increased with the incorporation of waterborne epoxy resin from the time sweep test conducted at the stress levels from 300 kPa to 500 kPa. On the other hand, the LAS test indicated that the trend of the predicted fatigue life of the emulsion residues was strain dependent. [ABSTRACT FROM AUTHOR]

Thermosetting polymers have higher heat resistance, chemical resistance, mechanical characteristics and structural integrity than thermoplastic polymers due to their three-dimensional networks of covalent bonds. The current status and challenges in the field of thermosetting polymer modified asphalts are reviewed in this article. Firstly, classification and application of thermosetting polymers are briefly introduced, and modification approaches of polymer modified asphalts are compared. Crucial factors in selecting polymers for asphalt modification are then analyzed. Further, the cure mechanisms, preparation methods and properties of thermosetting polymers, including epoxy resin, polyurethane, polyurea, unsaturated polyester resin, phenolic resin, furan resin and amino resin, for asphalt modification are discussed. Especially, the effect of components of epoxy resin and polyurethane on the properties of modified asphalts is described. To develop eco-friendly and sustainable asphalt materials, this article also reviews the use of bio-based thermosetting polymers, including epoxy resin, polyurethane and phenolic resin, in asphalt modification. Finally, self-healing and recyclable thermosetting polymer modified asphalts are highlighted as promising solution to the challenges of healability and recyclability of thermosetting polymers in asphalt modification after long-term service. [ABSTRACT FROM AUTHOR]

Interfacial characteristics of nanocomposites are critical limiting factors in the design of polymer nanocomposites. The nanocomposites have complex structures and play a pivotal role in controlling functional properties. Analysis of interfacial layers in polymer nanocomposites, existing between the polymer matrix and the nanoparticles plays a major role in determining their characteristics. High-frequency analysis of electrical conductivity and dielectric properties of carbon nanofillers which are embedded in an epoxy matrix were analysed using alternating current dielectric spectra. This article provides a correlation between the electrical transport properties and dielectric behaviour of epoxy carbon nanocomposites at different temperatures are investigated with variations in frequency. Electrical transport properties of nanocomposites are primarily dictated by electron tunnelling and matrix, nanofillers conductivity. Dielectric spectroscopy in the frequency range 10 Hz–8 MHz has been performed on epoxy nanocomposites with and without hybrid carbon nanofillers at one weight percentage (2:3 ratio). Dominant dielectric relaxation mode is observed in the base composite at a low-frequency region (≥10 Hz), whereas nanocomposite with hybrid carbon nanofillers is observed to induce two dielectric relaxations in the kHz region. Increase in non-monotonic variations in dielectric spectra makes the nanocomposite suitable for high temperature low sag conductor core, aerospace and cryogenic engineering applications. [ABSTRACT FROM AUTHOR]

Cement-based cementing materials have some disadvantages, such as high brittleness and poor mechanical properties. In the long-term production process of oil and gas wells, it is easy to damage, resulting in annulus pressure and interlayer channeling. However, curable resin-based cementing materials have the advantages of good toughness, high strength, and low elastic modulus, and have the potential as cementing materials. A water-based epoxy resin cementing fluid system suitable for cementing was obtained in this article, which has good toughness and high strength, and can directly replace cement slurry for cementing. When the temperature was 50 °C and 70 °C, the fluidity of water-based epoxy resin cementing fluid system was greater than 18 cm, and the thickening time was 74 minute and 128 minute, respectively. The 28 day compressive strength of the resin cured at 70 °C increased by 276.3% and the tensile strength increased by 117.9% compared with the blank cement paste. Scanning electron microscope test indicated that the matrix of water-based epoxy resin is denser than that of blank cement paste. Fourier transform infrared spectrometer and X-ray diffraction analyses demonstrate that the cured epoxy resin products are not affected by curing age. According to the thermogravimetric results, epoxy resin can be used in high temperature deep well. On the whole, replacing cement with water-based epoxy resin cementing fluid can improve the cementing quality, which has broad application value. [ABSTRACT FROM AUTHOR]

Three types of polyimide/polyamide imide/epoxy resin (PI/PAI/EP) coating materials filled with different amounts of WS2 and ZnO were designed, and the coatings were prepared on the surface of 1010 steel substrates using liquid spray coating technology. The mechanical and tribological characteristics of these coatings were investigated. The CoFs (coefficients of friction) of these coatings were lower than those of the copper alloy proposed to be replaced under dry sliding wear and water lubrication. The lowest CoF of 0.237 was achieved with 7.35 wt% WS2, and the highest CoF of 0.251 was observed for 4 wt% ZnO. However, the coating with 7.35 wt% WS2 had the lowest hardness and poorest load-bearing capacity under water lubrication. The coating with 4 wt % ZnO had the best load-bearing capacity and the lowest wear rate. The agglomeration of the coating on the substrate was influenced by the content of ZnO. The CoF of the coating was influenced by both the transfer film formed by WS2 and the amount of ZnO floating on the surface of the coating. The embedding of sand into the coating surface during friction increased the surface roughness, which led to an increase in the CoF. [ABSTRACT FROM AUTHOR]