Type Epoxy Research Articles

Experimental Study on the Effect of Bonding Area Dimensions on the Mechanical Behavior of Composite Single-Lap Joint with Epoxy and Polyurethane Adhesives

The effects of joint geometry parameters, such as adherend thickness (1.76, 3.52 mm), joint width (10, 20, 30 mm), and overlap length (10, 20 mm), on the behavior of single-lap joints (SLJs) under tensile loading are investigated in this study. Peak force, joint stiffness, shear stress, and normal stress are the investigated properties. SLJs are manufactured with carbon fiber composite adherends and two different types of adhesives, polyurethane and epoxy, which present a flexible and rigid mechanical response. The results showed that increasing all 3 geometric parameters (L, W, T) leads to a significant increase in the load capacity of polyurethane joints (on average, 88.4, 101.5, and 16.9%, respectively). For epoxy joints, these increases were 47.7, 100, and 46%, respectively. According to these results, W is the parameter with the most influence on the load capacity of the joints. However, it was observed that an increase in joint width has no significant effect on adhesive shear and a substrate’s normal stresses. Epoxy SLJs behave approximately elastically until failure, while polyurethane SLJ load-displacement curves include an initial linear elastic part followed by a more ductile behavior before the failure. Joint stiffness is affected by all the parameters for both adhesive types, except for overlap length, which led to a negligible effect on epoxy joints. Moreover, the damage surfaces for both types of joints are analyzed and the internal stresses (shear and peel) are assessed by using the analytical model of Bigwood and Crocombe.

Evaluation of EPDM waste in environmentally friendly epoxy hybrid composites

This study aims to reduce the production cost of composite materials, obtain composite materials with improved properties, and expand the applications of waste rubber composites using two different industrial wastes, ethylene-propylene-diene monomer rubber (EPDM) and tire waste pyrolysis solid product carbon black (CB). Composites were formed by adding EPDM waste or EPDM-CB mixture at 1:1, 1:3, and 3:1 ratios to bisphenol-A type epoxy resin in different weight ratios. Mechanical, water sorption, electrical conductivity, and flammability tests were applied to the composites. The effect of the EPDM:CB ratio and some environmental conditions on the mechanical properties of the hybrid composites were investigated. Composites with 3:1 weight ratio of EPDM:CB had the highest tensile strength, which varied between 115.5–158.6 MPa. Increasing the EPDM ratio in an epoxy matrix and hybrid filler decreased the composites’ density and tensile strength. EPDM-CB hybrid filler increased the thermal strength of epoxy. Mechanical properties are affected by water sorption, low temperature, and UV irradiation. Increasing the CB ratio in the hybrid filler decreased the flammability of the hybrid composites. ANOVA is applied to find the significant effect of different weight percentages of hybrid fillers and different varieties of fillers on the mechanical properties of composites.

Stability and Population of Radicals in Electrical Trees in Epoxy Resins Based on Electron Paramagnetic Resonance Spectroscopy

The stability and population of radicals in aged epoxy resins with different electrical trees are investigated by electron paramagnetic resonance. Branch trees and bush trees of various sizes are produced in three types of epoxy resins which are cured by different curing agents. By examining the lifetime of radicals in three epoxies, the mobility of polymer chains is found to act as a vital factor for stability. The recombination of radicals is faster in polymers with higher mobility, leading to a shorter lifetime of radical signals. A distinguishable singlet appears in specimens without visible tree channels, proving that radicals are a precursor of electrical trees. Among spectra from a series of branch trees, two species of radicals are found to be generated successively as tree size increases. By comparing the signal intensity of branch trees and bush trees of similar sizes, bush trees show a much smaller radical population, which is attributed to relatively low electrical stress at branch tips and slow degradation of polymer chains.

The effect of the corrosion inhibition of steel bar and the property of salt adsorption to salt adsorption type epoxy resin

Reinforced concrete structures in a salt-damaged environment are deteriorated by salt damage due to the influence of salt. As a repair measure, repair materials with salt adsorption performance and rebar rust prevention performance are used for inorganic materials. However, products with these added to organic materials are used for various purposes, which are used for various applications as repair materials. Unfortunately, there are few examples of its use becoming possible expected that measures against salt damage will be taken in various applications which have developed a “salt-adsorbing epoxy resin repair material” in which a salt-adsorbing agent is added to epoxy resin, which is an organic material. In addition, this research presented the salt adsorption effect and the corrosion inhibition effect on steel bars applied to each repair application.

Study of the Effect of Bioplasticizer Type of Epoxy Used Cooking Oil on the Mechanical Properties of Rubber Vulcanizate

Study of the Effect of Bioplasticizer Type of Epoxy Used Cooking Oil on the Mechanical Properties of Rubber Vulcanizate

Effect of a Heterogeneous Network on the Fracture Behavior of Epoxy Resins

Epoxy resins, which possess a three-dimensional network obtained by a curing reaction between epoxy and amine compounds, are in a glassy state at room temperature. They are therefore generally brittle and exhibit rather poor resistance to crack propagation, which is one of the greatest drawbacks for their practical application. To solve this problem, a better understanding of their fracture behavior, which is related to long-term durability, is strongly desired. We herein report on how the extent of network heterogeneity affects the fracture behavior of epoxy resins. Three types of epoxy resins were obtained under different curing conditions, which generated different extents of heterogeneity. The fracture behavior of the three epoxy resins was examined by in situ scanning electron microscopy in conjunction with microbeam X-ray scattering experiments. When the epoxy resin in which a notch was pre-introduced was stretched under a small strain, the internal network structure was deformed, and the extent was more significant with increasing heterogeneity. As further stretching was applied, a crack propagated from the notch. This occurred more easily with increasing heterogeneity. That is, the toughness of the epoxy resins decreased with increasing network heterogeneity. The knowledge obtained here will be useful for understanding and controlling the toughness of epoxy resins.

Formation Mechanism of a Heterogeneous Network in Epoxy Resins

In general, the network structure formed in epoxy resins is heterogeneous, and its extent is dependent on the curing temperature. Based on Fourier-transform infrared spectroscopy in conjunction with coarse-grained molecular dynamics simulations, we herein discuss the origin of mesoscopic heterogeneity in an epoxy resin composed of a typical epoxy base and diamine hardener, which react with each other in two steps. The rate balance of the first and second step reactions, which led to chain extension and branching, respectively, depended on the curing temperature; at a higher temperature, the second-step reaction became faster. Since the reaction proceeded more slowly at lower temperatures, a homogeneous domain was formed as unreacted substances were incorporated into the network. At higher temperatures, on the other hand, the reaction proceeded rapidly before unreacted substances were incorporated into the network, leaving isolated small fragments and nanoscale voids or free spaces in the domain. We also found that an actively reacting domain with a length scale of several tens of nanometers was formed even at a conversion lower than the gel point, regardless of the curing temperature. The connection of domains was also key to better understanding the temperature dependence of the hierarchical heterogeneity. The final network was found to be denser and more homogeneous at a lower temperature, while heterogeneous with many free spaces at a higher temperature. Our molecular picture of the network formation drawn by combining experimental and simulation techniques advances our current understanding of the heterogeneity formed in epoxy resins.

Influence mechanisms of epoxy degradation on surface traps and charge accumulation under DC electrical–thermal stress

As trapping sites for surface charges, the surface trap is an important factor affecting the insulation performance of the epoxy–SF6 interface, which is closely related to the microstructure and its evolution. However, existing studies often ignore the effect of the degradation of the epoxy surface on the surface traps and charge accumulation during the long-term service of the insulation system. In this study, the surface physicochemical evolution and its influence on surface traps of a typical epoxy–SF6 insulation structure were researched under a DC-temperature gradient condition, and an evolution mechanism of surface traps was proposed. The results show that the free radicals introduced during the material degradation process increase the density and depth of both positive and negative charge traps on the epoxy surface. The effect of free radicals formed by the cleavage of epoxy molecules on the electronic orbital and molecular electrostatic potential of epoxy molecules is the intrinsic reason for the evolution of surface trap evolution. This work may help to understand the long-term evolution mechanisms of the physicochemical characteristics of the epoxy–SF6 interface in DC field and may provide a theoretical basis for the long-term failure mechanism revealing and the insulation performance enhancement.

Detection of interface flaws in Concrete-FRP composite structures using linear and nonlinear ultrasonics based techniques

Timely and appropriate retrofitting of existing structures holds paramount importance to ensure the structural integrity and sustainability. Fiber Reinforced Polymer (FRP) composites with high corrosion resistance, strength and durability, have been increasingly used in recent years for retrofitting of concrete infrastructure. The effectiveness of retrofitting is primarily dependent on the appropriate integrity at the interface between FRP and concrete substrate. Presence of any interface flaw can jeopardize the structural performance. In the present study, investigations are carried out to detect the early stage flaws at the FRP-concrete interface using ultrasonic waves. Artificial flaws of different size are introduced in the adhesive (epoxy) layer of carbon based FRP composite concrete beam. Rayleigh waves (at different frequencies) are generated for measuring the response from different FRP composite-concrete specimens. The specimens consist of three different types of materials, namely, concrete, epoxy and FRP. Two different input excitation frequencies, i.e., 75 KHz and 250 KHz, are tried out during the experimental investigations. The output signals are processed using different linear and nonlinear ultrasonic methods. Numerical simulations are also performed to better understand the wave signals’ interactions with the multi-layer composite medium. The results showed that the linear ultrasonic methods are not able to provide a consistent information on presence and extent of flaws. Nonlinear ultrasonic methods showed significantly better performance for characterizing both small and large flaws considered in this investigation. Sensitivity analysis reveals that relatively new and promising nonlinear ultrasonic technique, namely, the Sideband Peak Count-Index (SPC-I) performs remarkably well for detection of flaws in FRP-concrete interface.

Preparation of Calcium Titanate Nanoparticles with Investigate the Thermal and Electrical Properties by Incorporating Epoxy

In recent years, the materials industry has begun to develop in the directions on enabling the effect of nanomaterials. Nanomaterials are one of the most basic materials that have helped in the development of industrial technology because of their unique properties. These properties make them spread in many areas, especially in the electrical and thermal. Still, traditional materials, at present, suffer from issues that restrict their use, such as thermal conductivity and electrical conductivity. Currently, nanomaterials owing to outstanding performance those traditional materials do not possess. In contrast, scientists have recently focused their efforts on increasing the (electrical and thermal) applications of epoxy resins. In this study, we combined nanoparticles (CaTiO3) with type epoxy resin (Quickmast 105) with different concentrations of CaTiO3 (0, 0.01, 0.02, 0.03, 0.04, 0.05 wt%) by casting. Several tests such as thermal conductivity, thermal expansion, electrical conductivity, dielectric constant and dielectric loss have been carried out. The test results showed a significant increase in thermal conductivity with increasing concentrations of nanoparticles in epoxy, decreasing thermal expansion by 28%, and increasing AC conductivity for all concentrations. The relative permittivity (dielectric constant) of epoxy nanocomposites remains nearly constant with increasing frequency. For dielectric loss, it can be seen that the epoxy nanocomposite's tan values are increasing also with high concentrations.

Viscoelastic model for analysing the behaviour of adhesive-bonded FRP-to-steel joints in civil engineering applications

Adhesively bonding fibre reinforced polymer (FRP) plates have been a mainstream method for strengthening civil engineering structures. The effectiveness of bonding strengthening is dependent on the performance of the adhesive layer. This study examines the time-temperature dependent viscoelasticity of a typical structural epoxy adhesive and develops a linear viscoelastic material model that can be used for numerical analysis. An accelerated test method involving dynamic mechanical analysis (DMA) and time-temperature superposition principle (TTSP) were used to characterise the structural adhesive. The corresponding limitations of this method were discussed, including decomposition effect, nonlinear viscoelasticity, applicability of TTSP, and further curing of the sample. The numerical study of the long-term behaviour of the single lap-shear FRP-to-steel joint found that a slightly warmer temperature (30 °C for this study) is beneficial for the bonded joint as it can reduce the concentrated shear stress with negligible increase in the shear strain. However, a higher temperature (50 °C for this study) that near the adhesive’s glass transition temperature (Tg) could be detrimental as it can lead to significant shear strain in the adhesive joint within the first year of service life.

Development of the epoxy resin phase change proppant based on the Pickering emulsification technology

Since the conventional solid proppant has many defects, such as poor migration and its rigid structures easy to plug cracks, liquid proppant has become a key development direction. A phase change proppant is developed based on the emulsified thermosetting resin system and evaluated in this paper. On the basis of the bisphenol A type epoxy resin, the phase change proppant system adopts the adduct of diethylene triamine and butyl glycidyl ether as epoxy resin curing agent and the SiO2 particles (1% of the resin mass) as the emulsifier, and then adds the hollow glass microspheres (1.25% of the resin mass) and the absolute ethyl alcohol (25% of the resin mass) as the thinner to reduce resin density and dilute resin. Proppant particles with major sizes of 4.5mm, 3mm, 2-2.5mm, 2mm, 1mm and 0.5mm are obtained through process optimization. After evaluation, the obtained proppants are of low density and high compressive strength, and their migration capability and flow conductivity are qualified for the exploitation of unconventional reservoirs with high closure pressures.

Study of the Behavior and the Mechanical Properties of Adhesively Bonded Polymer Matrix Composites Under Mechanical Loading

Glass fiber reinforced Polymer matrix composites (PMCs) have a complex set of properties - high specific strength and hardness, good corrosion and chemical resistance, and most of all low relative weight, making them the preferred material over metallic materials in a number of industries (aircraft, boat building, renewable energy facilities and many others). The main aim set in the present work was reduced to the obtaining of PMCs made by adhesive bonding of two composites with a matrix of different types of resin (vinyl ester and epoxy) and the study of their behaviour in determining their mechanical properties. The studies were carried out with four types of adhesively bonded PMCs made in the form of laminates produced from a combination of three types of resin (two types of vinyl ester and one type of epoxy resin) and reinforced with biaxial fiberglass. The aim is to combine the lack of shrinkage of the epoxy resin with the better mechanical properties and better productivity of the vinyl ester resin. An analysis to determine shear strength, tensile strength and bending strength of the investigated composites was made. A macrostructural fractographic analysis to investigate the material behaviour under mechanical loads was carried out.

Improving the Integrated Fabrication of Insulation Systems in Electric Drives by Injection Molding of Thermosets Due to Processing Conditions and Slot Design

The expanding demand for electro mobility in general and specifically for electrified vehicles requires the expansion of electro mobility technology with respect to variations in the requirements of the process and the application. Within the stator, the electrical insulation system has a high impact on the application properties. So far, limitations, such as the identification of suitable materials for the stator insulation or high costs in the processes, have hindered the implementation of new applications. Therefore, a new technology that allows integrated fabrication via the injection molding of thermosets is founded in order to expand the applications of stators. The possibility of the integrated fabrication of insulation systems to meet the demands of the application can be improved by the processing conditions and the slot design. Within this paper, two epoxy (EP) types with different fillers are investigated to show the impact of the fabrication process in terms of different parameters; these include the holding pressure or the temperature setup, as well as the slot design and with that the flow conditions. To evaluate the improvement in the insulation system of electric drives, a single slot sample, consisting of two parallel copper wires, was used. Then, the two parameters of the average partial discharge (PD) and the partial discharge extinction voltage (PDEV), as well as the full encapsulation detected by microscopy images, were analyzed. It was shown that both characteristics (electric properties-PD and PDEV; full encapsulation) could be improved in terms of an increase in the holding pressure (up to 600 bar) or a reduction in the heating time (around 40 s), as well as the injection speed (down to 15 mm/s). Further, an improvement in the properties can be reached by increasing the space between the wires, as well as the wire and the stack, due to a higher slot depth or by implementing flow-improving grooves that have a positive effect on the flow conditions. With that, the optimization of the integrated fabrication of insulation systems in electric drives via the injection molding of thermosets was enabled with respect to the process conditions and the slot design.

Sustainable production of recycled rubber waste composites with various epoxy systems: A comparative study on mechanical and thermal properties

In this study, ethylene-propylene-diene monomer rubber (EPDM) and tire waste powder (TW) were selected as filling materials for toughening various epoxy matrices, lowering composite materials costs and converting these wastes into valuable resources. Two types of bisphenol-A epoxy resins (ER1 and ER1diluted), and three types of epoxy resin blend systems with ER1diluted, CTBN rubber modified (ER2), and polyurethane modified (ER3) epoxies in 1:1 wt ratio were used as matrices. The effects of the rubber ratio and type, also the epoxy matrix on the composite properties were investigated. The TW composites' mechanical and thermal properties were higher than those of the EPDM composites. The best results for resin mixtures were obtained with ER3. The most suitable filling ratio of EPDM and TW varied between 20% and 30% by weight, depending on the matrix type. TW addition increased the impact strength of the ER1diluted and ER3-ER1diluted epoxy matrices. In terms of mechanical properties, the low ambient temperature was found to be more suitable than an aqueous medium.

Evaluation of spraying technique for heat-reflective coating on asphalt pavements

ABSTRACT Heat-reflective coating (HRC) for pavement can effectively mitigate urban heat island (UHI) and reduce pavement distresses, whose cooling effect, service performance and prospective applications have been widely reported, but construction technology investigation is still unavailable. Following this situation, the spraying technology was evaluated with a typical epoxy resin-based HRC, the Dual-Arrhenius viscosity model for coating curing was established, and the factors affecting the curing time were examined by applying typical correlation analysis. Besides, adhesion and abrasion tests were taken to discuss the effect of spraying conditions on mechanical properties. Results show that the available spraying duration of HRC is exponentially negatively correlated with temperature and duration is insufficient for spraying above 323 K. Raising the diluent content could delay the optimal spraying time with a litter effect on the available spraying duration. Pavement temperature is the main factor affecting the curing time and a 20 K increase could decrease the curing time by up to 34%. Repeated spraying after setting the former layer is the best spraying method for HRC, which can effectively improve adhesion and anti-abrasion.

The Effect of Powder and Emulsion Binders on the Tribological Properties of Particulate Filled Glass Fiber Reinforced Polymer Composites.

Investigations into polymer composites are mainly focused on properties dependent on glass fiber reinforcement and particulate fillers. In the present study, the effect of the binder was examined. The specimens were produced with two types of epoxy resin, with similar numbers of glass mat layers and similar proportions of quartz powder added. However, one group was fabricated with an emulsion binder in the glass mats and another group with a powder binder. Attention was concentrated on the tribological properties of the as-prepared composites, though their strength was examined as well. The hardness of the Sikafloor matrix was found to be much more sensitive to the applied binder than that of the MC-DUR matrix. No direct correlation between the microhardness and the specific wear rate was observed and increasing the particulate filler proportion did not cause a direct increase of the specific wear rate. In particular, the highest specific wear rate, around 350 J/g, was reached for both matrices with a 1% quartz addition when the emulsion binder was applied, while in the case of the powder binder it was with 6% quartz with the MC-DUR matrix, and there was no quartz addition with the Sikafloor matrix. The highest microhardness, HV0.5 = 25, in turn, was reached for the mats with the emulsion binder in the Sikafloor matrix with an addition of 10% quartz powder, while the highest friction coefficient was exhibited in the composite with the MC-DUR matrix, when 1% of the quartz powder and the emulsion binder were applied.

Americium-beryllium shield container optimization with new high alloyed stainless steel and composite material using MCNPX code

In this paper the goal is to optimize a shield for the americium-beryllium radioactive source, which generates a mixed neutron and gamma-ray radiation field, using two different materials designed with simultaneous moderation and absorption of neutrons and gamma-ray shielding in mind: a new type of stainless steel and epoxy resin (C21H25ClO5) composite with a 40% NiO additive. For this purpose, MCNPX was used and the equivalent dose rate for both types of radiation was calculated. After the optimization process, the shield volume experienced a 54% reduction while its weight, due to the use of a steel alloy, was increased by 3.56 %. At a distance of 1 m from the center of the source, the equivalent dose rate was reduced by 10.98% in comparison to that of the original system.

Development of Active-ester Type Epoxy Resin Curing Agents and its Practical Application to the Printed Wiring Boards of High-Speed Communication Devices.

Development of Active-ester Type Epoxy Resin Curing Agents and its Practical Application to the Printed Wiring Boards of High-Speed Communication Devices.

Enhancement the Crashworthiness Parameters Using Natural and Hybrid Composites under Axial Static Crushing

In automotive applications, replacing heavy and expensive materials with light and cheap natural fiber leads to noise reduction, strength enhancement and fuel management. Enhancing the absorption of energy, controlling the failure style of composite thin shell tube and utilizing it instead of thin-walled steel columns in vehicle structural parts can provide more protection for occupants during collisions. This research investigates the possibility of gradually replacing metallic materials with natural and hybrid fibers in industries. The hand layup technique is utilized to study the performance of fiber reinforced epoxy composite tubes under static crushing to examine the jute fiber effect with different fibers types on the failure mechanism. The research studies the effect of using different fibers types on stress and strain after determining the tubes load-displacement curves. Total of 48 specimens are fabricated at room temperature and tested with a constant speed 1.5 mm/sec using one resin (epoxy) type and three fibers types (Glass, Kevlar, Jute). Two circular and square geometries with three heights (200 mm,250 mm,300 mm) including two circular diameters and two square side lengths are used to investigate the crashworthiness parameters. The Kevlar and glass fiber tubes showed low and unstable behavior. Replacing two layers of Kevlar or Glass fiber by two layers of natural jute fiber enhanced the crash worthiness parameters particularly, failure type. The hybrid jute with Kevlar accomplished desirable and best results followed by hybrid jute with glass.