Thin Epoxy Research Articles

Effect of hyperbranched polymer as toughener on tensile, thermal and electrical properties of thin film epoxy composites

Abstract Due to the intrinsic brittleness of epoxy-based solder masks (SMs), hyperbranched polymers have emerged as potential alternatives for permanent SMs. However, the low glass transition temperature (Tg) of pure hyperbranched polymers is undesirable for SMs. Instead, they are more suitable to be used as toughening agent. Hence, this study investigates the influence of adding hyperbranched polyester polyol (HBP) on the thermal, mechanical, and electrical properties of epoxy composites. 15 wt% SiO2/epoxy composites were formulated with 0, 20 and 40 wt% HBP and dispersed via probe ultrasonication. The resulting composites were evaluated using Fourier transform infra-red (FT-IR), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine, dielectric and surface resistivity tests. Findings revealed that adding HBP increased the elongation at break by 10.34 % but reduced both tensile strength and tensile modulus. This may relate to the absence of an increasing absorption peak of O-H group in FT-IR. For thermal stability, the addition of 20 wt% HBP raised the Tmax by 13.38°C but lowered both T5% and Tonset. Tg and storage modulus also decreased with the addition of HBP. The surface resistivity and dielectric constant of the SiO2/epoxy composites increased with the addition of HBP, while a higher addition (40 wt%) of HBP caused a high dielectric loss. In short, 20 wt% HBP/15wt% SiO2/epoxy composite shows the best elongation at break, thermal and surface resistivity, which leads to less brittle and thermally stable SMs.

Synergistically enhanced electromagnetic absorption in barium ferrite/hollow carbon spheres/epoxy composites

Synergistically enhanced electromagnetic absorption in barium ferrite/hollow carbon spheres/epoxy composites

Correlations between the anti-corrosion properties and the photocatalytic behavior of epoxy coatings incorporating modified graphene oxide deposited on a zinc substrate.

This research aimed to create a substrate-coating system based on zinc and an epoxy resin incorporating modified graphene oxide, which possesses two key characteristics: effective resistance against corrosion and the ability to harness photocatalytic properties. Furthermore, correlations between the anti-corrosion properties and the photocatalytic behaviour of the coatings were made. Thin epoxy (EP) layers embedding 0.1 wt% graphene oxide (GO), reduced graphene oxide (rGO), and modified graphene oxide with (3-aminopropyl)-triethoxysilane (APTES) or poly(amidoamine) (PAMAM) dendrimer were applied on a zinc (Zn) substrate using the dip-coating method. Anti-corrosion properties of coated Zn samples were investigated through electrochemical impedance spectroscopy (EIS) measurements. They showed that the corrosion protection effect is more prominent for EP containing functionalized GO, the highest in the case of GO-PAMAM. The results of the EIS measurements indicated also that the corrosion protection provided by EP-rGO is smaller than that of EP. The photocatalytic properties of the coatings were studied by exposure of the samples to Methylene Blue (MB) solution followed by monitoring the model dye degradation through UV-Vis measurements. To determine the changes in the anti-corrosion properties due to photocatalysis, the coated Zn samples were put through additional EIS measurements. The same coatings applied to a glass substrate lacked photocatalytic properties, indicating that the Zn substrate is accountable for the degradation of MB. Furthermore, the incorporation of GO or functionalized GO into the coating amplifies this effect. From EIS spectra, it was determined that the protective properties loss observed after 3 days is due to coating delamination during exposure to MB solution, the EP-GO-APTES retaining the best adhesion of the coating, 98% remaining on Zn after a cross-hatch test. The corrosion measurements were complemented by examining the morphology and structure of the coatings and the modified GO particles. All things considered, the Zn/EP-GO-APTES system shows the best ability to break down organic pollutants, keeping a good anti-corrosive property and adhesion.

Investigation of the ductile deformation potential of microscale epoxy materials

Investigation of the ductile deformation potential of microscale epoxy materials

Mixed mode fracture toughness of epoxy molding compound/printed circuit board interface of semiconductor packages with respect to temperature and moisture

Interfacial delamination is a critical factor for dissimilar bi-material interfaces in terms of structural mechanical behavior and reliability. In this study, the mixed mode interfacial fracture toughness of a thin epoxy molding compound/printed circuit board bilayer with different mixities was measured via the asymmetric double cantilever beam test with a reinforced metal jig. Additionally, mode II fracture toughness properties were measured through the end notched flexure test. All tests were performed under various temperature and moisture absorption conditions below 100℃/85 %RH. Then, a finite element simulation was performed with the cohesive zone model technique to validate the experimentally measured fracture toughness values by comparing the load–displacement curves from the experiment and simulation. Additionally, the single leg beam test and its finite element simulation were conducted and compared for validation of the measured mixed mode fracture toughness values. It was demonstrated that the developed mixed mode fracture toughness measurement method could provide accurate fracture toughness, which could effectively predict the overall load–displacement curve and damage propagation behavior.

Investigation of factors affecting bond strength of thin epoxy overlay pavements

ABSTRACT This study investigated the factors influencing the bond strength between existing pavement and thin epoxy overlay via laboratory and field tests. Laboratory tests revealed that the highest bond strength occurred at a general temperature and relative humidity of 25 °C and 60%, respectively. The concrete surface profile (CSP) of the specimen was found to have no impact on the bond strength between the latex-modified concrete (LMC) and epoxy binder under favorable conditions. Field testing of well-maintained concrete pavements indicated that neither the existing pavement's pre-treatment process nor its resulting CSP affected the bond strength. However, the bond strength decreased with environmental and vehicle loadings six months after the overlay. A second field test conducted on a deteriorated bridge deck with an LMC pavement revealed that most of the damage occurred at a shallow depth in the existing pavement, demonstrating low bond strength just two days after construction owing to inadequate removal of the deteriorated section. The initially low bond strength increased over time as the epoxy binder permeated the deteriorated area and hardened at greater depths, thus making it necessary to thoroughly remove all deteriorated sections of the existing pavement before constructing a thin epoxy overlay.

Effect of graphene coating on modified and pristine carbon fibers on the tribological response of carbon fiber epoxy composites

Addition of graphene nanoplatelets (GNP) as nanofillers in carbon fiber reinforced polymer composites improves a range of mechanical properties e.g. flexural, tensile and fatigue. Multiple studies have reported that this occurs through the formation of a carbon-enriched interphase with intermediate properties between the epoxy, graphene and carbon fiber. However, even though GNPs act as a solid lubricant and have exceptional strength and thermal conductivity, the wear performance and failure mechanism of GNP-incorporated composites are still not understood. The current study aims to investigate the effect of GNP-coated-pristine as well as GNP-coated-oxidized carbon fibers on the wear performance of carbon fiber reinforced epoxy composites manufactured through vacuum-assisted resin transfer molding technique (VARTM). It has been found that specific wear rate and coefficient of friction were lower for GNPs added composites compared to pristine laminates and it was the least in the case of composites in which an optimum amount of GNPs was coated on oxidized carbon fibers. Moreover, smaller temperature within the specimens has been found during the wear test in the case of GNP-added laminates owing to the higher thermal conductivity of the GNPs. Worn surface morphology has shown formation of thin epoxy layers at lower number of cycles for all the laminates. Fiber breakage, debonding resulting in clean fibers and a large amount of wear debris has been seen on worn surfaces of pristine laminates. However, GNP-added laminates have shown less wear debris and enhanced fiber-epoxy bonding. The wear response has been correlated with the size of the interphase formed between the fiber and the epoxy.

Reconfigurable coupled-resonator acoustoelastic waveguides in fluid-filled phononic metaplates

We study numerically and experimentally acoustoelastic wave propagation in a two-dimensional phononic metaplate consisting of a periodic array of cups sitting on a thin epoxy plate that is perforated with cross holes. When all cups are filled with water, the metaplate possesses a complete band gap. Reconfigurable coupled-resonator acoustoelastic waveguides (CRAEWs) are created by locally emptying certain cups, thus introducing local resonances that are evanescently coupled. Straight and 90° bent periodic waveguides are considered, together with an aperiodic chain of 11 coupled resonators. The aperiodic chain has no definite spatial periodicity but supports collective resonances resulting from the coupling of nearest resonators. Lamb waves are experimentally excited by a piezoelectric patch and received by a scanning optical vibrometer. Experimental results for acoustoelastic wave propagation along both periodic and aperiodic CRAEWs are compared to a three-dimensional finite element model taking fluid–structure interaction into account. The propagation of confined acoustoelastic waves in the 90° bent waveguides and the collective resonances of the aperiodic chain of defected resonators are observed experimentally. Reconfigurability are realized based on the coupling of acoustoelastic waves in a phononic metaplate. Our results show plenty of potential possibilities for the practical design of reconfigurable and programmable elastic wave devices.

Microscopic testing of carbon fiber laminates with shape memory epoxy interlayer

For the first time, microscopic testing has been performed on shape memory polymer composites (SMPCs) which were manufactured by commercial materials already used in aerospace. Results from micro-tests have been compared with those from conventional memory-recovery cycling on macro-scale. Two shape memory polymer composite (SMPC) laminates were fabricated with different shape memory (SM) interlayer: one in the form of an uncured epoxy powder and the other in the form of a thin epoxy foam. The latter, in particular has been studied to evaluate lightweight and stiff sandwich structures with SM properties. The assessment of the manufacturing process by a hot press moulding technique was assessed through micro scale analysis using SEM and MicroCT analysis. DMA analyses were carried out to understand the interaction mechanisms between raw constituents. A Vickers micro-indentation examination before and after heating was able to assess the shape recovery behaviour at the micro-scale level. A nano-instrumental indentation was used to characterise the shape memory response under different loads at elevated temperatures. Whilst an instrumented thermo-mechanical test allowed to investigate the shape memory behaviour at macro-scale level. Results allow identifying the recovery mechanisms at the micro-scale which are responsible for the shape memory performances at the macro-scale. The higher recovery ability of the SM foam is confirmed in comparison with bulk interlayers.

The Effect of Different Fibre Lengths on the Mechanical Properties of Biocomposites

Kenaf is a nonwoody fibrous plant, and its fibre can be potentially used as a reinforcement in the matrix to produce biocomposite materials. The properties of biocomposite materials are highly dependent on the reinforcing material and the matrix used as a binder. This study used kenaf fibre as a reinforcing material with different compositions (10, 20, and 30 wt.%) and different fibre lengths (1 cm and 3 cm) in the matrix using the casting process. Low viscosity epoxy resin (635 thin epoxy resin) with a viscosity of 6 poise was used as the matrix. The results showed that the highest flexural strength, impact strength and shore hardness were obtained at a 30 wt.% kenaf fibre composition with a 1-cm kenaf fibre length, namely, 85 MPa, 338 KJ/m2 and 98 SHD, respectively. The length of the fibre in the matrix affects the mechanical properties of the resulting biocomposite. This condition is caused by kenaf fibres with a length of 1 cm being more dispersed in the matrix than fibres with a length of 3 cm.

Field Tests on Bond Strength and Skid Resistance of Thin Epoxy Overlay Pavements

Field Tests on Bond Strength and Skid Resistance of Thin Epoxy Overlay Pavements

Reconfigurable waveguides defined by selective fluid filling in two-dimensional phononic metaplates

We investigate two-dimensional phononic metaplates consisting of a periodic array of cups on a thin epoxy plate that is perforated with periodic cross holes. The cups are individually filled with water or remain empty, in view of creating reconfigurable phononic waveguides. Phononic band gaps exist for empty or filled epoxy cups, leading to waveguides defined with either positive or negative contrast. Straight and 90° bent waveguides are considered experimentally. Lamb waves are excited by a piezoelectric patch glued onto the metaplate and are imaged using a scanning laser vibrometer. Experimental results are compared to a three-dimensional finite element model of fluid–structure interaction. Passing and forbidden frequency ranges are identified for positive and negative contrast, and confined propagation is observed along the waveguides. Significantly, the propagation of acoustoelastic waves in the 90° bent waveguides is observed experimentally. Reconfigurability and reusability are thus realized based on the coupling of elastic waves in the solid and acoustic waves in the fluid. The results show plenty of potentiality for the practical design of multiplexed and programmable acoustic devices implemented with reconfigurable waveguides printed on demand in a phononic metaplate. • Reconfigurable waveguides with positive or negative contrast by filling fluids. • Bandgaps/passing bands exchange in 2D metaplates via fluid-solid interaction. • Propagation of acoustoelastic waves in 90°-bent waveguides is achieved experimentally.

Performance of Two Thin Epoxy Overlays on New Concrete under Laboratory and Outdoor Exposure Conditions

Thin epoxy overlays are used for improving the condition and extending the service life of bridge decks. The tensile bond pull-off strength, evaluated as per ASTM C1583, is used as the performance indicator. A failure in the substrate with a tensile strength of 250 pounds per square inch (psi) or greater is considered acceptable. However, the performance of in-service bridge decks when evaluated shows inconsistent results. Such studies failed to record and correlate the parameters that influence overlay performance during testing to clarify the observed variations. Laboratory studies by several researchers have documented a distinct performance difference when the overlays are exposed to room temperatures in comparison with elevated temperatures. However, the most influential parameters, such as the variation of substrate moisture against temperature and epoxy softening under elevated temperatures, were not measured and correlated to the observed performance. This study was initiated to provide clarification of the observed performance differences by evaluating the impact of concrete age at the time of epoxy application, concrete mix ingredients, exposure conditions, concrete microstructure development, and substrate moisture and temperature on the performance of two epoxy overlays. Experimental results confirm that (i) the performance of epoxy overlays improves when the concrete mix contains slag and (ii) substrate moisture vapor pressure and epoxy softening under elevated temperature negatively affect the overlay performance.

Low Profile Wideband Dual-Ring Slot Antenna for Biomedical Applications

In this study, a low-profile, co-planar waveguide (CPW) fed, wideband, and dual-ring slot antenna design for biomedical applications is proposed. The proposed antenna has a total area of 10 mm × 10 mm and a height of 0.4 mm, and is designed by using a thin and biocompatible FR4 epoxy (εr = 4.4) substrate to accomplish human body isolation and great flexibility obtained by implantation. This wideband antenna covers a large bandwidth of industrial scientific and medical (ISM) frequency band, including 902.8 MHz to 928 MHz, 1.395 GHz to 1.4 GHz, 1.427 GHz to 1.432 GHz, 2.4 GHz to 2.485 GHz, and above. The simulation results of return loss, voltage standing wave ratio (VSWR), impedance matching, gain, and radiation pattern of the proposed antenna are obtained through High Frequency Structure Simulator (HFSS) 14 software.

Thermal and Reliability Characterization of an Epoxy Resin-Based Double-Side Cooled Power Module

Abstract Wide-Band Gap (WBG) power devices have become a promising option for high-power applications due to the superior material properties over traditional Silicon. To not limit WBG devices’ mother nature, a rugged and high-performance power device packaging solution is necessary. This study proposes a Double-Side Cooled (DSC) 1.2 kV half-bridge power module having dual epoxy resin insulated metal substrate (eIMS) for solving convectional power module challenges and providing a cost-effective solution. The thermal performance outperforms traditional Alumina (Al2O3) Direct Bonded Copper (DBC) DSC power module due to moderate thermal conductivity (10 W/mK) and thin (120 mm) epoxy resin composite dielectric working as the IMS insulation layer. This novel organic dielectric can withstand high voltage (5 kVAC @ 120 μm) and has a Glass Transition Temperature (Tg) of 300°C, which is suitable for high-power applications. In the thermal-mechanical modeling, the organic DSC power module can pass the thermal cycling test over 1,000 cycles by optimizing the mechanical properties of the encapsulant material. In conclusion, this article not only proposes a competitive organic-based power module but also a methodology of evaluation for thermal and mechanical performance.

Laboratory Tests on Skid Resistance and Bond Strength of Thin Epoxy Polymer Concrete Overlays

Laboratory Tests on Skid Resistance and Bond Strength of Thin Epoxy Polymer Concrete Overlays

An experimental investigation on low-velocity impact response and compression after impact of a stochastic, discontinuous prepreg tape composite

The present paper investigated the impact and compression after impact behavior of thin carbon fiber epoxy plates manufactured from prepreg platelet molding compound (PPMC) with two different discontinuous fiber length, 25.5 mm and 12.7 mm, and compared it with the behavior of continuous fiber quasi-isotropic composite laminate with a similar plate thickness. The results of dynamic testing showed that PPMC/12.7 mm exhibited larger amount of absorbed energy, which correlated with larger damage area measured by ultrasonic inspection. Micro-CT analysis showed that a discontinuous fiber composite developed significant amount of through-thickness damage. C-scan measured damage area correlated well with the compression after impact testing results, which indicated that longer fibers provide for better damage tolerance.

Performance-Based Approach for Deciding the Age of New Concrete for Thin Epoxy Overlay Application

A thin epoxy overlay application is a capital preventive maintenance activity. Epoxy overlays reduce the rate of chloride ion ingress and extend bridge deck service life. Highway agency policies and manufacturer specifications require maintaining a 28-day curing period (7-day wet and 21-day dry curing) before the application of an epoxy overlay on bridge decks requiring new concrete for patches and repairs. Consequently, the contractors wait for 28 days to apply an epoxy overlay. Delaying application time increases project completion time and the cost of construction and mobility. The suitability of new concrete to receive epoxy overlays and the performance of overlays depend on several parameters including concrete strength, moisture, and tendency to crack. Such parameters depend on concrete mixture ingredients and wet and dry curing periods. This paper presents a performance-based procedure for evaluating the possibility of reducing the 28-day waiting period for a thin epoxy overlay application on new concrete. An experimental program was developed and executed to evaluate the impact of epoxy overlay application parameters and overlay performance using a tensile bond pull-off strength test. The results support developing a performance-based procedure for deciding on the suitable age of new concrete to receive a thin epoxy overlay. The pull-off bond strength of epoxy overlays applied at 7, 14, and 21 days, following a 7-day moist curing, shows the possibility of applying an epoxy overlay before the end of the 28-day curing period stipulated in the current specifications.

Impact of Concrete Mix Ingredients and Surface Treatments on Epoxy Overlay Performance

Epoxy overlays are applied on bridge decks after curing concrete in patches and repairs for 28 days. A tensile bond pull-off strength of at least 250 pounds per square inch (psi) is expected from a properly applied overlay. Even though the overlay performance at room temperature is mostly satisfactory, the performance at elevated temperatures is not convincing. The degradation of mechanical and adhesion properties of epoxy, shear stress at the concrete/overlay interface caused by thermal incompatibility, and the interface moisture vapor pressure are the commonly cited parameters for poor bond strength at elevated temperatures. A combined effect of these parameters results in the most unfavorable failure mode (which is bond failure at the concrete/overlay interface) at a strength lower than the specified limit of 250 psi. The moisture migration through concrete depends on many factors including moisture content along the depth of concrete, pore microstructure, exposure condition, and drying period. This study investigated the impact of concrete mix ingredients and surface treatments on the thin epoxy overlay bond strength. The results show that the use of concrete mixes with slag and penetrating sealant pretreatment improves the bond strength.

Evaluating the influence of radiative heat flux on convective heat transfer from a vertical plate in air using an improved heating plate

This article examines the influence of radiative heat flux on the accuracy of the results of free convective heat transfer in air. In order to carry out these tests, based on the experience gained during the operation of a plate heated on one side, compensated by a reverse heat loss flux counter-heater, a unique double-sided heating sandwich plate was designed and built, consisting of three thin epoxy resin plates reinforced with glass fibre. The paths of surface resistance thermometers were etched using photolithography on the two outer plates laminated on one side with copper. The traces of two resistance heaters were etched on both sides of the third, bilaterally laminated middle plate.