High Loss Factor Research Articles

Frequency and temperature dependent viscoelastic properties of natural rubber and nitrile butadiene rubber at different temperatures for vibration damping applications: an experimental study

The study aims to evaluate the frequency and temperature-dependent viscoelastic properties of natural rubber (NR) and nitrile butadiene rubber (NBR) for vibration damping applications. The dynamic mechanical analysis (DMA) tests were conducted on NR and NBR at low frequencies, from room temperature to 112 °C. The experimental data were fitted using the generalized Maxwell model, and vibration tests were conducted to obtain dynamic properties such as natural frequencies, damping ratio, and quality factor. The loss factor for NR increased significantly above 80 °C, while for NBR, it decreased above 50 °C. At higher temperatures, both NR and NBR exhibited faster relaxation, but NR had a higher loss factor, indicating a better damping ability. The relaxation strength of NR increased above 60 °C, whereas that of NBR decreased, highlighting the differences in their damping abilities. NBR showed greater damping ability at the first natural frequency, while NR performed better at the second and third natural frequencies. According to the experimental findings, NR proves to be better suited for damping in high-temperature conditions, while NBR is more suitable for low-temperature damping applications. The relaxation modulus of NR is lower than that of NBR at lower temperatures, leading to a better damping performance for NR at higher temperatures. The study recommends using NR for high-temperature applications where high damping is required and NBR for low-temperature applications that require moderate damping.

Mechanical properties of basalt/jute fiber composites to improve the phenomenon of drawing delamination

AbstractIn recent years, natural fibers have been commonly used to reinforce various polymers, resulting in composites with excellent mechanical properties. To address the challenge of delamination and significant fiber pull‐out in inter‐laminar hybrid composites during stretching, this study focused on preparing intra‐laminar hybrid textile composites using basalt fibers (BFs) and jute fibers (JFs) as raw materials. Moreover, the mechanical properties of BF/JF intra‐layer blended fabric composites were investigated. The prepared composites underwent tensile, flexural, impact, and dynamic mechanical analysis (DMA). The results indicated that intra‐laminar blended composites demonstrated superior mechanical properties compared to inter‐laminar blended fabric composites. The DMA results revealed that the intra‐laminar blended composites featured a high peak loss factor. Morphological analysis indicated enhanced stress transfer from fiber‐to‐fiber and fiber‐to‐matrix in the intra‐laminar blended composites.Highlights Fiber blending can expand the application areas of natural fibers. Fiber blending can reduce interlayer damage. Intra‐layer blending differs from interlayer hybrid composites. Strong bonding between fibers facilitates effective stress transfer. “Green” composites exhibit exceptional mechanical properties.

Reduction in Floor Impact Noise Using Resilient Pads Composed of Machining Scraps.

Floor impact noise is a significant social concern to secure a quiescent living space for multi-story building residents in South Korea. The floating floor, consisting of a concrete structure on resilient pads, is a specifically designed system to minimize noise transmission. This floating structure employs polymeric pads as the resilient materials. In this study, we investigated the utilization of helically shaped machining scraps as a resilient material for an alternative approach to floor noise reduction. The dynamic elastic modulus and loss factor of the scrap pads were measured using the vibration test method. The scrap pads exhibited a low dynamic elastic modulus and a high loss factor compared to the polymeric pads. Heavyweight impact sound experiments in an actual building were conducted to evaluate the noise reduction performance. The proposed pads showed excellent performance on the reduction in the structure-borne vibration of the concrete slab and resulting sound generation. The analytical model was used to simulate the response of the floating floor structure, enabling a parametric study to examine the effects of the resilient layer viscoelastic properties. Both experimental and analytical evidence confirmed that the proposed scrap pads contribute to the development of sustainable solutions for the minimization of floor impact noise.

Tuneable vibration control of beams using granular multilayer composite

We explore a passive control solution of bending waves in beams, which takes advantage of the dissipative properties of granular media. It consists in a layer of particles confined between two beams and interacting with each other through their contacts. The inter-particles contacts are intrinsically dissipative due to friction, which efficiently works under shear. In practice, the mechanical response of such a multilayer inherit Hertz contact mechanics, thus conferring confining pressure dependent elasticity and dissipation. Previous work have shown that the hysteretic shear behaviour of a granular medium confined in a box can be reasonably captured by a single DOF model using Dahl model fed by an effective medium theory of granular media. Using this reduced model together with finite element method, we simulate the dynamic response of a three-layer composite beam whose core is made of confined frictional particles. This model makes it possible to characterize its elastic and damping properties, revealing in particular a high and tuneable loss factor with respect to shear strain amplitude and confining pressure, suitable for vibro-acoustics applications.

Nanoporous amorphous carbon nanopillars with lightweight, ultrahigh strength, large fracture strain, and high damping capability

Simultaneous achievement of lightweight, ultrahigh strength, large fracture strain, and high damping capability is challenging because some of these mechanical properties are mutually exclusive. Here, we utilize self-assembled polymeric carbon precursor materials in combination with scalable nano-imprinting lithography to produce nanoporous carbon nanopillars. Remarkably, nanoporosity induced via sacrificial template significantly reduces the mass density of amorphous carbon to 0.66 ~ 0.82 g cm−3 while the yield and fracture strengths of nanoporous carbon nanopillars are higher than those of most engineering materials with the similar mass density. Moreover, these nanopillars display both elastic and plastic behavior with large fracture strain. A reversible part of the sp2-to-sp3 transition produces large elastic strain and a high loss factor (up to 0.033) comparable to Ni-Ti shape memory alloys. The irreversible part of the sp2-to-sp3 transition enables plastic deformation, leading to a large fracture strain of up to 35%. These findings are substantiated using simulation studies. None of the existing structural materials exhibit a comparable combination of mass density, strength, deformability, and damping capability. Hence, the results of this study illustrate the potential of both dense and nanoporous amorphous carbon materials as superior structural nanomaterials.

Polarization-controlled third harmonic generation by quasi-bound states in the continuum in silicon nanopillar metasurfaces

All-dielectric metasurfaces have received widespread attention due to their low intrinsic loss compared to the metallic counterparts. However, relatively high radiation loss and low quality (Q) factor of the dielectric nanostructures may significantly degrade their nonlinear optical efficiency. Here, we demonstrate that silicon-nanopillar-based metasurfaces supporting quasi bound states in the continuum (BICs) can greatly enhance the efficiency of third harmonic generation (THG). We show that symmetry-protected BICs form at the Γ-point of doubly degenerate band or nondegenerate band can be selectively transformed into quasi BIC through symmetry breaking of our silicon metasurfaces. Benefiting from the high Q and resonance enhancement by the quasi BICs, the THG conversion efficiencies of the silicon metasurface reaches 4.3 × 10-4 with a peak pump intensity of 1.3 GW/cm2, which can be four orders higher than that of a silicon planar film with the same thickness. In addition, the THG intensity is polarization-dependent for the single quasi BIC while it is polarization-independent for the doublet quasi BIC. Our results provide a new strategy for the design of high-efficiency silicon-based optical nonlinear devices.

Active Constrained Layer Damping of Beams with Natural Fiber Reinforced Viscoelastic Composites

Abstract Viscoelastic composite reinforced with natural fibers is proposed here for the damping treatment of structures for vibration attenuation. The constrained layer damping (CLD) method is found a prominent structural vibration damping method and as a result of the inclusion of natural fiber, substantial damping could be achieved due to the development of shear as well as extensional strains in the viscoelastic material. Finite element analysis of a substrate beam combined with CLD treatment is used to investigate the corresponding improvement in damping. The influence of various geometry of presently considered natural viscoelastic composite layers on the CLD treatment's damping performance has been evaluated and discussed. Damping performances of natural as well as synthetic fibers have been assessed and compared for using natural fibers in viscoelastic composite for various structural applications. The addition of natural fiber has resulted from enhanced damping capacity due to substantial friction at the natural fiber-matrix interface compared to the case of interface with synthetic fiber. Natural fiber attributes less stiffness and a higher loss factor as compared to synthetic fiber and the insertion of stiff fibers affects the polymer chain's movements, decreasing the matrix phase's damping behavior. The dynamic mechanical analysis test is performed to evaluate the damping characteristics in the form of loss factor, storage, and loss modulus over the temperature range from frozen state to melting state.

Design of acoustic coating for underwater stealth in low-frequency ranges

In this study, it is aimed to protect underwater vehicles against active sonar systems by anechoic coating. A matrix material with close acoustic impedance to water, resistivity to hydrostatic pressure, suitability for the marine environment, and high material loss factor is selected. At low frequencies, the inclusions in different shapes and sizes are added to the matrix material. Since solid inclusions will increase the coating mass considerably, air cavities are preferred as inclusions. More attention is paid to low-frequency absorption, especially below 1 kHz, because of advancing sonar technology. The acoustic performance of the designed models is compared in three frequency ranges: low (below 3 kHz), middle (3–6 kHz), and high (6–10 kHz). The designed models are constructed by considering hydrostatic pressure; hence, volume of air cavities is tried to decrease, while absorption performance is aimed to increase. Therefore, a conical cavity which commonly used in the literature is optimized by chancing its dimensions and location. Also, novel approaches, gong shape cavity, and sandglass cavities are introduced. The results show that, not only cavity shape, but also its location and dimensions are highly influential on absorption performance. High-volume cavities increase the absorption performance at the low-frequency range, but they are not effective at high frequencies. The gong shape and sandglass air cavities show broadband absorption; also, gong shape cavity volume is less than literature models. Thus, its usability increases at deep waters. The results of this study provide novel underwater acoustic coating models for various applications.

Imidazole ionic liquids-based ultra-broadband metamaterial absorbers from cross-architecture design

Room temperature ionic liquids (ILs) characterized by high dielectric loss factors and conductivity emerge as promising candidates for liquid-based metamaterial absorbers (LMMAs). In this work, the IL 1-ethyl-3-methyl-imidazolium dicyanamide was employed to construct an IL-based LMMA, leveraging a cross-architecture (C-A) design paradigm. Numerical analyses reveal that the C-A ILMMA achieves an absorption efficiency exceeding 90% within the frequency range of 7.5–57.8 GHz, translating to a relative absorption bandwidth of 153%. Moreover, the symmetrical configuration of the C-A ILMMA ensures its robust performance across a comprehensive range of polarization angles (0° to 90°), thereby underscoring its polarization insensitivity. Even with an increased incident angle of 60°, the C-A ILMMA sustains an absorption rate above 85% within the frequency intervals of 9.0–13.3 GHz and 24.7–60.0 GHz, highlighting its broad incident angle absorption capability. Owing to the superior thermal stability of the IL, the C-A ILMMA consistently maintains an absorption rate of over 90% across a temperature gradient from 20 °C to 100 °C. Mechanistic investigations reveal that the optimal absorption of the C-A ILMMA predominantly stems from dielectric polarization loss and the ionic current induced within the ILs. Subsequent experimental evaluations corroborate that the C-A ILMMA exhibits an absorptivity in excess of 90% over an ultra-broadband frequency spanning 10–40 GHz, aligning closely with numerical predictions. This IL-based C-A ILMMA not only augments the absorption bandwidth substantially but also enhances the adaptability of ILMMA in more rigorous environments, attributed to the commendable physicochemical properties of ILs.

Periodic additive acoustic black holes to absorb vibrations from plates

This paper first suggests a composite structure with periodic additive acoustic black holes (ABH) to absorb vibrations from plates. Different from conventional embedded ABHs, this additive configuration no longer compromises structural integrity. The suggested periodic structure forms a compact acoustic functional material. To analyze the vibration behavior of this coupled structure, we establish a theoretical model employing the Gaussian expansion method (GEM) and the nullspace method (NSM), and it is validated through finite element simulations. Subsequently, we develop a two-dimensional wave and Rayleigh–Ritz method (WRRM) to compute complex dispersion curves, with the imaginary part predicting absorption capability. Our findings reveal that the local resonance eigenmodes of the ABH plate with high loss factors dominate the damping effect, overshadowing the role of Bragg scattering. Furthermore, the introduction of a damping layer proves highly effective in absorbing local vibrations across a wide frequency band. Moreover, we then conduct parametric analyses on various aspects, including ABH order, central thickness, ABH plate thickness, and ABH radius. Notably, the latter two parameters exert a significant influence on damping performance, primarily due to the added mass they introduce. Finally, we examine a finite plate consisting of a 4 × 4 cell arrangement. This composite structure demonstrates substantial modal loss factors when local modes are activated. Moreover, in forced vibration tests, the additive ABHs prove highly effective in mitigating vibrations within the host plate.

Microfluidics investigation of the fracture/matrix interaction mechanisms during preformed particle gel (PPG) treatment in fractured porous media

Although water injection is one of the most common methods for enhancing the recovery from oil reservoirs, its effectiveness in severely heterogeneous porous media such as fractured rocks, is debatable. Preformed Particle Gel (PPG) treatment is one of the most promising methods which is considered for water shut-off in the near wellbore area or improving the sweep efficiency of the injected water deep in the reservoir. Recognizing the PPG transport mechanisms in fracture, fracture/matrix interactions during and after PPG treatment, and the contributing parameters on such mechanisms, is a prerequisite for designing an effective water shut-off process and possible enhanced oil recovery (EOR). With this aim, the dynamic behavior of PPG samples is studied in two different fractured porous media representing the near wellbore area (dual permeability model) and deep in the reservoir zones (single permeability model). During encroachment of the gel particles in fracture, the dehydration of gel produces a large volume of filtrate which sweeps the oil inside the matrix. PPG particles might go through deformation, shrinkage and/or breakage, before infiltrating into pores of matrix where they form an impermeable cake. The experimental results shows that formation of such cake, is one of the main affecting parameters in the performance of the conformance control and EOR. Additionally, the affecting parameters such as concentration of nano-silica (n-SiO2), width of fracture, particles size, ionic strength of brine and injection rate of gel were examined. The concentration of n-SiO2 affects the gel loss factor (ratio of loss modulus to storage modulus) and hence its encroachment behavior. The gel sample with 1 wt% n-SiO2 has the highest loss factor which makes it more favorable for water shut-off considering lower injection pressure and less volume required for treatment. The water shut-off treatment is more effective in the case of systems with wider fractures. Based on the size of the PPG particles, the plugging mechanisms of the fracture can be either direct plugging, bridge plugging or a combination of both mechanisms, however all the studied samples provided same degree of plugging efficiency in the performed experiments. Swelling the samples in brines with higher salinities reduces the required volume of gel, while the injection pressure remained unaffected. To reduce the required volume of gel, highest possible injection rate is recommended, since the shear thinning rheology of the gel damps increment of injection pressure. In the case of single permeability model, water shut-off treatment reduced the fracture conductivity effectively, so that in the subsequent flooding, the injected brine was diverted toward matrix and the displaced oil was recovered through the fracture. During water flooding stage after gel placement, the withstanding pressure of PPG must be taken into account to avoid gel rupture, movement and washout.

Effect of Microwave Hybrid Heating on Mechanical Properties and Microstructure of Sn3.0Ag0.5Cu/Cu Solder Joints

Microwave hybrid heating (MHH) has become soldering’s alternative method for lead-free solder alloys due to its benefits towards modern microtechnology, such as shorter processing time, lower energy consumption and lower defect rate. Nonetheless, it still requires susceptors to improve its heating performance, such as SiC, which is known for its high loss factor under low microwave frequencies. In this study, the effect of microwave hybrid heating on mechanical properties, as well as the microstructure of solder joint between Sn3.0Ag0.5Cu (SAC305) solder alloy and Cu substrate was investigated. Solder joint was created using MHH with different soldering parameters (amount of SiC in a range of 3-7g and exposure time in a range of 7-10min) between SAC305 solder alloy (in the form of wire and paste) and Cu substrate. Then, a lap shear test was carried out following a standard of ASTM D1002 to determine solder joint strength. Characterization was made using an optical microscope and scanning electron microscopy. Results showed that solder wire produced the highest solder joint strength with the value of 115.45 MPa when using 3.05g of SiC for 8.92min soldering time. Meanwhile, the solder paste produced 109.76MPa solder joint strength when using 3.03 g of SiC for 9.39 min soldering time. The intermetallic compound (IMC) form was scallop-like Cu6Sn5, both solder/substrate joints with a thickness of 2.87 μm for solder wire and 3.62 μm for solder paste. Nonetheless, an excessive amount of SiC would generate more heat in MHH and increase the IMC thickness as well as reduce shear strength, which eventually decreases the solder joint stability.

Energy Storage Performance and Dielectric Properties of Surface Fluorinated BOPP Films

Various composite films with high energy storage performance and/or dielectric strength have been fabricated. However, due to some reasons, few of them have been used in practice, and BOPP film is still regarded as the state-of-the-art capacitor dielectric film. Previous work has indicated that direct fluorination can improve the dielectric strength of BOPP films. Herein, as a continuation of previous work, the energy storage performance and basic dielectric properties of the surface fluorinated BOPP film are investigated. The charge-discharge experimental results show that the surface fluorinated BOPP sample has the maximum energy storage or release density of 5.27 or 4.43 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which is 59.8% or 44.6% higher than that of the virgin BOPP sample. The dielectric measurement results indicate that the surface fluorinated BOPP sample has slightly higher dielectric constant and dielectric loss than the virgin BOPP sample. The analyses of physicochemical characteristics reveal that the 0.75 μm thick fluorinated surface layer has a high degree of fluorination. The results of the calculation based on the three-layer dielectric model and the dielectric measurements further show that the fluorinated surface layer has high dielectric constant and loss factor, similar to non-perfluoropolymers. The enhancement of energy storage performance and dielectric strength is mainly attributed to the blocking of the fluorinated layer to electron injection from the cathode, due to a 60% reduction of the interfacial electric field and a decrease in free volume of the surface layer by the fluorination.

Exploring the Internal Patterns in the Design of Ultrawideband Microwave Absorbers

Microwave absorbers have been developed by various manufacturing technologies, such as injection molding and machining, in which their design parameters are mainly the external shape of the absorber and the dielectric properties of the material. Here, we use additive manufacturing to design and build absorbers with complex internal patterns. With this new design flexibility, absorbers with internal patterns, when compared with their solid versions, maintained their absorption performance. The absorbers were initially designed and optimized by simulations, built by a 3D printer, and experimentally measured. As a proof of concept, we built absorbers with fractal-type open internal patterns, using filaments with a high loss factor. In the experimental characterization with various angles of incidence, the absorbers with internal fractals showed attenuations greater than 20 dB at frequencies below 15 GHz and significantly better attenuations above 15 GHz, over 30 dB. The results demonstrated that fractal absorbers can attenuate 99% or more of the incident radiation over a wide frequency range, showing that internal patterns could be used as an additional design parameter.

Effect of polyurethane material design on damping ability

AbstractPolyurethane (PU) materials attract the interest of researchers for use in damping and vibration isolation. However, an undesirable property of pure polyurethane is a narrow temperature range of mechanical energy absorption. This study presented several ways to design damping PU materials based on two initial polyurethanes with different prepolymer compositions. The difference between the glass transition temperatures of initial PUs was 30°C. One way of designing was to obtain PU material based on a mixture of the two different prepolymers. Another way was to fabricate two‐layer composites from layers of different initial PUs. Тwo‐layer PU composites were fabricated in such ways as by sequential formation layer by layer or by gluing individual films. Continuous materials with a good connection between the layers were formed. Fourier transform infrared spectroscopy, light microscopy, contact angle measurements, and tensile tests were used for PU materials characterization. Dynamic mechanical analysis was used to investigate the viscoelastic properties and evaluate damping ability. The temperature ranges of effective damping (tan δ ≥ 0.3) from −27°C to 17°C and from −5°C to 42°C were shown for initial PUs. One high loss factor maximum for mixed‐base polyurethane was observed, and the temperature range of effective damping was from −20°C to 32°C. All designed two‐layer composites were shown two loss factor maxima. Their effective damping occurred either in one temperature range (−25°C to 29°C) or in two (−24°C to −14°C and −7°C to 37°C), depending on the design of the composite. The advantage of polyurethane materials design ways such as mixed‐base and two‐layer composite is the ease of control of the temperature region of effective damping. Proposed polyurethane materials designs offer a new approach to developing high‐performed damping materials.

Dynamic and quasi-static mechanical behavior of 3D metallic woven lattices

Complex mechanical systems can generate severe dynamic environments that require materials with optimized combinations of damping properties, elastic moduli, and service temperatures. In this study, woven lattices were manufactured with stainless steel (SS) and copper (Cu) wires via a three-dimensional (3D) weaving process to form SS, Cu, and SS–Cu lattices. Following fabrication, selective bonding using Cusil® was applied to either one or both sides of the SS–Cu weaves to form single-sided bonded SS–Cu composite (B1C) lattices and double-sided bonded SS–Cu composite (B2C) lattices. Measurements of dynamic and quasi-static mechanical properties of both unbonded and bonded weaves demonstrate that all three unbonded lattices exhibit high loss factors with a relatively low normalized effective elastic modulus. In contrast, the bonded SS–Cu lattices exhibit lower loss factors but higher normalized effective elastic moduli. We attribute the high loss factors and relative low moduli to wire rearrangement during deformation in the form of wire sliding and rotation that becomes partially inhibited when we bond Cu wires on one or both sides of the SS–Cu weaves. We discuss sources for the observed variations in properties and demonstrate an ability to both tune and obtain exceptional damping and moderate stiffness in architected metallic lattices.

Re-use of jute fiber hybrid nonwoven breather within laminated composite applications: A case study

Jute/polyester hybrid nonwoven mats were developed as an alternative to the conventional nylon or polyester breather to reduce the use of synthetic polymers and associated waste generated during composite manufacturing. However, end-of-life breathers still face the challenge of waste management. In this study, a circular economy strategy for multiple applications of waste hybrid nonwoven breathers was thus proposed to study their recycling possibilities. Hybrid nonwoven breathers were first used to facilitate the autoclave forming of carbon fiber-reinforced plastics, and non-destructive and mechanical tests were performed to determine the quality. The used breathers were then recycled and reused in three ways: directly as reinforcing material and in hybrid combinations with glass fibers and ramie fibers for the production of new composites. Results of quality checks show that the hybrid nonwoven breather is a viable alternative to commercial breathers. The thermal, mechanical, and damping properties of the composites incorporating reused material were investigated. The hybrid nonwoven breather/Glass fiber composites show superior thermal and mechanical properties as well as improved damping properties. The hybrid nonwoven breather/Ramie fiber composites have the advantages of low density and high loss factor reaching up to 0.1572. The product of specific modulus and loss factor was then used as the figure of merit to estimate the structural damping properties of the composites. Both glass fiber and ramie fiber hybrid composites presented a higher figure of merit with 0.86 and 0.83 GPa/(g/cm3), respectively. Therefore, hybrid nonwoven breathers can be adapted to replace synthetic materials in semi-structural applications.

Patterned MXene-enabled switchable health monitoring and electromagnetic protection for architecture

Health monitoring of architectures and customization of electromagnetic (EM) radiation-free spaces are crucial for the transformation of future high-quality life, especially special life environments. Herein, a health monitored strain array and EM protective coating are obtained by tailoring the MXene composites, where electron transport plays an irreplaceable role in functional regulation. The EM response signal of the periodic patterned MXene is sensitive to the structural deformation of the array, and its sensitivity reaches 96 MHz/%. When the Ti3C2Tx composite serves as an EM coating, the shielding effect of the customized room is ∼99.8%. The EM performance of the Ti3C2Tx composite can be switched between absorbing and shielding by tuning its electrical conductivity. The optimal EM absorption performance is up to −54.8 dB with the bandwidth over 3.02 GHz, and the average interference shielding performance surpass 30 dB with the contribution of absorption of 26.44 dB due to the high loss factor. This result provides a reference for the application of EM functional materials in the field of building, especially for the design of high-standard buildings such as hospitals, military bases, and kindergartens.

Dynamic mechanical, ballistic and tribological behavior of luffa aegyptiaca fiber reinforced coco husk biochar epoxy composite

AbstractIn the current work, light weight epoxy bio‐composites are created for low‐cost technological applications using luffa aegyptiaca fiber and biochar particles derived from coco husk (CHB). This study aims to evaluate the effects of CHB particles added at different concentrations (3 vol% and 5 vol%) on the dynamic mechanical, ballistic and tribology behavior of epoxy composites constructed from luffa aegyptiaca fiber with different fiber loading (20%, 30% and 40 vol%). The composites are prepared using hand layup process provided with post curing operation. The combination of 3 vol% CHB particles and 40 vol% luffa aegyptiaca fiber having the improved viscoelastic properties by means of high storage modulus (5.05 GPa) and low loss factor (0.31). Moreover, this composite shows better ballistic properties in terms of low velocity impact energy (17.1 J). The optical image of impact damage behavior shows minimum damage of impactor on the composite and penetration effect found to be lower. This luffa aegyptiaca fiber reinforced epoxy composite also shows the lowest value of coefficient of friction (COF) with 0.48 and the lowest specific wear rate of 0.011 mm3/Nm. These epoxy composites made from luffa aegyptiaca fiber and CHB particles may be useful in a variety of engineering applications that can use materials for manufacture sporting goods, home furnishings, food packaging, and transportation.

Theoretical reasons for rapid heating of vegetable oils by microwaves

Water and high-moisture foods are readily heated in microwaves due to their relatively high dielectric loss factors. Vegetable oil, on the other hand, has a much smaller loss factor (about 1/100th that of water), and is generally believed to be unsuitable for microwave heating. In this study, we conducted experiments to compare heating rates between vegetable oil and pure water in a 2450 MHz microwave oven. We found that the vegetable oil samples were heated rapidly in microwaves, and even faster (1.4–2.0 times) than the water samples. To provide a theoretical explanation, we developed a 3-D computer simulation model. The simulation revealed an approximately 10-fold stronger electric field in oil compared to water, resulting in a similar amount of microwave power being absorbed by the oil and water samples. As the absorbed microwave power was converted into thermal energy, the oil samples were heated faster due to their smaller specific heat (1/2 that of water). But we also found that when the dimensions of oil are smaller than half the microwave wavelength, oil is heated slower than water due to the absence of hot spot areas. This study provides a theoretical explanation for microwave heating of vegetable oils and demonstrates opportunities for utilizing microwave energy to electrify industrial heating of vegetable oils.