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The coexistence of PM2.5 pollution and the ongoing pandemic poses significant risks to human health. Protective masks incorporating high-efficiency particulate air filters offer adequate protection against PM2.5 particles. Micro/nanofibrous nonwovens, including melt-blown and electrospun nonwovens, are essential filter materials. This study focuses on the filtration mechanism and geometric structure design of multi-level structured micro/nanofibrous nonwovens. A comprehensive investigation was conducted on a filter core material composed of polyacrylonitrile, a polystyrene electrospun membrane, a polypropylene (PP) melt-blown membrane, and a supporting outer layer of a PP spun-bonded membrane. The resulting nonwovens exhibited exceptional filtration efficiency of 99.98% for PM0.3 particles, with a low pressure drop of 60 Pa at 32 L/min inlet air velocity. Filtration efficiencies of 99.99% and 100% were achieved for PM1.0 and PM2.5 particles, respectively. These characteristics make the designed composite nonwovens a very promising filter material for masks. The study contributes to understanding filtration mechanisms and developing advanced high-efficiency filter materials, enhancing protection against airborne pollutants. [ABSTRACT FROM AUTHOR]

This paper introduces the inertial amplifier viscoelastic tuned mass dampers (IAVTMD). The viscoelastic materials are implanted inside the core material of the inertial amplifier tuned mass dampers. The standard linear solid models are applied mathematically to formulate the viscoelastic material. H 2 and H ∞ optimization mechanisms apply to derive the exact mathematical closed-form formulations for optimal design parameters for novel inertial amplifier viscoelastic tuned mass dampers. The optimum IAVTMD installs at the top of the structures to mitigate the dynamic responses, determining the dynamic responses analytically through transfer function formation. At first, IAVTMD's dynamic response reduction capacity compares with the conventional tuned mass damper's (CTMD) dynamic response reduction capacity. As a result, H 2 optimized IAVTMD's dynamic response reduction capacity is significantly 20.87% and 26.47% superior to two well-established H 2 optimized conventional tuned mass damper's dynamic response reduction capacity. In addition, H ∞ optimized IAVTMD has 15.48% more dynamic response reduction capacity than H ∞ conventional tuned mass damper. H 2 and H ∞ optimized tuned mass damper inerters with optimal closed-form solutions are introduced in this paper. A higher damper mass ratio and a lower inerter mass ratio are recommended to produce H 2 and H ∞ optimized tuned mass damper inerter (TMDI) with a lower frequency and damping ratio in an affordable range. Accordingly, H 2 and H ∞ optimized IAVTMD's dynamic response reduction capacities are significantly 6.94% and 23.29% superior to H 2 and H ∞ optimized TMDI's dynamic response reduction capacity. The closed-form expressions for optimal design parameters of inertial amplifier viscoelastic tuned mass dampers and tuned mass damper inerters are mathematically correct and effective for practical applications. [ABSTRACT FROM AUTHOR]

This study investigates the impact and after-impact compression behavior of sandwich structures with carbon fiber composite face-sheets consisting of various polymeric core structures. In particular, the performance of polypropylene foam core with closed cell structure, which is new to engineering applications, against other polymeric core structures was investigated. Sandwich panels were subjected to three different impact energies and after-impact compression tests were conducted on each sample to reveal their damage tolerances and load-carrying capabilities. In-situ acoustic measurements were made to fully understand the damage and evolution mechanisms in the after-impact compression tests. Honeycomb polypropylene (PP) foam, polyvinyl chloride (PVC), and extruded polystyrene (XPS) foam were used as core materials. As a result of the tests, it was obtained which damage types occurred at which force levels. PP core panels exhibited different impact behavior compared to conventional sandwich core structures and were successful in preventing damage to the face sheets. [ABSTRACT FROM AUTHOR]

This study investigated the potential for improving the mechanical behavior of glass fiber polyester composites by using symmetric hybrid sandwich configurations that combine continuous woven composite and different discontinuous reinforcements used as a core. The discontinuous reinforcements included sheet molding compound (SMC), bulk molding compound (BMC), and the discontinuous prepreg based platelets that were chopped from the woven trim scrap. Hybrid sandwich configurations using different core materials exhibited improvements in flexural mechanical properties, while providing more progressive failure under both flexural and compressive loading. Compressive strength in polyester SMC and woven laminate was significantly lower than flexural strength, while BMC and chopped platelets exhibited similar levels of strength in flexure and compression. Overall, hybridized compression molding produced sandwich structures can be used to control the failure progression and to improve the structural characteristics of composite, especially under flexural loads. The trim scrap core sandwich configuration had mechanical properties comparable with the BMC core hybrid. Therefore, trim scrap upcycling can be an efficient approach to reducing the amount of material waste during the manufacturing. [ABSTRACT FROM AUTHOR]

Wicking in textiles is a key property of fabric moisture permeability, which has been found to be dominant in the comfort-maintaining mechanism of apparel products, especially for sportswear that has high requirements for sweat transfer. Various methods have been given in order to improve moisture transfer behavior of fabrics, among which fiber modification is the most direct and ideal way. In this article, a design-driven yarn structure spinning model for moisture wicking improvement is established by using a helically shaped covering material to limit the inter-fiber spacings of the staple core yarn so that an improvement in effective capillary channels with better continuity can be achieved. The developed yarn constructions combine the advantages of natural and synthetic fibers, showing significant improvements on moisture wicking performance, fast-drying effects as well as commercial values. Experiments on the fabrics made in accordance achieved excellent results both before and after washing. For the most efficient fabric 5 with cotton-linen as the core material, the average diffusion time was decreased by 86.4% and 66.5% before and after washing, compared with the core yarn. Excessively large water absorption rates of the control fabrics were limited and decreased by 22.1% and 32.4%. The evaporation rates of the fabric were increased by 25.6% and 18.5%, indicating obvious improvements in fast drying effects. Through various experiments, the optimal spinning parameters were investigated which provided methods and established foundations for subsequent research. The finding in this study offer the possibility of fiber moisture performance modification with high efficiency, low cost, and environmental sustainability. [ABSTRACT FROM AUTHOR]

Lattice truss core sandwich composite (LTCSC) panels can exhibit high compressive performance until failure is caused by compressive fracture of the composite strut. Early failure of the core-facesheet and central nodes, as well as fiber misalignment, can hinder the full potential of an LTCSC. This study aimed at improving the compressive stiffness and strength of LTCSC panels through minimizing the fiber misalignment and fabrication issues, while strengthening the central and core-facesheet nodes. The lost-molding technique was used to fabricate LTCSC panels, which were then subjected to quasi-static flatwise compression testing. Relative positioning of neighboring composite struts, modification of the carbon fiber path, and strengthening of the core-facesheet node significantly improved the compressive performance of the panels. Based on the findings, compressive strength and stiffness of LTCSC panels can be improved about 100% and 300%, respectively, with minimal increase in weight. Fabricated LTCSC panels were found to demonstrate competitive specific compressive properties in comparison with conventional core materials. [ABSTRACT FROM AUTHOR]

Spiropyran and spiroxazine photochromics have attracted increasing attention in optical data storage, optical switches, and anti-counterfeiting for decades. To expand the applications of spiropyran and spiroxazine, the durability and multi-color changes of spiropyran and spiroxazine still need to be explored. In this article, based on the subtractive principle of dyes, multi-color spiropyran and spiroxazine microcapsules with uniform particle sizes were prepared by the interfacial polymerization method via using compounds (spiropyran and spiroxazine) of different colors as the core material, and polyurethane as the shell material. Among them, toluene diisocyanate and polyethylene glycol constitute the hard and soft segments of polyurethane, respectively. The color of spiropyran and spiroxazine microcapsules can effectively switch between color and colorless, showing excellent photo fatigue resistance. The average particle size of microcapsules is 2.951 µm, and the particle distribution index value is 0.314, which shows the particle size is small and uniform. The maximum thermal decomposition temperature is 426°C, demonstrating good thermal stability. The hydrophobic photochromic fabric was prepared by coating multi-color spiropyran and spiroxazine microcapsules on cotton knitted fabric and hydrophobic treatment. The hydrophobic photochromic fabric is hydrophobic and stain resistant, and exhibits multi-color dynamic switching and long-lasting use. After 50 cycles of washing, the water contact angle of the fabric remains about 109°, showing its good washing resistance and water repellency. In addition, spiropyran and spiroxazine microcapsules are also applied in template and screen printing to impart rich and dynamic color-changing effects to fabrics, fabricating photochromic fabrics. Photochromic fabrics have potential applications in civilian and military fields. [ABSTRACT FROM AUTHOR]

Implementation of natural fibers like kenaf in composite laminates has been the focus of many researchers. The considerable price of Low-Velocity Impact (LVI) testing, as well as the time constraints imposed by the short duration of this experiment, and prior reports of the obedience of Quasi-Static Indentation (QSI) test findings to LVI test results, have encouraged researchers to employ QSI instead of LVI. This work compares the mechanical characteristics of composite laminates consisting of chopped glass and kenaf fibers as a core and investigates the effect of hybridizing the mentioned chopped fibers as the core of a laminate. Three types of laminates with different core materials were fabricated to do this research. The results showed that among the laminates with the same weight, kenaf core laminate has the highest resistance against indentation and has the best performance in terms of absorbed energy, peak load, and damaged region. Using chopped kenaf fiber instead of chopped glass fiber can increase the absorbed energy and the peak load by 36% and 17%, respectively. Also, hybridizing the mentioned chopped fibers has not fully maximized the properties of the composite laminate during the QSI test. Finally, finite element modelling of the laminates was performed, and the numerical and experimental results were pretty aligned. [ABSTRACT FROM AUTHOR]

Prestressed fit is a new type of composite and metal connection. Compared with the traditional connection, it has the advantages of maintaining fiber continuity, high controllability, and high stability. According to the analytical model, the important parameters of the prestressed joint such as friction coefficient, lap length and winding tension are proposed. The influence of the parameters on the joint performance and stress distribution is studied by the finite element method. The abnormal end phenomenon, the stress relaxation phenomenon, and the stress mutation phenomenon caused by demolding during the joint forming process are explained, and the design of the layering method is optimized. The results show that the end effect makes the relationship between the lap length and the peak torque of the joint nonlinear, and increasing the lap length is beneficial to reduce this effect; before and after demolding, the end stress increases sharply; reducing the winding tension and selecting high modulus core mold materials are conducive to reducing stress relaxation; 90°inner ply angle and ± 45°outer ply angle are ideal layup methods for joint composite materials. [ABSTRACT FROM AUTHOR]

In this study, carbon fiber/thermoplastic (Elium®) honeycombs were manufactured using the resin infusion process in a customized metallic mold. Honeycomb cores, based on different carbon fiber layers, were manufactured to achieve four different fiber weight fraction composites. Two different types of specimens, based on a single honeycomb cell and five honeycomb cells, were prepared and subjected to compression loading. The results of these tests were compared with data from similar honeycomb structures based on carbon fiber–reinforced epoxy composite. It has been shown that the compressive strength and the specific energy absorption capacity of the honeycombs increase rapidly with increasing fiber weight fraction. The specific energy absorption capability of the novel thermoplastic honeycomb structures has been shown to be as high as 50 kJ/kg which compares favorably with other energy-absorbing core materials. The thermoplastic honeycomb specimens exhibited a similar specific energy absorption capability and an improved compressive strength compared to their epoxy counterparts. Furthermore, the CF/thermoplastic honeycombs exhibited enhanced structural stability and displayed a more uniform and progressive core failure mode than the longitudinal splitting observed in the CF/epoxy honeycombs. The honeycomb core that exhibited the best performance was then used to manufacture thermoplastic sandwich specimens based on CF/thermoplastic face sheets. Three point bend tests were conducted to determine the flexural strength of the sandwich samples and to identify the failure modes. Optical micrographs revealed that the flexural damage was primarily due to the core crushing and adhesive failure between the core and the composite skins. [ABSTRACT FROM AUTHOR]

To obtain a good ride quality and smooth car body motion, many studies have focused on the damper. Passive dampers are unable to respond actively to changes in the environment; hence many studies are being conducted on semi-active dampers that use magnetorheological (MR) fluids. As the damping characteristics of the MR damper, such as the response time, control gain, and gradient of the damping force curve, can significantly affect the control performance of the vehicle, the damping characteristics of the MR damper should be carefully considered. Accordingly, in this study, we developed a method for selecting the damping characteristics of an MR damper for specific vehicle types and analyze the relation between the dynamic characteristics of MR damper and driving performances. To achieve this objective, we demonstrated that the damping characteristics can be tuned according to the additional flow path, groove, and core material. To confirm the enhancement of the ride quality, vibration control performance, and steering stability, the skyhook controller was considered. Since we obtained the suitable damping characteristics that met the requirements under random road profiles and bumpy roads, the realization of these characteristics will enable us to satisfy the driving requirements. [ABSTRACT FROM AUTHOR]

Composite sandwich panels are applied to numerous structures owing to their excellent mechanical properties and thermal performance. In marine craft, sandwich panels are located on the inner walls as an insulation system for the liquefied natural gas (LNG) cargo containment systems (CCSs). Polyurethane foam (PUF), as an insulation material, is commonly used as the core material against a cryogenic temperature of –163°C for the LNG CCSs. Owing to its excellent thermal performance that prevents heat flow from the outside, and because LNG is transported at cryogenic temperatures, PUF is the preferred choice as a core material. However, the LNG CCS is subjected to fluid impact load due to sloshing during a laden voyage, and therefore, the core material needs to be reinforced. In this study, a reinforcement material made of hollow glass bubbles (HGBs) was added to PUF to help withstand the sloshing loads, and the performance of the specimens was investigated in terms of their impact strength and absorption energy. The mechanical impact strength of the final products was investigated through an impact test at cryogenic temperatures and the absorption energy was analyzed along with the dynamic compressive behavior of the sandwich panels. [ABSTRACT FROM AUTHOR]

Wave energy can be dissipated gradually when it is propagated in viscoelastic damping material (VDM) composite structures. In this paper, after the specimens with different opening ratios (ORs) of VDM layer are prepared, the elastic wave energy propagation and dissipation characteristic of periodically perforated VDM cored sandwich structures are investigated by an experimental method. The sandwich structures are discretized into several testing points in our experiment. When the complex velocity, equivalent effective mass, and external excitation forces have been obtained at each testing point by sensors, the energy dissipation in the sandwich structure is determined based on the energy dissipation mechanism of wave transmission in solid. The experimental results are then compared with theoretical and numerical simulation results. By analyzing the computational accuracy of theoretical and numerical results using experimental data, it is shown that high consistency between theoretical, numerical, and experimental results can be achieved, especially in the medium-frequency and high-frequency ranges. Thus, our experimental results demonstrate that periodically perforated VDM sandwich structures can be applied to engineering practice for their good performance of dissipation characteristics in the middle-frequency and high-frequency ranges. [ABSTRACT FROM AUTHOR]

Glass fabric reinforced thin sandwich panel and carbon fabric reinforced thin sandwich panel of thickness close to 2.5 mm were studied to explore an alternative skin material for the outer body of various machines and appliances. The polyester foam Coremat XM of 2 mm thickness was used as core material in the thin sandwich panels. The panels were fabricated by vacuum bagging process and characterized through two plate tests: (i) low-velocity normal impact loading under a drop weight impact test set up and (ii) transverse static loading of a plate. The damage area, indentation depth and permanent depression over damage area, energy absorption capability, load-deflection relation and failure modes were observed under the test. The impact drop test was simulated by LS-DYNA. The properties of glass fabric reinforced thin sandwich panel and carbon fabric reinforced thin sandwich panel were compared with those of 0.8-mm-thick MS sheet, a widely used skin material for the outer body of various machines and appliances. [ABSTRACT FROM PUBLISHER]

Sandwich composite materials are widely used within the marine industry, particularly as hull panels. Water impact loads, known as slamming, can be very significant for these structures, particularly for high-speed craft. The transient nature of slamming loads means that the loads are applied very quickly, which can cause stress and strain rates that are high enough to affect the resulting strength of the core material, particularly for polymeric foams. The aim of this paper is to characterise the shear strength of cores at slamming relevant loading rates. Two testing approaches are used: a custom servo-hydraulic beam testing system and a drop-weight impact testing machine. Core materials studied included aramid honeycomb, cross-linked and linear polyvinyl chloride, polyethylene terephthalate and styrene acrylonitrile foams, representing a range of different levels of ductility and maximum elongation. For the moderate and high elongation core materials, there were significant increases in shear strength for dynamic loads; however, the strength of most of the materials does not appear to be sensitive to the exact loading rate. [ABSTRACT FROM AUTHOR]

This article details a procedure for sizing single cantilever beam (SCB) test specimens that are used to characterize facesheet–core debonding in sandwich structure. The characterization is accomplished by measuring the critical strain energy release rate, Gc, associated with the debonding process. The sizing procedure is based on an analytical representation of the SCB specimen, which models the specimen as a cantilever beam partially supported on an elastic foundation. This results in an approximate, closed-form solution for the compliance–debond length relationship of the specimen. The solution provides a series of limitations that can be imposed on the specimen dimensions to help ensure the specimen behaviour does not violate assumptions made in the derivation of the data reduction method used to calculate Gc. Application of the sizing procedure to actual sandwich systems yielded SCB specimen dimensions that would be practical for use. The method is specifically configured for incorporation into a draft testing protocol to be developed into an ASTM International testing standard. [ABSTRACT FROM AUTHOR]

Fiber-reinforced plastic (FRP) is a general kind of composite material used in many industries. This study examines the print-through phenomenon (PTP) via quantitative measurements on the gel-coated surface of FRP specimens. Moreover, finite element analysis is also adopted in this investigation. Based on a large number of experiments and computations, an average parameter, the arithmetic mean deviation is utilized to determine the degree of the PTP. Further, the reflections of a light image on a FRP surface were observed in photographs. Experimental results show that insulating residual stress can reduce PTP. Adding a core-mat layer to the FRP stacking scheme is a good solution for minimizing the PTP. In addition to using the core-mat materials, substitute materials used to prevent the PTP are also investigated. [ABSTRACT FROM PUBLISHER]

This article suggests two useful methods to obtain true stress-strain curves with the variation of the strain rate ranging from 0.001 to 200/s using a finite element technique and optimization for two typical polymers: a polypropylene; and a polypropylene composite. The polypropylene is adopted as a core material of a vehicle's instrument panel and the polypropylene composite sustains the passenger-side air bag module (PAB module) as a structural member. Their dynamic tensile characteristics are important to predict deformation modes of the PAB module which undergoes high speed deformation during air bag expansion. Since the polymers are temperature sensitive materials, the dynamic tensile tests were performed at the three levels of temperature: the low temperature (-30°C); the room temperature (21°C); the high temperature (85°C). During tensile tests of two polypropylene composites, the gage region in the specimen of the polypropylene composite elongates uniformly while that of the polypropylene does not elongate uniformly. In the case of the polypropylene, experimental stress-strain curves were modified by enforcing the load response calculated by finite element analysis coincident with that of the experiment. In the case of the polypropylene composite, experimental stress-strain curves were scaled by applying change rate of the gage length. Stress-strain curves of both cases provide excellent performance in their numerical response with the finite element analysis. The material properties obtained are indispensible to estimate the high speed deformation mode during air bag expansion at both normal and harsh operating conditions. [ABSTRACT FROM AUTHOR]

To achieve high energy absorption under edgewise compression loading, sandwich composites must experience a progressive failure that includes compression failure of the facesheets. This investigation focused on sandwich core design for energy absorption through the use of failure mode maps. Predictive models for global buckling, facesheet wrinkling, and facesheet compression failure were used to construct failure mode maps as a function of sandwich core thickness and density. Predicted failure loads and initial failure modes were found to be in good agreement with results from edgewise compression testing. Sandwich configurations experiencing facesheet compression failure as the initial failure mode were found to produce the highest energy absorption. These results suggest that sandwich composites may be designed for enhanced energy absorption through the proper selection of core materials and geometries. [ABSTRACT FROM AUTHOR]

The in situ fracture toughness of six core materials was measured using a new test method. The materials tested were seven composite sandwich panels fabricated using vacuum-assisted resin transfer molding (VARTM). The core materials were PVC or balsa of different densities. All of the core materials were tested with E-glass--vinylester face-sheets, while one was tested with carbon--epoxy face-sheets. The fracture tests were conducted using a modified Cracked Sandwich Beam (CSB) test configuration. The cracks in the foam-core panels grew in the subinterface region and paralleled the interface. The distance from the interface to the location of the sub-interface crack was related to the mismatch in the material properties between the face-sheet and core. The fracture toughness of the PVC core materials ranged from 367 to 1350 J/m². The results for the sandwich specimens with PVC cores were compared to the Mode I fracture toughness of the neat PVC foamcore materials and values obtained from in situ testing of foam-cored sandwich panels using the Tilted Sandwich Debond (TSD) specimen with no tilt angle. The in situ fracture toughness of the core materials in a sandwich panel was found to be significantly higher than the Mode I fracture toughness of core material even though the cracks grew completely within the core. The crack growth in the balsa-cored panels was significantly different than that of the cracks in the foam panels. The cracks in the balsa panels grew in one of the three distinct fashions: as an interface crack when bonding between face-sheet and core was weak, or when the bonding was strong, as a through-the-thickness crack, or a sub-interface crack. The fracture toughness of the sandwich specimens with balsa-core materials ranged from 693 to 1008 J/m². The results from the balsa-cored panels were compared to results obtained from similar balsa-cored sandwich materials using the Single Cantilever Beam (SCB) specimen. [ABSTRACT FROM AUTHOR]

Presents a study which evaluated ultralightweight carbon foams in load-carrying structures as core material in a sandwich construction. Compressive properties of carbon foams; Shear properties of carbon foams; Analysis of load-displacement and load-strain curves of sandwich beams under four-point static loading.

Presents a study that evaluated an integrated sandwich composite adopting three-dimensional (3-D) woven fabrics as the core material for its effective elastic modulus. Difficulties in developing suitable theoretical models for 3-D woven sandwich composites; Methods used in assessing the suitable theoretical model for predicting the elastic modulus of composite structures; Discussion of experimental results as compared with a prediction of an elastic modulus.

Presents laboratory results in 3-point bend tests of sandwich beams with carbon-epoxy faces and polyurethane cores to demonstrate that the modes of failure in the tests correspond to those predicted by the analyses. Reason for the vague understanding of the strength properties of sandwich construction; Evaluation of the methodology for predicting failure in sandwich beams with fiber composite faces and foam cores under concentrated loading; Comparison between the predicted and observed failure modes.