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The physical, mechanical, and thermal properties of new nonwoven materials based on heat-resistant fibers were studied. An analysis of existing nonwoven materials of various fibrous compositions, as well as effective water-repellent compositions, was carried out. A technique has been developed for the production of hydrophobized nonwoven materials using solutions of fluorine-containing latex. Bulk density values of samples were determined, thermogravimetric analysis was carried out, mechanical properties (values of breaking load and elongation at break), water absorption, and other technical characteristics of the developed material were studied, and an experimental batch was manufactured. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The large-scale use of composite materials reinforced with carbon–aramid hybrid fabric in various outdoor applications, which ensures increased mechanical resistance including in impact loadings, led to the need to investigate the effects of aggressive environmental factors (moisture absorption, temperature, thermal cycles, ultra-violet rays) on the variation of their mechanical properties. Since the literature is still lacking in research on this topic, this article aims to compare the low-velocity impact behaviour of two carbon–aramid hybrid composite materials (with and without rubber core) and to investigate the effects of water absorption on impact properties. The main objectives of this research were as follows: (i) the investigation of the mechanical behavior in tests for two impact energies of 25 J and 50 J; (ii) comparison of the results obtained in terms of the force, displacement, velocity, and energy related to the time; (iii) analysis of the water absorption data; (iii) low-velocity impact testing of wet specimens after saturation; (iv) comparison between the impact behaviour of the wet specimens with that of the dried ones. One of the main findings was that for the wet specimens without rubber core, absorbed impact energy was 16% less than the one recorded for dried specimens at an impact energy of 50 J. The failure modes of the dried specimens without rubber core are breakage for both carbon and aramid fibres, matrix cracks, and delamination at matrix–fibre interfaces. The degradation for the wet specimens with rubber core is much more pronounced because the decrease in the absorbed impact energy was 53.26% after 10,513 h of immersion in water and all the layers were broken. [ABSTRACT FROM AUTHOR]

Copyright of Industria Textila is the property of Institutul National de Cercetare-Dezvoltare pentru Textile si Pielarie and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nanoparticles are known to enable the modification of the properties of the material they are integrated into. In the context of ballistic protection, previous works have demonstrated that graphene and Montmorillonite (MMT) particles included in high‐density polyethylene (HD‐PE) and used as a matrix enable an increase in the ballistic performance, of consolidated woven aramid fabrics. Furthermore, the ballistic performance has been reported to be influenced by the in‐plane shear properties of the impacted materials. In this context, quasi‐static and high‐rate in‐plane shear tests have been conducted on two types of reinforcements, aramid, and carbon woven fabrics, consolidated by a high‐density polyethylene matrix enriched by graphene, MMT and a mix of graphene and MMT nanoparticles. The conducted investigations provide for the first time in the literature the results of high‐rate in‐plane shear tests on aramid woven reinforcement consolidated with nanoparticle‐enriched and not enriched high‐density polyethylene composites. Despite the use of the same reinforcement and enriched matrix material as in previous works of literature, no significant differences in terms of in‐plane shear behavior have been observed for any of the different types of nanoparticles integrated into the matrix. Nevertheless, the obtained results demonstrate a clear strain rate sensitivity of the tested materials. Highlights: Aramid and carbon fabrics were consolidated with nanoparticle‐enriched HD‐PEQuasi‐static and high‐rate in‐plane shear tests were conductedNo influence of the nanoparticles could be identifiedA clear strain‐rate sensitivity could be identified for both composites [ABSTRACT FROM AUTHOR]

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The demands of body armor on level of protection, weight, flexibility and comfort have always been difficult to strike an optimal balance. Most studies aim to promote the impact resistance of bulletproof materials, flexibility and comfort have not been sufficiently emphasized. Weft-knitted insertion fabric has excellent flexibility and body fitting ability, and the insertion yarns dissipate energy rapidly. In this paper, flexible composite laminates reinforced by aramid weft-knitted insertion fabrics (WKIFs) were developed. The ballistic performance was comprehensively studied based on the external damage appearance and internal damage image by high velocity impact tests and X-ray computed tomography. The finite element analysis was carried out to further explore the damage modes and failure mechanisms of composite materials. The results show that laminates reinforced by WKIFS have the potential to be applied in the bullet-proof field with the ballistic limit velocity of 365.31 m/s, 339.76 m/s and 338.29 m/s, respectively. For the laminates reinforced by weft-insertion fabrics, the front layers tend to be destroyed in shear, while the back layers are more probably to fail in tension. Further, the specific damage modes of the laminate were affected by the impact velocity of projectile. This study is of great significance to the development of flexible bullet-proof composite materials. [ABSTRACT FROM AUTHOR]

The high mechanical properties, corrosion resistance and low production costs of aluminum alloys make their use in the aerospace and automobile industries attractive. Addition of reinforcement, and heat treatment are important factors in increasing the physical and mechanical properties of these alloys. In this study, squeeze casting method was used to produce aramid reinforced Al7075 matrix materials and their mechanical, physical and microstructural properties were investigated. The physical (hardness) and mechanical (tensile, flexural) properties of Aramid/Al7075 material were compared with base alloy. Then, the effects of the aging process on the hardness, tensile and flexural strengths of 8%Aramid/Al7075 material (the best mechanical properties) and base alloy were investigated. The polished surfaces of the materials and the fracture surfaces after the tensile test were examined using Scanning Electron Microscopy (SEM), while the phase characterization after aging was performed using X-ray diffraction (XRD). The highest hardness values of non-aged materials were obtained in 12% aramid reinforced material. The highest flexural and tensile stress were obtained from 8% aramid reinforced material among non-aged materials, and their strengths were determined as 454 and 278 MPa, respectively. With an increase in aging time, the mechanical and physical properties of the materials exhibited a significant improvement. However, it was observed that these properties started to decrease after a certain aging time. In heat-treated Aramid/Al7075 materials, the lowest and highest hardness values were obtained as 184 and 205 HB, respectively, after aging for 8 and 20 h. The highest tensile strength (523 MPa) of the Al7075 alloy was obtained at the end of 20 h. The highest tensile strength of aramid reinforced material was obtained as 512 MPa at 16 h aging time. [ABSTRACT FROM AUTHOR]

This study examines the machinability of hybrid fiber metal laminates (HFML), which are made by nickel–chromium alloy (IN-625) metal-cored carbon (Ca)/aramid (Ar) fiber laminate using ultrasonic vibration-coupled microwire electrical discharge machining (UV-μWEDM). Since UV-μWEDM parameters significantly impact the erosion rate (ER) and surface undulation (SU), the main objective was to identify the optimal machining parameters. The input variables include the pulse on (Pon), pulse off (Poff), current (IC), cutting inclination (CI), and servo voltage (SV) coupled with ultrasonic vibration (UV). The empirical findings show that the servo voltage (SV) significantly impacts ER (73.93%) and SU (70.02%). The performance categorization order of significant influencing variable is SV>Poff>CI>Pon>IC. The desirability interpretation generated the optimum setting for minimizing SU and maximizing ER is Pon=8μs, Poff=14μs, SV=50V, IC=3A, and CI=30∘. Scanning electron microscopic (SEM) images were used to perform the micro-interlayer analysis on the machined surface. Moreover, creating an appropriate HFML is necessary to cut various shapes and sizes to satisfy the demands of diverse applications. 60% of components in the aerospace sector are reportedly rejected in real time due to dimension departure, poor surface finish, and damage found in the final assembly. Investigating the viability of cutting-edge machining techniques like UV-μWEDM is crucial to minimize damage and improve the quality of HFMLs. [ABSTRACT FROM AUTHOR]

In order to predict the anti-stabbing performance of aramid flexible composite and to investigate the basic law of the response of aramid flexible composites to knife penetration, aramid flexible composites were prepared by impregnation with multi-phase shear thickening solution and coating with silicon carbide/thermoplastic polyurethane as well as extraction and quasi-static stabbing experiments. Finite element simulations of a single-layer quasi-static knifed aramid composite model and a multi-layer dynamic knifed aramid composite model were established by refining the friction coefficients, and Python script was used to effectively simplify the modeling process to investigate the anti-knife stabbing mechanism of aramid flexible composites. The results show that the friction coefficient between yarns of the silicon carbide/thermoplastic polyurethane coated aramid composites is the highest. The friction coefficient between yarns impregnated with shear thickening solution is good and does not limit yarn stretching deformation, and has good anti-stabbing property. The main failure mode of multi-layer aramid fabric during dynamic puncture process is yarn breakage and yarn deformation is less. The establishment of the model can provide a reference for fast and accurate prediction of the anti-stabbing properties of flexible composites. [ABSTRACT FROM AUTHOR]

This study presents the effect caused by the saline environment (artificial seawater) on the physical and tribological properties of laminated composite materials reinforced with aramid fibers when they are subjected to erosive wear by sand particles. Composite materials made by epoxy resin and reinforced with glass fiber, carbon fiber and hybrid fiber (aramid with carbon) were studied. The laminates were superficially reinforced with layers of Kevlar fiber and prepared by the vacuum-assisted resin infusion process. The samples were subjected to a seawater accelerated aging process at 70°C for 1122 h. To reproduce erosive wear conditions of marine structural components, sea sand was used as solid particle under conditions of 4.5 bar of pressure, impact speed of 4.7 m/s and impact angle of 90°. The results showed that aged materials absorb more impact energy with respect to unaged counterparts, causing less material loss and a less depth in the wear track. The information generated by this research work may serve for the design and durability analysis of marine structures such as tidal turbine blades. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metals is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Compartmental shielding, using methods such as the conductive encapsulation of flexible polymer fibers, provides electrical pathways that are effective for electromagnetic interference (EMI) shielding in textile-based EMI shields. However, controlling the skin depth with electrically insulating polymer constituents remains challenging, particularly by requiring the high electrical conductivity of the encapsulants on the surface. Here, we demonstrate that the highly conductive single-walled carbon nanotube (SWCNT) polyelectrolytes provide a certain level of electrical conductivity (∼106 S/m) with effective percolation that reduces the skin depth to approximately 3 μm. This experimental skin depth was well-matched with the theoretical value of the skin depth. Sufficient charge accumulation in the SWCNT encapsulants with a hierarchical structure indicates the remarkable conductive features of the SWCNT polyelectrolytes and successfully demonstrates absorption-dominant EMI shielding. The macroscopic square mesh consisted of core/shell aramid/SWCNT fibers, exhibiting an ordered structure across multiple length scales, a modified hierarchy, and a superior EMI shielding effectiveness (SE), particularly in absorption. In particular, an EMI SE (i.e., 32 dB) of approximately 99.9% was achieved using a square mesh with an aperture width of 3 mm. The square meshes demonstrated excellent flexibility, thermal stability (Td > 500 °C), and mechanical robustness (σ = 2.26 ± 0.16 GPa, E = 79.0 ± 1.8 GPa, and ε = 2.99 ± 0.09%). [ABSTRACT FROM AUTHOR]

Warp knitting creates very challenging dynamics due to its high production speeds. On the one hand, this makes it method of choice for many products in various fields. On the other hand, not all materials are suitable for such high productivity. With the current generation of machines being limited to only achieve their maximum speed of around 4,400 min−1 with highly elastic yarns, it is desired to gain a deeper insight into yarn behavior in such highly dynamic environments. Among other influences, resonance effects gain high significance as they may result in high loads on the used materials; therefore, yarn breakages interrupt the production and decrease the quality of the product. To extend the material choice, especially high-performance fibers, for high productivity, a deep understanding of the intrinsic properties of the yarn is required. In particular, the viscoelastic properties are of importance. This study proposes a method to determine these characteristics using the dynamic mechanical analysis method. For the purpose of finding the damping in the transversal direction to the yarn axis, the variant of free oscillation is chosen. For the trials, a high-speed camera is suspended above a testing rig. On this rig, a yarn sample is clamped and then displaced from its rest position. The resulting oscillation is recorded and later extracted from the video. From the decrement of the maxima of the amplitude and corresponding time intervals, the damping factor is determined. It decreases with higher initial deflection. Summarised the developed trial setup proved suitable for the determination of the viscoelastic properties in transversal direction. [ABSTRACT FROM AUTHOR]

Composite materials fabricated via additive manufacturing are becoming more relevant in ready-for use products used in engineering applications like aerospace structures, propellers, electric vehicles, or sandwich cores. Continuous Fiber Reinforced Polymeric (CFRP) composites are 3D-printed composites with tailor-made properties due to the capability of the printing process to deposit matrix and fiber whenever required. However, CFRP products behave differently and have lower mechanical properties than traditional composites. This study aimed to analyze the impact strength of CFRP specimens with gyroid infill and the effects of two build (flat and on-edge) and two raster (0° and 45°) orientations on impact behavior. The gyroid infill helps to obtain a light-weight structure and it has been used in energy absorption applications showing excellent mechanical behavior in thermoplastic 3D-products. The specimens were manufactured using Onyx as the matrix and aramid fiber as the reinforcement materials. The impact energy absorption of CFRP composites was measured using unnotched Izod impact specimens. The impact tests results were statistically analyzed, revealing that the build orientation directly and significantly affects the impact behavior, resulting in higher impact absorption when flat orientation is used to produce CFRP composites. The impact strength of CFRP composites increased 8 times, and 2 times for flat and on-edge oriented specimens, respectively compared to pure Onyx specimens. The variation in impact energy absorption between raster orientations in both build orientations was not significant, the difference in flat-oriented specimens at 0° and 45° was only 0.2 J, and between on-edge-oriented specimens at 0° and 45° was only 0.089 J. Also, the after impact specimens were analyzed to categorize the different failure modes observed. The after-impact analysis showed poor impregnation between aramid and onyx layers, causing delamination, fiber bridging, and fiber exposure failures. The combination of Aramid, Onyx, and a non-solid infill (gyroid) demonstrated positive results in impact behavior, obtaining high-impact absorption (165 kJ/m2) with no more than 56 % of fiver volume. The impact properties information of CFRP composites made with aramid fibers is still very scarce, joined to the lack of information on the impact properties of CFRP composites with non-solid infill, like gyroids or sinusoidal path infills. The results of this research open the possibility of using non-solid infill in CFR process that can be used to manufacture and test ready-for-use CFRP products in tasks that require high-strength, low-weight structures and impact energy absorption.

Hybrid nanocomposites have emerged as a promising solution for engineering applications associated with reduced costs and weight aiming to enhance performance in special areas such as ballistic protection. This study delves into the development of hybrid nanocomposites featuring a high-density polyethylene matrix modified with graphite nanoplatelets and reinforced by aramid and jute fabrics. The incorporation of GNP significantly influences the crystalline structure of the GNP/HDPE matrix, as evidenced by Raman and X-ray diffraction analyses. Furthermore, it assumes an important role in modifying the crystallization and glass transition temperatures (Tc and Tg) and influencing the dynamic mechanical behavior. Specifically, it increases viscoelastic stiffness, raises the storage modulus by more than 30 %, and reduces the tanδ value. In addition, replacing 5 layers of jute fabric with an equivalent number of aramid layers maintains comparable ballistic performance to a 20-layer aramid nanocomposite. This substitution yields a remarkable 659.41 J of absorbed energy and a limit velocity of 405.72 m/s. Additionally, a hybrid nanocomposite comprising 10 layers each of jute and aramid showcases impressive ballistic resistance against 9 mm caliber ammunition, achieving 419.84 J of absorbed energy and a limit velocity of 320.13 m/s. Scanning electron microscopy analysis exposes the intricate fracture mechanisms, encompassing phenomena such as crazing, GNP/HDPE fibrillation, fiber rupture, and debonding. These mechanisms are significant in the composite's energy absorption during a projectile impact. Moreover, a cost-benefit analysis underscores the potential of hybrid nanocomposites in ballistic protection by simultaneously reducing both helmet weight and cost in 7 % and 40 %, respectively.

Honeycomb panels made of aluminum and composite materials—aramid, or Kevlar—are widely used in aviation, space, automotive, and other fields due to their unique characteristics: high strength and rigidity, low density, and good thermal insulation properties. However the mechanical processing of products made of honeycomb materials faces several difficulties, and one of the technologies that effectively solves the problems of cutting products made of honeycomb materials is ultrasonic cutting. In this paper, the finite element method is used to study the frequency properties necessary for designing tools for ultrasonic cutting of products made of honeycomb materials with operating frequencies around 20 kHz and various geometric parameters for cutting different variants of honeycomb constructions. The results of analyzing the wave dimensions of specialized ultrasonic triangular and disk-type instruments depending on geometry features are shown, along with the experimental results for a number of developed variants. [ABSTRACT FROM AUTHOR]

In this study, quasi-static punch shear test was conducted on aramid fiber-reinforced composite (AFRC) laminates consisting of different ratios of graphene nanoplatelet (GNP), carboxyl (COOH) functionalized multi-walled carbon nanotube and their hybrid combinations. Two different punch nose geometries (conical and ogival) and two different support span-to-punch ratios (SPR = Ds/Dp = 2 and 4) were employed in the experiments. The results indicate that the ogival punch geometry causes deformation at a higher load while also reaching the maximum load at a lower displacement compared to the conical punch. Moreover, incorporation of nanoparticles increased the energy required for complete penetration compared to non-reinforced AFRC. In particular, the composite containing 0.2% GNP demonstrated the most significant increase in energy required for complete penetration, showing a remarkable 32.30% improvement with the conical punch configuration. Similarly, the 0.1% hybrid composite exhibited a substantial 42.13% increase in complete penetration energy under the ogival punch configuration. Although the energy required for complete penetration is expected to increase as the SPR ratio rises from 2 to 4, this trend is not particularly evident due to embrittlement caused by the nanoadditives. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the physical properties of yarns made with different blend ratios of meta-aramid, para-aramid, flame-resistant (FR) viscose, and antistatic nylon fibers, as well as the tensile strengths and burning behaviors of fabrics made from these yarns. For this purpose, 10 different yarns of two different linear densities were produced using five different blend ratios, which are commonly used in the production of fire-resistant fabrics, and knitted fabrics were produced from these yarns, with the same knitting machine and the same production parameters. Physical properties of the yarns and tensile properties and burning characteristics of the knitted fabrics were measured according to commonly applied standards, and the results obtained were evaluated using the SPSS statistical program. The findings of this study are that the blend ratios of meta-aramid, para-aramid, FR viscose, and antistatic nylon fibers have statistically significant effects on the unevenness, humidity, and tenacity of the yarns, as well as on the tensile properties and burning characteristics of the fabrics. It was found that, with an increase of the aramid fiber ratio in the blend, the tensile values of the yarns and fabrics increased. The lowest moisture contents were recorded for 100% para-aramid yarns but the highest moisture contents were recorded for yarns whose blends contained FR viscose fibers. The yarns whose blends contained antistatic nylon fibers exhibited the greatest unevenness and the most thin and thick places and neps. [ABSTRACT FROM AUTHOR]

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the positive results of most of the studies using virgin fibres to reinforce asphalt mixes, this work proposes the use of recycled fibres in order to go a step further in terms of environmental impact and cost-efficiency. Different experimental asphalt concrete (AC) mixtures are proposed, incorporating three types of recycled fibres. Mechanical performance is assessed through the Marshall, water sensitivity and wheel tracking tests, as well as stiffness and fatigue tests to assess dynamic performance. The results obtained from the different tests performed are analysed by means of a multi-criteria analysis to obtain the asphalt mix with the best performance. The results show that all the tested fibres are suitable for the reinforcement of asphalt mixtures, as the values obtained improved those of the reference mixture, although without reaching the behaviour of a mixture with polymer modified bitumen (PMB). The recycled aramid fibres showed the best results.

The large-scale use of composite materials reinforced with carbon–aramid hybrid fabric in various outdoor applications, which ensures increased mechanical resistance including in impact loadings, led to the need to investigate the effects of aggressive environmental factors (moisture absorption, temperature, thermal cycles, ultra-violet rays) on the variation of their mechanical properties. Since the literature is still lacking in research on this topic, this article aims to compare the low-velocity impact behaviour of two carbon–aramid hybrid composite materials (with and without rubber core) and to investigate the effects of water absorption on impact properties. The main objectives of this research were as follows: (i) the investigation of the mechanical behavior in tests for two impact energies of 25 J and 50 J; (ii) comparison of the results obtained in terms of the force, displacement, velocity, and energy related to the time; (iii) analysis of the water absorption data; (iii) low-velocity impact testing of wet specimens after saturation; (iv) comparison between the impact behaviour of the wet specimens with that of the dried ones. One of the main findings was that for the wet specimens without rubber core, absorbed impact energy was 16% less than the one recorded for dried specimens at an impact energy of 50 J. The failure modes of the dried specimens without rubber core are breakage for both carbon and aramid fibres, matrix cracks, and delamination at matrix–fibre interfaces. The degradation for the wet specimens with rubber core is much more pronounced because the decrease in the absorbed impact energy was 53.26% after 10,513 h of immersion in water and all the layers were broken.

The present research aimed to develop laminated hybrid-composite with aramid woven fabric and curaua non-woven mat, to evaluate the possibility of using as military ballistic helmets. It explores the potential of hybrid solutions, which are more socio-environmentally sustainable and cheaper. All hybrid composites were produced in non-alternate layers model. In addition to hybrid configurations, epoxy laminated composites reinforced with only aramid woven fabric or only curaua non-woven mat were also investigated, with 73 and 58 vol.% of reinforcement, respectively. The cold compression molding process was used for all composites. The ballistic characterization was performed through protection level determination and residual velocity tests to estimate the ballistic limit and absorbed energy, with their corresponding reduction maps. As results, composites with 15 layers of aramid (52 vol.%) and one layer of curaua (15 vol.%) obtained the maximum level of ballistic protection. For composites with two layers of curaua the ballistic limit estimate was 292 m/s, which is ∼15% lower than the limit of the 9 mm projectile velocity corresponding to the maximum level (level II), compared to the composite commonly used in ballistic helmets. Curaua non-woven mat structure and its positioning behind the aramid woven fabric, as well as the lower total number of layers, reduced the ballistic resistance capacity of the hybrid composites. Although the proposed configurations with curaua non-woven mat did not meet the ballistic level requirement of the Brazilian COBRA helmet, these mentioned results are a strong indication of the enormous potential of hybrid composite for military helmet applications.

Fiber-reinforced polymer (FRP) has been used for seismic retrofitting and structural reinforcement over recent decades. Numerous researchers have created stress–strain models based on experimental data to predict the mechanical properties of FRP-confined concrete. In this study, circular and square cross-section specimens with different design concrete strength were prepared, and the compressive strength of the specimens confined with different layers of aramid FRP (AFRP) were measured in compressive tests. A constitutive model was proposed to simulate the uniaxial compressive stress–strain relationship of the AFRP-confined concrete, which was derived from the Mohr–Coulomb failure envelope theory, and the corresponding axial strain was determined from the regression analysis. The internal friction angle of the proposed constitutive model was determined for the cylindrical concrete specimens confined with one and two layers of AFRP. The compressive strength of one and two layers of AFRP-confined concrete specimens were used to obtain the parameters of the constitutive model; the absolute average error between experimental and predicted compressive strength was 7.01%. Then, the constitutive model was used to predict the strength of a three-layer AFRP-confined concrete specimen, and the absolute average error was 4.95%. The cross-sectional shape coefficient of the square concrete specimen was obtained analytically. Substituting the cross-sectional shape coefficient into the proposed constitutive model, the average absolute error of the square cross-section concrete specimen was about 3.84%. The results indicated that the proposed constitutive model can predict the compressive strength of circular and square cross-section concrete specimens confined with AFRP. [ABSTRACT FROM AUTHOR]

Pushing the limits of synthetic polymers in terms of stiffness and strength, aromatic polyamide fibers–like Kevlar®–are used for demanding applications in the form of fiber assemblies as ropes. The unique mechanical performance of aramid fiber is intimately linked to its hierarchical structure and orientation, induced during the spinning process. Surprisingly, after nearly 60 years of heavy use, very little is known about damage mechanisms and rational explanation of such high resistance. We report an experimental investigation of the fiber damage mechanisms at the single fiber scale (diameter ≅ 10 μm) with the aim to establish a link with the microstructure. Damage mechanisms and crack propagation are observed in situ for the first time and unveil a widespread damage over the entire length of the fiber in the form of a network of transverse and longitudinal cracks. These observations make it possible to draw a novel scenario of fracture that mitigates the small strain failure hypothesis. To shed light on the crucial role of microfibril cooperativity in fracture toughness, a slight twist is applied to the single fiber to promote tortuosity and frictional contacts between microfibrils. Statistical fracture analysis demonstrated the beneficial impact of such torsion on early failure events, since lowest fracture stresses are shifted to higher stresses. [ABSTRACT FROM AUTHOR]

Copyright of Arab International Journal of Digital Art & Designs is the property of Arab Institution of Knowledge Management and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Textiles & Engineers / Tekstil ve Mühendis is the property of Union of Chambers of Turkish Engineers & Architects, Chamber of Textile Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Flame-retardant (FR) workwear with good flame/heat protection and washing durability is significant in various fields like petrochemical industry, and there are fast growing needs and new requirements to develop FR yarns with superior flame-resistance, high strength, low hairiness and reasonable cost. However, current aramid or FR viscose yarns cannot well meet these requirements. Herein, by using a cost-effective mid-length fiber vortex yarn technology, this work developed a newly FR viscose/meta-aramid blended yarn with enhanced mechanical properties and flame-resistance, including tensile strength up to 14.4 cN/tex, elongation up to 7.8%, hairiness S3 value as low as 40, and limiting oxygen index value as high as 39.6%. The unique yarn structure of wrapped fiber-sheath and straight fiber-core was studied in terms of twist angle, twist factor, and core ratio in the yarn. Moreover, spinning trials were conducted to systematically learn influences of fiber proportion and spinning parameters, and a statistical model was established by response surface methodology to predict the structure and properties of blended yarn under certain FR viscose/aramid fiber ratio and spinning parameters, which can serve as a guide to manipulate the yarn properties as well as minimizing the fiber cost. This study proposes a cost-effective method to develop high-performance FR blended yarns, which will greatly promote the development of high value-added FR textiles. [ABSTRACT FROM AUTHOR]

Hybrid composites are expanding applications in cutting-edge technology industries, which need materials capable of meeting combined properties in order to guarantee high performance and cost-effectiveness. This original article aimed for the first time to investigate the hybrid laminated composite thermal behavior, made of two types of fibers: synthetic Twaron® fabric and natural curaua non-woven mat, reinforcing epoxy matrix. The composite processing was based on the ballistic helmets methodology from the North American Personal Armor System for Ground Troops, currently used by the Brazilian Army, aiming at reduced costs, total weight, and environmental impact associated with the material without compromising ballistic performance. Thermal properties of plain epoxy, aramid fabric, and curaua mat were evaluated, as well as the other five configurations of hybrid laminated composites. These properties were compared using thermogravimetric analysis (TGA) with its derivative (DTG), differential thermal analysis (DTA), and thermomechanical analysis (TMA). The results showed that the plain epoxy begins thermal degradation at 208 °C while the curaua mat at 231 °C and the aramid fabric at 477 °C. The hybrid laminated composites curves showed two or three inflections in terms of mass loss. The only sample that underwent thermal expansion was the five-aramid and three-curaua layers composite. In the third analyzed temperature interval, related to the glass transition temperature of the composites, there was, in general, an increasing thermal stability behavior. [ABSTRACT FROM AUTHOR]

Arc explosion accidents in live working seriously threaten the safety of power workers. At present, the mainstream arc protective clothing material is aramid and blends of aramid. However, aramid will produce toxic gas under high temperature combustion, which is harmful to the health of operators. Therefore, it is a special challenge to study fabrics that are friendly to the human body and have a highly protective performance to protect electrical workers. Polyimide is nontoxic and has excellent high temperature resistance, flame retardation, and mechanical properties. In this paper, polyimide was proposed to be used as an arc protective clothing material. In order to explore the feasibility of polyimide in the field of arc protection, molecular dynamics simulation was used to compare the heat resistance of polyimide and aramid in terms of bond order and glass transition temperature. Referring to ASTM F1959 and IEC 61482-1-1, an arc test apparatus was built to test the protective properties of materials. The protection failure mechanism was analyzed by comparing the safety protective performance of polyimide and aramid fabric under the arc. It was found that polyimide has better arc thermal protective performance and break open threshold. The simulation and test results show that polyimide can be used as a material for arc protective clothing to improve protective performance. [ABSTRACT FROM AUTHOR]

This paper investigates the fragment performance of several composite panels for attaching to the inside walls of a building structure. These panels were developed using different types of fiber woven fabrics (W0, W90) combined with distinct layers orientations (angle-ply effect) of L0/0 and L0/15. Aramid, E-glass, and S-glass fiber fabrics impregnated with thermosetting epoxy resin, and a prepreg of Ultra High Molecular Weight Polyethylene (HB24) were employed. The panels are subjected to ballistic impact using different fragments under impact velocities in the range of 120 to 420 m/s. In order to measure the energy absorbed by the ballistic panels, the impact velocity and the residual velocity of the fragment were measured with laser chronographs placed before and after the laminated test specimens. The paper demonstrates quantitatively that the angle-ply laminates produced using L0/15 woven fabric orientation presented a higher impact energy absorption, promoting higher reductions on the fragment residual velocity compared to the L0/0 orientations. The laminates produced using UHMWPE fibers (HB24) presented better ballistic properties compared to the other fibers. Furthermore, it was noted that the energy dissipation rate is linearly correlated with the impact velocity and is independent of the fragment geometry. [ABSTRACT FROM AUTHOR]

A novel composite based on conducting polymer, polyaniline/aramid, was prepared with the aim of capturing carbon dioxide. Polyaniline was synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate and subsequently used for modification of the aramid surface. The prepared polyaniline/aramid composite was characterized using electrokinetic analysis, scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption/desorption isotherms for determination of specific surface area and porosity and using carbon dioxide adsorption/desorption isotherms for determination of carbon dioxide capture. The capture capacity markedly increased from 22 cm3 g−1 for pristine aramid to 60 cm3 g−1 for the polyaniline/aramid composite. The results show that the new composite material could be used as an effective adsorbent of carbon dioxide and for applications based on its adsorption. The vision of advanced adsorbents with properties controlled by electric potential applied to conducting polymers is worth being considered. © 2023 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

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This paper discussed the effectiveness of the hybrid use of fiber-reinforced polymer (FRP) reinforcement for the seismic retrofitting of substandard reinforced concrete (RC) columns. Four columns, except for the reference, were retrofitted with externally embedded FRP (EE–FRP) bars in a longitudinal and external FRP jacket in the transverse directions. The test parameter was the configuration of the FRP bars that were used for retrofitting along the longitudinal direction (e.g., single or hybrid use of different types of FRP bars, such as aramid (AFRP), glass (GFRP), or carbon fiber–reinforced polymers (CFRP). The test results indicated that a significant enhancement in the lateral load capacity (≤198% in the unstrengthened column) could be achieved through the hybrid use of FRP bars under reversed cyclic lateral displacement and a constant axial load without a significant sacrifice in deformability. In addition, the test results yielded insights into the strain (ɛ) capacities of longitudinal FRP bars in tension and their contribution to compression resistance under reversed cyclic lateral loading conditions. In addition, an analytical study was conducted to predict the cyclic flexural behavior in substandard RC columns that were retrofitted through the single or hybrid use of EE–FRP bars that considered the debonding behavior of longitudinal CFRP bars with a smooth surface. [ABSTRACT FROM AUTHOR]

The flow responses of aramid and cellulose nanowhisker (fibrids) or CNCs (cellulose nanocrystal) suspended in a sulfuric acid and water respect at loadings of about 17% weight fraction was determined in transient shear flow. The effect of temperature and shearing conditions were examined. Aramid solution exhibits strong shear thinning with power law indices about 0.2-0.3, and cellulose nanowhisker suspension indices is below 0.15. Formation of an interacting flocculated network at rest is the reason for the large relative viscosity and offers the least flow resistance during shear flow. The structure formed at rest is easily destroyed, and this is the reason for the observed shear thinning. Evolution of shear stress data versus time over four of shear rate were described the structure of nematic phase in aramid\sulfuric acid solution. Also shear rheology results of nanowhisker/water suspension show shear thinning behavior, and behave as a plastic system at different temperature. For spinning process, the aramid\sulfuric acid dope through the air gap entered into cold water. Orientation of polymer solution emerged from the spinneret and through very high extensional shear in the air gap resulted in excellent tensile properties of the final spun fibers.

The main focus of this research is to analyze the physical, mechanical, and dynamic-mechanical properties of the high-performance polymer composite. The composites are fabricated by hot compressing basalt and aramid fibers with UHMWPE (Ultra High Molecular Weight Poly Ethylene) at 200°C temperature and 200 bar pressure. Four different weight fractions of composites were fabricated namely UBA 1 having 70% UHMWPE, 10% basalt and 20% aramid; UBA 2 having 70% UHMWPE, 15% basalt and 15% aramid; UBA 3 having 70% UHMWPE, 20% basalt and 10% aramid; UBA 4 having 70% UHMWPE, 30% basalt and no aramid. The tensile strength, impact strength, hardness, and storage modulus of UBA 4 were found to be greater compared to the other composites. The UBA1 shows the highest flexural strength compared to the other samples. From XRD, the average crystalline size was calculated as 3.02 nm. The SEM image of the composites shows good adhesion of fibers and matrix in both UBA 1 and UBA 4. The dynamic mechanical properties of UBA 4 were also found to be better compared to all four samples for structural application.

A quaternary copolymer water emulsion (denoted as PBMAA) and its natural drying film are firstly obtained with methyl methacrylate (MMA)， butyl acrylate (BA)， acrylic acid (AA) and acrylamide (AM) as monomers. Then， Kevlar-1313 of aramid (denoted as K-1313) is added to modify the copolymer (denoted as K-PBMAA) and the adding ratio is optimized in order to improve the strength and wear resistance of this film. The prepared solid nano-SiO2 (denoted as S-SiO2 ) and hollow nano-SiO2 (denoted as H-SiO2 ) are also added into K-PBMAA respectively to prepare nanocomposite leather finishing agents (denoted as S-SiO2/K-PBMAA and H-SiO2/K-PBMAA) that are applied for finishing sheepskin. It is found that the thermal decomposition temperature of the coating increases from 404 ℃ to 411 ℃ and the mechanical properties increases from 4. 03 MPa to 8. 67 MPa when K-1313 and nano-SiO2 are introduced at the same time. [ABSTRACT FROM AUTHOR]

Polyimide (PI) aerogels have attracted extensive attention in the field of building insulation due to their low‐thermal conductivity, excellent thermal stability, and great flame retardancy. However, poor mechanical strength was the main factor which restrict their extensive applications. Herein, we report a simple strategy to prepare thermal insulating aramid/PI aerogel composites with high mechanical strength as well as flame retardancy through mold‐forming and freeze‐drying methods. A series of lightweight aramid felt reinforced PI aerogel composites were prepared by interfacial adhesion between aramid fiber and PI aerogel, and the most striking sample PI‐3 displayed favorable comprehensive performance, including good tensile property (8.88 MPa), bursting performance (299 N), thermal insulation property (0.0341 W/m·K), thermal stability and self‐extinguishing behavior. This strategy can be applied to many types of organic aerogel materials that used in the aspects of insulation and thermal protection in extreme environments. [ABSTRACT FROM AUTHOR]

Copyright of Cotton Textile Technology is the property of Cotton Textile Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, adhesive wear of woven E-Glass fabric reinforced composites filled with aramid, B4C and mica particles at 0.5% wt. and 1.5% wt. ratios were carried out under dry sliding conditions. The effects of filler type, applied loads (5, 10 and 15 N) and sliding distances (250, 500 and 750 m) on the tribological behavior of the composites were investigated on the pin-on-disc device. As a result of the studies, it was determined that the friction coefficient in aramid reinforced composites was lower than the other reinforced composites. In wear volume due to wear, it was observed that the aramid wear volume was less. In addition, Wear volume increased with increasing load for all particle reinforcements. But, the highest wear volume occurred in the neat wear sample at 15 N load conditions. For the wear rate and wear volume, the fillers have shown improvement up to 1.5% wt. in the composite. 1.5% wt. aramid-filled glass fiber woven composites showed the lowest wear rate: 2.82 × 10−4 mm3/N-m (at 15 N normal load). In addition, in the scanning electron microscope images taken, it was observed that there were breaks in the size of 15.07 µm in the epoxy and 61.11 µm in the fibers. The use of aramid with particle reinforcement rather than fiber is important for wear. In addition, the lowest wear volume was 65% more resistant at 1.5% wt aramid reinforcement and at 15 N load compared to the unreinforced composite in the abrasion tests. [ABSTRACT FROM AUTHOR]

It is important to achieve high strength, high modulus of elasticity, good energy damping for lightweight armor materials. For this purpose, two or more similar or different materials are combined at the macro level. In this way, a new structure emerges that we call composite material. A composite is a new structure in which the good properties of the components in its structure become evident in the material. Research on the production and mechanical properties of composites that meet the needs of the developing technology continues. Military personnel, armored vehicles and many security elements are tested in the field with a lot of threats (such as mines, armor piercing ammunition, explosives etc.). Therefore, the armor used by security elements should be strengthened without compromising features such as lightness, cost and longterm use. This study covers the development of Kevlar's ballistic properties by impregnating Shear Thickening Fluid (STF). STF is composed of silica (AEROSIL 200) and polyethylene glycol (PEG 400). STF-impregnated Kevlar fibers have been subjected to impact testing at low and high speeds. Low-speed tests were carried out with a drop tower. High-speed tests were carried out according to NIJ 0101.06 Level II standards. The mass fraction of silica in the STF was determined as the research parameter. The change in the behavior of the materials with the change of silica ratio was investigated; Although improvements were observed in energy dissipation in low-speed impacts, it was noted that ballistic behavior improved up to a certain point, and then the improvement in behavior decreased. [ABSTRACT FROM AUTHOR]