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The influence of fiber type on the mechanical behavior of high-strength strain-hardening cement-based composites (HS-SHCC) during and after exposure to elevated temperatures of up to 200 °C was investigated. The fibers under investigation were made of ultra-high molecular-weight polyethylene (UHMWPE), para-aramid-copolymer (Aramid) and as as-spun and high-modulus poly(p-phenylen-2,6-benzobisoxazol), i.e., PBO-AS and PBO-HM. Based on the considerably higher thermal stability of Aramid and PBO fibers in comparison to UHMWPE, the effect of elevated temperatures on the tensile behavior of SHCC made with Aramid and PBO was expected to be less pronounced. Nevertheless, the SHCC made with UHMWPE fiber yielded a significantly superior multiple cracking and pre-peak ductility up to 150 °C both during and after thermal exposure. At 105 °C, the SHCC reinforced with UHMWPE fiber yielded only a small reduction in tensile strength and a considerable increase in strain capacity. The composites made with Aramid and PBO fibers yielded a pronounced degradation in tensile strength and strain capacity already at 105 °C and a considerably weaker recovery of ductility when cooled down to the room temperature. At 200 °C all composites except those containing Aramid fiber exhibited no multiple cracking and brittle failure with dramatically reduced tensile strength.

Micro−/nanofibers attract extensive attention of being used as reinforcing agents in polymer composites. Fibrillated fibers have a hierarchical network structure, and a larger specific surface area. Thus, they provide additional anchorage sites in the composite, enhancing the bonding strength between different constituents. In this work, aramid fibrillated micro−/nanofibers (AFMNs) were prepared by a refining process. Styrene‐butadiene latex (SBL) was used as the matrix, and it was mixed with AFMNs, formed AFMN/SBL composites. The mass fractions of AFMNs in the matrix are adjusted to 2%, 4%, 6%, and 8%. The microstructure of AFMNs and the fracture surfaces of AFMN/SBL composites were investigated by microscopical techniques. The results showed that the elastic modulus and tensile strength of AFMN/SBL composites are higher than that of the pure styrene‐butadiene latex film, except tensile strain. With the increase of fiber content, the elastic modulus and tensile strength of AFMN/SBL composites increased from 5.15 MPa to 19.66 MPa and 2.35 MPa to 4.23 MPa, respectively. However, the tensile strain decreased from 101% to 35%. The calculated elastic modulus of Halpin‐Tsai equation is close to the experimental values when the mass fractions of AFMNs is less than 6%. [ABSTRACT FROM AUTHOR]

The use of additives in asphalt mixtures has been an important option in order to prolong the durability of the road infrastructure. Several works have reported that the utilization of synthetic fibers (e.g., plastic fibers) visibly enhance the overall mechanical performance of asphalt mixtures. The objective of this experimental study is to understand the physicochemical mechanisms leading to this superior response. With this in mind, two synthetic fibers were selected in order to analyze their effect within a conventional dense asphalt mixture used in Switzerland. The mechanical performance of the experimental mixtures along with the thermal properties of the fibers were evaluated. First, it was concluded that the fiber reinforced asphalt mixtures could perform similarly to the standard mixtures prepared with polymer modified binder. In addition, it was confirmed by imaging analysis that the reinforcing effect was associated to the physical presence of the fibers within the asphalt matrix.

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.)

To improve the reliability and design of body armor, it is imperative to understand the failure modes and the degradation rates of the materials used in armor. Despite the best efforts of manufacturers, some vulnerability of armor materials to aging due to hydrolytic or oxidative environments is expected and may result in the degradation of material properties such as tensile strength. In this work, p- aramid yarns from two manufacturers were exposed to environmental conditions of various fixed temperature and humidity combinations. The maximum temperature and humidity condition was 70℃ and 76% relative humidity (RH). Tensile tests were performed on specimens extracted at several different times over the course of at least 1 year to determine the change in ultimate tensile strength and failure strain as a function of time, temperature, and humidity. Molecular spectroscopy was used to investigate any chemical changes as a result of the aging. The p -aramid materials were found to be generally resistant to degradation at most conditions, showing changes of less than 10% only at the highest temperature and humidity conditions. [ABSTRACT FROM AUTHOR]

Copyright of China Textile Leader is the property of China Textile Information Center 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.)

Efforts to extract energy from waste organic solutions can not only support clean environments but also help to alleviate the energy crisis. Here, a bioinspired ultrastrong nanocomposite membrane is developed via the layer‐by‐layer method based on aramid nanofiber‐graphene oxide (AGO) with good mechanical properties for salinity gradient energy harvesting from organic solutions. Benefiting from the 1D and 2D network interlocking arrangement, the AGO membrane shows an unprecedented mechanical stress of 688 MPa and maintains its integrity after soaking in organic solvents for 24 h. Impressively, when LiCl is diluted in methanol, the AGO membrane device with a working area of 113 mm2 produces a current and a measured power generation of 28 ± 11 µA and 3140 ± 960 nW (Cfeed = 2 mol L−1), respectively. Thus, the working area of the AGO membrane for salinity gradient energy harvesting and temperature‐related energy harvesting enables its use in practical applications. In addition, 14 cells with the methanol‐LiCl solution (Cfeed = 1 mol L−1) can produce a voltage up to 1.82 V to light a liquid crystal display. Therefore, this AGO nanocomposite membrane presents a promising avenue to harvest salinity gradient energy from organic solutions. [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 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.)

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, reduced graphene oxide and aramid/reduced graphene oxide were used a filler in polyethylene which is easy to process. Composite materials containing 0.1% of polymer were prepared by melt blending method using thermokinetic mixer and hot-cold isostatic press. Mechanical tensile analysis of the composites were examined. The results showed that these solid composites containing very low amounts (0.1%) of nano additives can be used easily in conventional plastic processing. [ABSTRACT FROM AUTHOR]

This work presents a numerical modelling study on the bending response and failure mechanisms of aramid skin/aluminium honeycomb core sandwich panels under quasi-static bending loads. These composite sandwich panels are widely used in aerospace and automotive industries, in spite of the limitations for their use in complex structures, such as the extensive experimental testing needed at the component and full-size structural levels, which are expensive and time-consuming. The aim of this study was to capture the initiation of different failure mechanisms and their multiple interactions, which are known to strongly influence the observed microscopic behaviour of the material. Furthermore, a series of detailed Finite Element models were built and analysed in an attempt to replicate the complex damage mechanisms observed experimentally. The results show good correlation between numerical models and experimental results, both in terms of the global load–displacement behaviour and the observed damage mechanisms, including skin in-plane shear and compression damage, intralaminar fracture, delamination within the skin and core crushing. No debonding between the core and the skins was evidenced. It is proposed that this modelling approach can become a feasible alternative to component-level experimental testing when designing complex sandwich structures. [ABSTRACT FROM AUTHOR]

The influence of multilayer assembly on protection against infrared laser light was investigated. Multilayer assembly was exposed to a pulsed laser device, Marcatex 150 Flexi, with wavelength of 10.6 μm. Marking Speed [bits.ms–1] is the influenced parameter of laser irradiation. It presents the speed of burning. Multilayer assembly was consisted of three layers of textile materials. The first layer was top layer made of aramid, glass or Basalt fabric. The second layer is middle layer made of wool fabric. The third layer is bottom layer made of cotton fabric. Temperature of multilayer assembly was measured on the top and bottom layer of sample by contactless thermometer. Multilayer assembly was analysed by scanning electron microscopy before and after laser irradiation. The temperature of the bottom layer of multilayer assembly consist of aramid-wool-cotton was 74 °C at marking speed of 40 bits.ms–1. It is the lowest temperature. It can be concluded that the multilayer assembly containing aramid-wool-cotton provided the best protection against laser irradiation. [ABSTRACT FROM AUTHOR]

A superhydrophobic aramid fabric with a novel self-cleaning ability and excellent chemical stability was prepared by the two-step coating technique using an easily available material system consisting of a polytetrafluoroethylene (PTFE) membrane, particles of PTFE and silica (SiO2). The chemical resistant layer was achieved through compounding aramid fabric with the PTFE membrane, for which the contact angle was varied from completely infiltrating to 130°. Then the PTFE-coated fabric was modified with PTFE and SiO2 particles to obtain the superhydrophobic layer. The hydrophobicity was significantly enhanced with a contact angle of 154° and rolling angle of 4° due to the role of low surface energy and rough micro/nano structures. Furthermore, the PTFE/SiO2-coated fabric eventually fabricated could withstand at least 300 cycles of abrasion and strong acid/alkaline attacks for 100 hours. In addition, the breathable performance and flexibility of the coated fabric were within our acceptable ranges. The simple but effective PTFE/SiO2-coated fabric may be useful for the development of individual protective clothing for emergency rescue applications. [ABSTRACT FROM AUTHOR]

All-polyamide composites containing up to 30 vol% highly dispersed PPTA nanofibrils with diameters in the range 50–500 nm were prepared by melt-compounding polyamide 6,10 (PA610) with chopped poly(p -phenylene terephthalamide) (PPTA) fibers in the temperature range 260–300 °C using a twin-screw extruder. Injection moldings prepared from these composites showed not only large increases in tensile strength with respect to the unmodified PA610 matrix at temperatures well below the matrix melting point but also significant increases in melt elasticity. The melt elasticity was further enhanced by high-temperature heat treatments under quiescent conditions. It is suggested that the implied interfacial reinforcement may involve transamidation, which is known to occur extensively in polyamide melts. [Display omitted] • All-polyamide PA610-based composites containing up to 30 vol% PPTA nanofibrils. • In situ fibrillation of the PPTA during high-temperature extrusion compounding. • Significantly increased tensile strength and HDT compared with unmodified PA610. • Increased melt elasticity, further enhanced by high-temperature heat treatment. • Transamidation at the PA610-PPTA interface may contribute to interfacial interactions. [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.)

Cord reinforced rubber hose was widely used in automobile,aviation,aerospace and other fields. Meeting mechanical performance was the key to the safe use. In this paper,modeling of knitting cord was probed firstly. Then mechanical performance of aramid cord reinforced EPDM rubber hose was analyzed by ANSYS. Finally influence of cord’s needle number on mechanical properties of rubber hose was researched. The results show that maximum stress of cord is more than three hundred of times of maximum equivalent stress of rubber and maximum deformation of rubber is several times of maximum deformation of the cord when hose is imposed 0. 24 MPa inner pressure. And rubber and cord will not be destroyed. Experimental Bursting pressure of rubber hose is 2. 04 MPa,which is 97% of forecast bursting pressure 2. 10 MPa. With cord ’s needle number increasing,equivalent stress and deformation of cord and rubber all decrease sharply at first then tend to be gentle.

The discovery of oil fields in deepwater over the last decades led the oil and gas industry to the necessity of replacing the steel wire cables of the mooring systems of offshore platforms by polymeric ropes. These systems must be designed to work for at least 20 years without showing substantial loss in tensile strength or in their mechanical behavior along this period. However, some polymers present degradation by seawater through the process of hydrolysis, and the question whether it affects significantly the materials' ultimate tensile strength arises. Accelerated hydrolysis tests were conducted in yarn samples of aramid at high temperature in order to use the Arrhenius correlation to predict their lifetime under service conditions. In order to decouple the total degradation into a thermal and a purely hydrolytic part, separate aging experiments were performed into a dry chamber and the conclusion was that thermal degradation does not play a significant role in the total degradation of aramid due to the water submersion at the temperatures tested. [ABSTRACT FROM AUTHOR]

Soft body armour panels using p-aramid (Technora) fabrics with three different levels of thread densities were developed in this research. Shear thickening fluid (STF) was synthesized using silica nano-particle (100 nm) and polyethylene glycol (PEG). Fabrics were coated with 60% (w/w) STF to improve their resistance against low-velocity bullets (165 m s−1). For neat fabrics, all the bullets fired from 0.38″ calibre revolver pierced the multilayer fabric panel. However, impact energy absorption increased with the increase in thread density in fabric. After coating with shear thickening fluid, panels having four layers of fabric stopped all the bullets fired. It was possible to reduce the weight of panel by 23% after the STF treatment whilst ensuring bullet stoppage. [ABSTRACT FROM AUTHOR]

Aramid carbon nanotube conductive papers (ACP) were prepared by using multi-walled carbon nanotubes as conductive agent and aramid fiber as the matrix. The ACP were used as the anode current collector of SnO 2 lithium ion batteries (LIBs) instead of copper foil. The structure was characterized by X-ray diffraction analysis (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The electrochemical performance was characterized by Galvanostatic charge-discharge test. As a result, the ACP performed better than copper foil. After 60 cycles at a current density of 100 mA/g, the specific capacity can be maintained at 876 mAh/g, and the SnO 2 /ACP electrode exhibited excellent rate performance. • Preparation of aramid-carbon nanotube conductive paper as the current collector instead of copper foil of SnO 2 material. • The active material SnO 2 is pressed into the aramid fiber and carbon tube structure by hot pressing process to improve the interfacial properties between them. • The prepared paper aramid-carbon nanotube conductive paper has both excellent mechanical properties of aramid paper and electrical conductivity of carbon tubes. • SnO 2 lithium-ion battery exhibits excellent electrochemical performance and maintains good specific capacity. [ABSTRACT FROM AUTHOR]

This research presents the stab resistance and thermo-physiological comfort properties of the fabrics prepared from high-performance fibres of aramid (i.e. Kevlar®) and ballistic nylon. The fabric samples were coated with boron carbide to improve the stab resistance properties. The quasistatic stab tests were performed using NIJ 0115.00 standard knife (P1) on the Instron tensile testing machine. The thermo-physiological comfort properties of the fabric samples were evaluated by measuring the air permeability, water-vapour resistance and thermal resistance. It was observed that the application of the coating significantly increased the stab resistance properties of the fabrics. Furthermore, the air permeability was significantly reduced; whereas, the water-vapour resistance and thermal resistance were significantly increased with the application of coating. Hence, the coated fabrics will have to compromise the comfort aspects to achieve the desired protection level, which is the prime requirement for the stab resistant textile materials. [ABSTRACT FROM AUTHOR]

• Microcellular aramid films have been obtained using exclusively ionic liquids. • Density has been diminished from 1.4 g⋅cm−3 down to 0.37 g⋅cm−3. • Average cell size lies in the microcellular range (between 1 and 8 μm). • Cellular morphology can be controlled through the ionic liquid proportion. • Thermally induced phase-separation process has been investigated. We prepared microporous aramid films through a simple, inexpensive and green way, using ionic liquids (IL) as porosity promoters. Commercial poly(m -phenylene isophthalamide) (MPIA) films with different IL proportions were prepared, and then microporous films were obtained by removing the IL in distilled water. Microporous films presented density values between 0.34 and 0.71 g⋅cm−3 (around five times lower to commercial MPIA), with a homogeneous and controlled cellular morphology dependent on the proportion of the IL, showing cell sizes in the microcellular range (radii between 1 and 8 µm). Thermal, mechanical and electrical properties (specifically ionic conductivity) of the aramid films were analyzed to evaluate the influence of the IL proportion. Finally, it was observed that the MPIA/IL system presented a reversible thermally induced phase-separation process around 60 °C, which was characterized through AFM-Raman images and spectra, together with the variation of the ionic conductivity. [ABSTRACT FROM AUTHOR]

The development of impact resistant hybrid composites for ballistic applications is a recent trend. The increased energy absorption and reduced weight are some of the advantages for using these composites. Hybrid composites constituted of ultra-high molecular weight polyethylene (UHMWPE) laminates and aramid fiber fabrics were obtained by autoclave molding. The dynamic compression test was performed using a Split Hopkinson pressure bar with a standard deformation rate. The V50 ballistic limit test was carried out following the military standard MIL-STD-662F. The ballistic table NIJ Standard 0108.01 was taken as a reference and 9 mm Luger FMJ and.44 Mag Lead SWC EXPP ammunition were used. The dynamic-mechanical properties of the hybrid composites were evaluated. The composites exhibited an areal density of 5.30 ± 0.05 kg.m−2, meeting the required criteria in NIJ 0108.01. The V50, maximum stress, tenacity, storage modulus and tan delta peak height depended on the proportion of UHMWPE used in the hybrid composites: the best results were obtained for the composites with 75% UHMWPE and 25% aramid. [ABSTRACT FROM AUTHOR]

Abstract This paper presents the results of an experimental and numerical study of the behavior of circular hollow section (CHS) steel tubes strengthened by Aramid fiber-reinforced polymer (AFRP). The aramid fiber used for this experiment is available under the trade name of Kevlar 49. In this study, thin-walled circular steel tubes externally bonded with fiber in the hoop direction were tested under axial compression to examine the effects of the AFRP thickness, on their axial load carrying and shortening capacity. The three-dimensional finite element models (FEM) of AFRP strengthened circular hollow section (CHS) was developed using ANSYS Workbench Ver. 19.0 and ACP (ANSYS Composite Prep/Post) tool considering both geometric and material nonlinearities. The effects combined of AFRP damage and interlaminar failures for the bonded interface are modeled within FEM using "Hashin" failure criteria and Cohesive Zone Model (CZM), respectively, to provide an accurate simulation. The results involving the failure modes, load vs. axial shortening curve and ultimate load capacity, were obtained from the experimental and numerical simulation and compared for validation. Both the experimental and numerical results are consistent, demonstrating that AFRP external strengthening can considerably enhance the strength of steel tube columns by 96% for short tubes and 23% for long tubes using 3 mm thickness of AFRP. Highlights • Conducted an experimental study of AFRP strengthening circular hollow section columns with different wrapping parameters. • Developed and validated FE models to simulate AFRP strengthened short and long CHS columns. • Conducted a parametric study on the effect of AFRP and steel thickness and length of the columns on the axial capacity. • The strength and stiffness of the AFRP strengthened specimens significantly improved compared to the control specimens. [ABSTRACT FROM AUTHOR]

Low axial compressive strength of high‐performance organic fibers is one of the most prominent problems for their application in advanced technologies. In this paper, N, N'‐diphenyl‐1,4‐phenylacetyleneamide (DPAA) as a novel external cross‐linker was synthesized. It was confirmed that DPAA could react itself and quickly form cross‐linking network above 210 °C with pore width of 1–30 nm. Then DPAA was introduced into some typical high‐performance organic fibers through post‐swelling process, followed by annealing at 250 °C. It was found that DPAA would in‐situ form cross‐linking network inside the fiber, which was regarded as semi‐interpenetration structure. Compressive strength of Kevlar‐49 fiber modified through this method increased by nearly 70% and corresponding tensile strength didn't deteriorate. When PBO, heterocyclic aramid and polyimide fibers were modified by the same procedure, their compressive strength showed 25, 36 and 72% enhancement respectively. Therefore, DPAA is an effective modifier to enhance compressive strength of high‐performance organic fibers and shows great universality. N, N'‐diphenyl‐1,4‐phenylacetyleneamide (DPAA) is synthesized as external cross‐linker. It is introduced into high‐performance fibers to in situ form semi‐interpenetration structure, which shows positive effect on compressive properties of the fibers. In addition, the method shows great universality for different fibers. [ABSTRACT FROM AUTHOR]

Abstract Fibrous materials have been extensively used in forms of Fibre Reinforced Polymers (FRP) as strengthening composites for civil construction. In the last years a new generation of inorganic-based fibrous strengthening systems are ongoing to be investigated all over the world, under the names of Fibre/Fabric Reinforced Cementitious Mortars/Matrix (FRCM) or Textile Reinforced Mortars (TRM), which indicate the same family of materials. In this new systems generally long dry fibres, in forms of soft nets are put in direct contact with a cementitious or lime-based matrix. In some other cases the reinforcement is represented by a pre-cured FRP grid, inserted within the inorganic plaster. The fibres that are used may vary from glass, basalt, aramid, carbon to steel. The presence of a matrix with high alkaline content may generate durability problems for the fibrous reinforcement, especially in those cases in which glass or basalt fibres are recommended and used. The experimental study presented herein reports and discusses the residual mechanical tensile properties of different dry and impregnated fibres, after exposure to four different ageing protocols in alkaline solutions. SEM microscopy images are also illustrated to show the damage at fibre level that was observed in the cases of vulnerable fibres. Important recommendation are provided for future research, also addressed to possible future design guidelines and acceptance criteria of new FRCM/TRM strengthening systems. [ABSTRACT FROM AUTHOR]

Poor solubility of high‐performance polymer has always been a leading bottleneck for its application. Para‐aramid fiber as a typical high‐performance fiber owns significant hydrogen‐bond interaction and chloride salts are generally needed to provide Cl− ions as hydrogen‐bond acceptors for its dissolution. In this paper, Poly‐(benzimidazole‐terephthalamide) (PABI) which complexed with by‐product HCl (PABI‐HCl) during polymerization was fabricated and by‐product HCl was regarded as potential Cl− ions donor. CH3COONa as cosolvent was added in DMAc to dissolve PABI‐HCl. It was confirmed that solubility of PABI‐HCl in DMAc could be improved significantly in existence of CH3COONa. The finding was characterized by conductivity measurement, UV‐Vis spectra, Atomic Absorbance Spectra and Thermogravimetric analysis etc. By‐product HCl as a strong acid was converted into CH3COOH due to existence of CH3COO− in solution. Then it would release Cl− ions and they could interact with secondary amide of aramid to disrupt interaction among macromolecules. Therefore, aramid was dissolved successfully by utilizing by‐product HCl and no external Cl− ions donor was needed. A novel method about dissolving aramid is reported. CH3COONa is selected as cosolvent in the dissolution process. CH3COO− ions it offers can convert HCl which is the by‐product during polymerization of aramid into CH3COOH and in situ release Cl− ions which are strong hydrogen‐bond acceptors. They can break original intermolecular interaction of aramid to make it dissolve in traditional organic solvents. [ABSTRACT FROM AUTHOR]

The particle size, morphology, chemical structure, crystallization property and thermal stability of mica from two different producing areas were characterized and analyzed respectively. The aramid mica paper was then prepared by using them, and the effect of mica particle size on the mechanical and dielectric properties of the paper were studied. The results show that mica raw materials and their particle size in different producing areas have a great influence on the performance of aramid mica paper, The scale of mica is relatively pure, with high crystallinity, larger diameter and thickness, and complete shedding, which is helpful to improve the mechanical and dielectric properties of aramid mica paper, while compared with the scales of mica, different particle sizes of mica powder have lower purity, lower degree of shredding and serious fragmentation, which will reduce the properties of aramid mica paper. In addition, with the decrease of the particle size, the mica sheet structure is damaged and further fragmentation occurs. The massive fine particles increase, which impedes the binding between the fibers and impedes the bonding between the aramid fibers, resulting in a decrease in mechanical dielectric properties of the aramid mica paper. [ABSTRACT FROM AUTHOR]

• The theoretical model can accurately predict the stabbing resistance performance of soft body armor made of aramid with resin or unidirectional PE composites. • The theoretical model can quickly obtain the time history data of penetration point and penetration depth, which are difficult to measure in experiment. • The theoretical model can guide the flexible and lightweight design of soft body armor. Soft body armor can effectively safeguard lives from stabbing attacks and they are mainly composed of fibrous composites. Currently, the evaluation of protective performance for soft body armor is mainly conducted by experiments or numerical simulations, with theoretical methods have been rarely mentioned. In this study, a spring-mass based theoretical model has been established to predict the stabbing resistant performance of a soft body armor comprising aramid with resin or unidirectional UHMWPE composites. The theoretical results agree well with the experimental results where the error in maximum impact force of the knife is within 3.2% and the displacement within 1.7%. The layers of penetration are also identical. By only inputting hardness and stiffness of the specimen, the theoretical model can efficiently provide the performance of a soft body armor composed of fiber composite material under different impact energy levels. With the aid of this theoretical model, one can optimize the composition of a soft body armor to achieve minimum weight and thickness in practical applications. [ABSTRACT FROM AUTHOR]

• An in house pyrotechnical triple launcher is designed and implemented which can shoot three 1.102 g fragment simulating projectiles (FSP) with each shot. • The setup is used to test aramid dry fabrics against fragmentation. • The results show a drop in the target's ballistic limit of up to 13% against triple impacts compared to single impact tests. • Dynamic interactions of multi-site impacts generate multiple stress wave patterns which superimpose, elevating the stress-strain energy density of the material, decreasing its ballistic performance. The ballistic resistance of protective equipment against fragment impacts, such as those typically generated from explosions, has been a major concern the past 50years. The simplifications required to investigate the material response to multiple fragment impacts were set based on the technological limitations of the past. Still, current standardised ballistic testing methodologies consider the interactions between multiple impacting fragments negligible, simulating the multiple impulsive loads with single impact tests. This paper challenges this assumption, introducing the parameters of spacing, formation and timing between multiple impacts in a laboratory test method. An in house pyrotechnical triple launcher is designed and implemented which can shoot three 1.102 g Fragment Simulating Projectiles (FSP) with each shot. An add-on dispersion unit allows for adjusting the distances between the impact points. The control over the projectile velocities and the dispersion of the three impact points enables the simulation of a dense fragment cluster impact with specific characteristics. The setup is used to test Aramid dry fabrics against fragmentation. In total 53 specimens of 15 layers of Kevlar 29 plain weave fabrics are tested against single and triple impacts with two different levels of projectile dispersion. The results show a drop in the target's ballistic limit of up to 13% against triple impacts compared to single impact tests. The fabric's ballistic performance seems to improve with increasing the distances between the impact points. For every triple impact test, the parameters: impacting velocity, distances between impact points, alignment of impact points with the warp and weft directions and time intervals between impacting projectiles is documented. [ABSTRACT FROM AUTHOR]

Many existing reinforced concrete structures were constructed with substandard characteristics. Low quality concrete, poor transverse reinforcement details and insufficient flexural strength are among the most common deficiencies. While substandard structures are in need of retrofitting, particularly in seismic areas, problems such as high costs and disturbance to occupants are major obstacles for retrofit interventions. Fiber reinforced polymers can provide feasible retrofit solutions with minimum disturbance to occupants. In this study, the basic aim is to investigate the flexural seismic performance of substandard reinforced concrete columns retrofitted with embedded longitudinal fiber reinforced polymer reinforcement without increasing the original dimensions of the columns. In the experimental study, the reference and retrofitted columns were tested under constant vertical and reversed cyclic lateral loads. Three different connection methods of aramid fiber reinforced polymer reinforcement to the footing were investigated experimentally. A significant enhancement was obtained in lateral flexural strength through the proposed retrofitting method. Furthermore, it was observed that the cyclic lateral drift capacities of the retrofitted columns were as high as 3%, which can be deemed as quite satisfactory against seismic actions. The comparison of the experimental data with analytical calculations revealed that a conventional design approach assuming composite action between concrete and fiber reinforced polymer reinforcement can be used for flexural retrofit design. Experimental results also demonstrated that strain limit for longitudinal fiber reinforced polymer (FRP) reinforcement should be remarkably lower in case of reversed cyclic loading conditions.

We prepared high-performance aromatic copolyamides, containing bithiazole and thiazolo-thiazole groups in their main chain, from aromatic diamines and isophthaloyl chloride, to further improve the prominent thermal behavior and exceptional mechanical properties of commercial aramid fibers. The introduction of these groups leads to aramids with improved strength and moduli compared to commercial meta-oriented aromatic polyamides, together with an increase of their thermal performance. Moreover, their solubility, water uptake, and optical properties were evaluated in this work.