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Carbon fiber reinforced polymer composites have the advantages of being lightweight, having high strength and designability, and having been extensively used. However, the interlaminar toughness and delamination resistance of these composites are relatively poor due to their laminated structure and intrinsic brittleness of resin matrix. In this paper, commercialized free-standing carbon nanotube (CNT) films, drawn from CNT forests, were used to toughen the interlaminar interfaces of the composites. The effects of resin infiltration state and thickness of CNT films on the interlaminar toughening effect were systematically investigated. The results show that the pre-infiltration treatment of CNT films with acetone diluted epoxy resin solution can effectively improve the degree of resin infiltration. Compared with the samples containing untreated CNT film, the Mode I and Mode II interlaminar fracture toughness of the treated samples were significantly improved. The GIC reached a maximum of 1412.42 J/m2 at a CNT film thickness of 5 µm, which was about 61.38% higher than that of the baseline. At a CNT film thickness of 15 µm, the GIIC reached a maximum value of 983.73 J/m2, approximately 67.58% higher than that of the baseline. The corresponding toughening mechanisms were also systematically analyzed. [ABSTRACT FROM AUTHOR]

• A hierarchical toughening strategy was proposed for improving the interlaminar properties of GFRP. • The highest improvement of G IC,ini and G IC,prop values reached as much as 211 % and 174 %. • The multiscale fiber bridgings and interlaminar crossings are the key to achieve high interlaminar fracture toughness. Hierarchical toughening is commonly found in natural materials such as teeth, bone and seashells, which have evolved to withstand mechanical stresses. The incorporation of this mechanism into the design of synthetic materials, such as composites, has drawn much attention in recent decades. In this work, a carbon fiber felt (CFF) made of short carbon fibers was spray-coated with carbon nanotubes (CNT) to create a hierarchical structure that can be directly interleaved into glass fiber reinforced polymer (GFRP) composites for interlaminar toughening purpose. The results showed that the highest enhancement of G IC,ini and G IC,prop values reach as much as 211 % and 174 %, respectively, which far outweighs the state of the art. The fracture surfaces as well as crack propagation behaviors were comparatively investigated to get deep insight into the toughening mechanisms. It was found that multiscale fiber bridgings and interlaminar crossings are the key to achieving high interlaminar fracture toughness of laminate composites. [ABSTRACT FROM AUTHOR]

Highlights Carbon nanotube (CNT)‐polyetherimide (PEI) hybrid nanofibrous veils were prepared through the electrospinning process to function as an interlayer in carbon fiber reinforced polymer composites (CFRP), and the effects of the addition of the hybrid fiber veils on the interlaminar fracture properties and flexural properties of CFRP were investigated. The results showed that interleaving CNT/PEI hybrid veils can effectively avoid long‐troubled trade‐off between mode‐I interlaminar fracture toughness and in‐plane properties when using thermoplastic toughening materials. Specifically, the GIc value and flexural strength of the laminates were increased by as much as 86.2% and 14.3%, respectively when CNT content was reached up to 0.7 wt% in CNT/PEI hybrid veil. This method adopts ultra‐low PEI and CNT additions, and the limited quantity of these additives demonstrates a notably high interlaminar toughening efficiency while concurrently enhancing the strength, rendering it a promising strategy for both toughening and strengthening. PEI is used as a carrier to transport CNT to the CFRP interlaminar layers. PEI‐CNT hybrid fiber veils improve GIC and flexural strength of CFRP. PEI‐CNT hybrid fiber veils impede crack expansion through various mechanisms. This method adopts ultra‐low PEI and CNT additions. [ABSTRACT FROM AUTHOR]

"Interleaving" is widely used for interlaminar toughening of fiber-reinforced composites, and the structure of interleaving is one of the important factors affecting the toughening efficiency of laminates. Several experiments have demonstrated that compared to continuous and dense structures, toughening layers with structural heterogeneity can trigger multiple toughening mechanisms and have better toughening effects. On this basis, this work further investigates the application of heterogeneous toughening phases in interlaminar toughening of bidirectional GFRP. CNT was selected to construct toughening phases, which was introduced into the interlaminar of composites through efficient spraying methods. By controlling the amount of CNT, various structures of CNT toughening layers were obtained. The fracture toughness of modified laminates was tested, and their toughening mechanism was analyzed based on fracture surface observation. The results indicate that the optimal CNT usage (0.5 gsm) can increase the initial and extended values of interlayer fracture toughness by 136.0% and 82.0%, respectively. The solvent acetone sprayed with CNT can dissolve and re-precipitate a portion of the sizing agent on the surface of the fibers, which improves the bonding of the fibers to the resin. More importantly, larger discrete particles are formed between the layers, guiding the cracks to deflect in the orientation of the toughened layer. This generates additional energy dissipation and ultimately presents an optimal toughening effect. [ABSTRACT FROM AUTHOR]

• BFRP bars was treated by CNTs modified resin to improve the corrosion resistance in alkaline concrete environment. • The mechanical properties of untreated and treated BFRP bars with CNTs modified resin were evaluated after 180 d immersion. • The microcosmic deterioration mechanism of untreated and treated BFRP bars with modified resin CNTs were investigated using Micro-CT, FTIR, TG and SEM. The corrosion of basalt fiber-reinforced polymer (BFRP) bars restricts their use in alkaline concrete structures. However, developing high-performance resin can improve the anti-alkaline corrosion of BFRP bars. This work investigates the alkaline resistance of BFRP bars by coating carbon nanotubes (CNTs) modified epoxy resin incorporating varying CNTs contents (0, 0.1, 0.3, and 0.5 wt%). The durability of untreated and treated BFRP bars with CNT-modified resin was evaluated using water uptake, transverse shear, and interlaminar shear tests. Scanning electron microscopy (SEM) and X-ray micro-computed tomography (micro-CT) were also used to observe the surface corrosion morphology and interior deterioration of BFRP bars, respectively, while Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were applied to analyze the resin deterioration of BFRP bars. It was found that CNTs modified resin can significantly improve the alkaline resistance of BFRP bars. After 180 d of immersion, the interlaminar shear strength (ILSS) retention of untreated BFRP bars is 31.8%, while it is 63.3, 75.0, 91.3, and 93.7% for BFRP bars treated with 0, 0.1, 0.3, and 0.5 wt% CNTs modified resin, respectively. The improvements in ILSS retention of BFRP bars treated with 0.5 wt% CNTs modified resin are 61.9% and 30.4% more than untreated and pure resin-treated BFRP bars, respectively. BFRP bars treated with 0.3 and 0.5 wt% CNTs modified resin exhibit insignificant resin hydrolysis and less porosity than untreated BFRP bars. The effective prevention of hydroxyl ions into the interior of BFRP bars and the enhancement of the anti-crack behavior of resin by CNTs are the leading causes of corrosion resistance improvement in BFRP bars. The outcomes of this study provide insights into using CNTs modified resin to improve the durability of BFRP bars in marine concrete structures. [ABSTRACT FROM AUTHOR]

Ultrathin CNT fiber veils (100–300 nm thick) were used as interleaves to improve the interlaminar fracture toughness of unidirectional carbon fiber reinforced polymer composites. These veils, drawn from vertically aligned CNT forests, were directly deposited at the mid-plane of CFRPs either longitudinally or transversely to the carbon fiber. The results revealed that triggering multiple toughening mechanisms is the key to achieve high toughness FRP composites. When the veils were oriented parallelly to the carbon fiber, the crack propagates in a "zig-zag" manner, not only interacting with more CNTs, but also triggering more carbon fiber bridgings, leading to a steeply "rising" R-curve. The superiority and effectiveness of this technique is exemplified by the extremely thin toughening layers (about 300 nm thick) needed to remarkably improve the propagation value of Mode I interlaminar fracture toughness of the CFRP by approximately 107%. The Mode I toughening factor (η I), defined as the change in Mode I interlaminar fracture toughness per interleaf-to-ply thickness ratio, comes out as high as 713, which is far outweigh the state-of-the-art. However, transversely-placed CNT veils will seriously block the formation of carbon fiber bridgings, remarkably degrading the Mode I interlaminar toughness of the laminates. [Display omitted] [ABSTRACT FROM AUTHOR]

The mechanical properties of Kevlar® 29 single filaments and yarns with different gage lengths were investigated by utilizing an MTI miniature tester and an MTS load frame. Single yarns of 25 mm were also tested over four different strain rates using a drop-weight impact system. The experimental results showed that the mechanical properties of Kevlar® 29 are sensitive to gage length, structural size scale, and strain rate. The tensile strength decreased with increasing gage length and the structural scale from fiber to yarn, and increased with increasing strain rate. Weibull analysis was conducted to quantify the degree of variability in tensile strength. The obtained Weibull parameters were then used in an analytical model to simulate the stress–strain response of single yarn. Finally, Weibull parameters of single filaments with other gage lengths and strain rates were also obtained by fitting the stress–strain curves of single yarns with corresponding testing conditions. [ABSTRACT FROM AUTHOR]

Unidirectional carbon fiber reinforced polymer (CFRP) composites fabricated by Vacuum Assisted Resin Transfer Molding (VARTM) are tested at four initial strain rates (25, 50, 100 and 200 s −1 ) and six temperatures (−25, 0, 25, 50, 75 and 100 °C) on a servo-hydraulic high-rate testing system to investigate the effects of strain rate and temperature on their tensile properties and failure behaviors. A high speed digital camera is used to capture the deformation and failure behavior of the CFRP composites at a sampling rate of 20,000 fps with resolution of 256 × 256 pixels. In order to illuminate corresponding strain rate effect mechanism, carbon yarn samples are complementally tested under dynamic tensile loading at four different strain rates (40, 80, 120 and 160 s −1 ) utilizing an Instron drop-weight impact system. The stress–strain responses at these strain rates are discussed. A Weibull statistics model is used to quantify the degree of variability in tensile strength and to obtain Weibull parameters for engineering applications. The non-uniform strain and displacement fields as well as the damage process are characterized by digital image correlation (DIC) method. [ABSTRACT FROM AUTHOR]

Glass fiber reinforced composite (GFRP) samples were tested at different strain rates from quasi-static up to 160 s −1 and temperatures from −25 to 100 °C to investigate any possible effects on their mechanical properties and failure patterns. The experimental results show that the tensile strength, maximum strain and toughness increase with increasing strain rates at room temperature, and the Young’s modulus, tensile strength and toughness decrease with increasing temperatures at the strain rate of 40 s −1 . Weibull statistics were used to quantify the degree of variability in the tensile strength and obtain Weibull parameters for numerical simulations and engineering applications. [ABSTRACT FROM AUTHOR]

Enabling energy-storing functions in structural composites is an appealing strategy to reduce the weight of systems in electric transport. Structural power composites (SPC) can be made by introducing energy-storing layers in traditional composite laminates, either as embedded devices or as thin integrated interleaves simultaneously performing load-bearing and electrochemical energy storage functions. However, the solid electrolyte in these layered architectures is typically a soft polymer, thus making the SPC very prone to delamination. Mechanical interconnection using structural matrix bridges between plies, analogous to metal connectors, provides a solution to alleviate delamination risks while maintaining the structural integrity of the SPC even under the most unfavourable combinations of loads. This paper reports on the use of experimental tests and FEM simulations to study the micromechanics of interlaminar polymer connectors in SPCs. It explores the effect of the connector area on the shear strength and energy density. The results provide a validated methodology to design laminated structural composites with a tailored balance of multi-functional properties of wide application to SPC of different constituents, with electrochemical energy storage either as capacitors or batteries. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, aramid fiber (AF)/phenolic resin prepreg was fabricated by impregnating low content carbon nanotube (CNT)‐reinforced phenolic resin with aramid fabric through a two‐roll pressing process. Both non‐functionalized and carboxylic‐functionalized CNTs (CNTs and CNTs‐COOH) were used for comparison study. For each of the formulations, composite laminate was made by a hot‐pressing process with a number of the prepregs stacked together. Mechanical properties and ballistic performance of the laminates and material failure mechanisms were evaluated and analyzed. Both non‐functionalized and CNTs‐COOH can effectively improve the mechanical and ballistic performance of the laminates. With CNTs‐COOH reinforcement, better results were achieved. As compared with the laminate without CNT reinforcement, 1.0 wt% CNTs‐COOH‐reinforced laminate showed 19.41%, 22.29%, and 45.83% improvement in tensile, flexural, and adhesion shear strength, respectively. The ballistic test results showed that the V50 and the specific energy absorption (SEA) were increased by 5.77% and 13.44%, respectively. The correlation between mechanical and ballistic performance of the composites was analyzed and conducted. [ABSTRACT FROM AUTHOR]

The introduction of nanostructured interlayers is one of the most promising strategies for interlaminar reinforcement in structural composites. In this work, we study the failure mechanism and interlayer microstructure of aerospace-grade structural composites reinforced with thin veils of carbon nanotube produced using an industrialised spinning process. Samples of unidirectional carbon fiber/epoxy matrix composites interleaved with different composition CNT veils were prepared using hot press method and tested for interlaminar fracture toughness (IFT), measured in Mode-I (opening) and Mode-II (in-plane shear), and for interlaminar shear strength (ILSS), evaluated by the short beam shear (SBS) test. The crack propagation mode could be directly determined through fractography analysis by electron microscopy and resin/CNT spatial discrimination by Raman spectroscopy, showing a clear correlation between interlaminar reinforcement and the balance between cohesive/adhesive failure mode at the interlayer region. Composites with full resin infiltration of the CNT veils give a large increase of Mode II IFT (88%) to 1500 J/m2 and a slight enhancement of apparent interlaminar shear strength (6.5%), but a decrease of Mode I IFT (−21%). A toughening factor, defined as the relative increase in toughness per interleaf-to-ply thickness ratio, give a record-high value of 15.8 for Mode II IFT. The results help establish the role of interlayer infiltration, interlaminar crossings and formation of a carbon fiber bridgings, for interlaminar reinforcement with interleaves. [ABSTRACT FROM AUTHOR]

Textile-reinforced concrete (TRC) is used widely in thin-walled structures due to its unique construction characteristics and superior mechanical properties. However, previous studies of the dynamic flexural properties of alkali resistant (AR)-glass TRC thin plates did not consider the influence of exposure to high temperature. In this study, the effect of impact velocity (range from 1.29 to 4.04 m/s) on AR-glass TRC after exposure to elevated temperatures up to 400°C was investigated experimentally using a drop-tower impact system. AR-glass TRC specimens were heated to target temperatures (100°C, 200°C, 300°C, and 400°C) in a furnace and then tested at room temperature. The effects of exposure to high temperature and the strain rate of loading (impact velocity) on the flexural mechanical properties were measured, and the microstructure and damage evolution of the composites was evaluated. Results show that the strain rate had a direct effect on the flexural properties of AR-glass TRC composite under impact after exposure to high temperatures. Furthermore, the weakening effect of high temperature in AR-glass TRC material could equal or even exceed the hardening effect due to the strain rate. The results were evaluated by comparing dynamic flexural stress and toughness features. Finally, the high-temperature deterioration mechanism of AR-glass TRC material was determined by comparing the changes in the matrix–textile interface and the textile fracture after exposure to different temperatures. [ABSTRACT FROM AUTHOR]

Basalt textile reinforced concrete (BTRC) specimens were tested at different impact velocities of 0.77 m/s, 2.31 m/s and 4.62 m/s and temperatures of −25, 0, 25, 50 and 100 °C to study possible influences on their impact resistance and failure patterns. The experimental results indicate that the impact velocity, temperature, the number of basalt textile layers and boundary conditions can significantly affect the impact responses. At a constant temperature, both the maximum impact force and the energy absorption exhibit apparent increase with increasing impact velocity. On the other hand, experimental data indicate that for the same impact velocity, the maximum impact force and absorbed energy decrease with temperature at span of −25 °C to 100 °C. Both the maximum impact force and the energy absorption of the specimens are improved as the number of basalt textile layers increased from four to six. All specimens are able to absorb most of the kinetic energy under impact velocity of 4.62 m/s, since the basalt textile is mainly pulled out from the matrix. Under the impact velocity of 4.62 m/s, the fixed boundary increases the peak impact force, but reduces energy absorption compared with free boundary condition at the room temperature (25 °C). Failure patterns are significantly affected by the varying impact velocities, but not the temperature and boundary conditions. [ABSTRACT FROM AUTHOR]

Kevlar® 49 fabrics have excellent performances such as high elastic modulus and high impact resistance, which are widely used in ballistic systems, aerospace, fabric reinforced composite materials and other fields. The present work studied the multi-scale mechanical behaviors of Kevlar® 49 in the forms of fiber, yarn and fabric subjected to uniaxial tension. The experimental results showed that the material mechanical properties are dependent on structural size scale and gage length of samples. The tensile strengths decrease with increasing gage length and structural size scale from fiber to yarn, and to fabric, and follow Weibull distribution by conducting statistical analysis, which is used to quantify the degree of variability in the tensile strengths of fiber and yarn with different gage lengths. At last, user-defined subroutines (UMAT) in ANSYS were implemented to simulate the tensile behaviors of single yarn and fabric by using the constitutive models of fiber and yarn, respectively, which considered their Weibull distribution in tensile strength. This probabilistic approach can simulate the multi-scale tensile behaviors of Kevlar® 49 accurately and reveal the mechanisms of deformation and failure process based on the various size scales. This approach is also applicable to study the multi-scale behaviors of other fabrics once their properties and Weibull parameters are determined. [ABSTRACT FROM AUTHOR]

• Tensile strength depends on strain rates, temperatures, and coupling effects. • FRP composites are temperature sensitive due to the resin's softening. • FRP composites highly depend on reinforcement and resin properties. • Fiber breakage and fiber pullout become dominant at low and high strain rates, respectively. The fiber-reinforced polymer (FRP) composites are currently widely used in infrastructure construction, and the study on the dynamic performance and temperature sensitivity is still under investigation. Understanding the effects of strain rate and temperature on the tensile behaviour of FRP composites is vital to design the composite structures under harsh conditions (earthquake, explosion, or impact). Therefore, this study comprehensively reviews tensile performance of FRP composites under several strain rates (quasi-static, low, intermediate, and high) and temperatures. The tensile strength of FRP composites depends on the strain rates, temperatures, and coupling effect. The failure patterns of FRP materials are also reviewed at different strain rates and temperatures and found that fiber cracking and fiber pullout become dominant at low and high strain rates, respectively, which can help gain insight into failure mechanisums of FRP composites. [ABSTRACT FROM AUTHOR]

The flexural properties of basalt textile reinforced concrete (BTRC) specimens with pre-tension, short carbon, steel, and AR-glass fibers were investigated through three-point bending in a utilizing drop-weight impact setup. The flexural impact parameters, such as flexural strength, flexural modulus, ultimate strain, maximum strain, and energy absorption capacity, were determined under different impact velocities. The flexural strength and toughness of the BTRC specimens without pre-tension significantly increased when the impact velocity (1.0–3.0 m/s) and layers of basalt textiles were increased. By contrast, the flexural modulus initially increased and subsequently decreased with increasing impact velocity, whereas the loading rate exerted a marginal influence on the ultimate strain and the maximum strain. When the basalt textile had four reinforcement layers, the BTRC reinforced with 0.5 vol% of short carbon fiber or short steel fiber exhibited varied different flexural responses under different impact velocities (1.0–4.0 m/s); in particular, the BTRC reinforced with short steel fibers had a higher maximum strain. In addition, pre-tensioned BTRC with different short fibers were tested under an impact velocity of 1.0 m/s. The flexural strength decreased as the short carbon fiber and glass fiber contents increased. The highest flexural strength was observed in the pretensioned specimen with 0.5 vol% of short glass fiber and three layers of basalt textile. The addition of short fibers in cement matrix, the number of textile layer used as reinforcement, the pretension on textile, and the impact velocities used in the tests can significantly affect the flexural impact behavior of BTRC specimens. The Weibull parameters were analyzed to quantify the degree of variability in the flexural strength. [ABSTRACT FROM AUTHOR]

In this work, a dual-response ratiometric fluorescent probe (E)-3-(5-(2-nitrovinyl)thiophen-2-yl)-9-phenyl-9H-carbazole (NTPC) for high selectivity and sensitivity detection of ClO− and N 2 H 4 was successfully developed. This probe NTPC showed ratiometric fluorescent response to ClO− and N 2 H 4 , which induces obvious naked-eye color changes, respectively. In addition, the NTPC for ClO− and N 2 H 4 detection displayed low detection limits of 71.4 nM and 0.6 μM, respectively. And the sensing mechanism of NTPC with ClO− and N 2 H 4 was well confirmed by 1H NMR and HR-MS spectra. Moreover, this novel probe was applied to monitoring and differentiating ClO− and N 2 H 4 in living cells, and exhibits good biocompatibility and low cytotoxicity. A novel carbazole derivative have been designed and synthesized, which provided ratiometric fluorescence signal for detecting and differentiating ClO− and N 2 H 4 in living cells and exhibits low cytotoxicity. Unlabelled Image • A dual-response ratiometric fluorescent probe (NTPC) was prepared for the detection of hypochlorite and hydrazine. • NTPC for ClO− and N 2 H 4 detection displayed low detection limits of 71.4 nM and 0.6 μM, respectively. • NTPC was applied to monitoring and differentiating ClO− and N 2 H 4 in living cells. [ABSTRACT FROM AUTHOR]