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Low-cost surfactants are of great importance for many applications. Chitosan is one of the abundant promising candidates as a raw material for low-cost surfactants. However, how to tune the molecular structure to achieve high solubility, low surface tension, and good foam stability is a great challenge. Herein, the ‘comb-like’ zwitterionic polymer surfactant based on chitosan by partial N-alkylation and quaternization was prepared. The experimental results demonstrate that the length and degree of substitution of the alkyl chain have a significant influence on the properties of the products. Such comb-type zwitterionic polymer surfactants have good water solubility, and the water solubility can reach up to 85 g/L. Surface tension and foam performance tests reveal that such ‘comb-like’ zwitterionic polymer surfactants have excellent surface activity and good foam stability, especially for the products with a degree of substitution of 20%; their surface tension can be as low as 27.1 mN/m, and the foam stability can be improved by 59.32%.

It is challenging to investigate fast supramolecular processes due to the lack of appropriate characterization methods with high structural resolution. In thisstudy, microfluidic nuclear magnetic resonance (μFNMR) spectroscopy was employed to monitor the kinetics of threading and dethreading of a pseudo[6]rotaxane system. By employing high time resolution μF-NMR, 1H and two-dimensional (2D) rotating frame nuclear Overhauser effect spectroscopy (ROESY) NMR spectra were recorded at any timepoint within 1.5 s after the onset of the process. This technique enabled the successful identification of kinetic intermediates and rate-determining steps,usually impossible to determine by other spectroscopic techniques. Thus, our study demonstrates the capability of μF-NMR in investigating the mechanismof complex supramolecular systems.

A broadband wide-angle scanning array antenna with suppressed mutual coupling for 5G Sub-6G mobile communication applications is presented in this letter. To reduce mutual coupling, the metal columns are used in the dipole array antenna. The metal columns are positioned below the edge of the dipole, leading to the improved the impedance matching characteristics and a wider scanning angle. A 18 prototype of the suggested design has been manufactured and tested to ensure its usefulness. The overall dimension is 2.3300.2800.240 (0 is the free space wavelength at 2.5 GHz). The measured and simulated results are quite consistent. The main lobe achieves a scanning range of 60 at 2.5-4.5 GHz (57.1%, active VSWR

The full utilization of adsorption sites is crucial for adsorption technology. Metal-organic frameworks (MOFs), which are hot spot materials in environmental remediation, are not satisfied in many cases for their high specific surface area and relatively low adsorption capacity. In this work, a series of zirconium-iron bimetallic MOFs (ZrxFe(1-x)-MOF-808) was prepared. The optimal material (Zr0.8Fe0.2-MOF-808) possesses a superb adsorption capacity of 524 and 310 mg g–1 for antimonate and antimonite, respectively. The carboxyl and hydroxyl groups were identified as the main adsorption sites by FTIR and XPS. The role of Fe in the adsorption process of Zr0.8Fe0.2-MOF-808 were further explored by DFT simulations, four binding manners were discovered and consistent with the adsorption capacity data. Subsequently, the application potential tests proved that the Zr0.8Fe0.2-MOF-808 shows good anti-interference ability, wide pH adaptability, and recyclability. Overall, this high-performance bimetallic MOF has been analyzed from the macrocosm to microcosmic, which provides a certain support for the development of MOFs modification.

Carbon fiber reinforced plastic (CFRP) composites exhibit great potential in connecting with metallic materials to fabricate desired structures with superior properties. Since composite/metal structures are expected to experience corrosion and impact loading during their long-term service, this paper comprehensively studied the effects of high speed loading and cyclic salt spray-dry-wet exposure on dynamic responses of hybrid bonded-riveted CFRP/Al joints. Experimental results indicated that the joint load-carrying capability was relatively higher with increased loading speed. The peak load, fail displacement and energy absorption of joints were sensitive to salt spray exposure and progressively declined with higher aging time. A high speed camera was implemented to record the whole failure process of hybrid joints under dynamic loading for further progressive failure analyses. The representative specimens were selected to comparatively investigate their failure characteristics and found that the failure process of samples under high speed loading (5–10 m/s) was considerably different with respect to aging time and loading speed.

Chatter as a common and thorny problem occurs easily during robotic milling process, leading to the instability, severe tool wear and poor surface finish. In this work, an acoustic emission technique was employed to analyze a chatter phenomenon using root mean square (RMS) value and fast Fourier transform method during high-speed robotic milling of aluminum alloys (with cutting speed up to 678 m/min). A stability lobe diagram was proposed to predict the occurrence of chatter with various spindle speeds, which was considered as the most effective tool for chatter analysis. The underline mechanism and theoretical analysis were also presented to provide physical understanding of chatter stability. The cutting force model and robot structure model were firstly established to study chatter mechanism. The stability of a robotic milling system was then analyzed using a zero-order approximation method. Results showed that fast Fourier transform and the time-domain root mean square (RMS) value of acoustic emission signals could be effectively used for detection and verification of chatter in the robotic milling process. The stable cutting zone in the stability lobe diagram was in agreement with experimental results, which can help for the selection of reasonable cutting parameters to avoid chatter and improve efficiency during the high-speed robotic milling process.

Constructing a heterojunction photocatalyst is a significant method to enhance photocatalytic activity because it can promote the separation of photogenerated carriers. Herein, amorphous/crystalline contact Bi2S3/Bi4O7 heterostructure was successfully synthesized by in-situ sulfidation of Bi4O7. The amorphous Bi2S3 is diffused on the surface of Bi4O7 rod, enhancing the visible light response and improving the transport of photogenerated carriers. Various characterizations confirm that the rapid separation of photogenerated carriers leads to increased photocatalytic performance. The optimized Bi2S3/Bi4O7 heterostructure photocatalyst (BiS-0.15) exhibits the highest Cr(VI) reduction (0.01350 min−1) and RhB oxidation (0.08011 min−1) activity, which is much higher than that of pure Bi4O7 and Bi2S3/Bi4O7 mixture under visible light irradiation. This work provides new insights into the construction of efficient novel photocatalysts.

Abrasive waterjet machining was an effective method for cutting CFRP materials in various industries, while machining defects are inevitably observed especially for thick CFRP laminates due to the inherent characteristics of waterjet. In this work, a full factorial experimental array was employed totally involving 18 trials when using abrasive waterjet to cut CFRP laminate up to 10.0 mm thick. The influence of process parameters including hydraulic pressure, traverse speed, and stand-off distance on jet energy was deeply analyzed and the power-to-speed ratio (Ė/u) parameter was obtained, which was combined with the physical energy model of abrasive waterjet based on the energy method. The influence of process parameters on kerf characteristics/surface integrity and the mechanism of defects were further analyzed. Various surface defects along thickness direction were observed and corresponding mechanisms were investigated. Results showed that higher hydraulic pressure, lower traverse speed, and stand-off distance within in the selected range were preferred to obtain better surface quality. From the perspective of power-to-speed ratio (Ė/u), the surface roughness decreased rapidly up to ~ 68% with Ė/u increased from 20,000 to 40,000 J/m. When it exceeded 40,000 J/m, the downward trend gradually reduced and even became stable in the case of high stand-off distance. The level of kerf width generally increased with the increase of Ė/u irrespective of stand-off distance.

To promote the development of supercapacitors and their applications in modern electronics, it is crucial to explore novel supercapacitor electrode materials. As a representative member of the rising 2D MXenes, Ti3C2Tx MXene has shown tremendous potential for supercapacitor electrodes owing to its unique physicochemical properties. Here, the most recent advances in Ti3C2Tx-based supercapacitor electrodes are comprehensively reviewed, with an emphasis on the vital role that Ti3C2Tx MXene plays in the remarkable electrochemical performance and related mechanisms. The fabrication methods, electrode structures, working mechanisms, electrochemical performance and related influencing factors, mechanical properties and applications, as well as the associated advantages/disadvantages of Ti3C2Tx-based supercapacitor electrodes are thoroughly and exhaustively summarized and discussed. Based on the recent progress, the existing challenges along with the corresponding possible solutions, and the future prospects of Ti3C2Tx-based materials for supercapacitors are also outlined and discussed.

The use of abrasive waterjet to cut CFRP laminates has been proved to be feasible with several advantages compared with traditional machining methods, while relatively poor surface quality and kerf taper impede its application in automotive industry. In this work, the influence of various process parameters including hydraulic pressure, cutting speed and stand-off distance on surface integrity and kerf characteristics was comprehensively studied. A statistical model was further developed using response surface method involving 17 trials. Statistical analysis found that higher level of cutting speed led to the decrease of kerf width and the increase of surface roughness. Based on optimizing the expected function of responses, the minimum taper error of 0.058 mm and superior surface roughness (Ra) of 3.58 μm were obtained. Furthermore, hybrid machining strategy integrating AWJ and CNC milling processes was proposed to cut CFRP laminate in order to obtain both high efficiency and superior surface quality. The depth of cut for post-milling process was set down to 0.1 mm. It was found that kerf taper was completely removed with relatively flat surface, and surface roughness (Ra ~ 1.20 μm) was reduced by up to 5.61 μm with an overall decrease of about 80%.

Using silk fibroin as the base material, the drug-loaded microspheres are prepared by an emulsification method. In order to determine the drug-loading and drug-release performance parameters of the microspheres, the central composite design method is used to design and investigate the effects of the parameters of the microsphere preparation process, such as the oil-water ratio, stirring temperature, and stirring rate, on the microsphere particle size, drug-loading rate, and drug release rate. The "overall desirability" is taken as a comprehensive evaluation index, and the response surface method (RSM) and genetic algorithm-backpropagation (GA-BP) neural network GA-BP model are used to predict and evaluate the parameters of the drug-loaded microsphere preparation process. The root-mean-square error values obtained from the RSM and BP-GA model experiments are 0.000325 and 0.00022, respectively. The results show that the BP-GA model has better prediction accuracy and optimization ability than the RSM. The optimal microsphere preparation process conditions were determined to be as follows: a water-oil ratio of 10:1, at a temperature of 45°C with stirring at a speed of 400 rpm, the particle size of the microspheres is 1.392 μm, the drug-loading rate is 3.218%, and the drug release rate is 51.991%. The results of this study indicate that this approach is an effective method for the optimization of the parameters of the drug-loaded microsphere preparation process.

Semiconductor-based photoelectrocatalytic processes have attracted considerable research interest for solar energy collection and storage. Photoelectrocatalysis is a heterogeneous photocatalytic process in which a bias potential is applied to a photoelectrode, and thus the photoelectrocatalytic performance is closely related to the photoelectrode prepared by semiconductors. Among various semiconductors, metal-organic frameworks (MOFs) have attracted more and more attention because of their unique properties such as optical properties and adjustable structure. Herein, a comprehensive review on different MOFs (Ti-based, Zn-based, Co-based, Fe-based, Cu-based, and mixed metal-based MOFs) for heterogeneous photoelectrocatalysis is carried out and, in particular, the application of this technique for CO2 conversion and water splitting is discussed. In addition, the challenges and development prospects of MOFs in photoelectrocatalysis are also presented.

The compaction behavior of the 3D stitched fabric, which significantly affects the mechanical performance of the 3D stitched composites, has not been explored yet. Herein, the systematical compaction experiments were originally conducted to explore the influence of the stitching pattern and space on the compaction behavior of 3D stitched carbon fabric. The results reveal that the reduction of stitching space enhances the compression resistance, as the stitching thread restricts the yarn flattening and slippage. The diagonal stitched fabric presents the high compression resistance due to its relative uniformly distributed constraining forces acted on both warp and weft yarns. It is originally identified that the internal stress in the diagonal stitched fabric is more difficult to dissipate, since the stitching thread restricts the fibers movement. Besides, the diagonal stitched fabric with dense stitching space presents high permanent recovery ratio, suggesting that the near net shape perform can be more flexibly obtained.

The strain modulation on the magnetic and electronic transport properties of the ferromagnetic films is one of the hot topics due to the practical applications in flexible and wearable spintronic devices. However, the large strain-induced saturation magnetization and resistance change is not easy to achieve because most of the ferromagnetic films deposited on flexible substrates are polycrystalline or amorphous. Here, the flexible epitaxial γ'-Fe4N/mica films are fabricated by facing-target reactive sputtering. At a tensile strain with a radius of curvature (ROC) of 3 mm, the saturation magnetization (Ms) of the γ'-Fe4N/mica film is tailored significantly with a maximal variation of 210%. Meanwhile, the magnetic anisotropy was broadly tunable at different strains, where the out-of-plane Mr/Ms at a tensile strain of ROC = 2 mm is six times larger than that at the unbent state. Besides, the strain-tailored longitudinal resistance Rxx and anomalous Hall resistivity ρxy appear where the drop of Rxx (ρxy) reaches 5% (22%) at a tensile strain of ROC = 3 mm. The shift of the nitrogen position in the γ'-Fe4N unit cell at different bending strains plays a key role in the strain-tailored magnetic and electronic transport properties. The flexible epitaxial γ'-Fe4N films have the potential applications in magneto- and electromechanical wearable spintronic devices.

Adsorptive removal of phosphorus from wastewater is a good alternative to solve pollution problems, as well as provides the potential to recover phosphorus after the desorption process. The work he...

Defects exist ubiquitously in crystal materials, and usually exhibit a very different nature from the bulk matrix. Hence, their presence can have significant impacts on the properties of devices. Although it is well accepted that the properties of defects are determined by their unique atomic environments, the precise knowledge of such relationships is far from clear for most oxides because of the complexity of defects and difficulties in characterization. Here, we fabricate a 36.8° SrRuO3 grain boundary of which the transport measurements show a spin-valve magnetoresistance. We identify its atomic arrangement, including oxygen, using scanning transmission electron microscopy and spectroscopy. Based on the as-obtained atomic structure, the density functional theory calculations suggest that the spin-valve magnetoresistance occurs because of dramatically reduced magnetic moments at the boundary. The ability to manipulate magnetic properties at the nanometer scale via defect control allows new strategies to design magnetic/electronic devices with low-dimensional magnetic order., We manipulate the local magnetic properties of SrRuO3 at a grain boundary, providing new strategies to design atomic-sized magnetic/electronic devices with low-dimensional magnetic order via defect engineering.

In this work, the interlayer coupling dependent lithium intercalation induced phase transition in bilayer MoS2 (BL-MoS2) was investigated using an atomic-resolution annual dark-field scanning transmission electron microscope (ADF-STEM). It was revealed that the lithiation induced H → T' phase transition in BL-MoS2 strongly depended on the interlayer twist angle; i.e., the H → T' phase transition occurred in well-stacked H phase BL-MoS2 (with a twist angle of θt = 0°) but not for θt ≠ 0° BL-MoS2. The lithiated BL-MoS2 appeared in homophase stacking, either T'/T' or H/H (locally, no phase transformation) stacking, without any heterophase stacking such as H/T' or T'/H observed. This finding indicated the H → T' phase transition occurred via a domain-by-domain mode rather than layer-by-layer. Up to 15 types of stacking orders were experimentally identified locally in lithiated bilayer T'-MoS2, and the formation mechanism was attributed to the discrete interlayer translation with a unit step of (m/6a, n/6b) (m, n = 0, 1, 2, 3), where a and b were the primitive lattice vectors of T'-MoS2. Our experimental results were further corroborated by ab initio density functional theory (DFT) calculations, where the occurrence of different stacking orders can be quantitatively correlated with the variation of intercalated lithium contents into the BL-MoS2. The present study aids in the understanding of the phase transition mechanisms in atomically thin 2D transition metal dichalcogenides (TMDCs) and will also shed light on the precisely controlled phase engineering of 2D materials for memory applications.

Interlayer bonding quality is the key to the stability and durability of dam concrete. In this study, interlayer splitting tensile strength, relative permeability coefficient, and electric flux of dam concrete at different temperatures were tested. The relationships between equivalent age and strength coefficient, relative permeability coefficient ratio, and electric flux ratio were established. Meanwhile, a comprehensive early-warning and control system of dam interlayer bonding quality based on the above relationships was proposed. The results showed that the interlayer mechanical properties, impermeability, and anti-chloride ion permeability of dam concrete decreased with the increase of temperature. Moreover, the equivalent age was linearly correlated with strength coefficient, relative permeability coefficient ratio, and electric flux ratio of concrete. The correlation coefficients were 0.986, 0.973, and 0.924, respectively. In addition, the interlayer bonding quality of dam concrete can be effectively controlled by the early-warning system established according to the relationship between equivalent age and interlayer properties parameters.

Rotary Friction Welding (RFW) was conducted on SUS304 and A286 stainless steels in which, the joint forming stage was focused. Pipe structure specimens were welded firstly, from which the friction coefficient models were built as functions of friction linear speed, pressure and temperature. Based on the models, the friction heat distributions and temperature fields of rod structure specimens at different rotation speeds were characterized. Experiments of initiation and evolution of the corona-bond (i.e., plasticized metal) were carried out to verify the theoretical results. Welding time, as an application of the model, was analyzed with the corona-bond initiation and evolution. The results show that, friction coefficient models of SUS304 and A286 as functions of friction linear speed, pressure and temperature were constructed as f S U S 304 = 0.274 ∙ P - 0.936 ∙ T - 273 0.705 ∙ e x p ⁡ ( - 0.34 v ) and f A 286 = 0.15 ∙ P - 0.405 ∙ T - 273 0.475 ∙ e x p ⁡ ( - 0.705 v ) respectively. SUS304 concentrates the friction heat at the periphery where the corona-bond is consequently initiated, which varies little with rotation speed; whereas, A286 moves the concentration from the 0.60R to the center as the rotation speed increases, which implies the initiation location of the corona-bond that consequently shifts from 0.60R to axis zone. For rod structure specimens, the joint forming time determines the welding time of the joint welded at a preset burn-off. The joint forming time falls around 5 s for SUS304, which is roughly independent of rotation speed; Whereas, for A286, the joint forming time varies from 5 s to 20 s, which increases along with the rotation speed. Thus, both materials of RFW cover different welding time at a preset burn-off of 5 mm when the rotation speed changes from 500 rpm to 2000 rpm: SUS304 varies from 14 s to 18 s and A286 from 23 s to 35 s.

Hybrid bonded-riveted joint was designed for connecting CFRP and aluminum lightweight materials used for automotive structures. The mechanical performance of hybrid joints under a wide range of temperatures from -30 to 100 °C was extensively investigated. Differential scanning calorimetry (DSC) analysis was firstly applied to determine the glass transition temperature (Tg) of polyurethane adhesive and CFRP materials, as Tg value is very important for further understanding the effect of testing temperature on mechanical behavior of hybrid joints. Digital image correlation (DIC) technique was employed to analyze progressive failure process and full-field strain distribution of hybrid joints under tensile loading. Results showed that load-displacement curve profiles, crack propagation process, mechanical properties and failure mechanisms were highly related to the type of substrate material and testing temperature. Hybrid joint exhibited maximum strength degradation of 26% and 43% under -30 and 100 °C respectively compared to the performance recorded at room temperature, while it increased up to 8% at 60 °C. Failure mechanisms including cohesive failure, adhesive failure, bearing failure of CFRP together with shear fracture of rivet were observed for hybrid joints, and they are also highly related to substrate material and testing temperature.

Numerical simulation method was employed to reveal the mechanism of manufacturing a rotary friction welding joint, in which a two-dimensional finite element model was constructed based on a comprehensive friction coefficient model to simulate the thermo-mechanical coupling during rotary friction welding. Experiments were focused on rotary friction welding of SUS304 in diameter of φ25 mm at 900 rpm under 80 MPa, of which the joint were studied on evolutions of temperature field, stress fields (i.e., both stress-Z and effective stress) and tensile strength corresponding with the corona-bond evolution. Thereafter, the simulation focused on the effect of rotation speed that varied as 500–2500 rpm, in which the minimum welding time necessary to cover a welding cycle was issued. The finite element model was shown valid by the consistency of comparison between simulation and experiment. Transition temperature fields (in contours) were verified in good agreement with transition morphologies of the joints as experimentally characterized by the corona-bonds. The results show that, rotary friction welding process can be classified into two stages: the corona-bond evolution and the plastic flow. The former stage is characterized by the corona-bond that develops and fills out the interface, in which the temperature is kept raising and the stress field kept varying; whereas the latter stage is denoted by the extrusion of flash that keeps forming at constant temperature and stress fields (i.e., both stress-Z and effective stress). The tensile test reveals that the latter stage makes negligible contribution to the joint strength, which falls in the range as 660–688 MPa as the welding time is regulated from 1.8 to 15 s. Thus, time consumed on former stage was ascertained to be the minimum welding time, which ranges in 1.5–2.9 s for SUS304 in φ25 mm of diameter welded under 80 MPa at the rotation speed of 500–2500 rpm.

Fiber laser cutting is a promising alternative to the conventional methods in machining CFRP with high efficiency, while the influence of machined quality on strain distribution and mechanical behavior of CFRP laminates is yet not fully understand. The aim of this paper is to study the effect of laser cutting parameters on thermal defects and related mechanical performance. DIC technique was successfully employed to assess full-field strain distribution under tensile loading. The relationship between strain distribution and failure evolution/mode was also investigated. Results showed that various thermal defects including matrix recession, resin decomposition, fiber burrs and delamination were observed on entry and exit surfaces, while microcracks, cavities and striations were prevalent on machined surface. Tensile strength of CFRP laminate with open hole was highly related to applied laser processing parameters. DIC technique indicated that the crack propagation and failure mode were in good agreement with the high level of strains developed around the hole. Matrix-fiber interface cracking, fiber breakage and splitting were the main failure modes at test cessation.

Ferroelectric engineered pn doping in two-dimensional (2D) semiconductors hold essential promise in realizing customized functional devices in a reconfigurable manner. Here, we report the successful pn doping in molybdenum disulfide (MoS2) optoelectronic device by local patterned ferroelectric polarization, and its configuration into lateral diode and npn bipolar phototransistors for photodetection from such a versatile playground. The lateral pn diode formed in this way manifests efficient self-powered detection by separating ~12% photo-generated electrons and holes. When polarized as bipolar phototransistor, the device is customized with a gain ~1000 by its transistor action, reaching the responsivity ~12 A W−1 and detectivity over 1013 Jones while keeping a fast response speed within 20 μs. A promising pathway toward high performance optoelectronics is thus opened up based on local ferroelectric polarization coupled 2D semiconductors., Photodetectors based on two dimensional (2D) materials still suffer from low performance. Here, the authors tackle this issue by introducing a reconfigurable design enabled by locally tuning the doping of a 2D molybdenum disulfide film through the polarization of an underlying ferroelectric material.

Current reported works of preforming behaviors mainly focus on the fabrics without binder and under constant process parameters. By contrast, in this work, preforming experiments and analysis were systematically conducted for typical carbon fiber fabrics to explore the influences of binder contents and process parameters on the preforming behaviors. We clearly reveal that the binder content has remarkable influence on the preforming behaviors. Specifically, the increasing binder content will significantly enlarge the initial thickness and the compression distance and time. Besides, it is demonstrated that the relaxation ability is also enhanced with the adding binder. The binder can also lower the elastic recovery, and oppositely increase the viscoelastic recovery, leading remarkable increment of permanent deformation. It is found that the binder should not be unlimitedly added, since over adding binder can not pronouncedly enhance the relaxation rate, and the content of 4 wt % is a relative optimal value for preforming process. We further reveal that the compression thickness can be reduced by lowering the compression speed. This approach will oppositely raise the preforming time. Thus, the compression speed should be carefully selected with the comprehensive consideration of both desired volume fraction and efficient. For the carbon fiber fabrics both with and without binder, the recovery thickness increases with the increasing maximum pressure. Besides, as the holding time increases, the permanent recovery ratio is also remarkably raised. The results obtained here provide systematical process reference to the preforming process of the fabrics with binder.

Experimental data is presented in this paper relating to kerf characteristics and surface integrity when using abrasive waterjet slotting of Ti6Al4V/CFRP stacks with various processing conditions. The effect of typical parameters including traverse speed, hydraulic pressure, stand-off distance and stack configuration on machined quality was also studied. A full factorial experimental array was employed involving 16 trials. The statistical significance of individual processing parameter was determined using analysis of variance method. Results showed that lower level of traverse speed and higher hydraulic pressure were preferred to minimize taper angle. Negative taper angle was recorded on CFRP laminate when cutting stacks with Ti6Al4V/CFRP configuration. Typical kerf profile featured with X shape was generated when cutting stacks with Ti6Al4V/CFRP configuration, while it formed V shape when cutting CFRP/Ti6Al4V stack. Ti6Al4V/CFRP configuration was preferred during abrasive waterjet slotting in order to minimize barrel error variation (down to 1 μm) between CFRP and Ti6Al4V. Ridges, delamination, strip marks and craters were observed on most of the machined CFRP surfaces irrespective of cutting parameters, while abrasive ploughing and scratches were mainly found on the processed surfaces of titanium plate. CFRP/Ti6Al4V stack configuration was preferred to generate overall superior surface roughness during AWJ slotting CFRP-titanium multilayer stack.

Mechanical performance together with progressive failure process and failure modes of riveted, adhesively bonded and hybrid joints connecting CFRP and aluminum alloy with various overlap length were investigated. Experimental results showed that hybrid joints presented superior performance in terms of peak load and energy absorption, which increased by up to ~380%, 434% and ~19%, 56% respectively compared with solely riveted and bonded joints. Typical failure evolution photographs were taken with high speed camera for analyzing progressive failure process. Final failure modes of hybrid joints included rivet shear fracture, CFRP compressive deformation, adhesive failure, cohesive failure and light-fiber-tear failure.

Consider the severe thermal loads in thermal engineering applications of lightweight ZrO2 and ZrB2 corrugated sandwich structures, here, their heat transfer mechanism and characteristics are originally explored in this work. Finite element (FE) models for heat transfer of ZrO2 and ZrB2 sandwiches, sandwiches filled with insulation material and the corresponding bulk ceramics are respectively well established. The insulation efficiency, temperature gradient, thermal short effect and thermal-mechanical coupling effect are well calculated and analyzed. It is found that cavity radiation heat flux is increased with the height, leading to low insulation efficiency. The insulation material can block the cavity radiation, and hence can remarkably enhance the insulation efficiency and improve the temperature uniformity. Low temperature gradient is found in ZrO2 and ZrB2 sandwiches, while, remarkable temperature gradients are found in sandwiches filled with insulation material. With the increasing height, the insulation effect is improved, while the mechanical properties are weakened, suggesting pronounced thermal-mechanical coupling effect between loading bearing capacity and insulation effect. The heat transfer mechanism and characteristic revealed here provide the thermal basis for engineering applications of the ZrO2 and ZrB2 cellular sandwiches.

Current studies on crystallization kinetics for glass fiber-reinforced poly(ether ether ketone) mainly focused on short glass fiber-reinforced composites and their isothermal crystallization. It is worth noting that continuous glass fiber-reinforced poly(ether ether ketone) composite (CGF/PEEK) possesses relatively higher mechanical performance than short fiber-reinforced PEEK under high temperature. Here, for the first time, we investigate the non-isothermal crystallization kinetics and melting behavior of CGF/PEEK by differential scanning calorimetry at four different cooling rates. By evaluating the crystallite size of CGF/PEEK using X-ray diffraction, it is found that with the decreasing cooling rate, the crystallite size distribution evolves more uniform, and the size of crystallites enlarges. Besides, by systematical analysis, we find the modified Avrami equation can well describe crystallization behavior of the CGF/PEEK. The higher Avrami value of CGF/PEEK than pure PEEK indicates that CGF could introduce a more complex geometry effect on the crystallization. The addition of CGF greatly reduces the absolute value of crystallization activation energy of PEEK, suggesting that CGF can reduce the nucleation energy barrier. The obtained results illustrate that CGF can accelerate the nucleation rate due to heterogeneous nucleation while reduce the growth rate due to retarded polymer chain mobility. And the cooling conditions can influence crystal growth and morphology.

Current integrated thermal protection systems (ITPS) are generally devised with single layer metal sandwich panel and uniform insulation material, inevitably leading to limited thermal insulation effect and high risk of buckling failure. By contrast, here, ITPS, which incorporates graded insulation materials and multilayer ceramic matrix composite cellular sandwich panels, is devised to raise both thermal insulation effect and buckling strength. The effective thermal and mechanical properties are theoretically established. Transient heat transfer characteristics are numerically calculated. The results reveal that ITPS with specific graded insulation materials can present lower temperature and better temperature distribution uniformity than those of ITPS filled with uniform insulation material, demonstrating that graded insulation layers can firmly enhance the insulation effect. Besides, the insulation effect of ITPS, in which the densities and thermal conductivities of graded layers are taken arranged from low to high, is much better than those of ITPS which have opposite sequence. Moreover, the buckling strength is demonstrated to be significantly improved through the approach of integrating multilayer sandwich panels. The thermal short effect can be also suppressed, since it is demonstrated that the multilayer sandwich panels in the ITPS can reduce the temperature on bottom facesheet and raise the temperature distribution uniformity.

The preforming process of fiber fabrics in liquid composite molding presents remarkable viscoelastic behaviors, and gives significant effect on the overall mechanical properties of composite components. Thus, here, a unified viscoelastic model to predict the compression and relaxation viscoelastic behaviors in preforming process for the carbon fiber fabrics with binder is originally proposed. The physical meaning of each model parameter is rationally defined. Experiments for typical carbon fiber fabrics are conducted to validate the proposed model. The theoretical curves match well with the experimental measurements, and the correlation factors for different contents of binder are larger than 0.9, demonstrating the proposed model can well capture the stress evolution. Besides, we clearly reveal that in compression, the elastic stress is the main stress, and the viscoelastic stress is very small. Elastic modulus increases non-linearly and rapidly with the loading time. As the content of the binder increases, the elastic modulus gradually decreases due to the binder layer. For the relaxation stage, the total stress relaxation ratio is enlarged, while the elastic stress relaxation ratio is reduced, indicating the addition of binder can significantly improve the relaxation ability of the fabrics. The relationship of delay time τ : τ 0 w t τ 4 w t τ 8 w t τ 12 w t is experimentally confirmed, and is consistent with the theoretical prediction, suggesting the increasing binder enlarges the relaxation time. The proposed theoretical model here provides an approach to understand the viscoelastic responses in preforming process.

Strain-induced surface structures are very common in natural systems and they are very useful for a wide range of applications. In this work, we report on the formation, evolution and transition of multiple surface patterns in zinc/polydimethylsiloxane systems with varied film thicknesses under cyclic uniaxial loading. It is found that the mechanical compression leads to buckling patterns while the mechanical tension induces channel cracks. The buckling patterns include two classes of distinct morphologies: homogeneous wrinkling and localized buckle-delamination, depending on the film thickness. The morphological characteristics and in situ evolutional behaviors of the wrinkling, buckle-delamination and cracking are described and discussed in detail. The phenomenon of wrinkle-to-delamination transition is analyzed by a two-dimensional phase diagram and is used to measure the interfacial adhesion strength between the film and substrate. The report in this work can promote better understanding of the phenomenon of wrinkle-to-delamination transition and the complex interactions between the multiple surface patterns under mechanical loading.

The interfacial transition point isolated by maximum entropy production principle (MEPP) was used to construct a two-dimensional (2D) finite element (FE) model of continuous-drive rotary friction welding (RFW) with GH4169 superalloy. The transition point from sliding friction to shear friction was calculated based on the equal entropy of these two kinds of heat liberation mechanisms at this point. The FE model was shown valid by the consistency of comparison between simulation and experiment. The simulation issued an interfacial distribution of non-uniform heat intensity that determined the corona bond, which corresponded to higher temperature zone over the transition temperature. The influences of linear speed and friction pressure on welding time were examined, which showed that a shorter welding time could be acquired when the linear speed was about 1.96 m/s and the friction pressure is larger.

Flexible temperature sensors can be attached to the surface of human skin or curved surfaces directly for continuous and stable data measurements, and have attracted extensive attention in myriad areas. Carbon nanomaterials possess great potential for temperature sensing, and flexible temperature sensors based on carbon nanomaterials have demonstrated unique advantages such as high sensitivity, fast response, good mechanical adaptability, low-cost fabrication processes, high cycling stability and reliability. In this review, the working mechanisms, device structures, material compositions, fabrication technologies, temperature sensing properties, the crucial roles of carbon nanomaterials, specific advantages and existing limitations of different types of flexible temperature sensors based on carbon nanomaterials are comprehensively elaborated and discussed. Based on recent advances, conclusions are made and challenges as well as future perspectives are systematically outlined and discussed.

In this paper, a novel three-dimensional (3-D) Frequency Selective Surface (FSS) which is independent of incident angle is proposed. By mapping circular aperture unit elements of two-dimensional (2-D) FSS to spheres, an innovative 3-D FSS which contains annular aperture unit elements is designed. Through controlling structure parameters, the resonant frequency shift characteristics of the proposed 3-D FSS under oblique incidence can exhibit opposite tendency, which provides a possible way to offset the resonant frequency shift of the dielectric slab caused by different incidence angles. The performance of the proposed 3-D FSS loaded with dielectric slab demonstrates excellent resonance stability over a large range of oblique incidence, and the resonance frequency remains constant for different incident angles, even valid up until 80 degree.

In this report, the morpho-structural peculiarities and the crystallization mechanisms in solution-processed, solvent vapor annealed (SVA) thin films of rubrene (5,6,11,12-tetraphenylnaphthacene) on different substrates were investigated. The high-quality rubrene crystal films with a triclinic crystal structure were successfully prepared on the FTO substrates (glass slide coated with fluorine-tin-oxide) modified by PLA (polylactic acid) for the first time. The area coverage of rubrene crystal and the sizes of rubrene dendritic crystals increased with increasing thickness of PLA film and concentration of rubrene solution. For rubrene molecules, FTO wafers with rough surface provided the possibility of heterogeneous nucleation. During the SVA process, there were two kinds of forces acting on the diffusion of rubrene molecules: one force was provided by the residual chloroform solvent, which was perpendicular to the substrate, and the other force was provided by gaseous dichloromethane, which was parallel to the substrate. The synergy of these two forces was proposed to explain the nucleation and the crystallization processes of rubrene films. The higher nucleus of PLA/rubrene dendrites and the layer-by-layer stacking of needle-shaped nanocrystalline PLA/rubrene were important for exploring their kinetic formation process.

High-power fiber laser has been proven to be feasible for cutting carbon fiber reinforced polymers with several advantages including noncontact force, high efficiency and flexibility, while the characteristics of thermal damage and heat conduction in materials are not yet fully understood. Continuous-wave fiber laser was applied in this work to cut 2.0-mm-thick carbon fiber reinforced polymer laminates with different layup configurations. The influence of processing parameters including laser power and cutting speed on thermal damage was investigated. The characteristics of various thermal defects on different positions of machined surface were analyzed using high-resolution SEM and mathematical models. Interestingly, swollen fibers were observed and they connected together to form irregular swollen masses. According to further analysis on the initial heat distribution, it showed that cutting speed was the main factor affecting heat accumulation. In addition, modified heat conduction model was developed to analyze heat transfer within unidirectional carbon fiber reinforced polymer laminates in comparison with experimental results, which can be applied to predict heat affect zone during high-power fiber laser cutting composite materials.

A dual-band frequency selective surface (FSS) with large band ratio (BR) value for 5G communication is proposed and analyzed in this paper. This design is based on Patch-Aperture-Patch (PAP) model, and to cover both low-frequency and high-frequency bands of 5G communication without grating lobes, proper miniaturized elements are employed. In addition, unlike the traditional PAP structure, the exterior patches of designed unit don’t share the same dimension with the purpose of increasing the BR value. Simulation results show that the proposed FSS structure can generate band-pass response at 5 and 27 GHz, which are exactly the operation bands of 5G communication. In the meanwhile, there is no transmission window observed between two pass-bands and the out-of-band suppression is below -10 dB. The designed FSS has the advantages of low insertion loss, large band ratio, excellent polarization and azimuth stability and high out-of-band suppression, making it suitable for multiband 5G communication in the future.

Scanning transmission electron microscopy (STEM) is a powerful imaging technique and has been widely used in current material science research. The attempts of applying STEM (annual dark field (ADF)-STEM or annular bright field (ABF)-STEM) into biological research have been going on for decades while applications have still been limited because of the existing bottlenecks in dose efficiency and non-linearity in contrast. Recently, integrated differential phase contrast (iDPC) STEM technique emerged and achieved a linear phase contrast imaging condition, while resolving signals of light elements next to heavy ones even at low electron dose. This enables successful investigation of beam sensitive materials. Here, we investigate iDPC-STEM advantages in biology, in particular, chemically fixed and resin embedded biological tissues. By comparing results to the conventional TEM, we have found that iDPC-STEM not only shows better contrast but also resolves more structural details at molecular level, including conditions of extremely low dose and minimal heavy-atom staining. We also compare iDPC-STEM with ABF-STEM and found that contrast of iDPC-STEM is even further improved, moderately in lower frequency domains while highly with preserving high frequency biological structural details. For thick sample sections, iDPC-STEM is particularly advantageous. It avoids contrast inversion canceling effects, and by adjusting the depth of focus, fully preserves the contrast of structural details along with the sample. In addition, using depth-sectioning, iDPC-STEM enables resolving in-depth structural variation. Our results suggest that iDPC-STEM have the place and advantages within the future biological research.

Due to the poor thermal conductivity of phase change material (PCM), the application of the ice-cool storage sphere system is hindered. In this paper, the solidification performance of heat transfer after adding copper foam to the ice-cool storage sphere system is numerically studied by Computational Fluid Dynamic (CFD). The enthalpy-porosity method is used to describe the PCM solidification. Local thermal equilibrium is numerically adopted for modeling the heat transfer between the PCM and the solid matrix in copper foam. The variations of temperature field, ice front evolutions, solidification fraction, total solidification time, and cold storage capacity are investigated with the consideration of natural convection. The influence of surface temperature is explored by Stefan (Ste) number. A new evaluation index is proposed that can evaluate the cold storage performance of the energy storage system in real-time. The results show the metal foam focuses on accelerating the upper heat transfer due to the influence of natural convection in the plain ice storage sphere. The total ice storage time can be reduced by at least 72.7% in copper foam ice storage sphere with the porosity of 0.97, at the cost of very little ice storage capacity reduction. A higher porosity of copper foam is recommended with a compromise on the total melting time. This paper provides a clear and comprehensive vision of the metal foam effects of different temperatures and porosity inside the ice-cool storage sphere systems.

The stitching pattern and space play important roles in the mechanical behaviour of stitched composites, while their effects on interlaminar shear behaviour and corresponding damage suppression mechanism have not been studied. Here, the short beam shear (SBS) test and X-ray computed tomography (XCT) were systematically performed to explore the influences of different stitching patterns and spaces on the interlaminar shear behaviour and damage suppression mechanism of stitched composites. The SBS test results reveal that a reduction in the stitching space improves the interlaminar shear performance. Especially, when the stitching patterns enable the stitch thread to bind the load-bearing yarns, the final SBS load is increased after reaching the elastic limit. Furthermore, the XCT results identify the suppression mechanism. That is, the enclosed loops formed by the stitch thread separate the fabrics into several cells. Damage propagation is interrupted within the cells in the cross-sections containing the stitch thread. Damage propagation is also suppressed in the cross-sections parallel or perpendicular to the stitch thread. Stitched composites exhibit a lower damage extension and damaged volume than unstitched composites. In particular, when the stitching pattern is perpendicular to the damage propagation direction, the damage extension is significantly reduced and depends on the stitching space. The results obtained in this study can contribute to the mechanical performance design of stitched composites in future engineering applications through purposeful modulation of the stitching pattern and space.

Additive manufacturing technology has been increasingly applied to fabricate continuous fiber reinforced thermoplastic composites for its potential in fabricating complex structures. Owing to the limited thermal and mechanical properties of the matrix, it is a critical trend to develop high-performance thermoplastics to widen engineering applications. This study aims to comprehensively investigate the properties of the prepared CCF/PEEK filaments together with their printed composites. The filaments were fabricated via a thermo-mechanical coupling process and were characterized by micromorphology observation, thermal and mechanical test. It was found that the impregnation behavior, thermal stability and mechanical performance of the filaments were improved with the increase of mold temperature and decrease of traction speed. The performance of printed specimens was evaluated by mechanical test and fracture analysis. It was concluded that the additive manufacturing process promoted the secondary impregnation behavior of the filaments. Higher nozzle temperature and bed temperature together with lower layer thickness and printing speed enhanced the tensile strength of printed specimens with maximum value reached 509.56 MPa. Besides, the analysis of failure mechanism indicated that filament fracture, horizontal cracks and filament pullout together with fiber breakage, fiber pullout, unimpregnated fibers and pores were the dominant failure modes for all printed specimens.

Experimental data is presented relating to hole quality and feasibility studies when using continuous wave (CW) fiber laser to cut CFRP laminates (6.0 mm diameter hole) with single- and multi-pass strategy. The effect of typical processing parameters including laser power and cutting speed on thermal defect was also investigated. The statistical significance of individual cutting parameters was determined using main effects plot together with ANOVA analysis. Three methods were proposed to characterize HAZ based on the feature of thermal defect. According to statistical analysis, both cutting speed and laser power were significant with respect to HAZ (recorded at hole exit). The minimal value of HAZ was recorded with laser power of 650 W and cutting speed of 1100 mm/min. Energy per unit length (El) should be set above 40 J/mm to ensure cutting through CFRP laminates using fiber laser in high efficient machining process. Multi-pass strategy was investigated without setting pause/break time between each pass in order to increase cutting efficiency. Results showed limited improvement in terms of the level of HAZ even with cutting speed up to 10,000 mm/min, while machining time was significantly reduced to cut 6.0 mm diameter hole compared with single-pass strategy. For machining small holes with diameter down to 2.0 mm, high power fiber laser was not preferred due to severe thermal defect observed at hole entry and exit.

Polylactide-b-fullerene-b-poly(3-hexylthiophene) (PLA-b-C60-b-P3HT) triblock copolymer via a combination of 1,3-dipolar cycloaddition reaction and controlled ring-opening polymerization technique was successfully synthesized. The structure, morphology and crystallinity of PLA-b-C60-b-P3HT copolymer were characterized by 1H NMR, GPC, DSC, TGA, XRD, UV–vis, PL and AFM measurements. Nanoporous C60/P3HT films were easily prepared from PLA-b-C60-b-P3HT triblock copolymer by casting the copolymer followed by thermal annealing and chemical etching of the PLA chains. Fullerene molecules could self-assembly between P3HT and PLA to form a continuous film. An ordered nanoporous C60/P3HT film was formed in AFM by chemically etching the PLA microphase with NaOH solution. Photoluminescence analysis showed that the photoinduced electron transfer of the ordered nanoporous C60/P3HT film was significantly improved compared to the physically blending sample due to the increased interface between the P3HT and the C60.