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The introduction of metasurfaces has renewed Snell's law, and the metasurfaces can manipulate sound waves flexibly. In this paper, a coding metasurface with a simple and adjustable coding unit for sound wave transmission is proposed. By changing the orientation of a movable part in a fixed structure, conversion is achieved between two types of units with a phase difference of 180° and high transmittance (>75%). By combining the two types of units, the phases of sound waves can be regulated dynamically. Structural simulations are performed using finite-element software, and the beam splitting of the transmitted sound wave is verified by theoretical analysis and experiments under plane wave incidence in the frequency range of 4.7–5.7 kHz. In addition, the two types of units are used to design a coding Fresnel lens, and its simulated focusing performance is verified by experiments at 4.7–5.7 kHz. [ABSTRACT FROM AUTHOR]

Micro-scaled progressive sheet metal forming is a promising process for producing bulk microparts, given its advantages of high efficiency and low cost. To enhance forming quality and efficiency, it is important to have an in-depth understanding of the forming mechanism and model the forming process and fracture behavior accurately. However, the prediction of fracture formation in sheet materials at the micro-scale has not yet been well explored, and thus current knowledge is not sufficient to support the continued development and application of microforming technology. This study investigated progressive sheet forming of magnesium-lithium alloy sheets of different grain sizes to produce bulk microparts directly from sheet metal via shearing, extruding, piercing, and blanking. Using the Gurson–Tvergaard–Needleman (GTN) damage model, the effects of the size factor on the formation and evolution of voids were considered, and the shear-modified GTN model was established by combining Thomason's and Lemaitre's damage mechanics models. The modified model could predict not only the ductile fracture behavior dominated by tension under high-stress triaxiality at the micro-scale, but also the damage behavior controlled by shear deformation under low-stress triaxiality. The progressive forming process was simulated using the modified model, which was verified by experimentation and simulation. Comparisons of the experiments and simulations revealed the size effects on the forming defects and fracture behaviors of microparts during progressive sheet forming. The results show that the stress during deformation is mainly concentrated at the edge of microparts, and irregular geometric defects including burr, rollover, incline, and bulge become deteriorated with the increase of the initial grain size. This study enhances the understanding and prediction of ductile fracture in the micro-scaled progressive forming of sheet metals. [ABSTRACT FROM AUTHOR]

Although researchers have extensively investigated the dynamic mechanical properties of metallic materials at the macro-scale in terms of deformation mechanisms, strain rate strengthening and fracture mechanisms, they have rarely investigated the dynamic mechanical properties affected by size effects at the micro-/meso-scales. In this study, experiments on quasi-static compression and the split-Hopkinson pressure bar (SHPB) were conducted using oxygen-free high-conductivity (OFHC) copper with different geometrical and grain sizes to explore the size effects on various dynamic mechanical properties at the micro-/meso-scales. The experimental results showed that the quasi-static and dynamic mechanical properties of OFHC copper are affected by size effects at the micro-/meso-scales. In particular, OFHC copper was found to exhibit strain rate strengthening effects at the micro-/meso-scales, and the presence of micro-cracks was observed in the SHPB experimental specimens. In this study, after proposing a modified Johnson-Cook (J-C) constitutive model based on the surface layer model, we analysed the average relative error of the modified model and the original constitutive model. The influence of the size effect on the mechanical properties of materials is taken into account in the new modified constitutive model. The results of relative error analysis showed that the average relative errors for the original J-C model ranged from 3.2% to 18%, while the modified J-C model's results ranged from 2.2% to 11%. The accuracy of the modified model is greatly improved. Following finite element analysis based on the modified J-C model and the original model, the results showed that the modified J-C model agreed well with the experimental results. [ABSTRACT FROM AUTHOR]

• An ultrasonic imaging framework for NDE of parts with vertical surfaces is proposed. • Surface reconstruction of parts is derived from point cloud through photos. • By using surface reconstruction as background, ERTM aims at detecting internal flaws. • It succeeds in experiments where multiple flaws lie in parts with vertical surfaces. This work presents a new ultrasonic imaging framework for non-destructive evaluation of components with vertical or steeply dipping surfaces and demonstrates its ability of accurately characterizing multiple defects hidden in the interior of the component based on a limited coverage of ultrasonic linear phased array. Central to the framework is a point cloud-based elastic reverse time migration (PC-based ERTM) method. First, a surface reconstruction is derived from the point cloud provided through photos of an object from multiple views by bundle adjustment. Second, by taking the surface reconstruction as a geometric background estimate for elastic reverse time migration, the algorithm considers information of multiple scattering and mode conversions as well as multiple wave reflections from the component's bottom and aims at detecting internal defects. The effectiveness and accuracy of the PC-based ERTM approach is examined by experiments with multiple defects in extruded aluminum specimens with vertical surfaces. Experimental results show that notches and side-drilled holes in components can be reconstructed accurately. [ABSTRACT FROM AUTHOR]

Highlights Nowadays, it is still a huge challenge to predict the interlaminar shear strength (ILSS) of three‐phase carbon fiber reinforced polymer (CFRP). Herein, the three‐phase micromechanical model is innovatively constructed to predict the ILSS of CFRP, and the conception of new matrix is proposed by establishing a connection between the third phase and the matrix, which effectively solves the problem of uneven distribution of the third phase. To verify the accuracy of the micromechanical model, the Ti3C2Tx MXene/CFf/epoxy composites were fabricated by the co‐blending, layer‐by‐layer assembly and hot‐pressing technology, and the finite element simulation analysis was also performed based on the micromechanical model. The results show that the micromechanical model possesses high accuracy. Specifically, the experimental value of ILSS of the composite with 1 wt% Ti3C2Tx MXene content is 52.12 MPa, and the errors of simulation value (56.64 MPa) and theoretical prediction value (58.69 MPa) are 8.67% and 12.61% MPa, respectively. Besides, the detailed fracture mechanism of the composite is presented based on the fracture morphology and simulation results. It is believed that this work will provide more possibilities for the prediction of the interlaminar shear performance of three‐phase composites. A novel micromechanical model is used to predict the ILSS of three‐phase composite. The accuracy of the micromechanical model is verified by simulation and experiment. The main failure form of the Ti3C2Tx MXene/CFf/epoxy composite is matrix broken. The micromechanical model of the three‐phase composites has high accuracy. [ABSTRACT FROM AUTHOR]

Micro-forming is one of the major micro-manufacturing methods with promising application potentials, in which the damage response and fracture behavior need to be insightfully addressed. Among all the damage criteria to predict fracture, GTN model is a widely-used one and able to predict void-dominated fracture in micro-scale deformation. However, it is not very applicable under low stress triaxiality and shear-dominated condition. An in-depth understanding of shear damage and its potential size effect are crucial to explore the micro-scaled damage and fracture mechanisms. This research characterizes the size effect on flow stress via employing a combined constitutive model, and an approach for applying a phenomenological shear damage evolution law to the GTN-Thomason model via considering the size effect is developed. The prediction of micro-scaled fracture in a wide stress triaxiality range is thus enabled. Through simulation and experiment, the proposed model is validated and verified. In addition, stress state parameters including stress triaxiality, Lode parameter, and weight function, are also discussed, and the two damage parameters are analyzed quantificationally to reveal different fracture mechanisms occurring in different stress states and grain sizes. The research thus facilitates the physical insight and in-depth understanding of the size effect on damage evolution and fracture formation in micro-scaled plastic deformation of materials. Unlabelled Image • A new micro-scaled model is proposed for fracture under low stress triaxiality. • Shear damage and its size effect is considered in a phenomenological way. • Void and shear damage can be quantified by two independent parameters. • With the increase of grain size, fracture becomes more shear-dominated. [ABSTRACT FROM AUTHOR]

The development of flexible electronics has placed higher demands on electromagnetic interference (EMI) shielding materials, especially in terms of mechanical properties. Herein, a novel composite with excellent mechanical and EMI shielding properties was developed. The electrohydrodynamic atomization deposition approach was used to deposit Ti 3 C 2 T x MXene and graphene oxide (GO) nanosheets on carbon fiber fabric (CFf) surface, then they were assembled layer by layer with thermoplastic polyurethane (TPU) and thermoformed at high temperature to obtain MG/f-CFf/TPU composite. When the MXene/GO content increases, the mechanical performance of the composite is improved, mainly owing to the formation of chemical bonds and the presence of mechanical interlocking and van der Waals forces. Specifically, the tensile strength and interlaminar shear strength of the composite reach 140.98 MPa and 54.67 MPa, increasing by 72.45 % and 52.92 %, respectively. Benefitting from the unique lamellar structure, the maximum EMI-SE of MG/f-CFf/TPU composite is 38.29 dB. Besides, the MG/f-CFf/TPU composite also displays outstanding EMI-SE stability after 3000 times folding cycles. The flexible MG/f-CFf/TPU composite may provide more guidelines for the design of next-generation flexible EMI shielding materials. [Display omitted] • The mechanical and EMI shielding properties are improved by adding MXene/GO hybrids. • The tensile strength and ILSS of the composite are 140.98 MPa and 54.67 MPa, respectively. • The composite shows a superior EMI shielding effectiveness of 38.29 dB. • The composite displays outstanding flexibility and EMI-SE stability. [ABSTRACT FROM AUTHOR]

Laser shock clinching is a novel joining method derived from laser shock forming in which the metal foil is plastically deformed under the pulsed laser induced shock wave, and then two or more metal foils can be joined together based on plastic deformation. However, the present researches are less concerned with the mechanical joining behavior of metal foils during incremental impacts of multiple laser pulses. In the present study, the mechanical joining behavior of pure copper foil and pre-pierced stainless steel sheet in laser shock clinching was investigated. A finite element model was established to analyze the material flowing and clinching behavior of metal foils under multiple laser pulses. Based on the validated model, the deformation stages, thickness change, and shock wave propagation features were studied. The temperature rise during clinching was assessed considering both the compression by shock wave and plastic deformation at high strain rates. It is revealed that the laser shock clinching process can be divided into three deformation stages, that is, free bulging forming, radial expansion, and formation of interlock. Both experimental and numerical results prove that the formation of clinched joints relies on the plastic deformation of the joining partner I. The thinnest region of the joint locates at the material of the joining partner I in contact with the upper corner of the joining partner II. In addition, there is no obvious influence of temperature increase on the mechanical properties of joining partners. Moreover, the shock wave propagation characteristics along axial direction and the influence of laser power density on interlock value and thickness distribution were also discussed. [ABSTRACT FROM AUTHOR]

Electromagnetic shielding materials play a significant role in solving the increasing environmental problem of electromagnetic pollutions. The commonly used metal‐based electromagnetic materials suffer from high density, poor corrosion resistance, and high processing cost. Polymer composites exhibit unique combined properties of lightweight, good shock absorption, and corrosion resistance. In this study, a novel high angle sensitive composite is fabricated by combining carbon fiber (CF) fabric with thermoplastic polyurethane elastomer (TPU). The effect of stacking angle of CF fabric on EMI shielding performance of composite is studied. When the stacking angle of CF fabric changed, the electromagnetic interference (EMI) shielding effectiveness (SE) of CF fabric/TPU composite can reach a maximum of 73 dB, and the tensile strength can reach 168 MPa. In addition, the composite has anisotropic conductivity, which is conductive along the plane direction and nonconductive along the thickness direction. Moreover, the CF fabric/TPU composite manifests exceptional EMI‐SE/density/thickness value of 383 dB cm2 g−1, which is higher than most of current EMI shielding composites reported in literature. In summary, CF fabric/TPU composite is an excellent EMI shielding material that is lightweight, highly flexible, and mechanically robust, which can be applied to the field of aerospace and some intelligent electronic devices. [ABSTRACT FROM AUTHOR]

Nowadays, it is quite difficult to develop a facile, efficient, and easy large-scale production method to obtain the composite that can maintain a balance of Electromagnetic interference (EMI) shielding properties and mechanical properties. Herein, this work adopted the technology of electrohydrodynamic atomization deposition (EHDAD), layer-by-layer (LbL) assembly and heat-pressing to prepare carbon fiber fabric/graphene oxide/Fe 3 O 4 /epoxy (CFf/GO/Fe 3 O 4 /epoxy) composite. The research results show that the CFf/GO/Fe 3 O 4 /epoxy composite can maintain a good balance between mechanical and EMI performance. More specifically, the tensile strength of CFf/GO/Fe 3 O 4 /epoxy-4 composite can reach 565.1 MPa, which is higher than that of other composites reported previously. This can be attributed to the synergistic effect of covalent bonds and van der Waals forces improved the mechanical properties of the composite. Benefitting from the unique multi-layer structure and the synergistic effect of nanoparticles, the EMI shielding performance of CFf/GO/Fe 3 O 4 /epoxy composite can reach a maximum of 32.9 dB. The improvement of the EMI properties of composite was mainly attributed to the dielectric loss and magnetic loss. Surprisingly, the composite has excellent mechanical stability and EMI shielding stability even after long periods of storage. It is believed that this work opens up more possibilities to provide EMI shielding materials with outstanding mechanical properties. [Display omitted] • The facile, efficient and easy large-scale production method was adopted to fabricate carbon fiber fabric/graphene oxide/Fe 3 O 4 /epoxy composites. • The EMI shielding effectiveness of the multilayer-structured composite can achieve 32.9 dB, which can meet commercial applications. • The mechanical property of the composite was improved to 565.1 MPa owing to the synergistic effect of covalent bond and van der Waals force. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors have been extensively explored for their widespread applications in wearable electronic devices such as medical diagnosis and motion monitoring. In this paper, a facile method is adopted to prepare the ordered hierarchical structure array and then it is applied to improve the performance of capacitive flexible pressure sensors. The results indicate that the pressure sensor based on hierarchical structure array is with high sensitivity (0.382 kPa‐1), fast response and recovery time (26 and 25 ms), and its minimum detection pressure can reach 4 Pa. Besides, the sensor based on hierarchical structure array has also been successfully applied to the dynamic pulse monitoring of the neck, limb movement monitoring, and pressure monitoring in water cup grasping process, which shows high stability and reliability, demonstrating its broad application prospects. This research could provide useful guidance for the preparation and applications of high‐performance flexible pressure sensors. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cells have been used worldwide due to their high energy density and zero emissions. The metallic bipolar plate is the crucial component and has a significant effect on a cell's efficiency. However, the springback behavior of the metallic bipolar plate will greatly influence its forming accuracy in the micro-scale sheet metal forming process. Therefore, accurate calculation of the springback angle of the micro-scale metallic bipolar plate is urgent but difficult given the state of existing elastoplastic theory. In this paper, a constitutive model that simultaneously considers grain size effect and strain gradient is proposed to analyze micro-scale bending behavior and calculate springback angles. The specialized micro-scale four-point bending tool was designed to better calculate the springback angle and simplify the calculation step. A pure micro-bending experiment on a 316LN stainless steel sheet with a thickness of 0.1 mm was conducted to verify the constitutive model's accuracy. [ABSTRACT FROM AUTHOR]

The inhomogeneous tempered sorbite/bainite (TS/B) with various morphologies and orientations play a significant role in deformation coordination and damage evolution. In this paper, the influence of distinct morphologies and orientations of the mixed-grain structure with TS/B on the deformation heterogeneity were extensively investigated by in-situ tensile testing. Furthermore, a multi-scale model of dislocation density-based crystal plasticity (CP) coupled with the phase field method (PFM) was developed to illustrate the damage nucleation and its evolution via the representative volume element (RVE) modelling. The results shows that mixed-grain structure with TS/B exhibits non-homogeneous deformation during the tensile process, and the coarse grains bear the main plastic deformation, resulting in cross-slip traces and the wrinkling phenomenon at the grain boundary and the interior of coarse grains. Furthermore, the activation of slip systems was determined through slip trace analysis, and the slip transfer behavior between adjacent microstructure was analyzed. According to the critical resolved shear stress (CRSS), the {123}<111> slip system was determined to be the most activated slip system during the in-situ deformation. Hard-orientated lath-shaped B (M1) is more prone to accumulate low angle grain boundaries (LAGBs) than hard-orientated TS (M2) and soft-orientated granular B (M3), resulting in higher orientation rotation degree and geometrically necessary dislocations (GNDs) density of M1 than M2 and M3. The M1 exhibits the nucleation of damage during the initial deformation stage. In addition, compared with the M2 and M3, the Schmid factor (SF) of M1 dominates the transformation from hard orientation to soft orientation and the higher value of damage factor (φ) of M1 results in the more activated slip systems and local damage at high strain levels. This study provides new insights into elucidate the effects of TS/B morphologies and orientations on deformation heterogeneity and damage evolution in large-scale forged spindles for offshore wind power. • A new multi-scale model to describe the deformation heterogeneity and damage was established. • Hard-orientated lath-shaped bainite was prone to induce non-uniform deformation and a pronounced work hardening effect. • The damage heterogeneity can be attributed to the hard-oriented lath-shaped bainite. • To eliminate hard-orientated bainite and obtain uniform TS is beneficial to improve deformation uniformity and avoid local damage. [ABSTRACT FROM AUTHOR]

• The mechanical performance is improved by the introduction of MXene nanosheets. • The ILSS of the composite containing 2 wt% MXene is improved by 55.58%. • The composite displays outstanding mechanical stability. • The failure modes are fiber debonding, matrix fracture, and fiber breakage. Currently, poor mechanical properties limit the application of composite, especially the interlaminar shear strength (ILSS). Herein, this work employed a simple atomization deposition and co-blending method to introduce reinforcing phase on the interface and in the matrix, and then the unique multilayer-structured composites were fabricated by the technology of layer-by-layer assembly and hot-pressing. Benefiting from the presence of mechanical interlocking, hydrogen bonding, and van der Waals forces, the MXene on the interface and inside the matrix can both improve the ILSS of the composite. Specifically, when 0.5 wt% MXene nanosheets are deposited on the interface, the ILSS of the composite is increased by 21.41 %, and when 2 wt% MXene nanosheets are further introduced into the epoxy, the ILSS of the composite is improved by 55.58 %, reaching 59.96 MPa. Moreover, the ILSS of the composites shows good mechanical stability even after 30 days of storage. Besides, the failure modes of the composite were investigated, mainly including fiber debonding, matrix fracture and fiber breakage. This work adopts a facile and effective approach to prepare composites with excellent shear performance, which can provide more possibilities for the development of composites with high mechanical properties. [ABSTRACT FROM AUTHOR]

The forming defects at elevated temperature caused by the microstructural evolution such as grain size, crystal orientations are the critical issue that induced deformation inhomogeneity and local damage which severely limits the application of Al-Zn-Mg alloys in thin-walled structure manufacturing. In this study, the hot deformation behavior and microstructural evolution were investigated via hot stretching tests, electron backscatter diffraction (EBSD) and the transmission electron microscopy (TEM) characterization. Then, an integrated multiscale constitutive model coupled dislocation density based crystal plasticity (CP) model and phase field method (PFM) was established through the reconstructed configuration of deformation gradient emphasized on a damaged part. The coupled CP-PFM model was numerically implemented into Düsseldorf Advanced Material Simulation Kit (DAMASK) software. Subsequently, a set of virtual polycrystalline RVE models assigned with different average grain sizes and two types of RVE models with realistic crystal orientations were constructed from EBSD data. The experimental and simulation results of the Al-Zn-Mg alloy under hot tensile loading showed that the grain size refinement leads to the increase of grain boundary density, which leads to the rapid increase of dislocation density, uniform damage distribution and better work hardening ability. In addition, the coordination of the activation of different slip systems between adjacent grains will lead to the uneven distribution of dislocation density and local damage. [Display omitted] • An integrated crystal plasticity and phase-field anisotropic damage model is newly established. • Fracture mechanisms are revealed by recrystallization induced grain refinement. • Grain size and orientations affects grain boundaries density, and further dominates deformation inhomogeneity. • The damage is more likely to occur between grains with smaller Schmid factor. [ABSTRACT FROM AUTHOR]

• MWCNTs deposition can give aramid fibers conductivity. • PDA makes MWCNT easier and more effective to deposit on the aramid fiber. • The addition of MWCNTs increases the average phase modulus of the composite. With wearable smart textiles playing an increasingly important role in people's life, aramid fiber (AF) stands out among high-performance materials due to its outstanding flexibility, high strength, and impact resistance. However, its excellent insulation makes it unable to sense and respond to external stimuli, which seems to be a call to multiwalled carbon nanotubes (MWCNTs) with high conductivity. In this paper, the effect of MWCNTs in enhancing the electrical properties and interfacial strength of aramid fiber reinforced polymer (AFRP) composites was researched. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) proved that the polydopamine (PDA) layer and MWCNTs were successfully grafted onto the surface of the AF. Scanning electron microscopy (SEM) showed that the distribution of MWCNTs on the fiber surface is quite uniform and dense. As a result, the adhesion of PDA is more conducive to the deposition of MWCNTs, compared with the pristine aramid fiber. The modified fiber AF-PDA-MWCNTs obtained a resistance on the order of 104 MΩ without reducing its mechanical properties (the tensile strength has obtained an increase of 10.59%). The composite material may also have good interface properties, with the interlaminar fracture toughness G I increased by 200.99%. After being endowed with electrical properties, aramid fibers have strong potential in wearable textiles due to their flexibility, high sensitivity to various deformations, and excellent safety protection performance. [ABSTRACT FROM AUTHOR]

Ultra-high performance flexible superhydrophobic surfaces have attracted great research interests, which are widely used in anti-fog, anti-icing, anti-fouling, self-cleaning, and other fields. However, ultra-high hydrophobic properties and complex manufacturing processes are still huge challenges to be solved. In this paper, a facile construction strategy of ultra-high performance flexible and controllable superhydrophobic films was proposed, combining the template transfer and electrospinning methods. The effects of electrospinning parameters on the microstructure and surface wettability were systematically studied, and the controllable preparation of films with different wettability was realized. Under the stable Cassie-Baxter state, the contact angle of prepared superhydrophobic films could reach 172° and the sliding angle could reach 3°. In addition, the stretchability, abrasion resistance, and chemical durability tests were also conducted in simulated harsh real-world environments. The results indicated that the films still exhibited superior performances. For the practical demonstration, the films are expected to be used as protective films for windshields, outdoor electronic screens, and solar cells due to the inherent optical properties and excellent fouling resistance performance. [Display omitted] [ABSTRACT FROM AUTHOR]

Non-destructive evaluation (NDE) techniques are widely used to detect and characterize different defects in engineering structures. However, the highly sensitive real-time quantitative imaging of irregularly shaped defects in large-area metallic structures remains challenging if conventional NDE approaches are used. In this paper, a speckle interferometer with unlimited minimal shearing amount – based on a simple imaging setup without the need to tilt any optical components – is explored for the application of detection and characterization of complex-shaped defects in metallic plates. This technology is able to directly yield strain measurements, allowing the defects to be detected by identifying induced strain concentrations under stress loading. Acoustic waves are used as stress loading for this imaging system with the advantage of a deeper penetration depth and a larger area of inspection as compared to conventional loading methods, e.g. thermal loading. The spatial carrier technique is introduced to quantitatively reconstruct the phase distribution, which contains information of the strain measurement from a single recording. To achieve the near real-time imaging of defects with relative insensitivity against noise, the image pairs are continuously recorded and correlated using the sequential subtraction method. The performance of the imaging system was tested with experimental data. The results demonstrate that the imaging system can generate high-quality images to provide good detection and characterization properties regarding irregularly shaped notches as well as accurate sizing of different notch dimensions. This work introduces a promising practical NDE tool for the near real-time, non-contacting and quantitative detection of subsurface defects with complex geometries in large-area metallic structures. • NDE application of SUCPSI is suitable for large area and near real-time inspection. • Acoustic wave excitation has the advantages of deep penetration depth, large area inspection and tunable driving frequency. • The sequential subtraction is first introduced to SUCPSI and appears better suited for on-line testing. [ABSTRACT FROM AUTHOR]

Silver (Ag) micro-nano structure array is widely adopted in surface-enhanced Raman scattering (SERS) substrate for biological detection applications. The high-precision and high-efficiency construction of an ordered Ag micro-nano structure array becomes a crucial problem to be solved. In this study, the roll-to-plate (R2P) process was adopted for high-resolution and high-throughput fabrication of an ordered micro-pyramid array on the silver sheet, which could have a larger surface area to adsorb more probe molecules and possess potential to further expand the arrangement of hotspots in SERS application. The effects of main process parameters were analyzed through both single-factor and Box–Behnken design (BBD) experiments, including roller gap, temperature and speed. Based on single-factor experiments, it was found that the effect of roller speed was relatively small while the roller gap and temperature could cause significant effects on forming results. According to BBD experiments, it was known that the roller gap was the most important process parameter. A better process window for R2P embossing of the micro-pyramid array could be obtained, that was the temperature between 85 °C and 100 °C, the speed between 200 and 300 r min−1, and the gap between 0.10 and 0.12 mm. This research could provide beneficial guidance for high-precision and high-efficiency fabrication of ordered micro-nano structure arrays. [ABSTRACT FROM AUTHOR]

This study investigates the off-epicentral measurement system and methodology of laser-ultrasonic shear waves in the ablative regime, subsequently focusing on its application to the elastic-moduli evaluation. The proposed scheme facilitates the measurement of the shear-wave velocity by using the crosscorrelation of successive shear-wave pulse echoes, ensuring high reliability and reproducibility of the calculation results. Since the geometric diffraction induced by the finite dimensions of laser-ultrasonic source and receiver can increase the measurement error, far-field diffraction correction for the off-epicenter detection has been derived theoretically. Results have shown that the far-field diffraction correction error is of the same order as random error mainly caused by the finite observation time, signal-to-noise ratio and frequency bandwidth, and therefore cannot be neglected. The feasibility of this approach is then demonstrated by inspecting annealed commercial purity titanium plates. Good agreement of experimentally measured and theoretical values of shear-wave velocity confirms the validity of the proposed approach. The ultrasonic measurement-determined shear modulus shows a maximum deviation of ＋3.6% from the standard value of an isotropic material. • Off-epicenter measure system and method of laser-ultrasonic shear waves are given. • Far-field diffraction corrections on phase velocity measured at off-epicenter are calculated. • Far-field diffraction correction is of the same order as the time and distance measure error. • Good agreement of NDE-determined and standard elastic moduli is obtained. [ABSTRACT FROM AUTHOR]

Eigenvalue topology optimization problem has been a hot topic in recent years for its wide applications in many engineering areas. In the previous studies, the applied materials are usually assumed as elastic, and the resulting structural eigenfrequencies are obtained by solving a linear eigenvalue problem. However, many engineering materials, such as viscoelastic materials, have frequency-dependent modulus, which results in a more complicated nonlinear eigenvalue problem. This paper presents a systematic study on the nonlinear eigenvalue topology optimization problem with frequency-dependent material properties. The nonlinear eigenvalue problem is solved by a continuous asymptotic numerical method based on the homotopy algorithm and perturbation expansion technique, which involves higher-order differentiation of the nonlinear term and shows a fast convergence. Several schemes are proposed to improve the computational accuracy, applicability, and robustness of the method for the application in topology optimization, including Faà di Bruno's theorem, bisection method, and inverse iteration based eigenvector modification method. Three optimization problems are solved to demonstrate the effectiveness of the developed methods, including the maximization of the fundamental frequency, the eigenfrequency separation interval between two adjacent eigenfrequencies of given orders, and the eigenfrequency separation interval at a given frequency. Numerical examples show the large influence of the frequency-dependent material properties on the optimized results and validate the effectiveness of the developed method. [ABSTRACT FROM AUTHOR]

[Display omitted] • The composite was prepared by electrohydrodynamic atomization deposition, layer-by-layer stacking and hot pressing technology. • The synergistic strengthening effect of van der Waals forces and covalent bonds improved the tensile strength of the composite. • The composite showed outstanding resistance stability, flexibility and electromagnetic interference shielding stability. It is a challenge to design Ti 3 C 2 T x MXene-based electromagnetic interference (EMI) shielding composites with excellent mechanical properties. Herein, a highly robust, flexible and durable Ti 3 C 2 T x MXene/carbon fiber fabric/thermoplastic polyurethanes (Ti 3 C 2 T x MXene/CFf/TPU) composite was fabricated through simple electrohydrodynamic atomization deposition, layer-by-layer stacking and hot pressing technology. The synergistic strengthening effect of van der Waals forces and covalent bonds can improve the tensile strength of the composite up to170.2 MPa, which is far greater than that of other MXene-based composites previously reported. In addition, the EMI shielding performance of the Ti 3 C 2 T x MXene/CFf/TPU composite also improved with increasing MXene mass fraction, reaching 40.4 dB, which can be attributed to the dielectric loss provided by conductive fillers and the enhanced absorption within the sandwich structure. More interestingly, the composite retained excellent resistance stability, EMI-SE stability and flexibility, even after multiple bending and releasing cycles. This work provides a facile and environmentally-friendly method for preparing composites with excellent EMI shielding properties and mechanical properties, which may provide more possibilities for applications in intelligent wear and electronic wireless communication equipment. [ABSTRACT FROM AUTHOR]