Bent Structure Research Articles

Multi-scale finite element analysis of laser-assisted forming of CF/PEEK composite corner structures

Laser-assisted forming can significantly increase the forming efficiency of thermoplastic composites. However, when forming CF/PEEK curved corner structures using laser-assisted forming, bending spring-back generated by the prepreg tape constrains the shape accuracy of the component. The bending deformation of unidirectional resin matrix composite materials is highly nonlinear. In this study, a multi-scale finite element method is used to obtain the bending properties of CF/PEEK composites for bending spring-back phenomenon of thermoplastic composite samples and predict the spring-back angle of CF/PEEK corner structures fabricated via laser-assisted forming. The average material properties were first calculated using RVE. Following this, a mesoscale model was developed to analyze kink deformation of the composite. Finally, the macroscopic prepreg bending spring-back was calculated. It was determined that the main mechanism of corner forming corresponds to the occurrence of a fiber kinking phenomenon on the interior of the corner. Furthermore, spring-back deformation is caused by residual stresses resulting from insufficient fiber kinking. The accuracy of the simulation results is verified via corner forming experiments. This study contributes to a deeper understanding of the spring-back mechanisms of laser-assisted forming of corner structures and provides a theoretical guidance for precision forming of multilayer thermoplastic composite bent structures.

Biomimetic hair-assisted GaN optical devices for bidirectional airflow detection

Airflow sensing plays a pivotal role in numerous fields, including medicine, industry, and environmental monitoring. However, detecting bidirectional airflow using a single sensing unit poses significant challenges. In this work, a miniature airflow sensing device is introduced, utilizing a GaN optical chip integrated with a biomimetic hair structure. The sensing device comprises a monolithic GaN chip that handles both light emission and detection. The biomimetic hairs, constructed from nylon fibers and PDMS film, undergo structural bending in converting airflow signals into optical changes, modulating the light captured by the on-chip detector. The intensity of the airflow directly correlates with the bending extent of the biomimetic hair, facilitating the precise detection of airflow rates through changes in the photocurrent. The integrated device can measure a wide range of airflow rates from −23.87 ms−1 to 21.29 ms−1, and exhibit a rapid response time of 13 ms and a detection limit of 0.1 ms−1. Characterized by its compact size, fast response time, and bidirectional detection ability, the developed device holds immense potential for applications in breath detection, speech recognition, encoding information, and the realization of logic operations.

Comparative Analysis of FSW and SFSW Welded Joints of EN AW 1200 Aluminum Alloy

Friction stir welding is a research direction within ISIM Timisoara, with contributions and results obtained in several research projects carried out in this field. The paper presents results obtained by ISIM Timisoara regarding FSW welding in ambient environment and in liquid working environment (submerged friction stir welding SFSW) of EN AW 1200 aluminum alloy, using a welding tool made of steel, with threaded cylindrical pin. FSW welding in liquid working environment aims to avoid overheating of the welding tool and welding device during the joining process, as well as achieving better results compared to FSW welding in ambient environment. The evaluation of welded joints included structural analysis, hardness measurements, tensile and bending tests. A comparative analysis of the results obtained in the FSW / SFSW welding experiments carried out for the EN AW 1200 aluminum alloy is presented. The obtained results are useful for the outline of the future experimental research programs which will be carried out within the ongoing Nucleu project PN 23.37.01.02, regarding friction stir processing in ambient and in a liquid environment of this material.

Polarization-Selective Metamaterial Absorber Using Tailored Y-Shaped SRR for UWB Device and Doppler Navigation Aids Applications

In this paper, we present an unprecedented metamaterial absorber design exhibiting exceptional characteristics in electromagnetic wave absorption. The proposed bent Y-shaped structure, fabricated on an FR-4 substrate with copper patches, showcases remarkable performance across a diverse frequency spectrum. Through exhaustive simulations in CST, this design manifests eight distinct resonant frequencies, achieving absorption rates exceeding 90% at each resonance. The resonances, strategically spanning from L-band (3.728 GHz) through S-band, C-band, X-band, Ku-band, and K-band up to 22.664 GHz, signify unparalleled versatility and efficacy in mitigating electromagnetic radiation. It investigates the equivalent circuit parameters of a proposed metamaterial absorber design, focusing on inductance (L), capacitance (C), and resistance (R). This paper investigates the applications of UWB devices at 3.728 GHz and Doppler navigation aids at the 13.4 GHz frequency as regulated by the Federal Communications Commission. It includes a discussion on near-zero refractive Index Metamaterials (NZRIM), highlighting their potential utilization in achieving extraordinary control over wave behaviour. Notably, the absorber's inherent polarization insensitivity fortifies its adaptability in various applications. Additionally, the metamaterial exhibits near-zero or negative permittivity, altering electric response, while simultaneously demonstrating permeability absolute zero throughout all frequency bands sparking new avenues for exploration and challenging conventional electromagnetic theories.

Direct laser writing of curved SERS for light-guided enhancement

Flexible SERS substrates, typically used on irregular surfaces, have unexplored optomechanical effects that could enhance performance. We developed a micromechanically bending structure, i.e. microbender, to study how bending affects SERS substrates’ performance. Optical simulations of nanopillar arrays on micro-curved surfaces showed a 25–134 % improvement in mean-field localization at the pillar tips for arrays with pillar diameters of 0.4–1 μm, pitches of 0.5–0.8 μm, and heights of 0.5–4.5 μm. Raman measurements showed that SERS intensity increases when in a curved state due to enhanced light scattering, guiding, and field localization. A curved array of 6 μm tall pillars (0.5 μm diameter, 1 μm spacing) produced Raman intensities similar to dense single-voxel arrays with shorter 0.8 μm pillars (0.2 μm diameter, 0.2 μm gaps) in the planar state. This finding suggests that low resolution fabrication technologies can produce curved SERS substrates with similar performance to high resolution planar SERS, offering an alternative to the current “smaller is better” trend through post-fabrication manipulation.

Finite element methods for the stretching and bending of thin structures with folding

Finite element methods for the stretching and bending of thin structures with folding

Shrinkage and deformation of material extrusion 3D printed parts during sintering: Numerical simulation and experimental validation

Material extrusion 3D printing (ME3DP) combined with sintering is a low-cost additive manufacturing technique for fabricating components of difficult-to-print metals, such as copper, aluminum, and ceramics. However, the sintering process includes complex material science, such as volumetric shrinkage and free structural bending, to identify the relative density and deformation of a 3D printed sample. The prediction of the relative density and deformations during the sintering process provides information to the design engineer to optimize the design of the CAD model before sintering. In this study, a phenomenological model based on constitutive equations was developed to predict the density and structural deformation during the sintering process of pure copper components fabricated by ME3DP using metal injection molding feedstock. The densification rate was determined using shrinkage estimation with an isothermal stairway heating cycle in a vertical dilatometer. Furthermore, different sets of experiments were performed with a load on the probe with long isothermal heating cycles at 850, 900, 950, 1000, and 1050 °C in a vertical dilatometer to estimate the axial viscosity of the copper. The constitutive equations were solved using the solid mechanics module with user-defined creep in COMSOL Multiphysics by considering isotropic assumptions. Two types of geometries, cube and overhanging I section, were used to predict shrinkage and deformation during the sintering process. The developed model successfully predicted the relative density based on shrinkage and structural deformation owing to gravity during the sintering process.

Self-Powered, Flexible, Wireless and Intelligent Human Health Management System Based on Natural Recyclable Materials.

Combining wearable sensors with modern technologies such as internet of things and big data to monitor or intervene in obesity-induced chronic diseases, such as obstructive sleep apnea, type II diabetes, cardiovascular diseases, and Alzheimer's disease, is of great significance to the self-health management of human beings. This study designed a loofah-conducting graphite four friction layer enhanced triboelectric nanogenerator (LG-TENG) and developed a health management system for human motion recognition and early warning of sleep breathing abnormalities. By uniformly spraying and depositing conductive graphite on the surface of the loofah and the elastic film cross-interlocking bending structure design, the signal strength of the LG-TENG has been improved by 390%. The stable output signal is still maintained after 1500 s of continuous operation at a frequency of 2 Hz. LG-TENG can realize accurate motion analysis by muscle contraction state. Combining different deep learning models resulted in 98.1% accuracy in recognizing seven categories of displacement speeds for an individual and 96.46% accuracy in recognizing seven categories of displacement speeds for three individuals. In addition, the sleep breathing monitoring early warning system was developed by integrating Bluetooth wireless transmission and upper computer analysis technology. This system aims to analyze and provide real-time warnings for sleep-breathing abnormalities. This research promotes an innovation of TENG technology based on the advantages of natural materials, recyclability and low cost. It offers new ideas for self-health management and scientific exercise for obese people, showing a broad application prospect.

Multiscale Damage Identification Method of Beam-Type Structures Based on Node Curvature

This paper proposes a multiscale damage identification method for beam-type structures based on node curvature. Firstly, based on the assumption that micro-damage has little effect on stress redistribution and the basic relationship between structural bending moment and curvature, combined with the denoising function of wavelet analysis, the linear matrix equation before and after node curvature damage is solved using the singular value decomposition (SVD) method. Then, the theoretical feasibility of this method is verified with laboratory tests of a simply supported beam. Finally, the damage sensitivity and noise resistance of this method are verified using field measurements of a beam bridge. The results show that the nodal curvature serves as an indicator parameter for damage identification in beam-type structures, enabling the precise localization of damage within these structures. When utilizing a multiscale finite element model for analysis, the nodal curvature enhances the ability to identify both the location and severity of damage within small-scale elements. Furthermore, this method can provide a reference for the damage identification and health monitoring of other types of bridges.

Manipulation of Supramolecular Chirality in Bicontinuous Networks of Bent-Shaped Polycatenar Dimers.

Bicontinuous cubic liquid crystalline (LC) phases are of particular interest due their possible applications in electronic devices and special supramolecular chirality. Herein, we report the design and synthesis of first examples of achiral bent-shaped polycatenar dimers, capable of displaying mirror symmetry breaking in their cubic and isotropic liquid phases. The molecules have a taper-shaped 3,4,5-trialkoxybenzoate segment connected to rod-like building unit terminated with one terminal flexible chain. The two segments were connected using an aliphatic spacer with seven methylene units to induce bending of the whole structure. Investigated by the small-angle X-ray scattering (SAXS), a double network achiral cubic phase Cub/Ia3 d, which is a meso-structure, and a chiral triple network cubic phase Cub/I23[*] are formed. The molecules self-assemble into molecular helices and progress along the networks. Interestingly, different linking groups such as ester or azo linkages and core fluorination lead to distinct local helicity, resulting in an alkyl chain volume dependent phase transition sequence Ia3d(L)-I23*-Ia3d(S). The re-entry of Iad phase and loss of supramolecular chirality is attributed to the delicate influence of steric effect at the mono-substitute end and interhelix interaction. Besides, aromatic core fluorination was proved to be a successful tool stabilizing the cubic phases in these dimers.

Contribution of Torsional Vibration Modes and the Influence on Period Ratios in the Seismic Response of Elastic Plate Bent Frame Structures

The structural characteristics of large-span structures inherently differ from those of conventional multistorey structures, making it challenging to accurately describe the contribution of various vibration modes to the overall response using traditional dynamic response analysis methods. Based on the response spectrum method, this paper investigates the influence of the first torsional mode on the overall effects of large-span structures. It proposes a new metric, called the torsional mode contribution factor, to characterize the contribution of torsional modes. Focusing primarily on single-span frames, the study explores the impact of factors such as eccentricity ratio, aspect ratio, and roof stiffness on the torsional mode contribution factor. Additionally, the relationship between the period ratio and the torsional mode contribution factor is examined to assess the necessity of controlling the period ratio. The findings reveal that the contribution of torsional modes to the overall seismic response varies significantly under different conditions, such as eccentricity ratio, aspect ratio, roof stiffness, and torsional stiffness. The torsional mode’s contribution is minimal for small eccentricity ratios, with the response primarily driven by translational modes. As eccentricity increases, translational-torsional coupling becomes more pronounced, amplifying the influence of torsional modes on the overall dynamic response. The study also highlights that increasing roof stiffness and aspect ratios can mitigate torsional effects to a certain extent. Still, excessive eccentricity ratios and stiffness may result in higher torsional contributions. Additionally, it is found that increasing torsional stiffness reduces the influence of torsional modes but does not eliminate the overall torsional deformation. The proposed torsional mode contribution factor offers an effective way to quantify these effects, demonstrating that traditional control methods, such as period ratio control, may not fully capture the torsional contributions.

Facilely Achieving Near-Infrared-II J-Aggregates through Molecular Bending on a Donor-Acceptor Fluorophore for High-Performance Tumor Phototheranostics.

Constructing J-aggregated organic dyes represents a promising strategy for obtaining biomedical second near-infrared (NIR-II) emissive materials, as they exhibit red-shifted spectroscopic properties upon assembly into nanoparticles (NPs) in aqueous environments. However, currently available NIR-II J-aggregates primarily rely on specific molecular backbones with intricate design strategies and are susceptible to fluorescence quenching during assembly. A facile approach for constructing bright NIR-II J-aggregates using prevalent donor-acceptor (D-A) molecules is still lacking. In this study, we present a facile method that transforms D-A molecules into J-aggregates by simply bending the molecule through introducing a methyl group, enabling high-performance NIR-II phototheranostics. The TAA-BT-CN molecule exhibits hypsochromic-shift absorption upon forming H-aggregated NPs, while the designed mTAA-BT-CN with a bent structure demonstrates a bathochromic shift of over 100 nm in absorption upon forming J-aggregated NPs, leading to much enhanced NIR-II emission beyond 1100 nm. With respect to its H-aggregated counterpart with the aggregation-caused quenching (ACQ) phenomenon, the J-aggregated mTAA-BT-CN NPs exhibit a 7-fold increase in NIR-II fluorescence owing to their aggregation-induced emission (AIE) property as well as efficient generation of heat and reactive oxygen species under 808 nm light excitation. Finally, the mTAA-BT-CN NPs are employed for whole-body blood vessel imaging using NIR-II technology as well as imaging-guided tumor phototherapies. This study will facilitate the flourishing advancement of J-aggregates based on prevalent D-A-type molecules.

Insights into freeze-cast hierarchical water–glass foams via in situ time-lapse phase-contrast enhanced microcomputed tomography: Correlating composition, microstructure, and compression failure

We demonstrate how continuous freeze-casting without post-treatment sintering may be successfully employed using a pure water–glass (WG) solution to fabricate hierarchically porous foams lacking a morphology gradient along the freeze direction. By adjusting the water content (dilution) and/or the alkali ratio of the solution, we achieved lamellar structures with sub-features or cellular structures, with porosities spanning ∼65% to 83%. The WG foams exhibit astounding mechanical properties; notably, foams with a relatively low density of ∼0.33 g/cm3 demonstrated the highest compressive strength (5 MPa), due to their microstructure and pore morphology. In situ uniaxial compression tests combined with phase-contrast enhanced micro-computed tomography in a synchrotron revealed bending, buckling, fracture and splitting of the lamellar structures as main failure mechanisms. Our newly developed approach of continuous freeze-casting of pure WG solutions with an improved understanding of the relationship between composition, structure, and failure mechanisms provide a basis for a customized design and manufacture of a wide range of freeze-cast WG-based materials for applications ranging from biomedicine to energy generation and storage.

Analysis of the deformation of conical shells made by 4D Printing of composites

4D printing of composites (4DPC) is a technique that allows the manufacturing of composite structures to shape without the use of a complex-shaped mold. Instead, only a flat mold is utilized. This innovative technique has been employed to make composite leaf springs with performance comparable to metallic springs, omega stiffeners, and corrugated core for flexible wings. Recently, this technique was applied to fabricate composite conical shells. While experimental work has successfully demonstrated the transformation from flat to conical shape, the development of a numerical method to replicate this transformation is highly desirable. The availability of such method not only provides theoretical support for the experimental result, it also provides means to develop other shapes. The lay-up sequence for transforming flat to conical shapes involves curvilinear fibers. Most if not all finite elements currently available deal only with straight fibers (even though the boundaries of the element may be curved). The objective of this research is to examine the efficiency of the analysis for the deformation of composite from flat to curve made by 4DPC by special finite elements containing curved fibers. The developed finite elements were used to determine the shapes of conical shells made using multiple distinct lay-up sequences. The direction of bending in curvilinear fiber structures is significantly influenced by the orientation of the fibers. This highlights the critical role of fiber orientation and layer composition in achieving desired shapes in 4D printed composites.

Enhancing gas-liquid mixing effect in pipelines: Experimental and numerical investigations of blind tee and traditional elbow

Blind tees, as typical upstream component for multiphase flow measurements, can promote the gas-liquid mixing in pipelines. However, detailed investigations on the mixing mechanism in blind tees are still scarce. This study employs a combination of experiments and numerical simulations on bubble flow in bend pipes to analyze two-phase flow dynamics in both the traditional elbow and blind tee. Firstly, the swirling phenomena at the outlet of bending structures are revealed using the measured flow images, and the dominant modes of gas distribution are extracted with proper orthogonal decomposition method to conduct a low-dimensional spatiotemporal analysis. Then, the mixing mechanism and vorticity distribution in different bending structures are compared using numerical results. Finally, the influences of bending structures and gas-liquid flow conditions on the mixing performance are comprehensively assessed. Results indicate that blind tee has a better mixing performance than traditional elbow, which significantly improves the gas distribution uniformity at the bend outlet. With the increase of volume gas content, the vortex intensity and frequency at the blind tee outlet increase, resulting in an increase in the uniformity of gas distribution. Moreover, the blind tee exhibits a shorter distance of turbulence dissipation than the traditional elbow. Therefore, a more uniform and stable bubble flow can be obtained within the range of 6D-8D downstream of the blind tee.

Asymmetric main-chain twisted small molecules for efficient polymer solar cells

Polymer solar cells (PSCs) based on small molecules with twisted backbones as electron acceptors, have many advantages over their planar counterparts, such as upshifted molecular energy levels, better charge extraction performance, enhanced extinction coefficient, extended carrier lifetime and reduced recombination rate, which are very helpful in improving the power conversion efficiencies (PCE). The present study was designed to synthesize two new small molecules with main-chain twisted structures that include an asymmetric electron donor core thiophene-phenylene-thieno[3,2-b]thiophene, namely i-T-TT and i-T-TT-4F, to investigate the “structure-property” correlation of main-chain twisted acceptors. Both asymmetric molecules exhibit bent geometric structures, and the fluorinated acceptor i-T-TT-4F possesses a more red-shifted spectrum, improved molar extinction coefficient, and deepened molecular energy levels. As a result, when combined with the middle bandgap polymer donor J52, there was a remarkable efficiency of 12.22 % for the device of i-T-TT-4F, higher than that of i-T-TT (9.51 %). Our research illustrates the importance of the main-chain twisted asymmetric electron-donating core and fluorinated end-capping group in the construction of efficient PSCs.

Colorimetric sensing of fatty acids in organic solvents using polydiacetylene-based nanocomposites

Colorimetric detection of long chain fatty acids by polydiacetylenes (PDAs)-based sensors is quite a challenge, mainly due to their relatively low solubility in aqueous media. In this study, we developed PDA/Zn2+/ZnO nanocomposites in various organic solvents for detecting fatty acids. Oleic acid and steric acid were used as representatives of fatty acids with bent and linear structures, respectively. The nanocomposites dispersed in ethanol exhibited blue-to-red color transition upon increasing the concentration of oleic acid. The use of other solvents including 1-butanol, 1-hexanol, 1-octanol, 1,4-dioxane, hexane, octane and toluene affected the sensitivity of nanocomposites. Furthermore, incorporating cetyltrimethylammonium bromide (CTAB) into the structure of the nanocomposites resulted in a systematic increase of sensitivity. The use of organic solvents simplified the method and allowed direct sensing of the fatty acids. Paper-based sensor was fabricated and utilized as a mobile test kit. This class of colorimetric sensors can also distinguish the bent and linear structures of fatty acids. Our study extends the utilization of PDA-based materials as colorimetric sensors of fatty acids in food industries.

Behavior of corroded HSC beams repaired by sprayed UHTCC and textile: Experimental study and theoretical analysis

Behaviors of twelve high strength concrete (HSC) beams were studied, including one control specimen, five corroded but non-repaired beams, and six corroded beams repaired by sprayed ultra-high toughness cementitious composites (UHTCC) with or without textile reinforcement. Galvanostatic accelerated corrosion technique was adopted, and three targeted corrosion levels (5 %, 10 %, and 15 %) were selected for each tensile steel bar. Corrosion-induced results, such as voltage change, crack initiation, concrete spalling, corrosion crack length and width, and non-uniform corrosion of steel bars were studied and compared with the results observed in normal strength concrete (NSC) beams. Structural behaviors, including failure modes and load-displacement responses were investigated through four-point bending tests. Results revealed that compared to NSC beams, HSC beams sustained more severe damages under a comparable corrosion level. Spalling was observed at a relatively lower corrosion ratio of 4.43 % and the maximum non-uniform corrosion coefficient, which was defined as the ratio of the maximum corrosion ratio to the average corrosion ratio, was 4.28. Corrosion-induced bonding degradation can alter the failure mode of corroded specimens in bending tests from bending to debonding. For repaired beams, however, the bonding degradation effect was reduced and bending failure was observed for all specimens. The bearing capacity of the beams repaired with sprayed UHTCC cannot be restored with a 12.42 % corrosion ratio, while the beams repaired with sprayed UHTCC/textile can recover their capacity even at a 13.6 % corrosion ratio. Furthermore, an improved theoretical model based on the fiber section analysis and virtual work method was developed to predict structural bending responses. The comparison of the experimental and theoretical results indicated the average corrosion ratio-based method may overestimate the loading capacity, especially for the beams with severe corrosion.

Deformation Characteristics and Influence Factors of Shear Force Lateral Stiffness Matching Index for Non-Rigid Plate Bent Frame Structures

The period ratio and the drift ratio are commonly used as plane regularity control indices for multi-story buildings. However, they fail to reasonably reflect the regularity of lateral force-resisting component configuration and deformation characteristics in non-rigid plate bent frame structures. This study focuses on the analysis of non-rigid single-span bent frames, examining the variation patterns of a suitable regularity index for non-rigid plate bent frame structures, referred to as the shear force lateral stiffness matching index, under various parameters. Additionally, it introduces indices to quantify the deformation response of non-rigid plate bent frame structures, providing a detailed analysis of the impact of factors such as eccentricity, torsional stiffness, and roof slab stiffness on the deformation characteristics of non-rigid plate bent frame structures and the shear force lateral stiffness matching index. The results show that the shear force lateral stiffness matching index can reflect the inconsistency in the horizontal displacement response of lateral force-resisting components caused by deformations in the roof slab. The proposed indices for torsional and bending deformations accurately quantify the roof slab’s deformation response, revealing the horizontal deformation characteristics of lateral force-resisting components in non-rigid frames. When eccentricity is present, the stiffness of the roof slab has a non-monotonic effect on the torsional component of the structural seismic response.

Bending Analysis of Multiwall Carbon Nanotube Reinforced Functionally Graded Composite Cylindrical Shell

The curved structural components of aircraft, automobiles, and marine vessels, such as cylindrical panels, are primarily exposed to loading, which can result in bending failure, particularly in lightweight structures. The bending analysis of cylindrical panels made of functionally graded multiwall carbon nanotube (FG-MWCNT) epoxy composites is subjective in this study. In the first section, FG-MWCNT composite cylindrical panels are simulated in the ANSYS software. There are three methods for distributing uniaxially aligned reinforcements. The material properties of the carbon nanotubes uniformly distributed and functionally graded over the thickness of the shell structure are estimated using an extended rule of mixture micromechanical model that incorporates certain useful characteristics. To demonstrate the effectiveness and applicability of the proposed finite element approach, deflection data are presented. The analysis of the shell structure's bending includes an investigation of the impact of CNT volume fraction, boundary condition, lengthto-thickness ratio, and other geometrical factors