Flexible Shape Research Articles

4D printing of hard magnetic soft materials based on NdFeB particles

Magnetic soft materials (MSM) show excellent potential in soft robotics, biomedicine, and sensors because of their excellent magnetic response, reversible deformation, and controlled motion. A hard magnetic soft material (HASM) that can be obtained by adding hard magnetic particles to a soft material matrix. By programing the spatial magnetization profile of the HASM object and manipulating the driving magnetic field, it exhibits excellent shape manipulation performance with unconstrained, reversible deformation transformation and controlled motion. In this study, a HASM ink consisting of hard magnetic NdFeB particles with a soft silicone rubber matrix was prepared. A 4D printing strategy using 3D injection printing technology combined with origami magnetization technology is used to fabricate 3D structured HASM objects for flexible shape programmability. A variety of programed shapes of HASM straight beams with bionic fish tails were fabricated by 4D printing strategy. The HASM straight beam is driven by the magnetic field, which can quickly realize the transformation and change of the preset shape as well as the shape of the HASM beam. The HASM bionic fish tail can swing rapidly under the action of the driving magnetic field. It shows a broad potential in the field of soft and bionic robots.

Surface quality improvement for 316L additive manufactured prototype based on magnetorheological polishing

Abstract. Additive manufacturing has attracted increasing attention in recent years due to its flexibility and near-net shaping advantages. Although recent advancements in metal additive manufacturing accuracy have met the post-processing requirement for dimensional tolerance, the finishing post-processing of functional surfaces must be further investigated in conjunction with material characteristics. This research aims to investigate the use of a flexible process in the polishing of additive molding samples. As an example, the surface of a 316L stainless steel sample formed by powder bed laser melting was polished using magnetorheological polishing technology. Magnetic field simulation was used to create a longitudinally staggered magnetorheological polishing tool. Surface roughness and residual stress were studied with process parameters such as abrasive content, magnetic particle content, machining gap, and spindle speed. Results show that the polishing effect is better at 4 % and 40 % abrasive and magnetic particles, respectively. The surface roughness Ra is 99 nm when the working gap is 0.6 mm, the surface roughness Ra value is the lowest when the spindle speed is 600 r min−1. The surface roughness was reduced to 61.43 nm after polishing the sample under improved processing conditions (4 % abrasive, 40 % magnetic, 0.6 mm working clearance, 600 r min−1 spindle speed). A nano-scale smooth surface can be obtained by powder bed laser melting and magnetorheological polishing of 316L stainless steel.

Turbine Endwall Contouring Through Advanced Optimization Techniques

AbstractNon-axisymmetric endwall profiling offers features to simultaneously mitigate aerodynamic losses and hot gas ingestion in axial turbines. This paper presents an optimization methodology to generate a contoured surface integrated with real geometrical effects such as blade fillets and a rim seal channel with the aim of achieving higher efficiencies while reducing hot gas ingestion. The contoured rotor platform is constructed using a B-spline surface clamped in the axial direction. In the azimuthal direction, the surface is unclamped to allow geometrical continuity across the periodic boundaries. The endwall parameterization is used to optimize a rotor hub platform of a high-pressure turbine stage. A differential evolution optimizer is used to rank individuals in terms of efficiency. The single-objective optimization is set to maximize the aerodynamic efficiency and it is defined such that it accounts for the flow non-uniformity through a mixed-out averaging procedure. Engine representative conditions typical of a two-stage high-pressure turbine are used as boundary conditions. Geometrical and aerodynamic constraints are set to guarantee a fair comparison among individuals and to meet engine requirements. Two surface parameterizations, which use a different number of design variables but share the same construction strategy, are presented to show the trade-off between the number of degrees-of-freedom and the aerodynamic improvement. Different purge flow conditions are considered to assess the robustness of the optimization results at off-design conditions for relevant geometries. The aim of this paper is to show the advanced shape flexibility of the implemented parameterization for contoured platforms featuring technological effects such as blade fillet and rim seal channel. The work provides design guidelines to setup engine-realistic constraints for endwall contour optimization of turbine stages.

Phonological–semantic flexibility and its role in reading for Chinese kindergarten children

AbstractThe present study aimed to examine the role of phonological–semantic flexibility (PSF) in learning to read Chinese. PSF refers to a specific flexibility applied to process the dual linguistic dimensions of words (i.e., sound and meaning). A correlational study (Study 1) was conducted to determine the unique contribution of PSF to three aspects of early reading abilities, including word reading accuracy, word reading fluency and reading comprehension. A total of 190 Chinese kindergarten children were tested on a PSF task and a range of cognitive, linguistic and reading tasks. Results of hierarchical regressions showed that PSF uniquely and significantly contributed to the reading abilities beyond the effects of established cognitive factors (IQ, working memory, inhibition control, and cognitive flexibility) and linguistic factors (syllable skills, morphological skill and vocabulary skill). In the second part, an intervention study (Study 2) was conducted in which two groups of kindergarten children received explicit training on PSF (27 children) and colour–shape flexibility (26 children) respectively. Children in the PSF group showed significantly more improvement in PSF and word reading fluency than the control group. Overall, the present study demonstrated the theoretical and practical importance of PSF for learning to read Chinese.

Parachute shape ultra‐wideband wearable antenna for remote health care monitoring

SummaryWireless body area networks (WBAN) is used to measure patients' health conditions continuously. Different kinds of sensors are required to measure health conditions. When such types of antennas are used on the human body, they are flexible with the movements. The usage of wearable devices is currently increasing in the biomedical field. The presented wearable antenna is suitable for biomedical applications. The presented ultra‐wideband (UWB) flexible parachute shape wearable antenna is fabricated on a jeans textile substrate. The prototype antenna has a −10 dB measured impedance bandwidth of 5800 MHz (7 to 12.8 GHz) with average radiation efficiency of 75.28%. The prototype antenna's size is 40 × 40 mm2 (1.32 × 1.32 at centre frequency 9.9 GHz) and a peak gain of 4.5 dB at 12.33 GHz. The fabricated antenna is suitable for biomedical applications in X‐band frequencies and can be implemented with a low‐cost manufacturing process. The radiating element is made by conductive copper tape. Muscle‐equivalent phantoms are used to analyze the body effect on antenna performance. The radiation effect emitted by the presented antenna on the human body is calculated by the specific absorption rate (SAR) value. The maximum SAR value of the proposed antenna is 1.84 W/kg at 12.33 GHz. This leads to promising results for wearable applications related to remote health care monitoring, such as biotelemetry and mobile health with a sensor‐driven approach.

Polysaccharides based rapid self-crosslinking and wet tissue adhesive hemostatic powders for effective hemostasis

Hemostatic powders with flexible shape are widely used for the noncompressible and inaccessible hemorrhage wounds. However, current hemostatic powders display poor wet tissue adhesion and fragile mechanical strength of the powder-supported blood clots, leading to compromised hemostasis efficacy. Herein, a bi-component of carboxymethyl chitosan (CMCS) and aldehyde-modified hyaluronic acid grafted with catechol groups (COHA) was designed. Upon absorption of blood, the bi-component powders (CMCS-COHA) spontaneously self-crosslinks into an adhesive hydrogel within 10 s, tightly adhering to wound tissue to form a pressure-resistant physical barrier. During gelation, the hydrogel matrix captures and locks the blood cells/platelets to generate a robust thrombus in the bleeding sites. Compared with traditional hemostatic powder Celox™, CMCS-COHA displays superior blood coagulation and hemostatic performance. More importantly, CMCS-COHA has inherent cytocompatibility and hemocompatibility. These prominent advantages in rapid and effective hemostasis, adaptability to fit irregulate defective wound, easy preservation, facile usage, and bio-safety, make CMCS-COHA a promising hemostatic in emergency situations.

Magnetic properties of a high-density iron dust core without binders

Iron dust cores produced from insulated iron particles via the powder metallurgy pressure-forming process are suitable for small motor cores, reactor cores, and inductors because of their high shape flexibility. However, the dust core’s magnetic properties are inferior to those of conventional laminated cores because the insulation materials and silicon resins between iron particles to reduce eddy current losses degrade the magnetic properties of the core. Unfortunately, there is no researches of the iron dust cores without binders such as resin to improve the magnetic properties. Therefore, this paper investigates the magnetic properties of iron dust cores without binders. Assessments revealed that the dust core of gas-atomized iron powder with an average particle size of 49μm had the best magnetic properties. On further assessments, while the insulation layer’s thickness was around 60 nm, the density of gas atomized iron powder core was over 7.6 g/cm3. At 50 Hz and 1 kHz, DC hysteresis iron losses and eddy current loss of 49μm gas atomized iron dust cores without a binder showed lower values than those of the conventional powder core with a binder.

2D QSAR ANALYSIS OF CARBONITRILE BASED INHIBITORS OF CATHEPSIN S AS POTENTIAL ANTIRHEUMATIC AGENTS

2D QSAR has been performed on a series of pyridine carbonitrile and trifluoromethyl phenyl derivatives. 53 compounds were divided into training and test sets out of which 37 compounds generated a final QSAR model. The most significant model with n = 37, r = 0.916, r2 = 0.762, r2 cv = 0.759, s value = 0.388, f value = 41.76 was developed using MLR analysis. For PLS, the fraction of variance explained = 0.806 was observed. A comparable PLS model with r2 = 0.806 and Neural model with r2 = 0.853 indicated good internal predictability of the model. External test set validation provided r2 values of 0.744 and 0.768 for MLR and PLS analysis, respectively. Dipole moment Z Component, Log P, Shape flexibility index, and Vamp LUMO descriptors proved to be significant for inhibition of Cathepsin S. These findings will be effective in designing more potent and effective Cathepsin S inhibitors

A universal model for power converters of battery energy storage systems utilizing the impedance-shaping concepts

Battery energy storage systems (BESSs) render different services in microgrids (MGs) depending on the MG connection mode. In the grid-connected mode, the BESS optimally injects/absorbs power, operated by a power converter controlled as the grid-feeding voltage source converter (GFD-VSC). In the islanded mode, the BESS may work as distributed slack bus controlled by the grid-forming VSC (GFM-VSC). However, for performing with a desirable performance, the GFD-VSC and the GFM-VSC demand different grid characteristics. Specifically, the GFD-VSC has a grid-synchronization issue and may become unstable in weak grids with high inductive impedance. Contrarily, the GFM-VSC reveals better performance when connected to the MG through a feeder with high inductive impedance. Besides, switching between different operating modes may cause undesirable transients. This issue can be addressed by the impedance shaping concept that is realized through the control design of the power converter. However, there is limited flexibility for impedance shaping using conventional PI-based controllers. To this end, in this paper, a universal controller is proposed, which is developed based on the impedance shaping concept. Also, sliding mode control (SMC) is used to overcome the undesirable transients due to switching between operating modes. The effectiveness of the control structure is evaluated in islanded operation, under weak grid connection, and FRT transients in MATLAB/Simulink.

Experimental and analytical investigation of the flexural behaviour of stiffened hollow glulam beams reinforced with fibre reinforced polymer

With specific force transmission characteristics and flexible shaping capability, glulam components have been extensively used in long-span and multi-storey composite timber architectures. In this study, we propose a hollow glulam beam design with stiffening plates in a hollow rectangular cross section with high flexural behaviour and stability. To improve the bearing capacity, bottom of the beam was reinforced with fibre reinforced polymer. The flexural behaviour of the beam was analysed using experimental study, theoretical research, and finite element analysis. The results indicate that the bearing capacity of reinforced glulam beams improves marginally, and the reinforcement effect of carbon fibre reinforced polymer (CFRP) is better than that of basalt fibre reinforced polymer (BFRP). For stiffened hollow glulam beams in group ZR1 and ZR2, the ultimate bearing capacity increases after reinforcement with CFRP and BFRP. In this study, the experimental data were obtained by a four-point bending test, and the finite element model was established for verification. Additionally, an elastic theoretical calculation method is established for strengthening the bearing capacity of specimens and is validated via results of numerical simulation and testing.

Learning effectiveness of a flexible learning study programme in a blended learning design: why are some courses more effective than others?

Flexible learning addresses students’ needs for more flexibility and autonomy in shaping their learning process, and is often realised through online technologies in a blended learning design. While higher education institutions are increasingly considering replacing classroom time and offering more blended learning, current research is limited regarding its effectiveness and modifying design factors. This study analysed a flexible study programme with 133 courses in a blended learning design in different disciplines over more than 4 years with a mixed-methods approach. In the analysed flexible study programme, classroom instruction time was reduced by 51% and replaced with an online learning environment in a blended learning format (N students = 278). Student achievement was compared to the conventional study format (N students = 1068). The estimated summary effect size for the 133 blended learning courses analysed was close to, but not significantly different from, zero (d = − 0.0562, p = 0.3684). Although overall effectiveness was equivalent to the conventional study format, considerable variance in the effect sizes between the courses was observed. Based on the relative effect sizes of the courses and data from detailed analyses and surveys, heterogeneity can be explained by differences in the implementation quality of the educational design factors. Our results indicate that when implementing flexible study programmes in a blended learning design, particular attention should be paid to the following educational design principles: adequate course structure and guidance for students, activating learning tasks, stimulating interaction and social presence of teachers, and timely feedback on learning process and outcomes.

Experimental study on novel composite phase change materials with room-temperature flexibility and high-temperature shape stability in a battery thermal management system

Phase change materials have potential uses in battery thermal management because of their controllable phase change temperature and high latent heat. However, the application of phase change materials is limited by their strong rigidity, difficult assembly, high contact thermal resistance, low thermal conductivity, and leakage. In this study, a novel flexible composite phase change material (CPCM) with good mechanical properties is prepared, which can maintain flexibility at room temperature and shape stability at high temperatures. A thermoplastic styrene-based polymer (TPS) is used as the support material, paraffin is used as the phase change material, and expanded graphite is used as the reinforced thermal conductive filler. Results show that the composites have good flexibility and extensibility at room temperature and can maintain good shape stability at 60 °C and certain pressure. The contact thermal resistance of CPCM is 50% of the contact thermal resistance of similar materials. Thermal management experiments of single battery and square battery modules are designed. After six cycles of 2.5C high-rate discharge, the maximum temperature of the battery module cooled by CPCM is 2 °C and 10.4 °C lower than that of forced air cooling and natural air cooling, respectively. The temperature difference of the battery module is lower than 4.0 °C. This study shows that the new flexible CPCM thermal management system is easy to assemble and can reduce the temperature of battery modules, and this feature is conducive to the application of CPCM.

Bionic Mechanical Analysis of Dragonfly Wings: The Feasibility of Mesh Combination to Improve Structural Stiffness

The nodes of the object will show different degrees of deformation and displacement or even damage over time. The mesh structure is flexible and different mesh shapes and arrangements will affect the structural stiffness of the object. The unique structure of dragonfly wing veins allows the dragonfly to withstand pressures several times higher than itself and to fly freely. This study is based on dragonfly wing bionics to disassemble the structure of dragonfly wing vein geometry. And it aims to investigate the deflection under different geometries and three-dimensional spatial structures by using the drawing software Auto CAD to draw dragonfly sample graphics, the finite element software Hyper mesh to build the model and the solver OptiStruct to analyze the structure of wrinkling, arching deflection, z-direction maximum displacement, y-direction maximum rotation angle, combined displacement test under the different loads. The results show that: (1) The dragonfly wing vein mesh structure can enhance the stiffness under load. (2) In contrast, the displacement deformation of quadrilateral and combined hexagonal is smaller. (3) The structural stiffness of quadrilateral hexagon is enhanced as the height of wrinkling and arching increases. (4) The improvement of grid deflection with membrane structure is better than that without membrane structure. According to the above experimental results, the quadrilateral wrinkling and hexagonal arching structure has a significant improvement on the load bearing and deflection of the mesh, and has the potential to make structural optimization of the mesh series products, which is suitable for practical application and promotion.

A novel non-embedded, adjustable, and flexible shape memory alloy actuator for variable-area exhaust nozzle actuation.

The actuator is a fundamental component for a variable-area exhaust nozzle. Conventional actuators for variable-area exhaust nozzles are hydraulic actuators and electric motors. However, they are heavy, large, and structurally complex. Shape memory alloys (SMAs) are light, small, structurally simple, and have unique advantages not found in conventional actuators. However, SMA actuators occupy a large space in the radial direction and cannot be fixed to surfaces with different radii of curvature. Moreover, once designed, the actuating displacement of the actuator cannot be adjusted. To solve this problem, this study develops a novel non-embedded, adjustable, and flexible SMA actuator for variable-area exhaust nozzle actuation. An analytical model is presented to predict mechanical performance. Subsequently, experiments of this flexible SMA actuator are conducted to study the mechanical performance. A proof-of-concept, variable-area exhaust nozzle of the aeroengine is designed, fabricated, and tested to obtain the properties of the exhaust nozzle that are actuated by the flexible SMA actuator. In the experiments, the movement trajectory of the exhaust nozzle is captured using an image recognition technique, and the area changes of the exhaust nozzle are calculated. The results show that the actuator is flexible and can be bent at any angle from -90° to +90°. The actuating displacement of the flexible SMA actuator can be adjusted by increasing or decreasing the number of hinged units. In addition, the area change of the exhaust nozzle is 64.4%, exceeding the largest area change of 40% in previous studies on SMA-actuated exhaust nozzles.

Virtual element method for mixed-mode cohesive fracture simulation with element split and domain integral

We present a computational framework for mixed-mode cohesive fracture simulation based on the virtual element method (VEM). To represent an arbitrary crack path, the element splitting scheme is developed on a polygonal mesh to capitalize its flexibility in element shape. For the accurate evaluation of a crack-tip stress field and crack propagation direction, the virtual grid-based stress recovery scheme is tailored for VEM in conjunction with the maximum strain energy release rate criterion. The mixed-mode fracture examples are illustrated to validate the accuracy and robustness of the proposed computational scheme. Numerical results demonstrate that the domain integral method with the stress recovery scheme captures an accurate crack path without oscillation under the biaxial tensile stress state. Furthermore, the computed cracks using the element splitting scheme show that smooth and curved patterns on polygonal elements are in good agreement with the experimental results.

Application of Shape Memory Alloy Actuators to Vibration and Motion Control of Structural Systems: A Review

This paper comprehensively reviews effective control applications using shape memory alloy (SMA) actuators. Among many applications, this paper focuses on the vibration and stiffness control of flexible structures and shape control in the aerospace engineering field. In the vibration control of flexible structures, three different methods are introduced and discussed, including their merits and demerits. In addition, several control strategies, such as neuro-fuzzy controller, are investigated in terms of the implementation associated with the microchip. In the control process, the inherent hysteretic behavior of SMA is also reviewed as a feedforward loop or actuating force compensator. At the second part, applications on the morphing wing in the field of aerospace engineering are reviewed, and salient characteristics are discussed. In this review, the morphing wing, which is closely related to aircraft stability, is mainly investigated considering control logics and geometrical parameters. For easily understanding morphing control using SMA, a table which summarizes the main contribution of each research is presented. It is expected, since this review article provides numerous approaches for vibration and morphing control conducted over the last decade, it will be very helpful to the same research community to create novel ideas to achieve more advanced and effective results in vibration and morphing control using SMA actuators.

Mosaic Patterned Surfaces toward Generating Hardly-Volatile Capsular Droplet Arrays for High-Precision Droplet-Based Storage and Detection.

Precise detection involving droplets based on functional surfaces is promising for the parallelization and miniaturization of platforms and is significant in epidemic investigation, analyte recognition, environmental simulation, combinatorial chemistry, etc. However, a challenging and considerable task is obtaining mutually independent droplet arrays without cross-contamination and simultaneously avoiding droplet evaporation-caused quick reagent loss, inaccuracy, and failure. Herein, a strategy to generate mutually independent and hardly-volatile capsular droplet arrays using innovative mosaic patterned surfaces is developed. The evaporation suppression of the capsular droplet arrays is 1712 times higher than the naked droplet. The high evaporation suppression of the capsular droplet arrays on the surfaces is attributed to synergistic blocking of the upper oil and bottom mosaic gasproof layer. The scale-up of the capsular droplet arrays, the flexibility in shape, size, component (including aqueous, colloidal, acid, and alkali solutions), liquid volume, and the high-precision hazardous substance testing proves the concept's high compatibility and practicability. The mutually independent capsular droplet arrays with amazingly high evaporation suppression are essential for the new generation of high-performance open-surface microfluidic chips used in COVID-19 diagnosis and investigation, primary screening, in vitro enzyme reactions, environmental monitoring, nanomaterial synthesis, etc.

Novel solid-state metal powder surface modification process for additive manufacturing of metal matrix composites and alloys

Although metal additive manufacturing has been widely studied owing to its flexible product shape design, the material selection window for metal additive manufacturing remains narrow owing to limited feedstocks. To address the challenges in additive manufacturing, an innovative metal powder fabrication process was developed in this study. This process is known as surface modification and reinforcement transplantation (SMART), and it efficiently produces surface-modified feedstock powders, such as spheroidized, surface-alloyed, surface-coated, or composite powders, which facilitate the exploration of new alloys and composites via additive manufacturing. In this study, the working principles of the SMART process were established, and some practical applications of the SMART process were considered by fabricating specialized metal additive manufacturing feedstocks such as carbon nanotube-coated, Mo alloyed, and TiC particle-reinforced Inconel 625 powders. Furthermore, Mo-alloyed and TiC particle-reinforced powders were utilized in the directed energy deposition process to validate the performance of the SMART powder by fabricating Mo-controlled alloy and TiC particle-reinforced composites. The SMART process was compared with the existing processes and proved to be advantageous. Therefore, this study provides a novel method for producing feedstock powders for additive manufacturing.

Complete Study of an Original Power-Exponential Transformation Approach for Generalizing Probability Distributions

In this paper, we propose a flexible and general family of distributions based on an original power-exponential transformation approach. We call it the modified generalized-G (MGG) family. The elegance and significance of this family lie in the ability to modify the standard distributions by changing their functional forms without adding new parameters, by compounding two distributions, or by adding one or two shape parameters. The aim of this modification is to provide flexible shapes for the corresponding probability functions. In particular, the distributions of the MGG family can possess increasing, constant, decreasing, “unimodal”, or “bathtub-shaped“ hazard rate functions, which are ideal for fitting several real data sets encountered in applied fields. Some members of the MGG family are proposed for special distributions. Following that, the uniform distribution is chosen as a baseline distribution to yield the modified uniform (MU) distribution with the goal of efficiently modeling measures with bounded values. Some useful key properties of the MU distribution are determined. The estimation of the unknown parameters of the MU model is discussed using seven methods, and then, a simulation study is carried out to explore the performance of the estimates. The flexibility of this model is illustrated by the analysis of two real-life data sets. When compared to fair and well-known competitor models in contemporary literature, better-fitting results are obtained for the new model.

Enhanced Faraday rotation by a Fano resonance in substrate-free three-dimensional magnetoplasmonic structures.

Three-dimensional magnetoplasmonic nanostructures possess more novel and richer optical and magneto-optical (MO) behaviors compared with planar nanostructures, and exhibit attractive potential applications in micro-nano non-reciprocal photonic devices. However, fabrication of three-dimensional magnetoplasmonic nanostructures is difficult using the usual nanofabrication methods. This work constructs three-dimensional substrate-free Au/Co/Au structures prepared using focused ion beam (FIB) technology. In the three-dimensional split-ring structure, with y-polarized light normal incidence, a three-dimensional coupling current is formed between the vertical split-ring and the bottom square hole, which causes excitation of the Fano resonance. The Fano resonance causes a significant enhancement of the local magnetic field, resulting in a larger Faraday rotation (FR). The resonance also brings about a sign reversal of FR, which is related to the direction of the Lorentz force on electrons. Similar effects also exist in the three-dimensional nanopillar structure and the three-dimensional nanoring structure in the simulation results. Due to the high flexibility of FIB machining, the height and shape of the three-dimensional split-ring can be arbitrarily changed, which means the FR intensity and the position of the FR null point are tunable. The designed three-dimensional structures provide a new route to regulate the Faraday effect, and broaden the possibilities for the design and construction of MO devices.