Bending Curvature Research Articles

Experimental investigation of fatigue behavior of UHPFRC – RC composite deck slabs subjected to moving wheel loading

UHPFRC has been increasingly used as a bridge deck overlay material. Since bridge decks are exposed to severe mechanical action and harsh environmental conditions, the application of UHPFRC to bridge decks is an effective and wise utilization of UHPFRC’s excellent properties such as high strength and low permeability. This paper presents the result of a full-scale fatigue test of a reinforced concrete (RC) deck slab overlaid with UHPFRC (UHPFRC – RC composite deck slab) using a moving wheel load. The fatigue behavior of the UHPFRC – RC composite deck slab was analyzed using measurement data from the experimental test and discussed. The failure mode of the UHPFRC – RC composite deck slab was punching shear accompanied by near-interface concrete cracking and double curvature bending of the UHPFRC layer. The fatigue life of the UHPFRC – RC composite deck slab was estimated using an existing S-N relation of RC deck slabs subjected to moving wheel loads and a 30 mm thick UHPFRC overlay was found to increase the fatigue life of RC deck slabs by about five times.

Ultrafast Bi-Directional Bending Moisture-Responsive Soft Actuators through Superfine Silk Rod Modified Bio-Mimicking Hierarchical Layered Structure.

Development of stimulus-responsive materials is crucial for novel soft actuators. Among these actuators, the moisture-responsive actuators are known for their accessibility, eco-friendliness, and robust regenerative attributes. A major challenge of moisture-responsive soft actuators (MRSAs) is achieving significant bending curvature within short response times. Many plants naturally perform large deformation through a layered hierarchical structure in response to moisture stimuli. Drawing inspiration from the bionic structure of Delosperma nakurense (D. nakurense) seed capsule, here the fabrication of an ultrafast bi-directional bending MRSAs is reported. Combining a superfine silk fibroin rod (SFR) modified graphene oxide (GO) moisture-responsive layer with a moisture-inert layer ofreduced graphene oxide (RGO), this actuator demonstrated large bi-directional bending deformation (-4.06±0.09 to 10.44±0.00cm-1) and ultrafast bending rates (7.06cm-1s-1). The high deformation rate is achieved by incorporating the SFR into the moisture-responsive layers, facilitating rapid water transmission within the interlayer structure. The complex yet predictable deformations of this actuator are demonstrated that can be utilized in smart switch, robotic arms, and walking device. The proposed SFR modification method is simple and versatile, enhancing the functionality of hierarchical layered actuators. It holds the potential to advance intelligent soft robots for application in confined environments.

Bending and Stretching‐Insensitive, Crosstalk‐Free, Flexible Pressure Sensor Arrays for Human‐Machine Interactions

AbstractAccurate data acquisition from flexible sensors placed on deformable 3D freeform surfaces is of critical importance for many applications, such as wearable electronics, human‐machine interfaces, and soft robotics. However, the mechanical coupling between the sensor and the deformable subject surface to bending and stretching deformations can significantly reduce the accuracy of the acquired data. This study combines a polyimide (PI) micropore isolation layer (PIL) and serpentine electrodes with a flexible piezoresistive sensor to mitigate the issue of mechanical coupling. As a mechanical buffer to distribute the external pressure and reduce the strain concentration, the PIL can avoid the bending interference for bending curvature up to 256 m−1, while maintaining a high sensitivity of S > 21.5 kPa−1. The serpentine electrode design further allows the sensor to reliably acquire data in the presence of stretching up to 45% without cross‐talk. The versatility of the developed sensor is demonstrated in several human‐machine interaction scenarios, including gesture recognition and motion detection. The design strategies on materials and structures from this study can also be applied for the development of other flexible sensors with high sensitivity and low deformation interference to avoid the mechanical coupling between the sensor and the deformable surface.

The impact of post-cutoff bend curvature on channel kinematics in meandering rivers: an example from the Trinity River, Texas, USA

Abstract Neck and chute cutoffs along meandering rivers are near-instantaneous morphodynamic perturbations that drive modification of planform channel geometry and kinematics at the cutoff site and in adjacent bends. Despite their ubiquity, quantitative and predictive linkages between post-cutoff planform bend geometry and subsequent bend kinematics remain limited. Here, using a 37-year record of Landsat-derived river channel centrelines from a meandering reach of the Trinity River in Texas (USA) and a newly developed directed graph-based approach for high-resolution channel tracking, we identify a linkage between post-cutoff bend curvature and the magnitude, spatial extent, and temporal duration of cutoff influence on local and non-local channel bend kinematics. We further explore this relationship using a kinematic model of meandering applied to synthetically generated river reaches and the Landsat-derived Trinity River centrelines. While the model captures the observed linkages between post-cutoff bend curvature and resultant bend kinematics, it underpredicts the magnitude of cutoff influence observed in the real centreline data – particularly at the cutoff site – by up to one order of magnitude. Our results provide a promising advance in the characterization and prediction of the spatiotemporal impact of cutoffs on local and non-local post-cutoff channel bend kinematics.

Design, modeling, and control of a novel soft-rigid knee joint robot for assisting motion

AbstractThis paper presents the design, modeling, and control of a novel soft-rigid knee joint robot (SR-KR) for assisting motion. SR-KR is proposed to assist patients with knee joint injuries conducting gait training and completing walking movements. SR-KR consists of a novel soft-rigid bidirectional curl actuator, a thigh clamping structure, and a crus clamping structure. The actuating part of SR-KR is composed of soft materials, which ensures the wearing comfort and safety, while the wearing parts contain rigid structure, which ensures the efficient transmission of torque. The bending deformation model of SR-KR is established, which reveal the relationship among SR-KR’s bending curvature, working pressure, and output torque. Experiments show that SR-KR can provide more than 26.3 Nm torque for knee joint motion in human gait range. A double closed loop servo control system including attitude servo and pressure servo is built to better apply SR-KR. Mechanical property test, trajectory-driven test, and lower limb wearing test have been conducted, which show that SR-KR has ability to assist in lower limb motion and has potential in the fields of rehabilitation and human enhancement.

Unravelling Size-Dependent and Coupled Properties in Mechanical Metamaterials: A Couple-Stress Theory Perspective.

The lack of material characteristic length scale prevents classical continuum theory (CCT) from recognizing size effect. Additionally, the even-order material property tensors associated with CCT only characterize the materials' centrosymmetric behavior and overlook their intrinsic chirality and polarity. Moreover, CCT is not reducible to 2D and 1D space without adding couples and higher-order deformation gradients. Despite several generalized continuum theories proposed over the past century to overcome the limitations of CCT, the broad application of these theories in the field of mechanical metamaterials has encountered significant challenges. These obstacles primarily arise from a limited understanding of the material coefficients associated with these theories, impeding their widespread adoption. Implementing a bottom-up approach based on augmented asymptotic homogenization, a consistent and self-sufficient effective couple-stress theory for materials with microstructures in 3D, 2D, and 1D spaces is presented. Utilizing the developed models, material properties associated with axial-twist, shear-bending, bending-twist, and double curvature bending couplings in mechanical metamaterials are characterized. The accuracy of these homogenized models is investigated by comparing them with the detailed finite element models and experiments performed on 3D-printed samples. The proposed models provide a benchmark for the rational design, classification, and manufacturing of mechanical metamaterials with programmable coupleddeformation modes.

A real time study of the coupled electrochemical and mechanical behaviors of the spinel cathodes in LIBs.

Spinel cathode materials have great application prospects in lithium batteries (LIBs) due to their characteristics of abundant raw materials, simple preparation processes, and cobalt-free nature. During the electrochemical cycles, the specific capacity of the electrodes decreases significantly due to the dissolution of excess metal ions and mechanical degradation, which hinder their further application and development. Here, a bending curvature measurement system (BCMS) was designed to simultaneously measure the mechanical properties of the spinel cathodes during the electrochemical reaction. Three types of cathodes were chosen as the working cathode, and the coupled mechanical and electrochemical properties were analyzed to understand their degradation mechanism. During cycling, a hysteresis loop is observed for the curvature, modulus, plain strain, and stress, where LiMn2O4 (LMO) has the largest loop for the mechanical response while the LiNi0.5Mn1.5O4@Al2O3 (LNMO@Al) one has the smallest loop. Besides, the changing trend of LNMO@Al is the smallest in multiple cycles and it shows the more stable mechanical properties. This study shows from in situ mechanical measurements that the mechanical properties can greatly affect the electrochemical performance of the cathodes. These findings could offer new insights into the understanding of the electrochemical performance degradation in the spinel cathodes and can help develop strategies to enhance the performance of LIBs.

Analysis of Weakly Nonlinear Evolution Characteristics of Flow in the Constant Curvature Bend

Analysis of Weakly Nonlinear Evolution Characteristics of Flow in the Constant Curvature Bend

4D printing of shape memory polymer with continuous carbon fiber

Shape memory polymer composites (SMPCs) have gained attention for their shape memory effects and wide-ranging applications. Understanding the bending shape recovery characteristics of 3D printed SMPCs is crucial for optimizing their performance. This study focuses on investigating the influence of different fiber orientations of continuous carbon fiber (CCF) in thermally stimulated SMPC. By controlling printing parameters and fiber orientation during the 3D printing process, we fabricate tailor-made rectangular composite test specimens. These specimens are subjected to controlled bending above the glass transition temperature of the polymer, inducing temporary deformation. The subsequent shape recovery process is carefully captured through high-speed video. Precise measurements of the bending curvature over time are obtained using the row-by-row image processing technique and analyzed. The shape recovery rate, shape recovery ratio, and shape fixity ratio of the test specimens were evaluated as a function of three CCF layout arrangements as well as fiber infill density embedded in Shape Memory Polymer (SMP) test specimens. The results revealed that the addition of CCF in the polymer matrix has a significant impact on shape memory behavior. Vertically aligned CCF in the SMP matrix improves the shape recovery ratio (92.97% compared to 78.77% of the pure SMP sample), while horizontal alignment of CCF ensures maximum shape fixity ratio (91.78% compared to 66.22% of the pure SMP sample). The cross-aligned CCF sample provides good recovery as well as fixity values. Further, it was observed that the horizontal alignment of CCF yields the fastest recovery performance. The outcome confirms that optimizing the fiber orientation enhances shape memory performance. Also, 40% of fiber infill density had greater shape fixity and overall recovery performance when compared to 30% and 50%. These findings have implications for tailored and high-performance SMPCs in biomedical devices, aerospace components, and robotics. Understanding temporal curvature behavior enables optimizing the design of materials with precise control over shape recovery. This research contributes to the design and optimization of SMPCs for diverse applications.

Stretchable ionic composites for strain-insensitive dual-mode pressure and proximity sensors

Simultaneously sensing pressure and proximity allows for the detection of contact pressure and the distance of approaching objects. This dual functionality ensures precise human–machine interactions and real-time adaptive responses to dynamic environments, proving it useful in human–machine interfaces, robots, and wearable devices. In this study, we introduce a highly stretchable and strain-insensitive pressure and proximity sensor capable of maintaining its electrical properties under mechanical deformations, achieved by establishing a continuous conductive pathway through an ionic bridge between conductive fillers. The strain-insensitive and stretchable composite exhibits ΔR/R0 of 0.024 under stretching up to 140% after 1,000 times. When the strain-insensitive composite is combined with a micro-patterned insulating layer, the resulting piezoresistive pressure sensors exhibit uniform pressure sensing capability even under mechanical deformations of tensile strain (∼50%) and bending curvature (1.3 cm−1). Moreover, our pressure sensor can be functioned as a capacitive-type proximity sensor capable of identifying material, shape, and distance of approaching objects with high sensitivity (capacitance change (ΔC/C0) of −0.88). As a proof-of-concept demonstration, our dual-mode pressure sensor with a multichannel array enables real-time monitoring of contact/noncontact pressure distribution, including intensity, shape, and proximity regardless of mechanical interference and surface roughness. Our approach to achieving high sensitivity and selectivity for desired contact/noncontact stimuli independent of mechanical interferences offers a novel platform for practical sensor applications.

Determination of the Strain Tensor and the Elastic Stress Fields in a Diamond Plate with a High Bending Curvature Using Local Laue Diffraction Data

Cylindrically bent diamond single-crystal plates have a great potential for creating energy dispersive spectrometers and focusing crystal monochromators. When they are designed, it is necessary to take into account the significant stresses that appear on bending the plates. The strain tensor and the elastic stress fields in a cylindrically bent single-crystal (110) diamond plate are calculated. The calculations are based on experimental data obtained by local Laue diffraction. The calculation results can be used to design new X-ray optical devices with the ability to control their parameters.

Design of biodegradable gelatin resistive memory with remarkable performance

For electronic systems, the substrate can be treated as a cornerstone of the overall device structure. With the growth of green electronics, the development of biodegradable substrates is of great significance. Gelatin substrates demonstrate transparency, low temperature, low cost, and fully biodegradable. In particular, gelatin of porcine source (GP) possesses excellent elasticity and high amount of hydroxyproline, which significantly improves the structural stability and memory performance of the device. The device with Ag/gelatin/Ag structure on GP substrate has illustrated non-volatile memory characteristics to be reckoned with an ON/OFF ratio of over 105, uniformly distributed switching parameters (<20 %), and steady retention time (>104 s). It is striking that the resistive switching of the GP-based device maintains stability under various curvature bending stresses (ON/OFF ratio of approximately 105) and displays repeatable resistive states undergoes 1000 cycles of bending tests, not only provides excellent structural reliability and robust mechanical flexibility but also effectively suppresses leakage current in devices, which is beneficial for flexible memory applications. Furthermore, the device possesses outstanding thermal stability, and numerous resistive switching behaviors even at 70 °C are observed. The conductive mechanism may be attributed to the ionic migration in the Ag ions chelating in amine groups of gelatin on the basis of the compelling electrical evidence for Ag/gelatin/Ag/GP devices. The biomass substrate disintegrates entirely in PBS solution without toxic residues, providing a novel design guideline for biomedical applications inspired by implantable, interventional medical, and wearable electronics.

"Sweat-Driven" MXene Composites with Energy-Storage and Thermal-Management Multifunctions: A Platform for Versatile Electronic Skins.

Most exogenous electronic skins (e-skins) currently face challenges of complex structure and poor compatibility with the human body. Utilizing human secretions (e.g., sweat) to develop e-skins is an effective solution strategy. Here, a new kind of "sweat-driven" e-skin is proposed, which realizes energy-storage and thermal-management multifunctions. Through the layer-by-layer assembly of MXene-carbon nanotube (CNT) composite with paper, lightweight and versatile e-skins based on supercapacitors and actuators are fabricated. Long CNTs wrap and entangle MXene nanosheets, enhancing their long-distance conductivity. Furthermore, the CNT network overcomes the structural collapse of MXene in sweat, improving the energy-storage performance of e-skin. The "sweat-driven" all-in-one supercapacitor with a trilayer structure is patternable, which absorbs sweat as electrolyte and harnesses the ions therein to store energy, exhibiting an areal capacitance of 282.3 mF cm-2 and a high power density (2117.8 µW cm-2). The "sweat-driven" actuator with a bilayer structure can be driven by moisture (bending curvature of 0.9 cm-1) and sweat for personal thermal management. Therefore, the paper serves as a separator, actuating layer, patternable layer, sweat extractor, and reservoir. The "sweat-driven" MXene-CNT composite provides a platform for versatile e-skins, which achieve the interaction with humans and offer insights into the development of multifunctional wearable electronics.

Numerical Study of the Influence of Different Bending Shapes on the Heat Transfer Characteristics of Annular Cross Wavy Primary Surface Recuperator (CW-PSR)

The cross-wave primary surface recuperator (CW-PSR) is a dependable option as a recuperator for micro gas turbines (MGT). The micro CW-PSR studied in this paper is composed of 171 stacked curved plates, with each plate containing 33 micro heat transfer channels with equivalent diameters of less than 1 mm. In this study, the influence of bending curvature on the thermal performance of CW-PSR plates is investigated through three-dimensional numerical simulation with fluid–solid–thermal coupling. The results indicate that the variation in bending curvature studied can result in a noteworthy 8% difference in the total heat transfer coefficient of CW-PSR plates. A direct correlation between heat transfer capacity and secondary flow strength is derived mathematically, explaining the mechanism by which secondary flow enhances heat transfer. By employing this relationship, a comprehensive analysis of CW-PSR plates with diverse bending curvatures is conducted, effectively showcasing how curvature influences the secondary flow pattern and enhances the channel’s heat transfer capacity. In addition, this paper considers the comprehensive influence of the size parameters of the heat transfer unit and the bending curvature of the heat transfer plate on the heat transfer and flow characteristics of the CW-PSR, and a dominant mathematical expression is obtained, which can be used for the design of similar heat exchangers of the same type.

Computational Analysis of Rheological Secondary Flow in a Pipe-Manifold Containing In-Plane Double Bends

Non-Newtonian fluid flow in pipe bends is inevitable in industrial applications. Previous researchers have extensively explored Newtonian flow through curved ducts. However, the non-Newtonian counterpart gets little attention. We study the turbulent flow of shear-dependent fluids obeying the Power-Law model in a pipe manifold containing an in-plane double bend. Ostwald–de Waele's power law is used to model the fluid's rheology. We utilize computational fluid dynamics (CFD) to solve Reynolds-averaged Navier–Stokes (RANS) equations with the k-ε turbulence model. We validate our numerical results with previous experimental results. The in-plane double bend perturbs the flow in the pipe manifold to develop a Prandtl's secondary flow of the first kind. A fully developed flow at the bend upstream is disturbed due to the bend's curvature and regains its fully developed characteristics upon a certain downstream length after the exit of the bend. We study the rheological characteristics of the secondary flow within the bend and the evolution of fluid flow at the bend downstream. We demonstrate that the centrifugal force-dominated secondary flow increases with a decrease of the non-Newtonian power-law index. We capture the camel's-back-shaped velocity profiles within the bend due to accelerating-decelerating flow. The study reveals that the average flow velocity increases along the bend with a corresponding pressure head loss. We quantify this velocity rise by a newly introduced non-dimensional number, viz. enhancement ratio. The double bend's enhancement ratio decreases with an increase in n.

Determination of the Strain Tensor and the Elastic Stress Fields in a Diamond Plate with a High Bending Curvature Using Local Laue Diffraction Data

Determination of the Strain Tensor and the Elastic Stress Fields in a Diamond Plate with a High Bending Curvature Using Local Laue Diffraction Data

On the Tradeoff Between Spatial Resolution and High Curvature Bending in FBG-Based Shape Sensing

On the Tradeoff Between Spatial Resolution and High Curvature Bending in FBG-Based Shape Sensing

The effect of pre‐existing fabrics on plate bending and seismicity in Alaska subduction zone

AbstractRemnant fabrics inherited from mid‐ridge play a key role in variations of plate deformation, hydration and seismicity along subduction zones. However, the quantitative relationships between the orientation of these remnant faults, plate bending and seismic activity at subduction zones still remain unclear. Here, we investigated the flexure of the Alaska subducting plate and assessed the relations between plate flexural curvatures, trench–fabric angle and seismicity. The results show that the flexural curvature and seismicity have nearly linear relationships with the trench–fabric angle. We find that remnant faults are more likely to be reactivated by plate bending at low trench–fabric angle region, causing greater plate deformation, hydration, weakening and seismicity. Plate weakening in turn promotes flexural bending curvature, resulting in higher degree of fracture and more earthquakes. However, at the high trench–fabric angle region, it is inclined to form new trench‐parallel bending faults that have smaller bending curvature and less seismicity.

Analysis via 3D FEM of the Passing Capacity of Pipeline Inspection Gauges in Bends with Different Curvatures

Pipeline inspection gauges easily become wedged in offshore and onshore small-diameter pipelines (where the outer diameter, D, of the pipe is less than 150 mm), particularly at the bends. To reveal the relationship between PIG capacity and bend curvature radius, a quantitative study on the passing capacity of PIG was conducted in this paper from three key perspectives of performance: safe application, sealing, and driving. The results demonstrate that the pipeline inspection gauge exhibits better passing capacity as the curvature radius of the bend increases. To improve the poorest passing capacity, in the case of R = 3D, different numbers of grooves are opened in the cup. The results demonstrate that the cup with 24 square grooves has a substantial impact on optimizing the passing capacity of the pipeline inspection gauge. This enhancement results in improvements in safe application performance (40.8%), sealing performance (12.22%), and driving performance (17%). This research aims to expand our understanding of blockages in small-diameter pipelines and provide a basis for optimizing the structure of the pipeline inspection gauge for small-diameter pipelines.

Helical buckling of coiled tubing with initial bending curvature in three-dimensional curved wellbores

In this paper, a new buckling model of coiled tubing (CT) in a three-dimensional curved wellbore is established, considering the influence of the curvature and toolface angle of the wellbore and the initial CT bending curvature. First, with the wellbore curvature and toolface angle, the CT buckling configuration is based on the lower or outer curved side of the wellbore. When the initial CT bending curvature is less than the critical bending curvature, the initial CT configuration in the wellbore undergoes sinusoidal buckling; otherwise, the CT undergoes helical buckling. Second, the buckling model is solved by the energy method. After solving this buckling model, the critical CT helical buckling load, the critical bending curvature, and the quantitative relationship between the axial load and pitch can be obtained. Third, the CT contact force calculation method under a helical buckling configuration in a three-dimensional curved wellbore is given by combining the buckling model and the beam-column model. The influence of the initial bending curvature is also considered. Finally, the calculated values of the buckling model and contact force calculation method were compared with existing experimental data and published models to validate the proposed model. Therefore, the methods presented in this paper can be used to not only predict helical CT buckling but also optimize downhole engineering design parameters considering the influence of the initial bending curvature in more realistic drilling wellbore conditions.